embOS

Real-Time
Operating System

CPU-independent

User & reference guide

Software version 3.60

Document revision 0
Date: January 28, 2008

A product of SEGGER Microcontroller GmbH & Co. KG

www.segger.com
2 CHAPTER

Disclaimer
Specifications written in this document are believed to be accurate, but are not guar-
anteed to be entirely free of error. The information in this manual is subject to
change for functional or performance improvements without notice. Please make sure
your manual is the latest edition. While the information herein is assumed to be
accurate, SEGGER MICROCONTROLLER GmbH & Co. KG (the manufacturer) assumes
no responsibility for any errors or omissions. The manufacturer makes and you
receive no warranties or conditions, express, implied, statutory or in any communica-
tion with you. The manufacturer specifically disclaims any implied warranty of mer-
chantability or fitness for a particular purpose.
Copyright notice
You may not extract portions of this manual or modify the PDF file in any way without
the prior written permission of the manufacturer. The software described in this doc-
ument is furnished under a license and may only be used or copied in accordance
with the terms of such a license.
© 2008 SEGGER Microcontroller GmbH & Co. KG, Hilden / Germany

Trademarks
Names mentioned in this manual may be trademarks of their respective companies.
Brand and product names are trademarks or registered trademarks of their respec-
tive holders.
Registration
Register the software via email. This way we can make sure you will receive updates
or notifications of updates as soon as they become available. For registration, pro-
vide the following information:
Company name and address
• Your name
• Your job title
• Your email address and telephone number
• Name and version of the product
Send this information to: register@segger.com
Contact address
SEGGER Microcontroller GmbH & Co. KG
Heinrich-Hertz-Str. 5
D-40721 Hilden
Germany
Tel.+49 2103-2878-0
Fax.+49 2103-2878-28
Email: support@segger.com
Internet: http://www.segger.com

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
 3

Software and manual versions

This manual describes the current software version. If any error occurs, inform us
and we will try to assist you as soon as possible.
Contact us for further information on topics or routines not yet specified.
Print date: January 28, 2008

Software Manual Date By Description

General updates.
3.60 0 080117 OO
Chapter "System tick" added.
3.52 1 071026 AW Chapter "Task routines": Added OS_SetTaskName().
Chapter "Task routines": Added OS_ExtendTaskContext().
3.52 0 070824 OO Chapter "Interrupts": Updated, added OS_CallISR() and
OS_CallNestableISR().
3.50c 0 070814 AW Chapter "List of libraries" updated, XR library type added.
3.40C 3 070716 OO Chapter “Performance and resource usage“ updated,
Chapter “Debugging“, error codes updated:
- OS_ERR_ISR_INDEX added.
- OS_ERR_ISR_VECTOR added.
- OS_ERR_RESOURCE_OWNER added.
- OS_ERR_CSEMA_OVERFLOW added.
3.40C 2 070625 SK Chapter “Task routines“:
- OS_Yield() added.
Chapter “Counting semaphores“ updated.
- OS_SignalCSema(), additional information adjusted.
Chapter “Performance and resource usage“ updated:
- Minor changes in wording.
Chapter “Counting semaphores“ updated.
- OS_SetCSemaValue() added.
- OS_CreateCSema(): Data type of parameter InitValue
3.40A 1 070608 SK changed from unsigned char to unsigned int.
- OS_SignalCSemaMax(): Data type of parameter MaxValue
changed from unsigned char to unsigned int.
- OS_SignalCSema(): Additional information updated.
Chapter “Performance and resource usage“ added.
Chapter “Configuration of your target system (RTOSInit.c)“
renamed to “Configuration of your target system“.
3.40 0 070516 SK Chapter “STOP\WAIT\IDLE modes“ moved into
chapter “Configuration of your target system“.
Chapter “time-related routines“ renamed to “Time measure-
ment“.
Chapter 4: OS_CREATETIMER_EX(), additional information cor-
3.32o 9 070422 SK
rected.
Chapter 4: Extended timer added.
3.32m 8 070402 AW
Chapter 8: API overview corrected, OS_Q_GetMessageCount()
3.32j 7 070216 AW Chapter 6: OS_CSemaRequest() function added.
3.32e 6 061220 SK About: Company description added.
Some minor formating changes.
3.32e 5 061107 AW Chapter 7: OS_GetMessageCnt() return value corrected to
unsigned int.
3.32d 4 061106 AW
Chapter 8: OS_Q_GetPtrTimed() function added.

Chapter 3: OS_CreateTaskEx() function, description of parame-

ter pContext corrected.
Chapter 3: OS_CreateTaskEx() function, type of parameter
TimeSlice corrected.
3.32a 3 061012 AW
Chapter 3: OS_CreateTask() function, type of parameter
TimeSlice corrected.
Chapter 9: OS_GetEventsOccured() renamed to
OS_GetEventsOccurred().
Chapter 10: OS_EVENT_WaitTimed() added.
3.32a 2 060804 AW Chapter 3: OS_CREATETASK_EX() function added.
Chapter 3: OS_CreateTaskEx() function added.
3.32 1 060717 OO Event objects introduced. Chapter 10 inserted which describes
event objects.
Previous chapter "Events" renamed to "Task events"
3.30 1 060519 OO New software version.

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
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Software Manual Date By Description

3.28 5 060223 OO All chapters: Added API tables.
Some minor changes.
3.28 4 051109 AW Chapter 7: OS_SignalCSemaMax() function added.
Chapter 14: Explanation of interrupt latencies and high / low
priorities added.
3.28 3 050926 AW Chapter 6: OS_DeleteRSema() function added.
3.28 2 050707 AW Chapter 4: OS_GetSuspendCnt() function added.
3.28 1 050425 AW Version number changed to 3.28 to fit to current ombOS ver-
sion.
Chapter 18.1.2: Type of return value of OS GetTime32() cor-
rected
Chapter 4: OS_Terminate() modified due to new features of
3.26 050209 AW
version 3.26.
Chapter 24: Source code version: additional compile time
switches and build process of libraries explained more in detail.
3.24 041115 Chapter 6: Some prototype declarations showed in OS_SEMA
AW
instead of OS_RSEMA. Corrected.
3.22 1 040816 AW Chapter 8: New Mailbox functions added
OS_PutMailFront()
OS_PutMailFront1()
OS_PutMailFrontCond()
OS_PutMailFrontCond1()
3.20 5 040621 RS Software timers: Maximum timeout values and
AW OS_TIMER_MAX_TIME described.
Chapter 14: Description of rules for interrupt handlers
revised.
OS_LeaveNestableInterruptNoSwitch() added which was not
described before.
3.20 4 040329 AW OS_CreateCSema() prototype declaration corrected. Return
type is void.
OS_Q_GetMessageCnt() prototype declaration corrected.
OS_Q_Clear() function description added.
OS_MEMF_FreeBlock() prototype declaration corrected.
3.20 2 031128 AW OS_CREATEMB() Range for parameter MaxnofMsg corrected.
Upper limit is 65535, but was declared 65536 in previous
manuals.
3. 1 040831 AW Code samples modified: Task stacks defined as array of int,
because most CPUs require alignment of stack on integer
aligned addresses.

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
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Software Manual Date By Description

3.20 1 031016 AW Chapter 4: Type of task priority parameter corrected to
unsigned char.
Chapter 4: OS_DelayUntil(): Sample program modified.
Chapter 4: OS_Suspend() added.
Chapter 4: OS_Resume() added.
Chapter 5: OS_GetTimerValue(): Range of return value cor-
rected.
Chapter 6: Sample program for usage of resource sema-
phores modified.
Chapter 6: OS_GetResourceOwner(): Type of return value
corrected.
Chapter 8: OS_CREATEMB(): Types and valid range of
parameter corrected.
Chapter 8: OS_WaitMail() added
Chapter 10: OS_WaitEventTimed(): Range of timeout value
specified.
3.12 1 021015 AW Chapter 8: OS_GetMailTimed() added
Chapter 11 (Heap type memory management) inserted
Chapter 12 (Fixed block size memory pools) inserted
3.10 3 020926 KG Index and glossary revised.
020924 KG Section 16.3 (Example) added to Chapter 16 (Time-related rou-
020910 KG tines).
Revised for language/grammar.
Version control table added.
Screenshots added: superloop, cooperative/preemptive multi-
tasking, nested interrupts, low-res and hi-res measurement.
Section 1.3 (Typographic conventions) changed to table.
Section 3.2 added (Single-task system).
Section 3.8 merged with section 3.9 (How the OS gains con-
trol).
Chapter 4 (Configuration for your target system) moved to after
Chapter 15 (System variables).
Chapter 16 (Time-related routines) added.

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
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User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
 7

About this document

Assumptions
This document assumes that you already have a solid knowledge of the following:
• The software tools used for building your application (assembler, linker, C com-
piler)
• The C programming language
• The target processor

• DOS command line.

If you feel that your knowledge of C is not sufficient, we recommend The C Program-
ming Language by Kernighan and Richie (ISBN 0-13-1103628), which describes the
standard in C-programming and, in newer editions, also covers the ANSI C standard.
How to use this manual
The intention of this manual is to give you a CPU- and compiler-independent intro-
duction to embOS and to be a reference for all embOS API functions.
For a quick and easy startup with embOS, refer to Chapter 2 in the CPU & Compiler
Specifics manual of embOS documentation, which includes a step-by-step introduc-
tion to using embOS.
Typographic conventions for syntax
This manual uses the following typographic conventions:

Style Used for

Body Body text.

Text that you enter at the command-prompt or that appears on the

Keyword
display (that is system functions, file- or pathnames).

Parameter Parameters in API functions.

Sample Sample code in program examples.

Reference Reference to chapters, tables and figures or other documents.

GUIElement Buttons, dialog boxes, menu names, menu commands.

Emphasis Very important sections

Table 1.1: Typographic conventions

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
8 CHAPTER

SEGGER Microcontroller GmbH & Co. KG develops

and distributes software development tools and ANSI
C software components (middleware) for embedded
systems in several industries such as telecom, medi-
cal technology, consumer electronics, automotive
industry and industrial automation.
SEGGER’s intention is to cut software development-
time for embedded applications by offering compact flexible and easy to use middleware,
allowing developers to concentrate on their application.
Our most popular products are emWin, a universal graphic software package for embed-
ded applications, and embOS, a small yet efficent real-time kernel. emWin, written
entirely in ANSI C, can easily be used on any CPU and most any display. It is comple-
mented by the available PC tools: Bitmap Converter, Font Converter, Simulator and
Viewer. embOS supports most 8/16/32-bit CPUs. Its small memory footprint makes it
suitable for single-chip applications.
Apart from its main focus on software tools, SEGGER developes and produces program-
ming tools for flash microcontrollers, as well as J-Link, a JTAG emulator to assist in devel-
opment, debugging and production, which has rapidly become the industry standard for
debug access to ARM cores.

Corporate Office: United States Office:

http://www.segger.com http://www.segger-us.com

EMBEDDED SOFTWARE SEGGER TOOLS

(Middleware)
emWin Flasher
Graphics software and GUI Flash programmer
emWin is designed to provide an effi- Flash Programming tool primarily for microcon-
cient, processor- and display control- trollers.
ler-independent graphical user
interface (GUI) for any application that J-Link
operates with a graphical display. JTAG emulator for ARM cores
Starterkits, eval- and trial-versions are USB driven JTAG interface for ARM cores.
available.
J-Trace
embOS JTAG emulator with trace
Real Time Operating System USB driven JTAG interface for ARM cores with
embOS is an RTOS designed to offer Trace memory. supporting the ARM ETM (Embed-
the benefits of a complete multitasking ded Trace Macrocell).
system for hard real time applications
with minimal resources. The profiling J-Link / J-Trace Related Software
PC tool embOSView is included. Add-on software to be used with SEGGER’s indus-
try standard JTAG emulator, this includes flash
emFile programming software and flash breakpoints.
File system
emFile is an embedded file system with
FAT12, FAT16 and FAT32 support.
emFile has been optimized for mini-
mum memory consumption in RAM and
ROM while maintaining high speed.
Various Device drivers, e.g. for NAND
and NOR flashes, SD/MMC and Com-
pactFlash cards, are available.

USB-Stack
USB device stack
A USB stack designed to work on any
embedded system with a USB client
controller. Bulk communication and
most standard device classes are sup-
ported.

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
 9

Table of Contents

1 Introduction to embOS ...................................................................................................15

1.1 What is embOS ....................................................................................... 16
1.2 Features................................................................................................. 17

2 Basic concepts...............................................................................................................19
2.1 Tasks ..................................................................................................... 20
2.2 Single-task systems (superloop) ................................................................ 21
2.3 Multitasking systems................................................................................ 22
2.3.1 Cooperative multitasking .......................................................................... 22
2.3.2 Preemptives multitasking.......................................................................... 23
2.4 Scheduling.............................................................................................. 24
2.4.1 Round-robin scheduling algorithm .............................................................. 24
2.4.2 Priority-controlled scheduling algorithm ...................................................... 24
2.4.3 Priority inversion ..................................................................................... 25
2.5 Communication between tasks .................................................................. 26
2.5.1 Global variables....................................................................................... 26
2.5.2 Communication mechanisms ..................................................................... 26
2.5.3 Mailboxes and queues .............................................................................. 26
2.5.4 Semaphores ........................................................................................... 26
2.5.5 Events ................................................................................................... 26
2.6 How task-switching works......................................................................... 27
2.7 Switching stacks...................................................................................... 28
2.8 Change of task status............................................................................... 29
2.9 How the OS gains control ......................................................................... 30
2.10 Different builds of embOS ......................................................................... 32
2.10.1 Profiling ................................................................................................. 32
2.10.2 List of libraries ........................................................................................ 32

3 Task routines .................................................................................................................33

3.1 Task routine API function overview ............................................................ 35
3.1.1 OS_CREATETASK() .................................................................................. 36
3.1.2 OS_CreateTask() ..................................................................................... 37
3.1.3 OS_CREATETASK_EX() ............................................................................. 39
3.1.4 OS_CreateTaskEx() ................................................................................. 40
3.1.5 OS_Delay()............................................................................................. 41
3.1.6 OS_DelayUntil() ...................................................................................... 42
3.1.7 OS_ExtendTaskContext().......................................................................... 43
3.1.8 OS_GetpCurrentTask() ............................................................................. 46
3.1.9 OS_GetPriority()...................................................................................... 47
3.1.10 OS_GetSuspendCnt() ............................................................................... 48
3.1.11 OS_GetTaskID() ...................................................................................... 49
3.1.12 OS_IsTask() ........................................................................................... 50
3.1.13 OS_Resume() ......................................................................................... 51
3.1.14 OS_SetPriority() ...................................................................................... 52
3.1.15 OS_SetTaskName() ................................................................................. 53
3.1.16 OS_SetTimeSlice()................................................................................... 54
3.1.17 OS_Suspend()......................................................................................... 55
3.1.18 OS_Terminate() ...................................................................................... 56
3.1.19 OS_WakeTask() ...................................................................................... 57
3.1.20 OS_Yield() .............................................................................................. 58

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4 Software timers ..............................................................................................................59

4.1 Software timers API function overview ....................................................... 61
4.1.1 OS_CREATETIMER() ................................................................................ 62
4.1.2 OS_CreateTimer() ................................................................................... 63
4.1.3 OS_StartTimer() ..................................................................................... 64
4.1.4 OS_StopTimer()...................................................................................... 65
4.1.5 OS_RetriggerTimer() ............................................................................... 66
4.1.6 OS_SetTimerPeriod() ............................................................................... 67
4.1.7 OS_DeleteTimer() ................................................................................... 68
4.1.8 OS_GetTimerPeriod()............................................................................... 69
4.1.9 OS_GetTimerValue()................................................................................ 70
4.1.10 OS_GetTimerStatus() .............................................................................. 71
4.1.11 OS_GetpCurrentTimer() ........................................................................... 72
4.1.12 OS_CREATETIMER_EX() ........................................................................... 73
4.1.13 OS_CreateTimerEx()................................................................................ 74
4.1.14 OS_StartTimerEx() .................................................................................. 75
4.1.15 OS_StopTimerEx() .................................................................................. 76
4.1.16 OS_RetriggerTimerEx() ............................................................................ 77
4.1.17 OS_SetTimerPeriodEx() ........................................................................... 78
4.1.18 OS_DeleteTimerEx() ................................................................................ 79
4.1.19 OS_GetTimerPeriodEx() ........................................................................... 80
4.1.20 OS_GetTimerValueEx() ............................................................................ 81
4.1.21 OS_GetTimerStatusEx() ........................................................................... 82
4.1.22 OS_GetpCurrentTimerEx()........................................................................ 83

5 Resource semaphores...................................................................................................85
5.1 Resource semaphores API function overview ............................................... 88
5.1.1 OS_CREATERSEMA() ............................................................................... 89
5.1.2 OS_Use() ............................................................................................... 90
5.1.3 OS_Unuse() ........................................................................................... 92
5.1.4 OS_Request() ......................................................................................... 93
5.1.5 OS_GetSemaValue()................................................................................ 94
5.1.6 OS_GetResourceOwner().......................................................................... 95
5.1.7 OS_DeleteRSema() ................................................................................. 96

6 Counting Semaphores ...................................................................................................97

6.1 Counting semaphores API function overview .............................................. 99
6.1.1 OS_CREATECSEMA() ..............................................................................100
6.1.2 OS_CreateCSema() ................................................................................101
6.1.3 OS_SignalCSema().................................................................................102
6.1.4 OS_SignalCSemaMax() ...........................................................................103
6.1.5 OS_WaitCSema() ...................................................................................104
6.1.6 OS_WaitCSemaTimed()...........................................................................105
6.1.7 OS_CSemaRequest() ..............................................................................106
6.1.8 OS_GetCSemaValue().............................................................................107
6.1.9 OS_SetCSemaValue() .............................................................................108
6.1.10 OS_DeleteCSema() ................................................................................109

7 Mailboxes.....................................................................................................................111
7.1 Why mailboxes?.....................................................................................112
7.2 Basics...................................................................................................113
7.3 Typical applications ................................................................................114
7.4 Single-byte mailbox functions ..................................................................115
7.5 Mailboxes API function overview...............................................................116
7.5.1 OS_CREATEMB() ....................................................................................117
7.5.2 OS_PutMail() / OS_PutMail1() ..................................................................118
7.5.3 OS_PutMailCond() / OS_PutMailCond1()....................................................119
7.5.4 OS_PutMailFront() / OS_PutMailFront1() ...................................................120
7.5.5 OS_PutMailFrontCond() / OS_PutMailFrontCond1() .....................................121

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7.5.6 OS_GetMail() / OS_GetMail1()................................................................. 122

7.5.7 OS_GetMailCond() / OS_GetMailCond1() .................................................. 123
7.5.8 OS_GetMailTimed()................................................................................ 124
7.5.9 OS_WaitMail()....................................................................................... 125
7.5.10 OS_ClearMB() ....................................................................................... 126
7.5.11 OS_GetMessageCnt() ............................................................................. 127
7.5.12 OS_DeleteMB() ..................................................................................... 128

8 Queues ........................................................................................................................129
8.1 Why queues? ........................................................................................ 130
8.2 Basics .................................................................................................. 131
8.3 Queues API function overview ................................................................. 132
8.3.1 OS_Q_Create() ..................................................................................... 133
8.3.2 OS_Q_Put() .......................................................................................... 134
8.3.3 OS_Q_GetPtr()...................................................................................... 135
8.3.4 OS_Q_GetPtrCond()............................................................................... 136
8.3.5 OS_Q_GetPtrTimed() ............................................................................. 137
8.3.6 OS_Q_Purge()....................................................................................... 138
8.3.7 OS_Q_Clear() ....................................................................................... 139
8.3.8 OS_Q_GetMessageCnt() ......................................................................... 140

9 Task events..................................................................................................................141
9.1 Events API function overview .................................................................. 143
9.1.1 OS_WaitEvent() .................................................................................... 144
9.1.2 OS_WaitSingleEvent() ............................................................................ 145
9.1.3 OS_WaitEventTimed() ............................................................................ 146
9.1.4 OS_WaitSingleEventTimed() ................................................................... 147
9.1.5 OS_SignalEvent() .................................................................................. 148
9.1.6 OS_GetEventsOccurred() ........................................................................ 149
9.1.7 OS_ClearEvents() .................................................................................. 150

10 Event objects .............................................................................................................151

10.1 Event object API function overview .......................................................... 153
10.1.1 OS_EVENT_Create() .............................................................................. 154
10.1.2 OS_EVENT_Wait() ................................................................................. 155
10.1.3 OS_EVENT_WaitTimed() ......................................................................... 156
10.1.4 OS_EVENT_Set() ................................................................................... 157
10.1.5 OS_EVENT_Reset() ................................................................................ 159
10.1.6 OS_EVENT_Pulse() ................................................................................ 160
10.1.7 OS_EVENT_Get()................................................................................... 161
10.1.8 OS_EVENT_Delete()............................................................................... 162

11 Heap type memory management...............................................................................163

11.1 Heap type memory manager API reference ............................................... 165

12 Fixed block size memory pools..................................................................................167

12.1 Memory pools API reference overview ...................................................... 169
12.1.1 OS_MEMF_Create()................................................................................ 170
12.1.2 OS_MEMF_Delete() ................................................................................ 171
12.1.3 OS_MEMF_Alloc() .................................................................................. 172
12.1.4 OS_MEMF_AllocTimed().......................................................................... 173
12.1.5 OS_MEMF_Request().............................................................................. 174
12.1.6 OS_MEMF_Release() .............................................................................. 175
12.1.7 OS_MEMF_FreeBlock() ........................................................................... 176
12.1.8 OS_MEMF_GetNumBlocks()..................................................................... 177
12.1.9 OS_MEMF_GetBlockSize()....................................................................... 178
12.1.10 OS_MEMF_GetNumFreeBlocks()............................................................... 179
12.1.11 OS_MEMF_GetMaxUsed() ....................................................................... 180
12.1.12 OS_MEMF_IsInPool() ............................................................................. 181

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13 Stacks ........................................................................................................................183
13.1 System stack.........................................................................................185
13.2 Task stack.............................................................................................186
13.3 Interrupt stack.......................................................................................187
13.4 Stacks API function overview ...................................................................188
13.4.1 OS_GetStackBase() ................................................................................189
13.4.2 OS_GetStackSize().................................................................................190
13.4.3 OS_GetStackSpace() ..............................................................................191
13.4.4 OS_GetStackUsed()................................................................................192

14 Interrupts....................................................................................................................193
14.1 Interrupt latency ....................................................................................195
14.1.1 Causes of interrupt latencies....................................................................195
14.1.2 Additional causes for interrupt latencies ....................................................195
14.2 Zero interrupt latency .............................................................................197
14.3 High / low priority interrupts....................................................................198
14.4 Rules for interrupt handlers .....................................................................199
14.4.1 General rules .........................................................................................199
14.4.2 Additional rules for preemptive multitasking ..............................................199
14.5 Calling embOS routines from within an ISR................................................200
14.5.1 Interrupts API function overview ..............................................................201
14.5.2 OS_CallISR() .........................................................................................202
14.5.3 OS_CallNestableISR() .............................................................................203
14.5.4 OS_EnterInterrupt() ...............................................................................204
14.5.5 OS_LeaveInterrupt() ..............................................................................205
14.5.6 OS_LeaveInterruptNoSwitch()..................................................................206
14.5.7 Example using OS_EnterInterrupt()/OS_LeaveInterrupt() ............................206
14.6 Enabling / disabling interrupts from C .......................................................207
14.6.1 OS_IncDI() / OS_DecRI()........................................................................208
14.6.2 OS_DI() / OS_EI() / OS_RestoreI() ..........................................................209
14.7 Definitions of interrupt control macros (in RTOS.h) .....................................210
14.8 Nesting interrupt routines........................................................................211
14.8.1 OS_EnterNestableInterrupt() ...................................................................212
14.8.2 OS_LeaveNestableInterrupt() ..................................................................213
14.8.3 OS_LeaveNestableInterruptNoSwitch()......................................................214
14.9 Non-maskable interrupts (NMIs) ..............................................................215

15 Critical Regions..........................................................................................................217
15.1 Critical regions API function overview........................................................219
15.1.1 OS_EnterRegion() ..................................................................................220
15.1.2 OS_LeaveRegion() .................................................................................221

16 Time measurement ....................................................................................................223

16.1 Low-resolution measurement ...................................................................225
16.2 Low-resolution measurement API function overview....................................226
16.2.1 OS_GetTime() .......................................................................................227
16.2.2 OS_GetTime32() ....................................................................................228
16.3 High-resolution measurement ..................................................................229
16.4 High-resolution measurement API function overview ...................................230
16.4.1 OS_Timing_Start() .................................................................................231
16.4.2 OS_Timing_End()...................................................................................232
16.4.3 OS_Timing_Getus() ................................................................................233
16.4.4 OS_Timing_GetCycles() ..........................................................................234
16.5 Example ...............................................................................................235

17 System variables........................................................................................................237
17.1 Time variables .......................................................................................239
17.1.1 OS_Time...............................................................................................239
17.1.2 OS_TimeDex .........................................................................................239

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17.2 OS internal variables and data-structures ................................................. 240

18 System tick.................................................................................................................241
18.1 Tickhandler........................................................................................... 243
18.1.1 OS_HandleTick() ................................................................................... 244
18.1.2 OS_HandleTick_Ex() .............................................................................. 245
18.2 Hooking into the system tick ................................................................... 246
18.2.1 OS_AddTickHook()................................................................................. 247
18.2.2 OS_RemoveTickHook()........................................................................... 248

19 Configuration of target system (BSP) ........................................................................249

19.1 Hardware-specific routines...................................................................... 251
19.2 Configuration defines ............................................................................. 252
19.3 How to change settings .......................................................................... 253
19.3.1 Setting the system frequency OS_FSYS .................................................... 253
19.3.2 Using a different timer to generate the tick-interrupts for embOS................. 253
19.3.3 Using a different UART or baudrate for embOSView .................................... 253
19.3.4 Changing the tick frequency.................................................................... 253
19.4 STOP / HALT / IDLE modes ..................................................................... 255

20 embOSView: Profiling and analyzing.........................................................................257

20.1 Overview .............................................................................................. 258
20.2 Task list window .................................................................................... 259
20.3 System variables window........................................................................ 260
20.4 Sharing the SIO for terminal I/O.............................................................. 261
20.4.1 Shared SIO API function overview............................................................ 262
20.4.2 OS_SendString() ................................................................................... 263
20.4.3 OS_SetRxCallback()............................................................................... 264
20.5 Using the API trace ................................................................................ 265
20.6 Trace filter setup functions...................................................................... 267
20.7 Trace filter API functions......................................................................... 268
20.7.1 OS_TraceEnable().................................................................................. 269
20.7.2 OS_TraceDisable()................................................................................. 270
20.7.3 OS_TraceEnableAll() .............................................................................. 271
20.7.4 OS_TraceDisableAll() ............................................................................. 272
20.7.5 OS_TraceEnableId()............................................................................... 273
20.7.6 OS_TraceDisableId() .............................................................................. 274
20.7.7 OS_TraceEnableFilterId()........................................................................ 275
20.7.8 OS_TraceDisableFilterId() ....................................................................... 276
20.8 Trace record functions............................................................................ 277
20.9 Trace record API function overview .......................................................... 278
20.9.1 OS_TraceVoid()..................................................................................... 279
20.9.2 OS_TracePtr() ....................................................................................... 280
20.9.3 OS_TraceData() .................................................................................... 281
20.9.4 OS_TraceDataPtr() ................................................................................ 282
20.9.5 OS_TraceU32Ptr() ................................................................................. 283
20.10 Application-controlled trace example ........................................................ 284
20.11 User-defined functions ........................................................................... 285

21 Debugging..................................................................................................................287
21.1 Runtime errors ...................................................................................... 288
21.2 List of error codes.................................................................................. 289

22 Performance and resource usage..............................................................................293

22.1 Introduction.......................................................................................... 294
22.2 Memory requirements ............................................................................ 295
22.3 Performance ......................................................................................... 296
22.4 Benchmarking ....................................................................................... 296
22.4.1 Measurement with port pins and oscilloscope............................................. 297

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22.4.1.1 Oscilloscope analysis ..............................................................................298

22.4.1.2 Example measurements AT91SAM7S, ARM code in RAM ..............................299
22.4.1.3 Example measurements AT91SAM7S, Thumb code in FLASH ........................300
22.4.1.4 Measurement with high-resolution timer....................................................301

23 Supported development tools ....................................................................................303

24 Limitations..................................................................................................................305

25 Source code of kernel and library ..............................................................................307

25.1 Building embOS libraries .........................................................................309
25.2 Major compile time switches ....................................................................310
25.2.1 OS_RR_SUPPORTED ...............................................................................310
25.2.2 OS_SUPPORT_CLEANUP_ON_TERMINATE ..................................................310

26 Additional modules.....................................................................................................311
26.1 Keyboard manager: KEYMAN.C ................................................................312
26.2 Additional libraries and modules ...............................................................313

27 FAQ (frequently asked questions) .............................................................................315

28 Glossary.....................................................................................................................317

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Chapter 1

Introduction to embOS

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16 CHAPTER 1 Introduction to embOS

1.1 What is embOS

embOS is a priority-controlled multitasking system, designed to be used as an
embedded operating system for the development of real-time applications for a vari-
ety of microcontrollers.
embOS is a high-performance tool that has been optimized for minimum memory
consumption in both RAM and ROM, as well as high speed and versatility.

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1.2 Features
Throughout the development process of embOS, the limited resources of microcon-
trollers have always been kept in mind. The internal structure of the realtime operat-
ing system (RTOS) has been optimized in a variety of applications with different
customers, to fit the needs of the industry. Fully source-compatible RTOS are avail-
able for a variety of microcontrollers, making it well worth the time and effort to
learn how to structure real-time programs with real-time operating systems.
embOS is highly modular. This means that only those functions that are needed are
linked, keeping the ROM size very small. The minimum memory consumption is little
more than 1 Kbyte of ROM and about 30 bytes of RAM (plus memory for stacks). A
couple of files are supplied in source code to make sure that you do not loose any
flexibility by using embOS and that you can customize the system to fully fit your
needs.
The tasks you create can easily and safely communicate with each other using a
complete palette of communication mechanisms such as semaphores, mailboxes, and
events.
Some features of embOS include:
• Preemptive scheduling:
Guarantees that of all tasks in READY state the one with the highest priority exe-
cutes, except for situations where priority inversion applies.
• Round-robin scheduling for tasks with identical priorities.
• Preemptions can be disabled for entire tasks or for sections of a program.
• Up to 255 priorities.
• Every task can have an individual priority => the response of tasks can be pre-
cisely defined according to the requirements of the application.
• Unlimited number of tasks
(limited only by the amount of available memory).
• Unlimited number of semaphores
(limited only by the amount of available memory).
• 2 types of semaphores: resource and counting.
• Unlimited number of mailboxes
(limited only by the amount of available memory).
• Size and number of messages can be freely defined when initializing mailboxes.
• Unlimited number of software timers
(limited only by the amount of available memory).
• 8-bit events for every task.
• Time resolution can be freely selected (default is 1ms).
• Easily accessible time variable.
• Power management.
• Unused calculation time can automatically be spent in halt mode .
power-consumption is minimized.
• Full interrupt support:
Interrupts can call any function except those that require waiting for data,
as well as create, delete or change the priority of a task.
Interrupts can wake up or suspend tasks and directly communicate with tasks
using all available communication instances (mailboxes, semaphores, events).
• Very short interrupt disable-time => short interrupt latency time.
• Nested interrupts are permitted.
• embOS has its own interrupt stack (usage optional).
• Frame application for an easy start.
• Debug version performs runtime checks, simplifying development.
• Profiling and stack check may be implemented by choosing specified libraries.
• Monitoring during runtime via UART available (embOSView).
• Very fast and efficient, yet small code.
• Minimum RAM usage.
• Core written in assembly language.
• Interfaces C and/or assembly.
• Initialization of microcontroller hardware as sources.

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Chapter 2

Basic concepts

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20 CHAPTER 2 Basic concepts

2.1 Tasks
In this context, a task is a program running on the CPU core of a microcontroller.
Without a multitasking kernel (an RTOS), only one task can be executed by the CPU
at a time. This is called a single-task system. A real-time operating system allows the
execution of multiple tasks on a single CPU. All tasks execute as if they completely
"owned" the entire CPU. The tasks are scheduled, meaning that the RTOS can
activate and deactivate every task.

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2.2 Single-task systems (superloop)

A superloop application is basically a program that runs in an endless loop, calling OS
functions to execute the appropriate operations (task level). No real-time kernel is
used, so interrupt service routines (ISRs) must be used for real-time parts of the
software or critical operations (interrupt level). This type of system is typically used
in small, uncomplex systems or if real-time behavior is not critical.

Task level Interrupt level

Superloop

ISR

Time
ISR
ISR (nested)

Of course, there are fewer preemption and synchronization problems with a super-
loop application. Also, because no real-time kernel is used, only one stack exists in
ROM, meaning that ROM size is smaller and less RAM is used up for stacks. However,
superloops can become difficult to maintain if the program becomes too large.
Because one software component cannot be interrupted by another component (only
by ISRs), the reaction time of one component depends on the execution time of all
other components in the system. Real-time behavior is therefore poor.

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2.3 Multitasking systems

In a multitasking system, there are different scheduling systems in which the calcu-
lation power of the CPU can be distributed among tasks.

2.3.1 Cooperative multitasking

Cooperative multitasking expects cooperation of all tasks. Tasks can only be sus-
pended by calling a function of the operating system. If they do not, the system
"hangs", which means that other tasks have no chance of being executed by the CPU
while the first task is being carried out. This is illustrated in the diagram below. Even
if an ISR makes a higher-priority task ready to run, the interrupted task will be
returned to and finished before the task switch is made.

Low priority task

Executing task is interrupted

ISR
ISR puts high priority
task in READY state

Interrupted task
Time is completed

High priority task

Higher priority task
Is executed

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2.3.2 Preemptives multitasking

Real-time systems like embOS operate with preemptive multitasking only. A real-
time operating system needs a regular timer-interrupt to interrupt tasks at defined
times and to perform task-switches if necessary. The highest-priority task in the
READY state is therefore always executed, whether it is an interrupted task or not. If
an ISR makes a higher priority task ready, a task switch will occur and the task will
be executed before the interrupted task is returned to.

Low priority task

Executing task is interrupted

ISR

ISR puts high priority High priority task

task in READY state;
Time task switch occurs
Higher priority task
Is executed

Interrupted task
is completed

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2.4 Scheduling
There are different algorithms that determine which task to execute, called
schedulers. All schedulers have one thing in common: they distinguish between tasks
that are ready to be executed (in the READY state) and the other tasks that are
suspended for any reason (delay, waiting for mailbox, waiting for semaphore, waiting
for event, and so on). The scheduler selects one of the tasks in the READY state and
activates it (executes the program of this task). The task which is currently executing
is referred to as the active task. The main difference between schedulers is in how
they distribute the computation time between the tasks in READY state.

2.4.1 Round-robin scheduling algorithm

With round-robin scheduling, the scheduler has a list of tasks and, when deactivating
the active task, activates the next task that is in the READY state. Round-robin can
be used with either preemptive or cooperative multitasking. It works well if you do
not need to guarantee response time, if the response time is not an issue, or if all
tasks have the same priority. Round-robin scheduling can be illustrated as follows:

All tasks are on the same level; the possession of the CPU changes periodically after
a predefined execution time. This time is called timeslice, and may be defined
individually for every task.

2.4.2 Priority-controlled scheduling algorithm

In real-world applications, different tasks require different response times. For
example, in an application that controls a motor, a keyboard, and a display, the
motor usually requires faster reaction time than the keyboard and display. While the
display is being updated, the motor needs to be controlled. This makes preemptive
multitasking a must. Round-robin might work, but because it cannot guarantee a
specific reaction time, an improved algorithm should be used.
In priority-controlled scheduling, every task is assigned a priority. The order of exe-
cution depends on this priority. The rule is very simple:
Note: The scheduler activates the task that has the highest priority of all
tasks in the READY state.
This means that every time a task with higher priority than the active task gets
ready, it immediately becomes the active task. However, the scheduler can be
switched off in sections of a program where task switches are prohibited, known as
critical regions.
embOS uses a priority-controlled scheduling algorithm with round-robin between
tasks of identical priority. One hint at this point: round-robin scheduling is a nice fea-
ture because you do not have to think about whether one task is more important
than another. Tasks with identical priority cannot block each other for longer than
their timeslices. But round-robin scheduling also costs time if two or more tasks of
identical priority are ready and no task of higher priority is ready, because it will con-
stantly switch between the identical-priority tasks. It is more efficient to assign a dif-
ferent priority to each task, which will avoid unnecessary task switches.

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2.4.3 Priority inversion

The rule to go by for the scheduler is:
Activate the task that has the highest priority of all tasks in the READY state.
But what happens if the highest-priority task is blocked because it is waiting for a
resource owned by a lower-priority task? According to the above rule, it would wait
until the low-priority-task becomes active again and releases the resource.
The other rule is: No rule without exception.
To avoid this kind of situation, the low-priority task that is blocking the highest-prior-
ity task gets assigned the highest priority until it releases the resource, unblocking
the task which originally had highest priority. This is known as priority inversion.

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2.5 Communication between tasks

In a multitasking (multithreaded) program, multiple tasks work completely sepa-
rately. Because they all work in the same application, it will sometimes be necessary
for them to exchange information with each other.

2.5.1 Global variables

The easiest way to do this is by using global variables. In certain situations, it can
make sense for tasks to communicate via global variables, but most of the time this
method has various disadvantages.
For example, if you want to synchronize a task to start when the value of a global
variable changes, you have to poll this variable, wasting precious calculation time
and power, and the reaction time depends on how often you poll.

2.5.2 Communication mechanisms

When multiple tasks work with one another, they often have to:
• exchange data,
• synchronize with another task, or
• make sure that a resource is used by no more than one task at a time.
For these purposes embOS offers mailboxes, queues, semaphores and events.

2.5.3 Mailboxes and queues

A mailbox is basically a data buffer managed by the RTOS and is used for sending a
message to a task. It works without conflicts even if multiple tasks and interrupts try
to access it simultaneously. embOS also automatically activates any task that is
waiting for a message in a mailbox the moment it receives new data and, if neces-
sary, automatically switches to this task.
A queue works in a similar manner, but handle larger messages than mailboxes, and
every message may have a individual size.
For more information, see the Chapter Mailboxes on page 111 and Chapter Queues
on page 129.

2.5.4 Semaphores
Two types of semaphores are used for synchronizing tasks and to manage resources.
The most common are resource semaphores, although counting semaphores are also
used. For details and samples, refer to the Chapter Resource semaphores on page 85
and Chapter Counting Semaphores on page 97. Samples can also be found on our
website at www.segger.com.

2.5.5 Events
A task can wait for a particular event without using any calculation time. The idea is
as simple as it is convincing; there is no sense in polling if we can simply activate a
task the moment the event that it is waiting for occurs. This saves a great deal of
calculation power and ensures that the task can respond to the event without delay.
Typical applications for events are those where a task waits for data, a pressed key, a
received command or character, or the pulse of an external real-time clock.
For further details, refer to the Chapter Task events on page 141 and Chapter Event
objects on page 151.

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2.6 How task-switching works

A real-time multitasking system lets multiple tasks run like multiple single-task pro-
grams, quasi-simultaneously, on a single CPU. A task consists of three parts in the
multitasking world:
• The program code, which usually resides in ROM (though it does not have to)
• A stack, residing in a RAM area that can be accessed by the stack pointer
• A task control block, residing in RAM.
The stack has the same function as in a single-task system: storage of return
addresses of function calls, parameters and local variables, and temporary storage of
intermediate calculation results and register values. Each task can have a different
stack size. More information can be found in chapter Stacks on page 183.
The task control block (TCB) is a data structure assigned to a task when it is created.
It contains status information of the task, including the stack pointer, task priority,
current task status (ready, waiting, reason for suspension) and other management
data. This information allows an interrupted task to continue execution exactly where
it left off. TCBs are only accessed by the RTOS.

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2.7 Switching stacks

The following diagram demonstrates the process of switching from one stack to
another.
The scheduler deactivates the task to be suspended (Task 0) by saving the processor
registers on its stack. It then activates the higher-priority task (Task n) by loading
the stack pointer (SP) and the processor registers from the values stored on Task n's
stack.

Task 0 Task n
Task Control Stack Task Control Stack
block block

variables variables
temp. storage temp. storage
ret. addresses ret. addresses
CPU CPU
registers registers
SP SP

Free Stack Free Stack

area area

Scheduler

CPU

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2.8 Change of task status

A task may be in one of several states at any given time. When a task is created, it is
automatically put into the READY state (TS_READY).
A task in the READY state is activated as soon as there is no other READY task with
higher priority. Only one task may be active at a time. If a task with higher priority
becomes READY, this higher priority task is activated and the preempted task
remains in the the READY state.
The active task may be delayed for or until a specified time; in this case it is put into
the DELAY state (TS_DELAY) and the next highest priority task in the READY state is
activated.
The active task may also have to wait for an event (or semaphore, mailbox, or
queue). If the event has not yet occurred, the task is put into the waiting state and
the next highest priority task in the READY state is activated.
A non-existent task is one that is not yet available to embOS; it has either not been
created yet or it has been terminated.
The following illustration shows all possible task states and transitions between
them.

Not existing

CREATETASK() Terminate()

TS_Ready Scheduler Active task

Delay()

Wait for event, TS_DELAY

mailbox or
semaphore

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2.9 How the OS gains control

When the CPU is reset, the special-function registers are set to their respective val-
ues. After reset, program execution begins. The PC register is set to the start
address defined by the start vector or start address (depending on the CPU). This
start address is usually in a startup module shipped with the C compiler, and is some-
times part of the standard library.
The startup code performs the following:
• Loads the stack pointers with the default values, which is for most CPUs
the end of the defined stack segment(s)
• Initializes all data segments to their respective values
• Calls the main() routine.
In a single-task-program, the main() routine is part of your program which takes
control immediately after the C startup. Normally, embOS works with the standard C
startup module without any modification. If there are any changes required, they are
documented in the startup file which is shipped with embOS.
The main() routine is still part of your application program. Basically, main() creates
one or more tasks and then starts multitasking by calling OS_Start(). From then on,
the scheduler controls which task is executed.
The main() routine will not be interrupted by any of the created tasks, because those
tasks are executed only after the call to OS_Start(). It is therefore usually recom-
mended to create all or most of your tasks here, as well as your control structures
such as mailboxes and semaphores. A good practice is to write software in the form
of modules which are (up to a point) reusable. These modules usually have an initial-
ization routine, which creates the required task(s) and/or control structures.
A typical main() looks similar to the following example:
Example
/***********************************************************************
*
* main
*
************************************************************************
*/

void main(void) {
OS_InitKern(); /* Initialize OS (should be first !) */
OS_InitHW(); /* Initialize Hardware for OS (in RtosInit.c) */
/* Call Init routines of all program modules which in turn will create
the tasks they need ... (Order of creation may be important) */
MODULE1_Init();
MODULE2_Init();
MODULE3_Init();
MODULE4_Init();
MODULE5_Init();
OS_Start(); /* Start multitasking */
}

With the call to OS_Start(), the scheduler starts the highest-priority task that has
been created in main().
Note that OS_Start() is called only once during the startup process and does not
return.

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The flowchart below illustrates the starting procedure:

Reset of
CPU

Load SP

Init memory

Init
Hardware
main() C reate task
Semaphore

embOS
Scheduler

Task Task

Task

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2.10 Different builds of embOS

embOS comes in different builds, or versions of the libraries. The reason for different
builds is that requirements vary during development. While developing software, the
performance (and resource usage) is not as important as in the final version which
usually goes as release version into the product. But during development, even small
programming errors should be caught by use of assertions. These assertions are
compiled into the debug version of the embOS libraries and make the code a bit
bigger (about 50%) and also slightly slower than the release or stack check version
used for the final product.
This concept gives you the best of both worlds: a compact and very efficient build for
your final product (release or stack check versions of the libraries), and a safer
(though bigger and slower) version for development which will catch most of the
common application programming errors. Of course, you may also use the release
version of embOS during development, but it will not catch these errors.

2.10.1 Profiling
embOS supports profiling in profiling builds. Profiling makes precise information
available about the execution time of individual tasks. You may always use the profil-
ing libraries, but they induce certain overhead such as bigger task control blocks,
additional ROM (approximately 200 bytes) and additional runtime overhead. This
overhead is usually acceptable, but for best performance you may want to use non-
profiling builds of embOS if you do not use this feature.

2.10.2 List of libraries

In your application program, you need to let the compiler know which build of embOS
you are using. This is done by defining a single identifier prior to including RTOS.h.

Build Define Description

XR: Extreme Smallest fastest build. Does not support
OS_LIBMODE_XR
Release round robin scheduling and task names.
Small, fast build, normally used for release
R: Release OS_LIBMODE_R
version of application
S: Stack check OS_LIBMODE_S Same as release, plus stack checking
SP: Stack check
OS_LIBMODE_SP Same as stack check, plus profiling
plus profiling
D: Debug OS_LIBMODE_D Maximum runtime checking
DP: Debug
OS_LIBMODE_DP Maximum runtime checking, plus profiling
plus profiling
DT: Debug
including Maximum runtime checking, plus tracing API
OS_LIBMODE_DT
trace, calls and profiling
profiling
Table 2.1: List of libraries

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Chapter 3

Task routines

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34 CHAPTER 3 Task routines

A task that should run under embOS needs a task control block (TCB), a stack, and a
normal routine written in C. The following rules apply to task routines:
• The task routine cannot take parameters.
• The task routine must never be called directly from your application.
• The task routine must not return.
• The task routine should be implemented as an endless loop, or it must terminate
itself (see examples below).
• The task routine needs to be started from the scheduler, after the task is created
and OS_Start() is called.
Example of task routine as an endless loop:
/* Example of a task routine as an endless loop */
void Task1(void) {
while(1) {
DoSomething() /* Do something */
OS_Delay(1); /* Give other tasks a chance */
}
}

Example of task routine that terminates itself

/* Example of a task routine that terminates */
void Task2(void) {
char DoSomeMore;
do {
DoSomeMore = DoSomethingElse() /* Do something */
OS_Delay(1); /* Give other tasks a chance */
} while(DoSomeMore);
OS_Terminate(0); /* Terminate yourself */
}

There are different ways to create a task; embOS offers a simple macro that makes
this easy and which is fully sufficient in most cases. However, if you are dynamically
creating and deleting tasks, a routine is available allowing "fine-tuning" of all param-
eters. For most applications, at least initially, using the macro as in the sample start
project works fine.

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3.1 Task routine API function overview

Routine Description
OS_CREATETASK() Creates a task.
OS_CreateTask() Creates a task.
OS_CREATETASK_EX() Creates a task with parameter.
OS_CreateTaskEx() Creates a task with parameter.
OS_Delay() Suspends the calling task for a specified period of time.
OS_DelayUntil() Suspends the calling task until a specified time.
OS_ExtendTaskContext() Make global variables or processor registers task specific.
Returns a pointer to the task control block structure of
OS_GetpCurrentTask()
the currently running task.
OS_GetPriority() Returns the priority of a specified task
OS_GetSuspendCnt() Returns the suspension count.
OS_GetTaskID() Returns the ID of the currently running task.
Determines whether a task control block actually belongs
OS_IsTask()
to a valid task.
Decrements the suspend count of specified task and
OS_Resume()
resumes the task, if the suspend count reaches zero.
OS_SetPriority() Assigns a specified priority to a specified task.
OS_SetTaskName() Allows modification of a task name at runtime.
OS_SetTimeSlice() Assigns a specified timeslice value to a specified task.
OS_Suspend() Suspends the specified task.
OS_Terminate() Ends (terminates) a task.
OS_WakeTask() Ends delay of a task immediately.
OS_Yield() Calls the scheduler to force a task switch.
Table 3.1: Task routine API list

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3.1.1 OS_CREATETASK()
Description
Creates a task.
Prototype
void OS_CREATETASK (OS_TASK* pTask,
char* pName,
void* pRoutine,
unsigned char Priority,
void* pStack);

Parameter Description
Pointer to a data structure of type OS_TASK which will be used as
pTask
task control block (and reference) for this task.
pName Pointer to the name of the task. Can be NULL (or 0) if not used.
pRoutine Pointer to a routine that should run as a task
Priority of the task. Must be within the following range:
Priority 1 <= Priority <=255
Higher values indicate higher priorities.
Pointer to an area of memory in RAM that will serve as stack area
pStack for the task. The size of this block of memory determines the size
of the stack area.
Table 3.2: OS_CREATETASK() parameter list

Additional Information
OS_CREATETASK() is a macro calling an OS library function. It creates a task and
makes it ready for execution by putting it in the READY state. The newly created task
will be activated by the scheduler as soon as there is no other task with higher
priority in the READY state. If there is another task with the same priority, the new
task will be placed right before it. This macro is normally used for creating a task
instead of the function call OS_CreateTask(), because it has fewer parameters and is
therefore easier to use.
OS_CREATETASK() can be called at any time, either from main() during initialization
or from any other task. The recommended strategy is to create all tasks during ini-
tialization in main() to keep the structure of your tasks easy to understand.
The absolute value of Priority is of no importance, only the value in comparison to
the priorities of other tasks.
OS_CREATETASK() determines the size of the stack automatically, using sizeof. This is
possible only if the memory area has been defined at compile time.
Important
The stack that you define has to reside in an area that the CPU can actually use as
stack. Most CPUs cannot use the entire memory area as stack.Most CPUs require
alignment of stack in multiples of bytes. This is automatically done, when the task
stack is defined as an array of integers.
Example
OS_STACKPTR int UserStack[150]; /* Stack-space */
OS_TASK UserTCB; /* Task-control-blocks */

void UserTask(void) {
while (1) {
Delay (100);
}
}

void InitTask(void) {
OS_CREATETASK(&UserTCB, "UserTask", UserTask, 100, UserStack);
}

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3.1.2 OS_CreateTask()
Description
Creates a task.
Prototype
void OS_CreateTask (OS_TASK* pTask,
char* pName,
unsigned char Priority,
voidRoutine* pRoutine,
void* pStack,
unsigned StackSize,
unsigned char TimeSlice);)

Parameter Description
Pointer to a data structure of type OS_TASK which will be used as
pTask
the task control block (and reference) for this task.
pName Pointer to the name of the task. Can be NULL (or 0) if not used.
Priority of the task. Must be within the following range:
Priority 1 <= Priority <=255
Higher values indicate higher priorities.
pRoutine Pointer to a routine that should run as task
Pointer to an area of memory in RAM that will serve as stack area
pStack for the task. The size of this block of memory determines the size
of the stack area.
StackSize Size of the Stack
Time slice value for round-robin scheduling. Has an effect only if
other tasks are running at the same priority.TimeSlice denotes
the time in embOS timer ticks that the task will run until it sus-
TimeSlice
pends; thus enabling another task with the same priority. This
parameter has no effect on some ports of embOS for efficiency
reasons.
Table 3.3: OS_CreateTask() parameter list

Additional Information
This function works the same way as OS_CREATETASK(), except that all parameters of
the task can be specified.
The task can be dynamically created because the stack size is not calculated auto-
matically as it is with the macro.
Important
The stack that you define has to reside in an area that the CPU can actually use as
stack. Most CPUs cannot use the entire memory area as stack.
Most CPUs require alignment of stack in multiples of bytes. This is automatically
done, when the task stack is defined as an array of integers.

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38 CHAPTER 3 Task routines

Example
/* Demo-program to illustrate the use of OS_CreateTask */

OS_STACKPTR int StackMain[100], StackClock[50];

OS_TASK TaskMain,TaskClock;
OS_SEMA SemaLCD;

void Clock(void) {
while(1) {
/* Code to update the clock */
}
}

void Main(void) {
while (1) {
/* Your code */
}
}

void InitTask(void) {
OS_CreateTask(&TaskMain, NULL, 50, Main, StackMain, sizeof(StackMain), 2);
OS_CreateTask(&TaskClock, NULL, 100, Clock,StackClock,sizeof(StackClock),2);
}

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
 39

3.1.3 OS_CREATETASK_EX()
Description
Creates a task and passes a parameter to the task.
Prototype
void OS_CREATETASK_EX (OS_TASK* pTask,
char* pName,
void* pRoutine,
unsigned char Priority,
void* pStack,
void* pContext);

Parameter Description
Pointer to a data structure of type OS_TASK which will be used as
pTask
task control block (and reference) for this task.
pName Pointer to the name of the task. Can be NULL (or 0) if not used.
pRoutine Pointer to a routine that should run as a task.
Priority of the task. Must be within the following range:
Priority 1 <= Priority <=255
Higher values indicate higher priorities.
Pointer to an area of memory in RAM that will serve as stack area
pStack for the task. The size of this block of memory determines the size
of the stack area.
pContext Parameter passed to the created task function.
Table 3.4: OS_CREATETASK_EX() parameter list

Additional Information
OS_CREATETASK_EX() is a macro calling an embOS library function. It works like
OS_CREATETASK(), but allows passing a parameter to the task.
Using a void pointer as additional parameter gives the flexibility to pass any kind of
data to the task function.
Example
The following example is delivered in the Samples folder of embOS.

/*------------------------------------------------------------------
File : Main_TaskEx.c
Purpose : Sample program for embOS using OC_CREATETASK_EX
--------- END-OF-HEADER --------------------------------------------*/

#include "RTOS.h"
OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */
OS_TASK TCBHP, TCBLP; /* Task-control-blocks */
/********************************************************************/
static void TaskEx(void* pData) {
while (1) {
OS_Delay ((OS_TIME) pData);
}
}
/*********************************************************************
*
* main
*
*********************************************************************/
int main(void) {
OS_IncDI(); /* Initially disable interrupts */
OS_InitKern(); /* initialize OS */
OS_InitHW(); /* initialize Hardware for OS */
/* You need to create at least one task before calling OS_Start() */
OS_CREATETASK_EX(&TCBHP, "HP Task", TaskEx, 100, StackHP, (void*) 50);
OS_CREATETASK_EX(&TCBLP, "LP Task", TaskEx, 50, StackLP, (void*) 200);
OS_SendString("Start project will start multitasking !\n");
OS_Start(); /* Start multitasking */
return 0;
}

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40 CHAPTER 3 Task routines

3.1.4 OS_CreateTaskEx()
Description
Creates a task and passes a parameter to the task.
Prototype
void OS_CreateTaskEx (OS_TASK* pTask,
char* pName,
unsigned char Priority,
voidRoutine* pRoutine,
void* pStack,
unsigned StackSize,
unsigned char TimeSlice,
void* pContext);)

Parameter Description
Pointer to a data structure of type OS_TASK which will be used as
pTask
the task control block (and reference) for this task.
pName Pointer to the name of the task. Can be NULL (or 0) if not used.
Priority of the task. Must be within the following range:
Priority 1 <= Priority <=255
Higher values indicate higher priorities.
pRoutine Pointer to a routine that should run as task.
Pointer to an area of memory in RAM that will serve as stack area
pStack for the task. The size of this block of memory determines the size
of the stack area.
StackSize Size of the Stack
Time slice value for round-robin scheduling. Has an effect only if
other tasks are running at the same priority.TimeSlice denotes
the time in embOS timer ticks that the task will run until it sus-
Timeslice
pends; thus enabling another task with the same priority. This
parameter has no effect on some ports of embOS for efficiency
reasons.
pContext Parameter passed to the created task.
Table 3.5: OS_Create_Task_Ex() parameter list

Additional Information
This function works the same way as OS_CreateTask(), except that a parameter is
passed to the task function.
An example of parameter passing to tasks is shown under OS_CREATETASK_EX().

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 41

3.1.5 OS_Delay()
Description
Suspends the calling task for a specified period of time.
Prototype
void OS_Delay (int ms);

Parameter Description
Time interval to delay. Must be within the following range:
ms 1 <= ms <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= ms <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 3.6: OS_Delay() parameter list

Additional Information
The calling task will be put into the TS_DELAY state for the period of time specified.
The task will stay in the delayed state until the specified time has expired. The
parameter ms specifies the precise interval during which the task has to be sus-
pended given in basic time intervals (usually 1/1000 sec). The actual delay (in basic
time intervals) will be in the following range: ms - 1 <= delay <= ms, depending on
when the interrupt for the scheduler will occur.
After the expiration of a delay, the task is made ready again and activated according
to the rules of the scheduler. A delay can be ended prematurely by another task or by
an interrupt handler calling OS_WakeTask().
Example
void Hello() {
printf("Hello");
printf("The next output will occur in 5 seconds");
OS_Delay (5000);
printf("Delay is over");
}

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42 CHAPTER 3 Task routines

3.1.6 OS_DelayUntil()
Description
Suspends the calling task until a specified time.
Prototype
void OS_DelayUntil (int t);

Parameter Description
Time to delay until. Must be within the following range:
1 <= (t - OS_Time) <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit
t
CPUs
1 <= (t - OS_Time) <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
Table 3.7: OS_DelayUntil() parameter list

Additional Information
The calling task will be put into the TS_DELAY state until the time specified.
The OS_DelayUntil() function delays until the value of the time-variable OS_Time
has reached a certain value. It is very useful if you have to avoid accumulating
delays.
Example
int sec,min;

void TaskShowTime() {
int t0 = OS_GetTime();
while (1) {
ShowTime(); /* Routine to display time */
OS_DelayUntil (t0 += 1000);
if (sec < 59) sec++;
else {
sec=0;
min++;
}
}
}

In the example above, the use of OS_Delay() could lead to accumulating delays and
would cause the simple "clock" to be slow.

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 43

3.1.7 OS_ExtendTaskContext()
Description
The function may be used for a varity of purposes. Typical applications include, but
are not limited to:
• global variables such as "errno" in the "C"-library, making the C-lib functions
thread-safe.
• additional, optional CPU / registers such as MAC / EMAC registers (mutliply and
accumulate unit) if they are not saved in the task context per default.
• Co-processor registers such as registers of a VFP (floating point coprocessor).
• Data registers of an add. hardware unit such as a CRC calculation unit
This allows the user to extend the task context as required by his system. A major
advantage is that the task extension is task specific. This means that the additional
information (such as floating point registers) needs to be saved only by tasks that
actually use these registers. The advatange is that the task switing time of the other
tasks is not affected. The same thing is true for the required stack space: Add. stack
space is required only for the tasks which actually save the add. registers.
Prototype
void OS_ExtendTaskContext(const OS_EXTEND_TASK_CONTEXT * pExtendContext);

Parameter Description
Pointer to the OS_EXTEND_TASK_CONTEXT structure which contains
pExtendContext the addresses of the specific save and restore functions which
save and restore the extended task context during task switches.
Table 3.8: OS_ExtendTaskContext() parameter list

Additional Information
The OS_EXTEND_TASK_CONTEXT structure is defined as follows:

typedef struct OS_EXTEND_TASK_CONTEXT {

void (*pfSave) ( void * pStack);
void (*pfRestore)(const void * pStack);
} OS_EXTEND_TASK_CONTEXT;

The save and restore functions have to be declared according the function type used
in the structure.
The sample below shows, how the task stack has to be addressed to save and restore
the extended task context.
OS_ExtendTaskContext() is not available in the XR libraries.
Example
The following example is delivered in the Samples folder of embOS.

----------------------------------------------------------------------
File : ExtendTaskContext.c
Purpose : Sample program for embOS demonstrating how to dynamically
extend the task context.
This example adds a global variable to the task context of
certain tasks.
-------- END-OF-HEADER -----------------------------------------------
*/
#include "RTOS.h"

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */
int GlobalVar;

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44 CHAPTER 3 Task routines

/*********************************************************************
*
* _Restore
* _Save
*
* Function description
* This function pair saves and restores an extended task context.
* In this case, the extended task context consists of just a single
* member, which is a global variable.
*/

typedef struct {
int GlobalVar;
} CONTEXT_EXTENSION;

static void _Save(void * pStack) {

CONTEXT_EXTENSION * p;
p = ((CONTEXT_EXTENSION*)pStack) - (1 - OS_STACK_AT_BOTTOM); // Create pointer
//
// Save all members of the structure
//
p->GlobalVar = GlobalVar;
}

static void _Restore(const void * pStack) {

CONTEXT_EXTENSION * p;
p = ((CONTEXT_EXTENSION*)pStack) - (1 - OS_STACK_AT_BOTTOM); // Create pointer
//
// Restore all members of the structure
//
GlobalVar = p->GlobalVar;
}

/*********************************************************************
*
* Global variable which holds the function pointers
* to save and restore the task context.
*/
const OS_EXTEND_TASK_CONTEXT _SaveRestore = {
_Save,
_Restore
};

/********************************************************************/

/*********************************************************************
*
* HPTask
*
* Function description
* During the execution of this function, the thread-specific
* global variable has always the same value of 1.
*/
static void HPTask(void) {
OS_ExtendTaskContext(&_SaveRestore);
GlobalVar = 1;
while (1) {
OS_Delay (10);
}
}

/*********************************************************************
*
* LPTask
*
* Function description
* During the execution of this function, the thread-specific
* global variable has always the same value of 2.
*/
static void LPTask(void) {
OS_ExtendTaskContext(&_SaveRestore);
GlobalVar = 2;
while (1) {
OS_Delay (50);
}
}

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG
 45

/*********************************************************************
*
* main
*/
int main(void) {
OS_IncDI(); /* Initially disable interrupts */
OS_InitKern(); /* initialize OS */
OS_InitHW(); /* initialize Hardware for OS */
/* You need to create at least one task here ! */
OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);
OS_CREATETASK(&TCBLP, "LP Task", LPTask, 50, StackLP);
OS_Start(); /* Start multitasking */
return 0;
}

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46 CHAPTER 3 Task routines

3.1.8 OS_GetpCurrentTask()
Description
Returns a pointer to the task control block structure of the currently running task.
Prototype
OS_TASK* OS_GetpCurrentTask (void);

Return value
OS_TASK*: A pointer to the task control block structure.
Additional Information
This function may be used for determining which task is executing. This may be help-
ful if the reaction of any function depends on the currently running task.

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 47

3.1.9 OS_GetPriority()
Description
Returns the priority of a specified task.
Prototype
unsigned char OS_GetPriority (OS_TASK* pTask);

Parameter Description
pTask Pointer to a data structure of type OS_TASK.
Table 3.9: OS_GetPriority() parameter list

Return value
Priority of the specified task as an "unsigned character" (range 1 to 255).
Additional Information
If pTask is the NULL pointer, the function returns the priority of the currently running
task. If pTask does not specify a valid task, the debug version of embOS calls
OS_Error(). The release version of embOS cannot check the validity of pTask and
may therefore return invalid values if pTask does not specify a valid task.
Important
This function may not be called from within an interrupt handler.

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48 CHAPTER 3 Task routines

3.1.10 OS_GetSuspendCnt()
Description
The function returns the suspension count and thus suspension state of the specified
task. This function may be used for examining whether a task is suspended by previ-
ous calls of OS_Suspend().
Prototype
unsigned char OS_GetSuspendCnt (OS_TASK* pTask);

Parameter Description
pTask Pointer to a data structure of type OS_TASK.
Table 3.10: OS_GetSuspendCnt() parameter list

Return value
Suspension count of the specified task as unsigned character value.
0: Task is not suspended.
>0: Task is suspended by at least one call of OS_Suspend().
Additional Information
If pTask does not specify a valid task, the debug version of embOS calls OS_Error().
The release version of embOS can not check the validity of pTask and may therefore
return invalid values if pTask does not specify a valid task. When tasks are created
and terminated dynamically, OS_IsTask() may be called prior calling
OS_GetSuspendCnt() to examine whether the task is valid. The remturned value can
be used for resuming a suspended task by calling OS_Resume() as often as indicated
by the returned value.
Example
/* Demo-function to illustrate the use of OS_GetSuspendCnt() */

void ResumeTask(OS_TASK* pTask) {

unsigned char SuspendCnt;
SuspendCnt = OS_GetSuspendCnt(pTask);
while(SuspendCnt > 0) {
OS_Resume(pTask); /* May cause a task switch */
SuspendCnt--;
}
}

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 49

3.1.11 OS_GetTaskID()
Description
Returns the ID of the currently running task.
Prototype
OS_TASKID OS_GetTaskID (void);

Return value
OS_TASKID: A pointer to the task control block. A value of 0 (NULL) indicates that no
task is executing.
Additional Information
This function may be used for determining which task is executing. This may be help-
ful if the reaction of any function depends on the currently running task.

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50 CHAPTER 3 Task routines

3.1.12 OS_IsTask()
Description
Determines whether a task control block actually belongs to a valid task.
Prototype
char OS_IsTask (OS_TASK* pTask);

Parameter Description
Pointer to a data structure of type OS_TASK which is used as task
pTask
control block (and reference) for this task.
Table 3.11: OS_IsTask() parameter list

Return value
Character value:
0: TCB is not used by any task
1: TCB is used by a task
Additional Information
This function checks if the specified task is still in the internal task list. If the task
was terminated, it is removed from the internal task list. This function may be useful
to determine whether the task control block and stack for the task may be reused for
another task in applications that create and terminate tasks dynamically.

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 51

3.1.13 OS_Resume()
Description
Decrements the suspend count of the specified task and resumes it, if the suspend
count reaches zero.
Prototype
void OS_Resume (OS_TASK* pTask);

Parameter Description
Pointer to a data structure of type OS_TASK which is used as task
pTask control block (and reference) for the task that should be sus-
pended.
Table 3.12: OS_Resume() parameter list

Additional Information
The specified task's suspend count is decremented. If the resulting value is 0, the
execution of the specified task is resumed.
If the task is not blocked by other task blocking mechanisms, the task will be set
back in ready state and continues operation according to the rules of the scheduler.
In debug versions of embOS, the OS_Resume() function checks the suspend count of
the specified task. If the suspend count is 0 when OS_Resume() is called, the
specified task is not currently suspended and OS_Error() is called with error
OS_ERR_RESUME_BEFORE_SUSPEND.

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52 CHAPTER 3 Task routines

3.1.14 OS_SetPriority()
Description
Assigns a specified priority to a specified task.
Prototype
void OS_SetPriority (OS_TASK* pTask,
unsigned char Priority);

Parameter Description
pTask Pointer to a data structure of type OS_TASK.
Priority of the task. Must be within the following range:
Priority
1 <= Priority <= 255 Higher values indicate higher priorities.
Table 3.13: OS_SetPriority() parameter list

Additional Information
Can be called at any time from any task or software timer. Calling this function might
lead to an immediate task switch.
Important
This function may not be called from within an interrupt handler.

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 53

3.1.15 OS_SetTaskName()
Description
Allows modification of a task name at runtime.
Prototype
void OS_SetTaskNamePriority (OS_TASK* pTask,
const char* s);

Parameter Description
pTask Pointer to a data structure of type OS_TASK.
s Pointer to a zero terminated string which is used as task name.
Table 3.14: OS_SetTaskName() parameter list

Additional Information
Can be called at any time from any task or software timer.
When pTask is the NULL pointer, the name of the currently running task is modified.

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54 CHAPTER 3 Task routines

3.1.16 OS_SetTimeSlice()
Description
Assigns a specified timeslice value to a specified task.
Prototype
unsigned char OS_SetTimeSlice (OS_TASK* pTask,
unsigned char TimeSlice);

Parameter Description
pTask Pointer to a data structure of type OS_TASK.
New timeslice value for the task. Must be within the following
TimeSlice range:
1 <= TimeSlice <= 255.
Table 3.15: OS_SetTimeSlice() parameter list

Return value
Previous timeslice value of the task as unsigned char.
Additional Information
Can be called at any time from any task or software timer. Setting the timeslice value
only affects the tasks running in round-robin mode. This means another task with the
same priority must exist.
The new timeslice value is interpreted as reload value. It is used after the next acti-
vation of the task. It does not affect the remaining timeslice of a running task.

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 55

3.1.17 OS_Suspend()
Description
Suspends the specified task.
Prototype
void OS_Suspend (OS_TASK* pTask);

Parameter Description
Pointer to a data structure of type OS_TASK which is used as task
pTask control block (and reference) for the task that should be sus-
pended.
Table 3.16: OS_Suspend() parameter list

Additional Information
If pTask is the NULL pointer, the current task suspends.
If the function succeeds, execution of the specified task is suspended and the task's
suspend count is incremented. The specified task will be suspended immediately. It
can only be restarted by a call of OS_Resume().
Every task has a suspend count with a maximum value of OS_MAX_SUSPEND_CNT. If
the suspend count is greater than zero, the task is suspended.
In debug versions of embOS, calling OS_Suspend() more often than
OS_MAX_SUSPEND_CNT times without calling OS_Resume(), the task's internal suspend
count is not incremented and OS_Error() is called with error
OS_ERR_SUSPEND_TOO_OFTEN.

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56 CHAPTER 3 Task routines

3.1.18 OS_Terminate()
Description
Ends (terminates) a task.
Prototype
void OS_Terminate (OS_TASK* pTask);

Parameter Description
Pointer to a data structure of type OS_TASK which is used as task
pTask
control block (and reference) for this task.
Table 3.17: OS_Terminate() parameter list

Additional Information
If pTask is the NULL pointer, the current task terminates. The specified task will ter-
minate immediately. The memory used for stack and task control block can be reas-
signed.
Since version 3.26 of embOS, all resources which are held by the terminated task are
released. Any task may be terminated regardless of its state. This functionality is
default for any 16-bit or 32-bit CPU and may be changed by recompiling embOS
sources. On 8-bit CPUs, terminating tasks that hold any resources is prohibited. To
enable safe termination, the embOS sources have to be recompiled with the compile
time switch OS_SUPPORT_CLEANUP_ON_TERMINATE activated.
Important
This function may not be called from within an interrupt handler.

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 57

3.1.19 OS_WakeTask()
Description
Ends delay of a task immediately.
Prototype
void OS_WakeTask (OS_TASK* pTask);

Parameter Description
Pointer to a data structure of type OS_TASK which is used as task
pTask
control block (and reference) for this task.
Table 3.18: OS_WakeTask() parameter list

Additional Information
Puts the specified task, which is already suspended for a certain amount of time with
OS_Delay() or OS_DelayUntil() back to the state TS_READY (ready for execution).
The specified task will be activated immediately if it has a higher priority than the
priority of the task that had the highest priority before. If the specified task is not in
the state TS_DELAY (because it has already been activated, or the delay has already
expired, or for some other reason), this command is ignored.

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58 CHAPTER 3 Task routines

3.1.20 OS_Yield()
Description
Calls the scheduler to force a task switch.
Prototype
void OS_Yield (void);

Additional Information
If the task is running on round-robin, it will be suspended if there is an other task
with the same priority ready for execution.

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Chapter 4

Software timers

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60 CHAPTER 4 Software timers

A software timer is an object that calls a user-specified routine after a specified

delay. A basically unlimited number of software timers can be defined with the macro
OS_CREATETIMER().
Timers can be stopped, started and retriggered much like hardware timers. When
defining a timer, you specify any routine that is to be called after the expiration of
the delay. Timer routines are similar to interrupt routines; they have a priority higher
than the priority of all tasks. For that reason they should be kept short just like
interrupt routines.
Software timers are called by embOS with interrupts enabled, so they can be inter-
rupted by any hardware interrupt. Generally, timers run in single-shot mode, which
means they expire only once and call their callback routine only once. By calling
OS_RetriggerTimer() from within the callback routine, the timer is restarted with its
initial delay time and therefore works just as a free-running timer.
The state of timers can be checked by the functions OS_GetTimerStatus(),
OS_GetTimerValue(), and OS_GetTimerPeriod().
Maximum timeout / period
The timeout value is stored as an integer, thus a 16-bit value on 8/16-bit CPUs, a 32-
bit value on 32-bit CPUs. The comparisons are done as signed comparisons, (because
expired time-outs are permitted). This means that only 15-bits can be used on 8/16
bit CPUs, 31-bits on 32-bit CPUs. Another factor to take into account is the maximum
time spent in critical regions. During critical regions timers may expire, but because
the timer routine can not be called from a critical region (timers are "put on hold"),
the maximum time that the system spends at once in a critical region needs to be
deducted. In most systems, this is no more than a single tick. However, to be safe,
we have assumed that your system spends no more than up to 255 ticks in a row in
a critical region and defined a macro which defines the maximum timeout value. It is
normally 0x7F00 for 8/16-bit systems or 0x7FFFFF00 for 32-bit Systems and defined
in RTOS.h as OS_TIMER_MAX_TIME. If your system spends more than 255 ticks without
break in a critical section (effectively disabling the scheduler during this time ... not
recommended), you have to make sure your application uses shorter timeouts.
Extended software timers
Sometimes it may be useful to pass a paramter to the timer callback function. This
allows usage of one callback function for different software timers.
Since version 3.32m of embOS, the extended timer structure and related extended
timer functions were implemented to allow parameter passing to the callback func-
tion.
Except the different callback function with parameter passing, extended timers
behave exactly the same as normal embOS software timers and may be used in par-
allel with normal software timers.

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 61

4.1 Software timers API function overview

Routine Description
OS_CREATETIMER() Macro that creates and starts a software-timer.
OS_CreateTimer() Creates a software timer without starting it.
OS_StartTimer() Starts a software timer.
OS_StopTimer() Stops a software timer.
OS_RetriggerTimer() Restarts a software timer with its initial time value.
OS_SetTimerPeriod() Sets a new timer reload value for a software timer.
OS_DeleteTimer() Stops and deletes a software timer.
OS_GetTimerPeriod() Returns the current reload value of a software timer.
OS_GetTimerValue() Returns the remaining timer value of a software timer.
OS_GetTimerStatus() Returns the current timer status of a software timer.
Returns a pointer to the data structure of the timer
OS_GetpCurrentTimer()
that just expired.
Macro that creates and starts an extended software-
OS_CREATETIMER_EX()
timer.
Creates an extended software timer without starting
OS_CreateTimer_Ex()
it.
OS_StartTimer_Ex() Starts an extended timer.
OS_StopTimer_Ex() Stops an extended timer.
OS_RetriggerTimer_Ex() Restarts an extended timer with its initial time value.
OS_SetTimerPeriod_Ex() Sets a new timer reload value for an extended timer.
OS_DeleteTimer_Ex() Stops and deletes an extended timer.
OS_GetTimerPeriod_Ex() Returns the current reload value of an extended timer.
Returns the remaining timer value of an extended
OS_GetTimerValue_Ex()
timer.
OS_GetTimerStatus_Ex() Returns the current timer status of an extended timer.
Returns a pointer to the data structure of the extended
OS_GetpCurrentTimerEx()
timer that just expired.
Table 4.1: Software timers API

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4.1.1 OS_CREATETIMER()
Description
Macro that creates and starts a software timer.
Prototype
void OS_CREATETIMER (OS_TIMER* pTimer,
OS_TIMERROUTINE* Callback,
OS_TIME Timeout);)

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Pointer to the callback routine to be called from the RTOS after
expiration of the delay. The callback function hast to be a void
Callback
function which does not take any parameter and does not return
any value.
Initial timeout in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 4.2: OS_CREATETIMER() parameter list

Additional Information
embOS keeps track of the timers by using a linked list. Once the timeout is expired,
the callback routine will be called immediately (unless the current task is in a critical
region or has interrupts disabled).
This macro uses the functions OS_CreateTimer() and OS_StartTimer(). It is sup-
plied for backward compatibility; in newer applications these routines should be
called directly instead.
OS_TIMERROUTINE is defined in RTOS.h as follows:
typedef void OS_TIMERROUTINE(void);

Source of the macro (in RTOS.h ):

#define OS_CREATETIMER(pTimer,c,d) \
OS_CreateTimer(pTimer,c,d); \
OS_StartTimer(pTimer);

Example
OS_TIMER TIMER100;

void Timer100(void) {
LED = LED ? 0 : 1; /* Toggle LED */
OS_RetriggerTimer(&TIMER100); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start Timer100 */
OS_CREATETIMER(&TIMER100, Timer100, 100);
}

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4.1.2 OS_CreateTimer()
Description
Creates a software timer (but does not start it).
Prototype
void OS_CreateTimer (OS_TIMER* pTimer,
OS_TIMERROUTINE* Callback,
OS_TIME Timeout);)

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Pointer to the callback routine to be called from the RTOS after
Callback
expiration of the delay.
Initial timeout in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
Table 4.3: OS_CreateTimer() parameter list

Additional Information
embOS keeps track of the timers by using a linked list. Once the timeout is expired,
the callback routine will be called immediately (unless the current task is in a critical
region or has interrupts disabled). The timer is not automatically started. This has to
be done explicitly by a call of OS_StartTimer() or OS_RetriggerTimer().
OS_TIMERROUTINE is defined in RTOS.h as follows:
typedef void OS_TIMERROUTINE(void);

Example
OS_TIMER TIMER100;

void Timer100(void) {
LED = LED ? 0 : 1; /* Toggle LED */
OS_RetriggerTimer(&TIMER100); /* Make timer periodical */
}

void InitTask(void) {
/* Create Timer100, start it elsewhere */
OS_CreateTimer(&TIMER100, Timer100, 100);
}

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4.1.3 OS_StartTimer()
Description
Starts a software timer.
Prototype
void OS_StartTimer (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.4: OS_StartTimer() parameter list

Additional Information
OS_StartTimer() is used for the following reasons:
• Start a timer which was created by OS_CreateTimer(). The timer will start with
its initial timer value.
• Restart a timer which was stopped by calling OS_StopTimer(). In this case, the
timer will continue with the remaining time value which was preserved by stop-
ping the timer.
Important
This function has no effect on running timers. It also has no effect on timers that are
not running, but have expired. Use OS_RetriggerTimer() to restart those timers.

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4.1.4 OS_StopTimer()
Description
Stops a software timer.
Prototype
void OS_StopTimer (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.5: OS_StopTimer() parameter list

Additional Information
The actual value of the timer (the time until expiration) is kept until
OS_StartTimer() lets the timer continue.

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4.1.5 OS_RetriggerTimer()
Description
Restarts a software timer with its initial time value.
Prototype
void OS_RetriggerTimer (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.6: OS_RetriggerTimer() parameter list

Additional Information
OS_RetriggerTimer() restarts the timer using the initial time value programmed at
creation of the timer or with the function OS_SetTimerPeriod().
Example
OS_TIMER TIMERCursor;
BOOL CursorOn;

void TimerCursor(void) {
if (CursorOn) ToggleCursor(); /* Invert character at cursor-position */
OS_RetriggerTimer(&TIMERCursor); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start TimerCursor */
OS_CREATETIMER(&TIMERCursor, TimerCursor, 500);
}

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4.1.6 OS_SetTimerPeriod()
Description
Sets a new timer reload value for a software timer.
Prototype
void OS_SetTimerPeriod (OS_TIMER* pTimer,
OS_TIME Period);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Timer period in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Period values are
1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
Table 4.7: OS_SetTimerPeriod() parameter list

Additional Information
OS_SetTimerPeriod() sets the initial time value of the specified timer. Period is the
reload value of the timer to be used as initial value when the timer is retriggered by
OS_RetriggerTimer().
Example
OS_TIMER TIMERPulse;
BOOL CursorOn;

void TimerPulse(void) {
if TogglePulseOutput(); /* Toggle output */
OS_RetriggerTimer(&TIMERCursor); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start Pulse Timer with first pulse = 500ms */
OS_CREATETIMER(&TIMERPulse, TimerPulse, 500);
/* Set timer period to 200 ms for further pulses */
OS_SetTimerPeriod(&TIMERPulse, 200);
}

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4.1.7 OS_DeleteTimer()
Description
Stops and deletes a software timer.
Prototype
void OS_DeleteTimer (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.8: OS_DeleteTimer() parameter list

Additional Information
The timer is stopped and therefore removed out of the linked list of running timers.
In debug builds of embOS, the timer is also marked as invalid.

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4.1.8 OS_GetTimerPeriod()
Description
Returns the current reload value of a software timer.
Prototype
OS_TIME OS_GetTimerPeriod (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.9: OS_GetTimerPeriod() parameter list

Return value
Type OS_TIME, which is defined as an integer between
1 and 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between
1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer
values.
Additional Information
The period returned is the reload value of the timer set as initial value when the
timer is retriggered by OS_RetriggerTimer().

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4.1.9 OS_GetTimerValue()
Description
Returns the remaining timer value of a software timer.
Prototype
OS_TIME OS_GetTimerValue (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.10: OS_GetTimerValue() parameter list

Return value
Type OS_TIME, which is defined as an integer between
1 and 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between
1 and <= 2 31 -1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer
values.
The returned time value is the remaining timer time in embOS tick units until expira-
tion of the timer.

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4.1.10 OS_GetTimerStatus()
Description
Returns the current timer status of a software timer.
Prototype
unsigned char OS_GetTimerStatus (OS_TIMER* pTimer);

Parameter Description
Pointer to the OS_TIMER data structure which contains the data of
pTimer
the timer.
Table 4.11: OS_GetTimerStatus parameter list

Return value
Unsigned character, denoting whether the specified timer is running or not:
0: timer has stopped
! = 0: timer is running.

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4.1.11 OS_GetpCurrentTimer()
Description
Returns a pointer to the data structure of the timer that just expired.
Prototype
OS_TIMER* OS_GetpCurrentTimer (void);

Return value
OS_TIMER*: A pointer to the control structure of a timer.
Additional Information
The return value of OS_GetpCurrentTimer() is valid during execution of a timer call-
back function; otherwise it is undetermined. If only one callback function should be
used for multiple timers, this function can be used for examining the timer that
expired.
The example below shows one usage of OS_GetpCurrentTimer(). Since version
3.32m of embOS, the extended timer structure and functions which come with
embOS may be used to generate and use software timer with individual parameter
for the callback function.
Example
#include "RTOS.H"

/********************************************************
*
* Types
*/
typedef struct { /* Timer object with its own user data */
OS_TIMER Timer;
void* pUser;
} TIMER_EX;

/********************************************************
*
* Variables
*/

TIMER_EX Timer_User;
int a;

/********************************************************
*
* Local Functions
*/

void CreateTimer(TIMER_EX* timer, OS_TIMERROUTINE* Callback, OS_UINT Timeout,

void* pUser) {
timer->pUser = pUser;
OS_CreateTimer((OS_TIMER*) timer, Callback, Timeout);
}

void cb(void) { /* Timer callback function for multiple timers */

TIMER_EX* p = (TIMER_EX*)OS_GetpCurrentTimer();
void* pUser = p->pUser; /* Examine user data */
OS_RetriggerTimer(&p->Timer); /* Retrigger timer */
}

/********************************************************
*
* main
*/
int main(void) {
OS_InitKern(); /* Initialize OS */
OS_InitHW(); /* Initialize Hardware for OS */
CreateTimer(&Timer_User, cb, 100, &a);
OS_Start(); /* Start multitasking */
return 0;
}

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4.1.12 OS_CREATETIMER_EX()
Description
Macro that creates and starts an extended software timer.
Prototype
void OS_CREATETIMER_EX (OS_TIMER_EX* pTimerEx,
OS_TIMER_EX_ROUTINE* Callback,
OS_TIME Timeout
void* pData)

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Pointer to the callback routine to be called from the RTOS after
expiration of the delay. The callback function hast to be of type
Callback
OS_TIMER_EX_ROUTINE which takes a void pointer as parameter
and does not return any value.
Initial timeout in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
A void pointer which is used as parameter for the extended timer
pData
callback function.
Table 4.12: OS_CREATETIMER_EX() parameter list

Additional Information
embOS keeps track of the timers by using a linked list. Once the timeout is expired,
the callback routine will be called immediately (unless the current task is in a critical
region or has interrupts disabled).
This macro uses the functions OS_CreateTimerEx() and OS_StartTimerEx().
OS_TIMER_EX_ROUTINE is defined in RTOS.h as follows:
typedef void OS_TIMER_EX_ROUTINE(void *);

Source of the macro (in RTOS.h ):

#define OS_CREATETIMER_EX(pTimerEx,cb,Timeout,pData) \
OS_CreateTimerEx(pTimerEx,cb,Timeout,pData); \
OS_StartTimerEx(pTimerEx)

Example
OS_TIMER TIMER100;
OS_TASK TCB_HP;

void Timer100(void* pTask) {

LED = LED ? 0 : 1; /* Toggle LED */
if (pTask != NULL) {
OS_SignalEvent(0x01, (OS_TASK*)pTask);
}
OS_RetriggerTimerEx(&TIMER100); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start Timer100 */
OS_CREATETIMER_EX(&TIMER100, Timer100, 100, (void*) &TCB_HP);
}

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4.1.13 OS_CreateTimerEx()
Description
Creates an extended software timer (but does not start it).
Prototype
void OS_CreateTimerEx (OS_TIMER_EX* pTimerEx,
OS_TIMER_EX_ROUTINE* Callback,
OS_TIME Timeout,
void* pData)

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Pointer to the callback routine of type OS_TIMER_EX_ROUTINE to
Callback
be called from the RTOS after expiration of the timer.
Initial timeout in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
A void pointer which is used as parameter for the extended timer
pData
callback function.
Table 4.13: OS_CreateTimerEx() parameter list

Additional Information
embOS keeps track of the timers by using a linked list. Once the timeout has expired,
the callback routine will be called immediately (unless the current task is in a critical
region or has interrupts disabled).
The extended software timer is not automatically started. This has to be done explic-
itly by a call of OS_StartTimerEx() or OS_RetriggerTimerEx().

OS_TIMER_EX_ROUTINE is defined in RTOS.h as follows:

typedef void OS_TIMER_EX_ROUTINE(void*);

Example
OS_TIMER TIMER100;
OS_TASK TCB_HP;

void Timer100(void* pTask) {

LED = LED ? 0 : 1; /* Toggle LED */
if (pTask != NULL) {
OS_SignalEvent(0x01, (OS_TASK*) pTask);
}
OS_RetriggerTimerEx(&TIMER100); /* Make timer periodical */
}

void InitTask(void) {
/* Create Timer100, start it elsewhere later on*/
OS_CreateTimerEx(&TIMER100, Timer100, 100, (void*) & TCB_HP);
}

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4.1.14 OS_StartTimerEx()
Description
Starts an extended software timer.
Prototype
void OS_StartTimerEx (OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Table 4.14: OS_StartTimereEx() parameter list

Additional Information
OS_StartTimerEx() is used for the following reasons:
• Start an extended software timer which was created by OS_CreateTimerEx().
The timer will start with its initial timer value.
• Restart a timer which was stopped by calling OS_StopTimerEx(). In this case,
the timer will continue with the remaining time value which was preserved by
stopping the timer.
Important
This function has no effect on running timers. It also has no effect on timers that are
not running, but have expired. Use OS_RetriggerTimerEx() to restart those timers.

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4.1.15 OS_StopTimerEx()
Description
Stops an extended software timer.
Prototype
void OS_StopTimerEx (OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Table 4.15: OS_StopTimerEx() parameter list

Additional Information
The actual time value of the extended software timer (the time until expiration) is
kept until OS_StartTimerEx() lets the timer continue.

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4.1.16 OS_RetriggerTimerEx()
Description
Restarts an extended software timer with its initial time value.
Prototype
void OS_RetriggerTimerEx (OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Table 4.16: OS_RetriggerTimerEx() parameter list

Additional Information
OS_RetriggerTimerEx() restarts the extended software timer using the initial time
value which was programmed at creation of the timer or which was set using the
function OS_SetTimerPeriodEx().
Example
OS_TIMER TIMERCursor;
OS_TASK TCB_HP;
BOOL CursorOn;

void TimerCursor(void* pTask) {

if (CursorOn != 0) ToggleCursor(); /* Invert character at cursor-position */
OS_SignalEvent(0x01, (OS_TASK*) pTask);
OS_RetriggerTimerEx(&TIMERCursor); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start TimerCursor */
OS_CREATETIMER_EX(&TIMERCursor, TimerCursor, 500, (void*)&TCB_HP);
}

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4.1.17 OS_SetTimerPeriodEx()
Description
Sets a new timer reload value for an extended software timer.
Prototype
void OS_SetTimerPeriodEx (OS_TIMER_EX* pTimerEx,
OS_TIME Period);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended software timer.
Timer period in basic embOS time units (nominal ms):
The data type OS_TIME is defined as an integer, therefore valid
Period values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 4.17: OS_SetTimerPeriodEx() parameter list

Additional Information
OS_SetTimerPeriodEx() sets the initial time value of the specified extended soft-
ware timer. Period is the reload value of the timer to be used as initial value when
the timer is retriggered the next time by OS_RetriggerTimerEx().
A call of OS_SetTimerPeriodEx() does not affect the remaining time period of an
extended software timer.
Example
OS_TIMER_EX TIMERPulse;
OS_TASK TCB_HP;

void TimerPulse(void* pTask) {

OS_SignalEvent(0x01, (OS_TASK*) pTask);
OS_RetriggerTimerEx(&TIMERPulse); /* Make timer periodical */
}

void InitTask(void) {
/* Create and start Pulse Timer with first pulse == 500ms */
OS_CREATETIMER_EX(&TIMERPulse, TimerPulse, 500, (void*)&TCB_HP);
/* Set timer period to 200 ms for further pulses */
OS_SetTimerPeriodEx(&TIMERPulse, 200);
}

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4.1.18 OS_DeleteTimerEx()
Description
Stops and deletes an extended software timer.
Prototype
void OS_DeleteTimerEx(OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the timer.
Table 4.18: OS_DeleteTimerEx() parameter list

Additional Information
The extended software timer is stopped and therefore removed out of the linked list
of running timers. In debug builds of embOS, the timer is also marked as invalid.

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4.1.19 OS_GetTimerPeriodEx()
Description
Returns the current reload value of an extended software timer.
Prototype
OS_TIME OS_GetTimerPeriodEx (OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended timer.
Table 4.19: OS_GetTimerPeriodEx() parameter list

Return value
Type OS_TIME, which is defined as an integer between
1 and 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between
1 and <= 2 31 -1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer
values.
Additional Information
The period returned is the reload value of the timer which was set as initial value
when the timer was created or which was modified by a call of
OS_SetTimerPeriodEx(). This reload value will be used as time period when the
timer is is retriggered by OS_RetriggerTimerEx().

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4.1.20 OS_GetTimerValueEx()
Description
Returns the remaining timer value of an extended software timer.
Prototype
OS_TIME OS_GetTimerValueEx(OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the timer.
Table 4.20: OS_GetTimerValueEx() parameter list

Return value
Type OS_TIME, which is defined as an integer between
1 and 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between
1 and <= 231-1 = 0x7FFFFFFF for 32-bit CPUs, which is the permitted range of timer
values.
The returned time value is the remaining timer time in embOS tick units until expira-
tion of the extended software timer.

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4.1.21 OS_GetTimerStatusEx()
Description
Returns the current timer status of an extended software timer.
Prototype
unsigned char OS_GetTimerStatusEx (OS_TIMER_EX* pTimerEx);

Parameter Description
Pointer to the OS_TIMER_EX data structure which contains the
pTimerEx
data of the extended timer.
Table 4.21: OS_GetTimerStatusEx parameter list

Return value
Unsigned character, denoting whether the specified timer is running or not:
0: timer has stopped
! = 0: timer is running.

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4.1.22 OS_GetpCurrentTimerEx()
Description
Returns a pointer to the data structure of the extended timer that just expired.
Prototype
OS_TIMER_EX* OS_GetpCurrentTimerEx (void);

Return value
OS_TIMER_EX*: A pointer to the control structure of an extended software timer.
Additional Information
The return value of OS_GetpCurrentTimerEx() is valid during execution of a timer
callback function; otherwise it is undetermined. If one callback function should be
used for multiple extended timers, this function can be used for examining the timer
that expired.
Example

#include "RTOS.H"

OS_TIMER_EX MyTimerEx;

/********************************************************
*
* Local Functions
*/

void cbTimerEx(void* pData) { /* Timer callback function for multiple timers */

OS_TIMER_EX* pTimerEx;

pTimerEx = OS_GetpCurrentTimerEx();
OS_SignalEvent(0x01, (OS_TASK*) pData);
OS_RetriggerTimer(pTimerEx); /* Retrigger timer */
}

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 85

Chapter 5

Resource semaphores

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86 CHAPTER 5 Resource semaphores

Resource semaphores are used for managing resources by avoiding conflicts caused
by simultaneous use of a resource. The resource managed can be of any kind: a part
of the program that is not reentrant, a piece of hardware like the display, a flash
prom that can only be written to by a single task at a time, a motor in a CNC control
that can only be controlled by one task at a time, and a lot more.
The basic procedure is as follows:
Any task that uses a resource first claims it calling the OS_Use() or OS_Request()
routines of embOS. If the resource is available, the program execution of the task
continues, but the resource is blocked for other tasks. If a second task now tries to
use the same resource while it is in use by the first task, this second task is sus-
pended until the first task releases the resource. However, if the first task that uses
the resource calls OS_Use() again for that resource, it is not suspended because the
resource is blocked only for other tasks.
The following diagram illustrates the process of using a resource:

USE()

Access resource

UNUSE()

A resource semaphore contains a counter that keeps track of how many times the
resource has been claimed by calling OS_Request() or OS_Use() by a particular task.
It is released when that counter reaches 0, which means the OS_Unuse() routine has
to be called exactly the same number of times as OS_Use() or OS_Request(). If it is
not, the resource remains blocked for other tasks.
On the other hand, a task cannot release a resource that it does not own by calling
OS_Unuse(). In the debug version of embOS, a call of OS_Unuse() for a semaphore
that is not owned by this task will result in a call to the error handler OS_Error().
Example of using resource semaphores
Here, two tasks access an LC display completely independently from each other. The
LCD is a resource that needs to be protected with a resource semaphore. One task
may not interrupt another task which is writing to the LCD, because otherwise the
following might occur:
• Task A positions the cursor
• Task B interrupts Task A and repositions the cursor
• Task A writes to the wrong place in the LCD' s memory.
To avoid this type of situation, every the LCD must be accessed by a task, it is first
claimed by a call to OS_Use() (and is automatically waited for if the resource is
blocked). After the LCD has been written to, it is released by a call to OS_Unuse().

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 87

/*
* demo program to illustrate the use of resource semaphores
*/
OS_STACKPTR int StackMain[100], StackClock[50];
OS_TASK TaskMain,TaskClock;
OS_SEMA SemaLCD;

void TaskClock(void) {
char t=-1;
char s[] = "00:00";
while(1) {
while (TimeSec==t) Delay(10);
t= TimeSec;
s[4] = TimeSec%10+'0';
s[3] = TimeSec/10+'0';
s[1] = TimeMin%10+'0';
s[0] = TimeMin/10+'0';
OS_Use(&SemaLCD); /* Make sure nobody else uses LCD */
LCD_Write(10,0,s);
OS_Unuse(&SemaLCD); /* Release LCD */
}
}

void TaskMain(void) {
signed char pos ;
LCD_Write(0,0,"Software tools by Segger ! ") ;
OS_Delay(2000);
while (1) {
for ( pos=14 ; pos >=0 ; pos-- ) {
OS_Use(&SemaLCD); /* Make sure nobody else uses LCD */
LCD_Write(pos,1,"train "); /* Draw train */
OS_Unuse(&SemaLCD); /* Release LCD */
OS_Delay(500);
}
OS_Use(&SemaLCD); /* Make sure nobody else uses LCD */
LCD_Write(0,1," ") ;
OS_Unuse(&SemaLCD); /* Release LCD */
}
}

void InitTask(void) {
OS_CREATERSEMA(&SemaLCD); /* Creates resource semaphore */
OS_CREATETASK(&TaskMain, 0, Main, 50, StackMain);
OS_CREATETASK(&TaskClock, 0, Clock, 100, StackClock);
}

In most applications, the routines that access a resource should automatically call
OS_Use() and OS_Unuse() so that when using the resource you do not have to worry
about it and can use it just as you would in a single-task system. The following is an
example of how to implement a resource into the routines that actually access the
display:

/*
* Simple example when accessing single line dot matrix LCD
*/
OS_RSEMA RDisp; /* Define resource semaphore */

void UseDisp() { /* Simple routine to be called before using display */

OS_Use(&RDisp);
}

void UnuseDisp() { /* Simple routine to be called after using display */

OS_Unuse(&RDisp);
}

void DispCharAt(char c, char x) {

UseDisp();
LCDGoto(x, y);
LCDWrite1(ASCII2LCD(c));
UnuseDisp();
}

void DISPInit(void) {
OS_CREATERSEMA(&RDisp);
}

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5.1 Resource semaphores API function overview

Routine Description
OS_CREATERSEMA() Macro that creates a resource semaphore.
OS_Use() Claims a resource and blocks it for other tasks.
OS_Unuse() Releases a semaphore currently in use by a task.
Requests a specified semaphore, blocks it for other tasks
OS_Request()
if it is available. Continues execution in any case.
Returns the value of the usage counter of a specified
OS_GetSemaValue()
resource semaphore.
Returns a pointer to the task that is currently using
OS_GetResourceOwner()
(blocking) a resource.
OS_DeleteRSema() Deletes a specified resource semaphore.
Table 5.1: Resource semaphore API overview

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5.1.1 OS_CREATERSEMA()
Description
Macro that creates a resource semaphore.
Prototype
void OS_CREATERSEMA (OS_RSEMA* pRSema);

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.2: OS_CREATESEMA() parameter list

Additional Information
After creation, the resource is not blocked; the value of the counter is 0.

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5.1.2 OS_Use()
Description
Claims a resource and blocks it for other tasks.
Prototype
int OS_Use (OS_RSEMA* pRSema);

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.3: OS_Use() parameter list

Return value
The counter value of the semaphore.
A value larger than 1 means the resource was already locked by the calling task.
Additional Information
The following situations are possible:
• Case A: The resource is not in use.
If the resource is not used by a task, which means the counter of the semaphore
is 0, the resource will be blocked for other tasks by incrementing the counter and
writing a unique code for the task that uses it into the semahore.
• Case B: The resource is used by this task.
The counter of the semaphore is simply incremented. The program continues
without a break.
• Case C: The resource is being used by another task.
The execution of this task is suspended until the resource semaphore is released.
In the meantime if the task blocked by the resource semaphore has a higher pri-
ority than the task blocking the semaphore, the blocking task is assigned the pri-
ority of the task requesting the resource semaphore. This is called priority
inversion. Priority inversion can only temporarily increase the priority of a task,
never reduce it.
An unlimited number of tasks can wait for a resource semaphore. According to the
rules of the scheduler, of all the tasks waiting for the resource, the task with the
highest priority will get access to the resource and can continue program execution.
Important
This function may not be called from within an interrupt handler.

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The following diagram illustrates how the OS_Use() routine works:

OS_Use(...)

Resource Yes, by Wait for resource

in use? other task to be released

Yes, by this task

No

Mark current task

as owner

Increase Usage
Usage counter = 1
counter

return return

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5.1.3 OS_Unuse()
Description
Releases a semaphore currently in use by a task.
Prototype
void OS_Unuse (OS_RSEMA* pRSema)

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.4: OS_Unuse() parameter list

Additional Information
OS_Unuse() may be used on a resource semaphore only after that semaphore has
been used by calling OS_Use() or OS_Request(). OS_Unuse() decrements the usage
counter of the semaphore which must never become negative. If this counter
becomes negative, the debug version will call the embOS error handler OS_Error()
with error code OS_ERR_UNUSE_BEFORE_USE. In the debug version OS_Error() will
also be called, if OS_Unuse() is called from a task which does not own the resource.
The error code in this case is OS_ERR_RESOURCE_OWNER.
Important
This function may not be called from within an interrupt handler.

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5.1.4 OS_Request()
Description
Requests a specified semaphore and blocks it for other tasks if it is available. Contin-
ues execution in any case.
Prototype
char OS_Request (OS_RSEMA* pRSema);

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.5: OS-Request() parameter list

Return value
1: Resource was available, now in use by calling task
0: Resource was not available.
Additional Information
The following diagram illustrates how OS_Request() works:

OS_Request (RSEMA*ps)

Resource in use by other task ? Yes return 0

No

Mark current task

In use by this task ? No
as owner

Yes

Inc Usage counter Usage counter = 1

return 1 return 1

Example
if (!OS_Request(&RSEMA_LCD) ) {
LED_LCDBUSY = 1; /* Indicate that task is waiting for */
/* resource */
OS_Use(&RSEMA_LCD); /* Wait for resource */
LED_LCDBUSY = 0; /* Indicate task is no longer waiting */
}
DispTime(); /* Access the resource LCD */
OS_Unuse(&RSEMA_LCD); /* Resource LCD is no longer needed */

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5.1.5 OS_GetSemaValue()
Description
Returns the value of the usage counter of a specified resource semaphore.
Prototype
int OS_GetSemaValue (OS_SEMA* pSema);

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.6: OS_GetSemaValue() parameter list

Return value
The counter of the semaphore.
A value of 0 means the resource is available.

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5.1.6 OS_GetResourceOwner()
Description
Returns a pointer to the task that is currently using (blocking) a resource.
Prototype
OS_TASK* OS_GetResourceOwner (OS_RSEMA* pSema);

Parameter Description
pRSema Pointer to the data structure for a resource semaphore.
Table 5.7: OS_GetResourceOwner() parameter list

Return value
Pointer to the task that is blocking the resource.
A value of 0 means the resource is available.

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5.1.7 OS_DeleteRSema()
Description
Deletes a specified resource semaphore. The memory of that semaphore may be
reused for other purposes or may be used for creating another resources semaphore
using the same memory.
Prototype
void OS_DeleteRSema (OS_RSEMA* pRSema);

Parameter Description
pRSema Pointer to a data structure of type OS_RSEMA.
Table 5.8: OS_DeleteRSema parameter list

Additional Information
Before deleting a resource semaphore, make sure that no task is claiming the
resources semaphore. The debug version of embOS will call OS_Error(), if a
resources semaphore is deleted when it is already used. In systems with dynamic
creation of resource semaphores, it is required to delete a resource semaphore,
before re-creating it. Otherwise the semaphore handling will not work correctly.

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Chapter 6

Counting Semaphores

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Counting semaphores are counters that are managed by embOS. They are not as
widely used as resource semaphores, events or mailboxes, but they can be very
useful sometimes. They are used in situations where a task needs to wait for
something that can be signaled one or more times. The semaphores can be accessed
from any point, any task, or any interrupt in any way.
Example of using counting semaphores
OS_STACKPTR int Stack0[96], Stack1[64]; /* Task stacks */
OS_TASK TCB0, TCB1; /* Data-area for tasks (task-control-blocks) */
OS_CSEMA SEMALCD;

void Task0(void) {
Loop:
Disp("Task0 will wait for task 1 to signal");
OS_WaitCSema(&SEMALCD);
Disp("Task1 has signaled !!");
OS_Delay(100);
goto Loop;
}

void Task1(void) {
Loop:
OS_Delay(5000);
OS_SignalCSema(&SEMALCD);
goto Loop;
}

void InitTask(void) {
OS_CREATECSEMA(&SEMALCD); /* Create Semaphore */
OS_CREATETASK(&TCB0, NULL, Task0, 100, Stack0); /* Create Task0 */
OS_CREATETASK(&TCB1, NULL, Task1, 50, Stack1); /* Create Task1 */
}

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6.1 Counting semaphores API function overview

Routine Description
Macro that creates a counting semaphore with an initial
OS_CREATECSEMA()
count value of zero.
Creates a counting semaphore with a specified initial
OS_CreateCSema()
count value.
OS_SignalCSema() Increments the counter of a semaphore.
Increments the counter of a semaphore up to a specified
OS_SignalCSemaMax
maximum value.
OS_WaitCSema() Decrements the counter of a semaphore.
OS_CSemaRequest() Decrements the counter of a semaphore, if available.
Decrements a semaphore counter if the semaphore is
OS_WaitCSemaTimed
available within a specified time.
OS_GetCSemaValue() Returns the counter value of a specified semaphore.
OS_SetCSemaValue() Sets the counter value of a specified semaphore.
OS_DeleteCSema() Deletes a specified semaphore.
Table 6.1: Counting semaphores API overview

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6.1.1 OS_CREATECSEMA()
Description
Macro that creates a counting semaphore with an initial count value of zero.
Prototype
void OS_CREATECSEMA (OS_CSEMA* pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.2: OS_CREATECSEMA() parameter list

Additional Information
To create a counting semaphore, a data structure of the type OS_CSEMA needs to be
defined in memory and initialized using OS_CREATECSEMA(). The value of a sema-
phore created using this macro is zero. If, for any reason, you have to create a sema-
phore with an initial counting value above zero, use the function OS_CreateCSema().

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6.1.2 OS_CreateCSema()
Description
Creates a counting semaphore with a specified initial count value.
Prototype
void OS_CreateCSema (OS_CSEMA* pCSema,
OS_UINT InitValue);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Initial count value of the semaphore:
InitValue 0 <= InitValue <= 216 = 0xFFFF for 8/16-bit CPUs
0 <= InitValue <= 232 = 0xFFFFFFFF for 32-bit CPUs
Table 6.3: OS_CreateCSema() parameter list

Additional Information
To create a counting semaphore, a data structure of the type OS_CSEMA needs to be
defined in memory and initialized using OS_CreateCSema(). If the value of the cre-
ated semaphore should be zero, the macro OS_CREATECSEMA() should be used.

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6.1.3 OS_SignalCSema()
Description
Increments the counter of a semaphore.
Prototype
void OS_SignalCSema (OS_CSEMA * pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.4: OS_SignalCSema() parameter list

Additional Information
OS_SignalCSema() signals an event to a semaphore by incrementing its counter. If
one or more tasks are waiting for an event to be signaled to this semaphore, the task
that has the highest priority will become the active task. The counter can have a
maximum value of 0xFFFF for 8/16-bit CPUs / 0xFFFFFFFF for 32-bit CPUs. It is the
responsibility of the application to make sure that this limit will not be exceeded. The
debug version of embOS detects an counter overflow and calls OS_Error() with error
code OS_ERR_CSEMA_OVERFLOW, if an overflow occurs.

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6.1.4 OS_SignalCSemaMax()
Description
Increments the counter of a semaphore up to a specified maximum value.
Prototype
void OS_SignalCSemaMax (OS_CSEMA* pCSema,
OS_UINT MaxValue );

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Limit of semaphore count value.
MaxValue 1 <= MaxValue <= 216 = 0xFFFF for 8/16-bit CPUs
1 <= MaxValue <= 232 = 0xFFFFFFFF for 32-bit CPUs
Table 6.5: OS_SignalCSemaMax() parameter list

Additional Information
As long as current value of the semaphore counter is below the specified maximum
value, OS_SignalCSemaMax() signals an event to a semaphore by incrementing its
counter. If one or more tasks are waiting for an event to be signaled to this sema-
phore, the tasks are put into ready state and the task that has the highest priority
will become the active task. Calling OS_SignalCSemaMax() with a MaxValue of 1 han-
dles a counting semaphore as a binary semaphore.

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6.1.5 OS_WaitCSema()
Description
Decrements the counter of a semaphore.
Prototype
void OS_WaitCSema (OS_CSEMA* pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.6: OS_WaitCSema() parameter list

Additional Information
If the counter of the semaphore is not 0, the counter is decremented and program
execution continues.
If the counter is 0, WaitCSema() waits until the counter is incremented by another
task, a timer or an interrupt handler via a call to OS_SignalCSema(). The counter is
then decremented and program execution continues.
An unlimited number of tasks can wait for a semaphore. According to the rules of the
scheduler, of all the tasks waiting for the semaphore, the task with the highest
priority will continue program execution.
Important
This function may not be called from within an interrupt handler.

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6.1.6 OS_WaitCSemaTimed()
Description
Decrements a semaphore counter if the semaphore is available within a specified
time.
Prototype
int OS_WaitCSemaTimed (OS_CSEMA* pCSema,
OS_TIME TimeOut);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
TimeOut Maximum time until semaphore should be available
Table 6.7: OS_WaitCSemaTimed parameter list

Return value
Integer value:
0: Failed, semaphore not available before timeout.
1: OK, semaphore was available and counter decremented.
Additional Information
If the counter of the semaphore is not 0, the counter is decremented and program
execution continues. If the counter is 0, WaitCSemaTimed() waits until the sema-
phore is signaled by another task, a timer, or an interrupt handler via a call to
OS_SignalCSema(). The counter is then decremented and program execution contin-
ues. If the semaphore was not signaled within the specified time, the program execu-
tion continues but returns a value of 0. An unlimited number of tasks can wait for a
semaphore. According to the rules of the scheduler, of all the tasks waiting for the
semaphore, the task with the highest priority will continue program execution.
Important
This function may not be called from within an interrupt handler.

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6.1.7 OS_CSemaRequest()
Description
Decrements the counter of a semaphore, if it is signaled.
Prototype
char OS_CSemaRequest (OS_CSEMA* pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.8: OS_CSemaRequest() parameter list

Return value
Integer value:
0: Failed, semaphore was not signaled.
1: OK, semaphore was available and counter was decremented once.
Additional Information
If the counter of the semaphore is not 0, the counter is decremented and program
execution continues.
If the counter is 0, OS_CSemaRequest() does not wait and does not modify the sema-
phore counter. The function returns with error state.
Because this function never blocks a calling task, this function may be called from an
interrupt handler.

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6.1.8 OS_GetCSemaValue()
Description
Returns the counter value of a specified semaphore.
Prototype
int OS_GetCSemaValue (OS_SEMA* pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.9: OS_GetCSemaValue() parameter list

Return value
The counter value of the semaphore.

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6.1.9 OS_SetCSemaValue()
Description
Sets the counter value of a specified semaphore.
Prototype
OS_U8 OS_SetCSemaValue (OS_SEMA* pCSema,
OS_UINT Value);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Count value of the semaphore:
Value 0 <= InitValue <= 216 = 0xFFFF for 8/16-bit CPUs
0 <= InitValue <= 232 = 0xFFFFFFFF for 32-bit CPUs
Table 6.10: OS_SetCSemaValue() parameter list

Return value
0: If the value could be set.
!= 0: In case of error.

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6.1.10 OS_DeleteCSema()
Description
Returns the counter value of a specified semaphore.
Prototype
void OS_DeleteCSema (OS_CSEMA* pCSema);

Parameter Description
pCSema Pointer to a data structure of type OS_CSEMA.
Table 6.11: OS_DeleteCSema() parameter list

Additional Information
Before deleting a semaphore, make sure that no task is waiting for it and that no
task will signal that semaphore at a later point.
The debug version of embOS will reflect an error if a deleted semaphore is signaled.

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Chapter 7

Mailboxes

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112 CHAPTER 7 Mailboxes

7.1 Why mailboxes?

In the preceding chapters, task synchronization by the use of semaphores was
described. Unfortunately, semaphores cannot transfer data from one task to another.
If we need to transfer data between tasks via a buffer for example, we could use a
resource semaphore every time we accessed the buffer. But doing so would make the
program less efficient. Another major disadvantage would be that we could not
access the buffer from an interrupt handler, because the interrupt handler is not
allowed to wait for the resource semaphore.
One way out would be the usage of global variables. In this case we would have to
disable interrupts every time and in every place that we accessed these variables.
This is possible, but it is a path full of pitfalls. It is also not easy for a task to wait for
a character to be placed in a buffer without polling the global variable that contains
the number of characters in the buffer. Again, there is a way out - the task could be
notified by an event signaled to the task every time a character is placed in the
buffer. That is why there is an easier way to do this with a real-time OS:
The use of mailboxes.

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7.2 Basics
A mailbox is a buffer that is managed by the real-time operating system. The buffer
behaves like a normal buffer; you can put something (called a message) in and
retrieve it later. Mailboxes usually work as FIFO: first in, first out. So a message that
is put in first will usually be retrieved first. "Message" might sound abstract, but very
simply just means "item of data". It will become clearer in the typical applications
explained in the following section.
The number of mailboxes is limited only by the amount of available memory.
Message size: 1 <= x <= 127 bytes.
Number of messages: 1 <= x <= 32767.
These limitations have been placed on mailboxes to guarantee efficient coding and
also to ensure efficient management. The limitations are normally not a problem.
For handling messages larger than 127 bytes, you may use queues. For more infor-
mation, refer to the Chapter Queues on page 129.

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7.3 Typical applications

A keyboard buffer
In most programs, you use either a task, a software timer or an interrupt handler to
check the keyboard. When detected that a key has been pressed, that key is put into
a mailbox that is used as a keyboard buffer. The message is then retrieved by the
task that handles the keyboard input. The message in this case is typically a single
byte that holds the key code; the message size is therefore 1 byte.
The advantage of a keyboard buffer is that management is very efficient; you do not
have to worry about it, because it is reliable, proven code and you have a type-ahead
buffer at no extra cost. On top of that, a task can easily wait for a key to be pressed
without having to poll the buffer. It simply calls the OS_GetMail() routine for that
particular mailbox. The number of keys that can be stored in the type-ahead buffer
depends only on the size of the mailbox buffer, which you define when creating the
mailbox.
A buffer for serial I/O
In most cases, serial I/O is done with the help of interrupt handlers. The communica-
tion to these interrupt handlers is very easy with mailboxes. Both your task programs
and your interrupt handlers store or retrieve data to/from the same mailboxes. As
with a keyboard buffer, the message size is 1 character.
For interrupt-driven sending, the task places the character(s) in the mailbox using
OS_PutMail() or OS_PutMailCond(); the interrupt handler that is activated when a
new character can be sent retrieves this character with OS_GetMailCond().
For interrupt-driven receiving, the interrupt handler that is activated when a new
character is received puts it in the mailbox using OS_PutMailCond(); the task
receives it using OS_GetMail() or OS_GetMailCond().
A buffer for commands sent to a task
Assume you have one task controlling a motor, as you might have in applications that
control a machine. A simple way to give commands to this task would be to define a
structure for commands. The message size would then be the size of this structure.

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7.4 Single-byte mailbox functions

In many (if not the most) situations, mailboxes are used simply to hold and transfer
single-byte messages. This is the case, for example, with a mailbox that takes the
character received or sent via serial interface, or normally with a mailbox used as
keyboard buffer. In some of these cases, time is very critical, especially if a lot of
data is transferred in short periods of time.
To minimize the overhead caused by the mailbox management of embOS, variations
on some mailbox functions are available for single-byte mailboxes. The general func-
tions OS_PutMail(), OS_PutMailCond(), OS_GetMail(), and OS_GetMailCond() can
transfer messages of sizes between 1 and 127 bytes each. Their single-byte equiva-
lents OS_PutMail1(), OS_PutMailCond1(), OS_GetMail1(), and OS_GetMailCond1()
work the same way with the exception that they execute much faster because man-
agement is simpler. It is recommended to use the single-byte versions if you transfer
a lot of single byte-data via mailboxes.
The routines OS_PutMail1(), OS_PutMailCond1(), OS_GetMail1(), and
OS_GetMailCond1() work exactly the same way as their more universal equivalents
and are therefore not described separately. The only difference is that they can only
be used for single-byte mailboxes.

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7.5 Mailboxes API function overview

Routine Explanation
OS_CREATEMB() Macro that creates a new mailbox.
OS_PutMail() Stores a new message of a predefined size in a mailbox.
OS_PutMail1() Stores a new message of a predefined size in a mailbox.
Stores a new message of a predefined size in a mailbox,
OS_PutMailCond()
if the mailbox is able to accept one more message.
Stores a new message of a predefined size in a mailbox,
OS_PutMailCond1()
if the mailbox is able to accept one more message.
Stores a new message of a predefined size into a mailbox
OS_PutMailFront() in front of all other messages. This new message will be
retrieved first.
Stores a new message of a predefined size into a mailbox
OS_PutMailFront1() in front of all other messages. This new message will be
retrieved first.
Stores a new message of a predefined size into a mailbox
OS_PutMailFrontCond() in front of all other messages, if the mailbox is able to
accept one more message.
Stores a new message of a predefined size into a mailbox
OS_PutMailFrontCond1() in front of all other messages, if the mailbox is able to
accept one more message.
Retrieves a new message of a predefined size from a
OS_GetMail()
mailbox.
Retrieves a new message of a predefined size from a
OS_GetMail1()
mailbox.
Retrieves a new message of a predefined size from a
OS_GetMailCond()
mailbox, if a message is available.
Retrieves a new message of a predefined size from a
OS_GetMailCond1()
mailbox, if a message is available.
Retrieves a new message of a predefined size from a
OS_GetMailTimed()
mailbox, if a message is available within a given time.
Waits until a mail is available, but does not retrieve the
OS_WaitMail()
message from the mailbox.
OS_ClearMB() Clears all messages in a specified mailbox.
Returns number of messages currently in a specified
OS_GetMessageCnt()
mailbox.
OS_DeleteMB() Deletes a specified mailbox.
Table 7.1: Mailboxes API overview

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7.5.1 OS_CREATEMB()
Description
Macro that creates a new mailbox.
Prototype
void OS_CREATEMB (OS_MAILBOX* pMB,
unsigned char sizeofMsg,
unsigned int maxnofMsg,
void* pMsg);)

Parameter Description
Pointer to a data structure of type OS_MAILBOX reserved for man-
pMB
aging the mailbox.
sizeofMsg Size of a message in bytes. ( 1 <= sizeofMsg <= 127 )
maxnoMsg Maximum number of messages. ( 1 <= MaxnofMsg <= 65535 )
Pointer to a memory area used as buffer. The buffer has to be big
pMsg enough to hold the given number of messages of the specified
size: sizeofMsg * maxnoMsg bytes.
Table 7.2: OS_CREATEMB() parameter list

Example
Mailbox used as keyboard buffer:
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

void InitKeyMan(void) {
/* Create mailbox, functioning as type ahead buffer */
OS_CREATEMB(&MBKey, 1, sizeof(MBKeyBuffer), &MBKeyBuffer);
}
Mailbox used for transfering complex commands from one task to another:

/*
* Example of mailbox used for transfering commands to a task
* that controls 2 motors
*/
typedef struct {
char Cmd;
int Speed[2];
int Position[2];
} MOTORCMD ;

OS_MAILBOX MBMotor;

#define MOTORCMD_SIZE 4

char BufferMotor[sizeof(MOTORCMD)*MOTORCMD_SIZE];

void MOTOR_Init(void) {
/* Create mailbox that holds commands messages */
OS_CREATEMB(&MBMotor, sizeof(MOTORCMD), MOTORCMD_SIZE, &BufferMotor);
}

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7.5.2 OS_PutMail() / OS_PutMail1()

Description
Stores a new message of a predefined size in a mailbox.
Prototype
void OS_PutMail (OS_MAILBOX* pMB,
void* pMail);
void OS_PutMail1 (OS_MAILBOX* pMB,
const char* pMail);

Parameter Description
pMB Pointer to the mailbox.
pMail Pointer to the message to store.
Table 7.3: OS_PutMail() / OS_PutMail1() parameter list

Additional Information
If the mailbox is full, the calling task is suspended.
Because this routine might require a suspension, it must not be called from an inter-
rupt routine. Use OS_PutMailCond()/OS_PutMailCond1() instead if you have to
store data in a mailbox from within an ISR.
Important
This function may not be called from within an interrupt handler.
Example
Single-byte mailbox as keyboard buffer:

OS_MAILBOX MBKey;
char MBKeyBuffer[6];

void KEYMAN_StoreKey(char k) {
OS_PutMail1(&MBKey, &k); /* Store key, wait if no space in buffer */
}

void KEYMAN_Init(void) {
/* Create mailbox functioning as type ahead buffer */
OS_CREATEMB(&MBKey, 1, sizeof(MBKeyBuffer), &MBKeyBuffer);
}

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7.5.3 OS_PutMailCond() / OS_PutMailCond1()

Description
Stores a new message of a predefined size in a mailbox, if the mailbox is able to
accept one more message.
Prototype
char OS_PutMailCond (OS_MAILBOX* pMB,
void* pMail);
char OS_PutMailCond1 (OS_MAILBOX* pMB,
const char* pMail);)

Parameter Description
pMB Pointer to the mailbox.
pMail Pointer to the message to store.
Table 7.4: OS_PutMailCond() / OS_PutMailCond1() overview

Return value
0: Success; message stored.
1: Message could not be stored (mailbox is full).
Additional Information
If the mailbox is full, the message is not stored.
This function never suspends the calling task. It may therefore be called from an
interrupt routine.
Example
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

char KEYMAN_StoreCond(char k) {
return OS_PutMailCond1(&MBKey, &k); /* Store key if space in buffer */
}

This example can be used with the sample program shown earlier to handle a mail-
box as keyboard buffer.

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7.5.4 OS_PutMailFront() / OS_PutMailFront1()

Description
Stores a new message of a predefined size at the beginning of a mailbox in front of
all other messages. This new message will be retrieved first.
Prototype
void OS_PutMailFront (OS_MAILBOX* pMB,
void* pMail);
void OS_PutMailFront1 (OS_MAILBOX* pMB,
const char* pMail);

Parameter Description
pMB Pointer to the mailbox.
pMail Pointer to the message to store.
Table 7.5: OS_PutMailFront() / OS_PutMailFront1() parameter list

Additional Information
If the mailbox is full, the calling task is suspended. Because this routine might
require a suspension, it must not be called from an interrupt routine. Use
OS_PutMailFrontCond()/OS_PutMailFrontCond1() instead if you have to store data
in a mailbox from within an ISR.
This function is useful to store "emergency" messages into a mailbox which have to
be handled quick.
It may also be used in general instead of OS_PutMail() to change the FIFO structure
of a mailbox into a LIFO structure.
Important
This function may not be called from within an interrupt handler.
Example
Single-byte mailbox as keyboard buffer:

OS_MAILBOX MBCmd;
char MBCmdBuffer[6];

void KEYMAN_StoreCommand(char k) {
OS_PutMailFront1(&MBCmd, &k); /* Store command, wait if no space in buffer*/
}

void KEYMAN_Init(void) {
/* Create mailbox for command buffer */
OS_CREATEMB(&MBCmd, 1, sizeof(MBCmdBuffer), &MBCmdBuffer);
}

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7.5.5 OS_PutMailFrontCond() / OS_PutMailFrontCond1()

Description
Stores a new message of a predefined size into a mailbox in front of all other mes-
sages, if the mailbox is able to accept one more message. The new message will be
retrieved first.
Prototype
char OS_PutMailFrontCond (OS_MAILBOX* pMB,
void* pMail);
char OS_PutMailFrontCond1 (OS_MAILBOX* pMB,
const char* pMail);)

Parameter Description
pMB Pointer to the mailbox.
pMail Pointer to the message to store.
Table 7.6: OS_PutMailFrontCond() / OS_PutMailFrontCond1() parameter list

Return value
0: Success; message stored.
1: Message could not be stored (mailbox is full).
Additional Information
If the mailbox is full, the message is not stored. This function never suspends the
calling task. It may therefore be called from an interrupt routine. This function is
useful to store "emergency" messages into a mailbox which have to be handled
quick. It may also be used in general instead of OS_PutMail() to change the FIFO
structure of a mailbox into a LIFO structure.

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7.5.6 OS_GetMail() / OS_GetMail1()

Description
Retrieves a new message of a predefined size from a mailbox.
Prototype
void OS_GetMail (OS_MAILBOX* pMB,
void* pDest);
void OS_GetMail1 (OS_MAILBOX* pMB,
char* pDest);

Parameter Description
pMB Pointer to the mailbox.
Pointer to the memory area that the message should be stored
at. Make sure that it points to a valid memory area and that there
pDest
is sufficient space for an entire message. The message size (in
bytes) was defined when the mailbox was created.
Table 7.7: OS_GetMail() / OS_GetMail1() parameter list

Additional Information
If the mailbox is empty, the task is suspended until the mailbox receives a new mes-
sage. Because this routine might require a suspension, it may not be called from an
interrupt routine. Use OS_GetMailCond/OS_GetMailCond1 instead if you have to
retrieve data from a mailbox from within an ISR.
Important
This function may not be called from within an interrupt handler.
Example
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

char WaitKey(void) {
char c;
OS_GetMail1(&MBKey, &c);
return c;
}

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7.5.7 OS_GetMailCond() / OS_GetMailCond1()

Description
Retrieves a new message of a predefined size from a mailbox, if a message is
available.
Prototype
char OS_GetMailCond (OS_MAILBOX * pMB,
void* pDest);
char OS_GetMailCond1 (OS_MAILBOX * pMB,
char* pDest);

Parameter Description
pMB Pointer to the mailbox.
Pointer to the memory area that the message should be stored
at. Make sure that it points to a valid memory area and that there
pDest
is sufficient space for an entire message. The message size (in
bytes) was defined when the mailbox was created.
Table 7.8: OS_GetMailCond() / OS_GetMailCond1() parameter list

Return value
0: Success; message retrieved.
1: Message could not be retrieved (mailbox is empty); destination remains
unchanged.
Additional Information
If the mailbox is empty, no message is retrieved, but the program execution contin-
ues.
This function never suspends the calling task. It may therefore also be called from an
interrupt routine.
Important
This function may not be called from within an interrupt handler.
Example
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

/*
* If a key has been pressed, it is taken out of the mailbox and returned to
* caller.
* Otherwise, 0 is returned.
*/
char GetKey(void) {
char c =0;
OS_GetMailCond1(&MBKey, &c)
return c;
}

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7.5.8 OS_GetMailTimed()
Description
Retrieves a new message of a predefined size from a mailbox, if a message is avail-
able within a given time.
Prototype
char OS_GetMailTimed (OS_MAILBOX* pMB,
void* pDest,
OS_TIME Timeout);

Parameter Description
pMB Pointer to the mailbox.
Pointer to the memory area that the message should be stored
at. Make sure that it points to a valid memory area and that there
pDest
is sufficient space for an entire message. The message size (in
bytes) has been defined upon creation of the mailbox.
Maximum time in timer ticks until the requested mail has to be
available. The data type OS_TIME is defined as an integer, there-
Timeout fore valid values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 7.9: OS_GetMailTimed() parameter list

Return value
0: Success; message retrieved.
1: Message could not be retrieved (mailbox is empty); destination remains
unchanged.
Additional Information
If the mailbox is empty, no message is retrieved, the task is suspended for the given
timeout. The task continues execution, according to the rules of the scheduler, as
soon as a mail is available within the given timeout, or after the timeout value has
expired.
Important
This function may not be called from within an interrupt handler.
Example
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

/*
* If a key has been pressed, it is taken out of the mailbox and returned to
* caller.
* Otherwise, 0 is returned.
*/
char GetKey(void) {
char c =0;
OS_GetMailTimed(&MBKey, &c, 10) /* Wait for 10 timer ticks */
return c;
}

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7.5.9 OS_WaitMail()
Description
Waits until a mail is available, but does not retrieve the message from the mailbox.
Prototype
void OS_WaitMail (OS_MAILBOX* pMB);

Parameter Description
pMB Pointer to the mailbox.
Table 7.10: OS_WaitMail() parameter list

Additional Information
If the mailbox is empty, the task is suspended until a mail is available, otherwise the
task continues.
The task continues execution, according to the rules of the scheduler, as soon as a
mail is available, but the mail is not retrieved from the mailbox.
Important
This function may not be called from within an interrupt handler.

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7.5.10 OS_ClearMB()
Description
Clears all messages in a specified mailbox.
Prototype
void OS_ClearMB (OS_MAILBOX* pMB);

Parameter Description
pMB Pointer to the mailbox.
Table 7.11: OS_ClearMB() parameter list

Example
OS_MAILBOX MBKey;
char MBKeyBuffer[6];

/*
* Clear keyboard type ahead buffer
*/
void ClearKeyBuffer(void) {
OS_ClearMB(&MBKey);
}

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7.5.11 OS_GetMessageCnt()
Description
Returns the number of messages currently available in a specified mailbox.
Prototype
unsigned int OS_GetMessageCnt (OS_MAILBOX* pMB);

Parameter Description
pMB Pointer to the mailbox.
Table 7.12: OS_GetMessageCnt() parameter list

Return value
The number of messages in the mailbox.
Example
char GetKey(void) {
if (OS_GetMessageCnt(&MBKey)) return WaitKey();
return 0;
}

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7.5.12 OS_DeleteMB()
Description
Deletes a specified mailbox.
Prototype
void OS_DeleteMB (OS_MAILBOX* pMB);

Parameter Description
pMB Pointer to the mailbox.
Table 7.13: OS_DeleteMB() parameter list

Additional Information
To keep the system fully dynamic, it is essential that mailboxes can be created
dynamically. This also means there has to be a way to delete a mailbox when it is no
longer needed. The memory that has been used by the mailbox for the control struc-
ture and the buffer can then be reused or reallocated.
It is the programmer's responsibility to:
• make sure that the program no longer uses the mailbox to be deleted
• make sure that the mailbox to be deleted actually exists (i.e. has been created
first).
Example
OS_MAILBOX MBSerIn;
char MBSerInBuffer[6];

void Cleanup(void) {
OS_DeleteMB(MBSerIn);
return 0;
}

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Chapter 8

Queues

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130 CHAPTER 8 Queues

8.1 Why queues?

In the preceding chapter, intertask communication using mailboxes was described.
Mailboxes can handle small messages with fixed data size only.
Queues enable intertask communication with larger messages or with messages of
various sizes.

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8.2 Basics
A queue consists of a data buffer and a control structure that is managed by the real-
time operating system. The queue behaves like a normal buffer; you can put
something (called a message) in and retrieve it later. Queues work as FIFO: first in,
first out. So a message that is put in first will be retrieved first.
There are three major differences between queues and mailboxes:
1. Queues accept messages of various size. When putting a message into a queue,
the message size is passed as a parameter.
2. Retrieving a message from the queue does not copy the message, but returns a
pointer to the message and its size. This enhances performance because the data
is copied only once, when the message is written into the queue.
3. The retrieving function has to delete every message after processing it.
Both the number and size of queues is limited only by the amount of available
memory. Any data structure can be written into a queue. The message size is not
fixed.

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8.3 Queues API function overview

Routine Description
OS_Q_Create() Creates and initializes a message queue.
OS_Q_Put() Stores a new message of given size in a queue.
OS_Q_GetPtr() Retrieves a message from a queue.
Retrieves a message from a queue, if one message is
OS_Q_GetPtrCond()
available or returns without suspension.
Retrieves a message from a queue within a specified
OS_Q_GetPtrTimed()
time, if one message is available.
OS_Q_Purge() Deletes the last retrieved message in a queue.
OS_Q_Clear() Deletes all message in a queue.
OS_Q_GetMessageCnt() Returns the number of messages currently in a queue.
Table 8.1: Queues API

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8.3.1 OS_Q_Create()
Description
Creates and initializes a message queue.
Prototype
void OS_Q_Create (OS_Q* pQ,
void*pData,
OS_UINT Size);

Parameter Description
Pointer to a data structure of type OS_Q reserved for the manage-
pQ
ment of the message queue.
pData Pointer to a memory area used as data buffer for the queue.
Size Size in bytes of the data buffer.
Table 8.2: OS_Q_Create() parameter list

Example
#define MEMORY_QSIZE 10000;
static OS_Q _MemoryQ;
static char _acMemQBuffer[MEMORY_QSIZE];

void MEMORY_Init(void) {
OS_Q_Create(&_MemoryQ, &_acMemQBuffer, sizeof(_acMemQBuffer));
}

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8.3.2 OS_Q_Put()
Description
Stores a new message of given size in a queue.
Prototype
int OS_Q_Put (OS_Q* pQ,
const void* pSrc,
OS_UINT Size);

Parameter Description
Pointer to a data structure of type OS_Q reserved for the manage-
pQ
ment of the message queue.
pSrc Pointer to the message to store
Size Size of the message to store
Table 8.3: OS_Q_Put() parameter list

Return value
0: Success; message stored.
1: Message could not be stored (queue is full).
Additional Information
If the queue is full, the function returns a value unequal to 0.
This routine never suspends the calling task. It may therefore also be called from an
interrupt routine.
Example
char MEMORY_Write(char* pData, int Len) {
return OS_Q_Put(&_MemoryQ, pData, Len));
}

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8.3.3 OS_Q_GetPtr()
Description
Retrieves a message from a queue.
Prototype
int OS_Q_GetPtr (OS_Q* pQ,
void** ppData);

Parameter Description
pQ Pointer to the queue.
ppData Address of pointer to the message to be retrieved from queue.
Table 8.4: OS_Q_GetPtr() parameter list

Return value
The size of the retrieved message.
Sets the pointer to the message that should be retrieved.
Additional Information
If the queue is empty, the calling task is suspended until the queue receives a new
message. Because this routine might require a suspension, it must not be called from
an interrupt routine. Use OS_GetPtrCond() instead. The retrieved message is not
removed from the queue. This has to be done by a call of OS_Q_Purge() after the
message was processed.
Example
static void MemoryTask(void) {
char MemoryEvent;
int Len;
char* pData;

while (1) {
Len = OS_Q_GetPtr(&_MemoryQ, &pData); /* Get message */
Memory_WritePacket(*(U32*)pData, pData+4, Len); /* Process message */
OS_Q_Purge(&_MemoryQ); /* Delete message */
}
}

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8.3.4 OS_Q_GetPtrCond()
Description
Retrieves a message from a queue, if one message is available.
Prototype
int OS_Q_GetPtrCond (OS_Q* pQ,
void** ppData);

Parameter Description
pQ Pointer to the queue.
ppData Address of pointer to the message to be retrieved from queue.
Table 8.5: OS_Q_GetPtrCond() parameter list

Return value
0: No message available in queue.
>0: Size of message that was retrieved from queue.
Additional Information
If the queue is empty, the function returns 0. The value of ppData is undefined. This
function never suspends the calling task. It may therefore also be called from an
interrupt routine. If a message could be retrieved, it is not removed from the queue.
This has to be done by a call of OS_Q_Purge() after the message was processed.
Example
static void MemoryTask(void) {
char MemoryEvent;
int Len;
char* pData;
while (1) {
Len = OS_Q_GetPtrCond(&_MemoryQ, &pData); /* Check message */
if (Len > 0) {
Memory_WritePacket(*(U32*)pData, pData+4, Len); /* Process message */
OS_Q_Purge(&_MemoryQ); /* Delete message */
} else {
DoSomethingElse();
}
}
}

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8.3.5 OS_Q_GetPtrTimed()
Description
Retrieves a message from a queue within a specified time if a message is available.
Prototype
int OS_Q_GetPtrTimed (OS_Q* pQ,
void** ppData,
OS_TIME Timeout);

Parameter Description
pQ Pointer to the queue.
ppData Address of pointer to the message to be retrieved from queue.
Maximum time in timer ticks until the requested message has to
be available. The data type OS_TIME is defined as an integer,
Timeout therefore valid values are
1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
Table 8.6: OS_Q_GetPtrCond() parameter list

Return value
0: No message available in queue.
>0: Size of message that was retrieved from queue.
Additional Information
If the queue is empty, no message is retrieved, the task is suspended for the given
timeout. The task continues execution, according to the rules of the scheduler, as
soon as a message is available within the given timeout, or after the timeout value
has expired.
Example
static void MemoryTask(void) {
char MemoryEvent;
int Len;
char* pData;
while (1) {
Len = OS_Q_GetPtrTimed(&_MemoryQ, &pData, 10); /* Check message */
if (Len > 0) {
Memory_WritePacket(*(U32*)pData, pData+4, Len); /* Process message */
OS_Q_Purge(&_MemoryQ); /* Delete message */
} else { /* Timeout */
DoSomethingElse();
}
}
}

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8.3.6 OS_Q_Purge()
Description
Deletes the last retrieved message in a queue.
Prototype
void OS_Q_Purge (OS_Q* pQ);

Parameter Description
pQ Pointer to the queue.
Table 8.7: OS_Q_Purge() parameter list

Additional Information
This routine should be called by the task that retrieved the last message from the
queue, after the message is processed.
Example
static void MemoryTask(void) {
char MemoryEvent;
int Len;
char* pData;

while (1) {
Len = OS_Q_GetPtr(&_MemoryQ, &pData); /* Get message */
Memory_WritePacket(*(U32*)pData, pData+4, Len); /* Process message */
OS_Q_Purge(&_MemoryQ); /* Delete message */
}
}

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8.3.7 OS_Q_Clear()
Description
Deletes all message in a queue.
Prototype
void OS_Q_Clear (OS_Q* pQ);

Parameter Description
pQ Pointer to the queue.
Table 8.8: OS_Q_Clear() parameter list

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8.3.8 OS_Q_GetMessageCnt()
Description
Returns the number of messages currently in a queue.
Prototype
int OS_Q_GetMessageCnt (OS_Q* pQ);

Parameter Description
pQ Pointer to the queue.
Table 8.9: OS_Q_GetMessageCnt() parameter list

Return value
The number of messages in the queue.

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Chapter 9

Task events

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142 CHAPTER 9 Task events

Task events are another way of communication between tasks. In contrast to sema-
phores and mailboxes, task events are messages to a single, specified recipient. In
other words, a task event is sent to a specified task.
The purpose of a task event is to enable a task to wait for a particular event (or for
one of several events) to occur. This task can be kept inactive until the event is sig-
naled by another task, a S/W timer or an interrupt handler. The event can consist of
anything that the software has been made aware of in any way. For example, the
change of an input signal, the expiration of a timer, a key press, the reception of a
character, or a complete command.
Every task has a 1-byte (8-bit) mask, which means that 8 different events can be
signaled to and distinguished by every task. By calling OS_WaitEvent(), a task waits
for one of the events specified as a bitmask. As soon as one of the events occurs, this
task must be signaled by calling OS_SignalEvent(). The waiting task will then be put
in the READY state immediately. It will be activated according to the rules of the
scheduler as soon as it becomes the task with the highest priority of all the tasks in
the READY state.

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9.1 Events API function overview

Routine Description
Waits for one of the events specified in the bitmask
OS_WaitEvent()
and clears the event memory after an event occurs.
Waits for one of the events specified as bitmask and
OS_WaitSingleEvent()
clears only that event after it occurs.
Waits for the specified events for a given time, and
OS_WaitEventTimed()
clears the event memory after an event occurs.
Waits for the specified events for a given time; after
OS_WaitSingleEventTimed()
an event occurs, only that event is cleared.
OS_SignalEvent() Signals event(s) to a specified task.
Returns a list of events that have occurred for a
OS_GetEventsOccurred()
specified task.
Returns the actual state of events and then clears
OS_ClearEvents()
the events of a specified task.
Table 9.1: Events API overview

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9.1.1 OS_WaitEvent()
Description
Waits for one of the events specified in the bitmask and clears the event memory
after an event occurs.
Prototype
char OS_WaitEvent (char EventMask);

Parameter Description
EventMask The events that the task will be waiting for.
Table 9.2: OS_WaitEvent() parameter list

Return value
All events that have actually occurred.
Additional Information
If none of the specified events are signaled, the task is suspended. The first of the
specified events will wake the task. These events are signaled by another task, a S/W
timer or an interrupt handler. Any bit in the 8-bit event mask may enable the corre-
sponding event.
Example
OS_WaitEvent(3); /* Wait for event 1 or 2 to be signaled */

For a further example, see OS_SignalEvent().

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9.1.2 OS_WaitSingleEvent()
Description
Waits for one of the events specified by the bitmask and clears only that event after
it occurs.
Prototype
char OS_WaitSingleEvent (char EventMask);

Parameter Description
EventMask The events that the task will be waiting for.
Table 9.3: OS_WaitSingleEvent() parameter list

Return value
All masked events that have actually occurred.
Additional Information
If none of the specified events are signaled, the task is suspended. The first of the
specified events will wake the task. These events are signaled by another task, a S/W
timer, or an interrupt handler. Any bit in the 8-bit event mask may enable the corre-
sponding event. All unmasked events remain unchanged.
Example
OS_WaitSingleEvent(3); /* Wait for event 1 or 2 to be signaled */

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9.1.3 OS_WaitEventTimed()
Description
Waits for the specified events for a given time, and clears the event memory after an
event occurs.
Prototype
char OS_WaitEventTimed (char EventMask,
OS_TIME TimeOut);

Parameter Description
EventMask The events that the task will be waiting for.
Maximum time in timer ticks until the events have to be signaled.
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 9.4: OS_WaitEventTimed() parameter list

Return value
The events that have actually occurred within the specified time.
0 if no events were signaled in time.
Additional Information
If none of the specified events are available, the task is suspended for the given
time. The first of the specified events will wake the task if the event is signaled by
another task, a S/W timer, or an interrupt handler within the specified TimeOut time.
If no event is signaled, the task is activated after the specified timeout and all actual
events are returned and then cleared. Any bit in the 8-bit event mask may enable the
corresponding event.
Example
OS_WaitEventTimed(3, 10); /* Wait for event 1 or 2 to be signaled within 10 ms */

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9.1.4 OS_WaitSingleEventTimed()
Description
Waits for the specified events for a given time; after an event occurs, only that event
is cleared.
Prototype
char OS_WaitSingleEventTimed (char EventMask,
OS_TIME TimeOut);

Parameter Description
EventMask The events that the task will be waiting for.
Maximum time in timer ticks until the events have to be signaled.
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 215-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 231-1 = 0x7FFFFFFF for 32-bit CPUs
Table 9.5: OS_WaitSingleEventTimed() parameter list

Return value
The masked events that have actually occurred within the specified time.
0 if no masked events were signaled in time.
Additional Information
If none of the specified events are available, the task is suspended for the given
time. The first of the specified events will wake the task if the event is signaled by
another task, a S/W timer or an interrupt handler within the specified TimeOut time.
If no event is signaled, the task is activated after the specified timeout and the
function returns zero. Any bit in the 8-bit event mask may enable the corresponding
event. All unmasked events remain unchanged.
Example
OS_WaitSingleEventTimed(3, 10); /* Wait for event 1 or 2 to be
signaled within 10 ms */

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9.1.5 OS_SignalEvent()
Description
Signals event(s) to a specified task.
Prototype
void OS_SignalEvent (char Event,
OS_TASK* pTask);

Parameter Description
The event(s) to signal:
1 means event 1
2 means event 2
4 means event 3
Event
...
128 means event 8.
Multiple events can be signaled as the sum of the single events
(for example, 6 will signal events 2 & 3).
pTask Task that the events are sent to.
Table 9.6: OS_SignalEvent() parameter list

Additional Information
If the specified task is waiting for one of these events, it will be put in the READY
state and activated according to the rules of the scheduler.
Example
The task that handles the serial input and the keyboard waits for a character to be
received either via the keyboard (EVENT_KEYPRESSED) or serial interface
(EVENT_SERIN):

/*
* Just a small demo for events
*/

#define EVENT_KEYPRESSED (1)

#define EVENT_SERIN (2)

OS_STACKPTR int Stack0[96], Stack1[64]; /* Task stacks */

OS_TASK TCB0, TCB1; /* Data area for tasks (task control blocks) */

void Task0(void) {
OS_U8 MyEvent;
while(1)
MyEvent = OS_WaitEvent(EVENT_KEYPRESSED | EVENT_SERIN)
if (MyEvent & EVENT_KEYPRESSED) {
/* handle key press */
}
if (MyEvent & EVENT_SERIN) {
/* Handle serial reception */
}
}
}

void TimerKey(void) {
/* More code to find out if key has been pressed */
OS_SignalEvent(EVENT_SERIN, &TCB0); /* Notify Task that key was pressed */
}

void InitTask(void) {
OS_CREATETASK(&TCB0, 0, Task0, 100, Stack0); /* Create Task0 */
}

If the task was only waiting for a key to be pressed, OS_GetMail() could simply be
called. The task would then be deactivated until a key is pressed. If the task has to
handle multiple mailboxes, as in this case, events are a good option.

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9.1.6 OS_GetEventsOccurred()
Description
Returns a list of events that have occurred for a specified task.
Prototype
char OS_GetEventsOccurred (OS_TASK* pTask);

Parameter Description
The task who's event mask is to be returned,
pTask
NULL means current task.
Table 9.7: OS_getEventsOccured() parameter list

Return value
The event mask of the events that have actually occurred.
Additional Information
By calling this function, the actual events remain signaled. The event memory is not
cleared. This is one way for a task to find out which events have been signaled. The
task is not suspended if no events are available.

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9.1.7 OS_ClearEvents()
Description
Returns the actual state of events and then clears the events of a specified task.
Prototype
char OS_ClearEvents (OS_TASK* pTask);

Parameter Description
The task who's event mask is to be returned,
pTask
NULL means current task.
Table 9.8: OS_ClearEvents() parameter list

Return value
The events that were actually signaled before clearing.

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Chapter 10

Event objects

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Event objects are another type of communication and synchronization objects. In

contrast to task-events, event objects are standalone objects which are not owned by
any task.
The purpose of an event object is to enable one or multiple tasks to wait for a partic-
ular event to occur. The tasks can be kept suspended until the event is set by another
task, a S/W timer, or an interrupt handler. The event can be anything that the soft-
ware is made aware of in any way. Examples include the change of an input signal,
the expiration of a timer, a key press, the reception of a character, or a complete
command.
Compared to a task event, the signalling function does not need to know which task
is waiting for the event to occur.

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10.1 Event object API function overview

Routine Description
Creates an event object. Has to be called before the
OS_EVENT_Create()
event object can be used.
OS_EVENT_Wait() Waits for an event and resets the event after it occurs.
Waits for an event with timeout and resets the event
OS_EVENT_WaitTimed()
after it occurs.
OS_EVENT_Set() Sets the events, or resumes waiting tasks.
OS_EVENT_Reset() Clears for example resets the event to un-signaled state.
Sets the event, resumes waiting tasks, if any, and then
OS_EVENT_Pulse()
resets the event.
OS_EVENT_Get() Returns the state of an event object.
OS_EVENT_Delete() Deletes the specified event object.
Table 10.1: Event object API overview

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10.1.1 OS_EVENT_Create()
Description
Creates an event object and resets the event.
Prototype
void OS_EVENT_Create (OS_EVENT* pEvent)

Parameter Description
pEvent Pointer to an event object data structure.
Table 10.2: OS_EVENT_Create() parameter list

Additional Information
Before the event object can be used, it has to be created once by a call of
OS_EVENT_Create(). On creation, the event is set in non-signaled state, and the list
of waiting tasks is deleted. Therefore, OS_EVENT_Create() must not be called for an
event object which was already created before. The debug version of embOS checks
whether the specified event object was already created and calls OS_Error() with
error code OS_ERR_2USE_EVENTOBJ, if the event object was already created before the
call of OS_EVENT_Create().
Example
OS_EVENT _HW_Event;
OS_EVENT_Create(&HW_Event); /* Create and initialize event object */

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10.1.2 OS_EVENT_Wait()
Description
Waits for an event and suspends the calling task as long as the event is not signaled.
Prototype
void OS_EVENT_Wait (OS_EVENT* pEvent)

Parameter Description
pEvent Pointer to the event object that the task will be waiting for.
Table 10.3: OS_EVENT_Wait() parameter list

Additional Information
If the specified event object is already set, the calling task resets the event and con-
tinues operation. If the specified event object is not set, the calling task is suspended
until the event object becomes signaled. pEvent has to address an existing event
object, which has to be created before the call of OS_EVENT_Wait(). The debug ver-
sion of embOS will check whether pEvent addresses a valid event object and will call
OS_Error() with error code OS_ERR_EVENT_INVALID in case of an error.
Important
This function may not be called from within an interrupt handler or software timer.
Example
OS_EVENT_Wait(&_HW_Event); /* Wait for event object */

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10.1.3 OS_EVENT_WaitTimed()
Description
Waits for an event and suspends the calling task for a specified time as long as the
event is not signaled.
Prototype
char OS_EVENT_WaitTimed (OS_EVENT* pEvent, OS_TIME Timeout)

Parameter Description
pEvent Pointer to the event object that the task will be waiting for.
Maximum time in timer ticks until the event have to be signaled.
The data type OS_TIME is defined as an integer, therefore valid
Timeout values are
1 <= Timeout <= 2 15-1 = 0x7FFF = 32767 for 8/16-bit CPUs
1 <= Timeout <= 2 31-1 = 0x7FFFFFFF for 32-bit CPUs
Table 10.4: OS_EVENT_Wait() parameter list

Return value
0 success, the event was signaled within the specified time.
1 if the event was not signaled and a timeout occured.
Additional Information
If the specified event object is already set, the calling task resets the event and con-
tinues operation. If the specified event object is not set, the calling task is suspended
until the event object becomes signaled or the timeout time has expired.
pEvent has to address an existing event object, which has to be created before the
call of OS_EVENT_WaitTimed(). The debug version of embOS will check whether
pEvent addresses a valid event object and will call OS_Error() with error code
OS_ERR_EVENT_INVALID in case of an error.
Important
This function may not be called from within an interrupt handler or software timer.
Example
if (OS_EVENT_WaitTimed(&_HW_Event, 10) == 0) {
/* event was signaled within tim out time, handle event */
...
} else {
/* event was not signaled within tim out time, handle timeout */
...
}

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10.1.4 OS_EVENT_Set()
Description
Sets an event object to signaled state, or resumes tasks which are waiting at the
event object.
Prototype
void OS_EVENT_Set (OS_EVENT* pEvent)

Parameter Description
pEvent Pointer to the event object which should be set to signaled state.
Table 10.5: OS_EVENT_Set() parameter list

Additional Information
If no tasks are waiting at the event object, the event object is set to signaled state.
If at least one task is already waiting at the event object, all waiting tasks are
resumed and the event object is not set to the signaled state. pEvent has to address
an existing event object, which has to be created before by a call of of
OS_EVENT_Create(). The debug version of embOS will check whether pEvent
addresses a valid event object and will call OS_Error() with error code
OS_ERR_EVENT_INVALID in case of an error.
Example
The following printout shows an example using event objects to synchronize tasks to
a hardware initilization function. This sample application can be found in
MAIN_Event.c, which is delivered in the Samples subdirectory of the embOS Start
folder.
/********************************************************************
* SEGGER MICROCONTROLLER SYSTEME GmbH
* Solutions for real time microcontroller applications
*********************************************************************
File : Main_EVENT.c
Purpose : Sample program for embOS using EVENT object
--------- END-OF-HEADER --------------------------------------------*/

#include "RTOS.h"

OS_STACKPTR int StackHP[128], StackLP[128]; /* Task stacks */

OS_TASK TCBHP, TCBLP; /* Task-control-blocks */

/********************************************************************/

/****** Interface to HW module **************************************/

void HW_Wait(void);
void HW_Free(void);
void HW_Init(void);

/********************************************************************/

/****** HW module ***************************************************/

OS_STACKPTR int _StackHW[128]; /* Task stack */

OS_TASK _TCBHW; /* Task-control-block */

/****** local data **************************************************/

static OS_EVENT _HW_Event;

/****** local functions *********************************************/

static void _HWTask(void) {
/* Initialize HW functionallity */

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OS_Delay(100);
/* Init done, send broadcast to waiting tasks */
HW_Free();
while (1) {
OS_Delay (40);
}
}

/****** global functions ********************************************/

void HW_Wait(void) {
OS_EVENT_Wait(&_HW_Event);
}

void HW_Free(void) {
OS_EVENT_Set(&_HW_Event);
}

void HW_Init(void) {
OS_CREATETASK(&_TCBHW, "HWTask", _HWTask, 25, _StackHW);
OS_EVENT_Create(&_HW_Event);
}

/********************************************************************/

/********************************************************************/

static void HPTask(void) {

HW_Wait(); /* Wait until HW module is set up */
while (1) {
OS_Delay (50);
}
}

static void LPTask(void) {

HW_Wait(); /* Wait until HW module is set up */
while (1) {
OS_Delay (200);
}
}

/*********************************************************************
*
* main
**********************************************************************/

int main(void) {
OS_IncDI(); /* Initially disable interrupts */
OS_InitKern(); /* Initialize OS */
OS_InitHW(); /* Initialize Hardware for OS */
HW_Init(); /* Initialize HW module */
/* You need to create at least one task before calling OS_Start() */
OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);
OS_CREATETASK(&TCBLP, "LP Task", LPTask, 50, StackLP);
OS_SendString("Start project will start multitasking !\n");
OS_Start(); /* Start multitasking */
return 0;
}

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10.1.5 OS_EVENT_Reset()
Description
Resets the specified event object to non-signaled state.
Prototype
void OS_EVENT_Reset (OS_EVENT* pEvent)

Parameter Description
Pointer to the event object which should be reset to non-signaled
pEvent
state.
Table 10.6: OS_EVENT_Reset() parameter list

Additional Information
pEvent has to address an existing event object, which has been created before by a
call of OS_EVENT_Create(). The debug version of embOS will check whether pEvent
addresses a valid event object and will call OS_Error() with the error code
OS_ERR_EVENT_INVALID in case of an error.
Example
OS_EVENT_Reset(&_HW_Event); /* Reset event object to non-signaled state */

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10.1.6 OS_EVENT_Pulse()
Description
Signals an event object and resumes waiting tasks, then resets the event object to
non-signaled state.
Prototype
void OS_EVENT_Pulse (OS_EVENT* pEvent);

Parameter Description
pEvent Pointer to the event object which should be pulsed.
Table 10.7: OS_EVENT_Pulse() parameter list

Additional Information
If any tasks are waiting at the event object, the tasks are resumed. The event object
remains unsignaled. The debug version of embOS will check whether pEvent
addresses a valid event object and will call OS_Error() with the error code
OS_ERR_EVENT_INVALID in case of an error.

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10.1.7 OS_EVENT_Get()
Description
Returns the state of an event object.
Prototype
unsigned char OS_EVENT_Get (OS_EVENT* pEvent);

Parameter Description
pEvent Pointer to an event object who’s state should be examined.
Table 10.8: OS_EVENT_Get() parameter list

Return value
0: Event object is not set to signaled state
1: Event object is set to signaled state.
Additional Information
By calling this function, the actual state of the event object remains unchanged.
pEvent has to address an existing event object, which has been created before by a
call of OS_EVENT_Create(). The debug version of embOS will check whether pEvent
addresses a valid event object and will call OS_Error() with error code
OS_ERR_EVENT_INVALID in case of an error.

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10.1.8 OS_EVENT_Delete()
Description
Deletes an event object.
Prototype
void OS_EVENT_Delete (OS_EVENT* pEvent);

Parameter Description
pEvent Pointer to an event object which should be deleted.
Table 10.9: OS_EVENT_Delete() parameter list

Additional Information
To keep the system fully dynamic, it is essential that event objects can be created
dynamically. This also means there has to be a way to delete an event object when it
is no longer needed. The memory that has been used by the event object’s control
structure can then be reused or reallocated.
It is your responsibility to make sure that:
• the program no longer uses the event object to be deleted
• the event object to be deleted actually exists (has been created first)
• no tasks are waiting at the event object when it is deleted.
pEvent has to address an existing event object, which has been created before by a
call of OS_EVENT_Create(). The debug version of embOS will check whether pEvent
addresses a valid event object and will call OS_Error() with error code
OS_ERR_EVENT_INVALID in case of an error. If any task is waiting at the event object
which is deleted, the debug version of embOS calls OS_Error() with error code
OS_ERR_EVENT_DELETE. To avoid any problems, an event object should not be deleted
in a normal application.

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Chapter 11

Heap type memory management

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ANSI C offers some basic dynamic memory management functions. These are mal-
loc, free, and realloc.
Unfortunately, these routines are not thread-safe, unless a special thread-safe imple-
mentation exists in the compiler specific runtime libraries; they can only be used
from one task or by multiple tasks if they are called sequentially. Therefore, embOS
offer task-safe variants of these routines. These variants have the same names as
their ANSI counterparts, but are prefixed OS_; they are called OS_malloc(),
OS_free(), OS_realloc(). The thread-safe variants that embOS offers use the stan-
dard ANSI routines, but they guarantee that the calls are serialized using a resource
semaphore.
If heap memory management is not supported by the standard C-libraries for a spe-
cific CPU, embOS heap memory management is not implemented.
Heap type memory management is part of the embOS libraries. It does not use any
resources if it is not referenced by the application (that is, if the application does not
use any memory management API function).
Note that another aspect of these routines may still be a problem: the memory used
for the functions (known as heap) may fragment. This can lead to a situation where
the total amount of memory is sufficient, but there is not enough memory available
in a single block to satisfy an allocation request.

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11.1 Heap type memory manager API reference

API routine Description
OS_malloc() Allocates a block of memory on the heap.
OS_free() Frees a block of memory previously allocated.
OS_realloc() Changes allocation size.
Table 11.1: Heap type memory manager API overview

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Chapter 12

Fixed block size memory pools

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Fixed block size memory pools contain a specific number of fixed-size blocks of mem-
ory. The location in memory of the pool, the size of each block, and the number of
blocks are set at runtime by the application via a call to the OS_MEMF_CREATE() func-
tion. The advantage of fixed memory pools is that a block of memory can be allo-
cated from within any task in a very short, determined period of time.

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12.1 Memory pools API reference overview

All API functions for fixed block size memory pools are prefixed OS_MEMF_.

API routine Description

Create / Delete
OS_MEMF_Create Creates fixed block memory pool.
OS_MEMF_Delete Deletes fixed block memory pool.
Allocation
Allocates memory block from a given memory pool.
OS_MEMF_Alloc
Wait indefinitely if no block is available.
Allocates memory block from a given memory pool.
OS_MEMF_AllocTimed Wait no longer than given timelimit if no block is avail-
able.
Allocates block from a given memory pool, if available.
OS_MEMF_Request
Non-blocking.
Release
OS_MEMF_Release Releases memory block from a given memory pool.
OS_MEMF_FreeBlock Releases memory block from any pool.
Info
OS_MEMF_GetNumFreeBlocks Returns the number of available blocks in a pool.
OS_MEMF_IsInPool Returns !=0 if block is in memory pool.
Returns the maximum number of blocks in a pool
OS_MEMF_GetMaxUsed
which have been used at a time.
OS_MEMF_GetNumBlocks Returns the number of blocks in a pool.
OS_MEMF_GetBlockSize Returns the size of one block of a given pool.
Table 12.1: Memory pools API overview

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12.1.1 OS_MEMF_Create()
Description
Creates and initializes a fixed block size memory pool.
Prototype
void OS_MEMF_Create (OS_MEMF* pMEMF,
void* pPool,
OS_U16 NumBlocks,
OS_U16 BlockSize);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Pointer to memory to be used for the memory pool. Required size
pPool
is: NumBlocks * (BlockSize + OS_MEMF_SIZEOF_BLOCKCONTROL).
Pointer to memory to be used for the memory pool. Required size
NumBlocks
is: NumBlocks * (BlockSize + OS_MEMF_SIZEOF_BLOCKCONTROL).
BlockSize Size in bytes of one block.
Table 12.2: OS_MEMF_Create() parameter list

Additional Information
OS_MEMF_SIZEOF_BLOCKCONTROL gives the number of bytes used for control and
debug purposes. It is guaranteed to be 0 in release or stack check builds. Before
using any memory pool, it has to be created. The debug version of libraries keeps
track of created and deleted memory pools. The release and stack check versions do
not.

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12.1.2 OS_MEMF_Delete()
Description
Deletes a fixed block size memory pool. After deletion, the memory pool and memory
blocks inside this pool can no longer be used.
Prototype
void OS_MEMF_Delete (OS_MEMF* pMEMF);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Table 12.3: OS_MEMF_Delete() parameter list

Additional Information
This routine is provided for completeness. It is not used in the majority of
applications because there is no need to dynamically create/delete memory pools.
For most applications it is preferred to have a static memory pool design; memory
pools are created at startup (before calling OS_Start()) and will never be deleted.
The debug version of libraries mark the memory pool as deleted.

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12.1.3 OS_MEMF_Alloc()
Description
Requests allocation of a memory block. Waits until a block of memory is available.
Prototype
void* OS_MEMF_Alloc (OS_MEMF* pMEMF,
int Purpose);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
This is a parameter which is used for debugging purpose only. Its
value has no effect on program execution, but may be remem-
Purpose
bered in debug builds to allow runtime analysis of memory allo-
cation problems.
Table 12.4: OS_MEMF_Alloc() parameter list

Return value
Pointer to the allocated block.
Additional Information
If there is no free memory block in the pool, the calling task is suspended until a
memory block becomes available. The retrieved pointer must be delivered to
OS_MEMF_Release() as a parameter to free the memory block. The pointer must not
be modified.

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12.1.4 OS_MEMF_AllocTimed()
Description
Requests allocation of a memory block. Waits until a block of memory is available or
the timeout has expired.
Prototype
void* OS_MEMF_AllocTimed (OS_MEMF* pMEMF,
int Timeout,
int Purpose);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Timelimit before timeout, given in ticks. 0 or negative values are
Timeout
permitted.
This is a parameter which is used for debugging purpose only. Its
value has no effect on program execution, but may be remem-
Purpose
bered in debug builds to allow runtime analysis of memory allo-
cation problems.
Table 12.5: OS_MEMF_Alloc_Timed()

Return value
!=NULL pointer to the allocated block
NULL if no block has been allocated.
Additional Information
If there is no free memory block in the pool, the calling task is suspended until a
memory block becomes available or the timeout has expired. The retrieved pointer
must be delivered to OS_MEMF_Release() as parameter to free the memory block.
The pointer must not be modified.

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12.1.5 OS_MEMF_Request()
Description
Requests allocation of a memory block. Continues execution in any case.
Prototype
void* OS_MEMF_Request (OS_MEMF* pMEMF,
int Purpose);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
This is a parameter which is used for debugging purpose only. Its
value has no effect on program execution, but may be remem-
Purpose
bered in debug builds to allow runtime analysis of memory allo-
cation problems.
Table 12.6: OS_MEMF_Request() parameter list

Return value
!=NULL pointer to the allocated block
NULL if no block has been allocated.
Additional Information
The calling task is never suspended by calling OS_MEMF_Request(). The retrieved
pointer must be delivered to OS_MEMF_Release() as parameter to free the memory
block. The pointer must not be modified.

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12.1.6 OS_MEMF_Release()
Description
Releases a memory block that was previously allocated.
Prototype
void OS_MEMF_Release (OS_MEMF* pMEMF,
void* pMemBlock);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
pMemBlock Pointer to the memory block to free.
Table 12.7: OS_MEMF_Release() parameter list

Additional Information
The pMemBlock pointer has to be the one that was delivered form any retrival func-
tion described above. The pointer must not be modified between allocation and
release. The memory block becomes available for other tasks waiting for a memory
block from the pool. If any task is waiting for a fixed memory block, it is activated
according to the rules of the scheduler.

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12.1.7 OS_MEMF_FreeBlock()
Description
Releases a memory block that was previously allocated. The memory pool does not
need to be denoted.
Prototype
void OS_MEMF_FreeBlock (void* pMemBlock);

Parameter Description
pMemBlock Pointer to the memory block to free.
Table 12.8: OS_MEMF_FreeBlock() parameter list

Additional Information
The pMemBlock pointer has to be the one that was delivered form any retrieval func-
tion described above. The pointer must not be modified between allocation and
release. This function may be used instead of OS_MEMF_Release(). It has the advan-
tage that only one parameter is needed. embOS itself will find the associated mem-
ory pool. The memory block becomes available for other tasks waiting for a memory
block from the pool. If any task is waiting for a fixed memory block, it is activated
according to the rules of the scheduler.

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12.1.8 OS_MEMF_GetNumBlocks()
Description
Information routine to examine the total number of available memory blocks in the
pool.
Prototype
int OS_MEMF_GetNumFreeBlocks (OS_MEMF* pMEMF);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Table 12.9: OS_MEMF_GetNumBlocks() parameter list

Return value
Returns the number of blocks in the specified memory pool. This is the value that
was given as parameter during creation of the memory pool.

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12.1.9 OS_MEMF_GetBlockSize()
Description
Information routine to examine the size of one memory block in the pool.
Prototype
int OS_MEMF_GetBlockSize (OS_MEMF* pMEMF);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Table 12.10: OS_MEMF_GetBlockSize() parameter list

Return value
Size in bytes of one memory block in the specified memory pool. This is the value of
the parameter when the memory pool was created.

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12.1.10 OS_MEMF_GetNumFreeBlocks()
Description
Information routine to examine the number of free memory blocks in the pool.
Prototype
int OS_MEMF_GetNumFreeBlocks (OS_MEMF* pMEMF);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Table 12.11: OS_MEMF_GetNumFreeBlocks() parameter list

Return value
The number of free blocks actually available in the specified memory pool.

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12.1.11 OS_MEMF_GetMaxUsed()
Description
Information routine to examine the amount of memory blocks in the pool that were
used concurrently since creation of the pool.
Prototype
int OS_MEMF_GetMaxUsed (OS_MEMF* pMEMF);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
Table 12.12: OS_MEMF_GetMaxUsed() parameter list

Return value
Maximum number of blocks in the specified memory pool that were used concurrently
since the pool was created.

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12.1.12 OS_MEMF_IsInPool()
Description
Information routine to examine whether a memory block reference pointer belongs to
the specified memory pool.
Prototype
char OS_MEMF_IsInPool (OS_MEMF* pMEMF,
void* pMemBlock);

Parameter Description
pMEMF Pointer to the control data structure of memory pool.
pMemBlock Pointer to a memory block that should be checked
Table 12.13: OS_MEMF_IsInPool() parameter list

Return value
0: Pointer does not belong to memory pool.
1: Pointer belongs to the pool.

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Chapter 13

Stacks

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The stack is the memory area used for storing the return address of function calls,
parameters, and local variables, as well as for temporary storage. Interrupt routines
also use the stack to save the return address and flag registers, except in cases
where the CPU has a separate stack for interrupt functions. Refer to the CPU &
Compiler Specifics manual of embOS documentation for details on your processor's
stack. A "normal" single-task program needs exactly one stack. In a multitasking
system, every task has to have its own stack.
The stack needs to have a minimum size which is determined by the sum of the stack
usage of the routines in the worst-case nesting. If the stack is too small, a section of
the memory that is not reserved for the stack will be overwritten, and a serious pro-
gram failure is most likely to occur. embOS monitors the stack size (and, if available,
also interrupt stack size in the debug version), and calls the failure routine
OS_Error() if it detects a stack overflow. However, embOS cannot reliably detect a
stack overflow.
A stack that has been defined larger than necessary does not hurt; it is only a waist
of memory. To detect a stack overflow, the debug and stack check builds of embOS
fill the stack with control characters when it is created and check these characters
every time the task is deactivated. If an overflow is detected, OS_Error() is called.

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13.1 System stack

Before embOS takes over control (before the call to OS_Start()), a program does
use the so-called system stack. This is the same stack that a non-embOS program for
this CPU would use. After transferring control to the embOS scheduler by calling
OS_Start(), the system stack is used only when no task is executed for the follow-
ing:
• embOS scheduler
• embOS software timers (and the callback).
For details regarding required size of your system stack, refer to the CPU & Compiler
Specifics manual of embOS documentation.

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13.2 Task stack

Each embOS task has a separate stack. The location and size of this stack is defined
when creating the task. The minimum size of a task stack pretty much depends on
the CPU and the compiler. For details, see the CPU & Compiler Specifics manual of
embOS documentation.

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13.3 Interrupt stack

To reduce stack size in a multitasking environment, some processors use a specific
stack area for interrupt service routines (called a hardware interrupt stack). If there
is no interrupt stack, you will have to add stack requirements of your interrupt ser-
vice routines to each task stack.
Even if the CPU does not support a hardware interrupt stack, embOS may support a
separate stack for interrupts by calling the function OS_EnterIntStack() at begin-
ning of an interrupt service routine and OS_LeaveIntStack() at its very end. In case
the CPU already supports hardware interrupt stacks or if a separate interrupt stack is
not supported at all, these function calls are implemented as empty macros.
We recommend using OS_EnterIntStack() and OS_LeaveIntStack() even if there is
currently no additional benefit for your specific CPU, because code that uses them
might reduce stack size on another CPU or a new version of embOS with support for
an interrupt stack for your CPU. For details about interrupt stacks, see the CPU &
Compiler Specifics manual of embOS documentation.

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13.4 Stacks API function overview

Routine Description
OS_GetStackBase() Returns the base address of a task stack.
OS_GetStackSize() Returns the size of a task stack.
OS_GetStackSpace() Returns the unused portion of a task stack.
OS_GetStackUsed() Returns the used portion of a task stack.
Table 13.1: Stacks API overview

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13.4.1 OS_GetStackBase()
Description
Returns a pointer to the base of a task stack.
Prototype
OS_STACKPTR* OS_GetStackBase (OS_TASK* pTask);

Parameter Description
The task who's stack base has to be returned.
pTask
NULL means current task.
Table 13.2: OS_GetStackBase() parameter list

Return value
The pointer to the base address of the task stack.
Additional Information
This function is only available in the debug and stack check builds of embOS, because
only these builds initialize the stack space used for the tasks.
Example
void CheckSpace(void) {
printf("Addr Stack[0] %x", OS_GetStackBase(&TCB[0]);
OS_Delay(1000);
printf("Addr Stack[1] %x", OS_GetStackBase(&TCB[1]);
OS_Delay(1000);
}

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13.4.2 OS_GetStackSize()
Description
Returns the size of a task stack.
Prototype
int OS_GetStackSize (OS_TASK* pTask);

Parameter Description
The task who's stack size should be checked.
pTask
NULL means current task.
Table 13.3: OS_GetStackSize() parameter list

Return value
The size of the task stack in bytes.
Additional Information
This function is only available in the debug and stack check builds of embOS, because
only these builds initialize the stack space used for the tasks.
Example
void CheckSpace(void) {
printf("Size Stack[0] %d", OS_GetStackSize(&TCB[0]);
OS_Delay(1000);
printf("Size Stack[1] %d", OS_GetStackSize(&TCB[1]);
OS_Delay(1000);
}

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13.4.3 OS_GetStackSpace()
Description
Returns the unused portion of a task stack.
Prototype
int OS_GetStackSpace (OS_TASK* pTask);

Parameter Description
The task who's stack space has to be checked.
pTask
NULL means current task.
Table 13.4: OS_GetStackSpace() parameter list

Return value
The unused portion of the task stack in bytes.
Additional Information
In most cases, the stack size required by a task cannot be easily calculated, because
it takes quite some time to calculate the worst-case nesting and the calculation itself
is difficult.
However, the required stack size can be calculated using the function
OS_GetStackSpace(), which returns the number of unused bytes on the stack. If
there is a lot of space left, you can reduce the size of this stack and vice versa.
This function is only available in the debug and stack check builds of embOS, because
only these builds initialize the stack space used for the tasks.
Important
This routine does not reliably detect the amount of stack space left, because it can
only detect modified bytes on the stack. Unfortunately, space used for register stor-
age or local variables is not always modified. In most cases, this routine will detect
the correct amount of stack bytes, but in case of doubt, be generous with your stack
space or use other means to verify that the allocated stack space is sufficient.
Example
void CheckSpace(void) {
printf("Unused Stack[0] %d", OS_GetStackSpace(&TCB[0]);
OS_Delay(1000);
printf("Unused Stack[1] %d", OS_GetStackSpace(&TCB[1]);
OS_Delay(1000);
}

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13.4.4 OS_GetStackUsed()
Description
Returns the used portion of a task stack.
Prototype
int OS_GetStackUsed (OS_TASK* pTask);

Parameter Description
The task who's stack usage has to be checked.
pTask
NULL means current task.
Table 13.5: OS_GetStackUsed() parameter list

Return value
The used portion of the task stack in bytes.
Additional Information
In most cases, the stack size required by a task cannot be easily calculated, because
it takes quite some time to calculate the worst-case nesting and the calculation itself
is difficult.
However, the required stack size can be calculated using the function
OS_GetStackUsed(), which returns the number of used bytes on the stack. If there is
a lot of space left, you can reduce the size of this stack and vice versa.
This function is only available in the debug and stack check builds of embOS, because
only these builds initialize the stack space used for the tasks.
Important
This routine does not reliably detect the amount of stack space used, because it can
only detect modified bytes on the stack. Unfortunately, space used for register stor-
age or local variables is not always modified. In most cases, this routine will detect
the correct amount of stack bytes, but in case of doubt, be generous with your stack
space or use other means to verify that the allocated stack space is sufficient.
Example
void CheckSpace(void) {
printf("Used Stack[0] %d", OS_GetStackUsed(&TCB[0]);
OS_Delay(1000);
printf("Used Stack[1] %d", OS_GetStackUsed(&TCB[1]);
OS_Delay(1000);
}

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Chapter 14

Interrupts

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In this chapter, you will find a very basic description about using interrupt service
routines (ISRs) in cooperation with embOS. Specific details for your CPU and
compiler may be found in the CPU & Compiler Specifics manual of the embOS docu-
mentation.
Interrupts are interruptions of a program caused by hardware. When an interrupt
occurs, the CPU saves its registers and executes a subroutine called an interrupt
service routine, or ISR. After the ISR is completed, the program returns to the
highest-priority task in the READY state. Normal interrupts are maskable; they can
occur at any time unless they are disabled with the CPU's "disable interrupt" instruc-
tion. ISRs are also nestable - they can be recognized and executed within other ISRs.
There are several good reasons for using interrupt routines. They can respond very
quickly to external events such as the status change on an input, the expiration of a
hardware timer, reception or completion of transmission of a character via serial
interface, or other types of events. Interrupts effectively allow events to be pro-
cessed as they occur.

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14.1 Interrupt latency

Interrupt latency is the time between an interrupt request and the execution of the
first instruction of the interrupt service routine.
Every computer system has an interrupt latency. The latency depends on various fac-
tors and differs even on the same computer system. The value that one is typically
interested in is the worst case interrupt latency.
The interrupt latency is the sum of a lot of different smaller delays explained below.

14.1.1 Causes of interrupt latencies

• The first delay is typically in the hardware: The interrupt request signal needs to
be synchronized to the CPU clock. Depending on the synchronization logic, typi-
cally up to 3 CPU cycles can be lost before the interrupt request has reached the
CPU core.
• The CPU will typically complete the current instruction. This instruction can take
a lot of cycles; on most systems, divide, push-multiple, or memory-copy instruc-
tions are the instructions which require most clock cycles. On top of the cycles
required by the CPU, there are in most cases additional cycles required for mem-
ory access. In an ARM7 system, the instruction STMDB SP!,{R0-R11,LR}; (Push
parameters and perm. register) is typically the worst case instruction. It stores
13 32-bit registers on the stack. The CPU requires 15 clock cycles.
• The memory system may require additional cycles for wait states.
• After the current instruction is completet, the CPU performs a mode switch or
pushes registers (typically, PC and flag registers) on the stack. In general, mod-
ern CPUs (such as ARM) perform a mode switch, which requires less CPU cycles
than saving registers.
• Pipeline fill
Most modern CPUs are pipelined. Execution of an instruction happens in various
stages of the pipeline. An instruction is executed when it has reached its final
stage of the pipeline. Because the mode switch has flushed the pipeline, a few
extra cycles are required to refill the pipeline.

14.1.2 Additional causes for interrupt latencies

There can be additional causes for interrupt latencies.
These depend on the type of system used, but we list a few of them.
• Latencies caused by cache line fill.
If the memory system has one or multiple caches, these may not contain the
required data. In this case, not only the required data is loaded from memory,
but in a lot of cases a complete line fill needs to be performed, reading multiple
words from memory.
• Latencies caused by cache write back.
A cache miss may cause a line to be replaced. If this line is marked as dirty, it
needs to be written back to main memory, causing an additional delay.
• Latencies caused by MMU translation table walks.
Translation table walks can take a considerable amount of time, especially as
they involve potentially slow main memory accesses. In real-time interrupt han-
dlers, translation table walks caused by the TLB not containing translations for
the handler and/or the data it accesses can increase interrupt latency signifi-
cantly.
• Application program.
Of course, the application program can cause additional latencies by disabling
interrupts. This can make sense in some situations, but of course causes add.
latencies.
• Interrupt routines.
On most systems, one interrupt disables further interrupts. Even if the interrupts
are re-enabled in the ISR, this takes a few instructions, causing add. latency.
• RTOS (Real-time Operating system).
An RTOS also needs to temporarily disable the interrupts which can call API-func-
tions of the RTOS. Some RTOSes disable all interrupts, effectively increasing

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interrupt latencies for all interrupts, some (like embOS) disable only low-priority
interrupts and do thereby not affect the latency of high priority interrupts.

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14.2 Zero interrupt latency

Zero interrupt latency in the strict sense is not possible as explained above. What we
mean when we say "Zero interrupt latency" is that the latency of high-priority inter-
rupts is not affected by the RTOS; a system using embOS will have the same worst-
case interrupt latency for high priority interrupts as a system running without
embOS.

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14.3 High / low priority interrupts

Most CPUs support interrupts with different priorities. Different priorities have two
effects:
• If different interrupts occur simultaneously, the interrupt with higher priority
takes precedence and its ISR is executed first.
• Interrupts can never be interrupted by other interrupts of the same or lower level
of priority.
How many different levels of interrupts there are depend on the CPU and the inter-
rupt controller. Details are explained in the CPU/MCU/SOC manuals and the CPU &
Compiler Specifics manual of embOS. embOS distinguishes two different levels of
interrupts: High / Low priority interrupts. The embOS port specific documentation
explains where "the line is drawn", which interrupts are considered high and which
interrupts are considered low priority. In general, the differences are:
Low priority interrupts
• May call embOS API functions
• Latencies caused by embOS
High priority interrupts
• May not call embOS API functions
• No Latencies caused by embOS (Zero latency)
Example of different interrupt priority levels
M16C CPUs support 8 interrupt priority levels. With embOS, the 3 highest priority
levels are treated as “High priority interrupts”. ARM CPUs support normal interrupts
(IRQ) and fast interrupt (FIQ). Using embOS, the FIQ is treated as “High priority
interrupt”.

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14.4 Rules for interrupt handlers

14.4.1 General rules
There are some general rules for interrupt handlers. These rules apply to both single-
task programming as well as to multitask programming using embOS.
• Interrupt handlers preserve all registers.
Interrupt handlers must restore the environment of a task completely. This
environment normally consists of the registers only, so the ISR has to make sure
that all registers modified during interrupt execution are saved at the beginning
and restored at the end of the interrupt routine
• Interrupt handlers have to be finished quickly.
Intensive calculations should be kept out of interrupt handlers. An interrupt han-
dler should only be used for storing a received value or to trigger an operation in
the regular program (task). It should not wait in any form or perform a polling
operation.

14.4.2 Additional rules for preemptive multitasking

A preemptive multitasking system like embOS needs to know if the program that is
executing is part of the current task or an interrupt handler. This is because embOS
cannot perform a task switch during the execution of an interrupt handler; it can only
do so at the end of an interrupt handler.
If a task switch were to occur during the execution of an ISR, the ISR would continue
as soon as the interrupted task became the current task again. This is not a problem
for interrupt handlers that do not allow further interruptions (which do not enable
interrupts) and that do not call any embOS functions.
This leads us to the following rule:
• Interrupt functions that re-enable interrupts or use any embOS function need to
call OS_EnterInterrupt() at the beginning, before executing any other com-
mand, and before they return, call either OS_LeaveInterrupt() or
OS_LeaveInterruptNoSwitch() as last command.
If a higher priority task is made ready by the ISR, the task switch then occurs in the
routine OS_LeaveInterrupt(). The end of the ISR is executed at a later point, when
the interrupted task is made ready again. If you debug an interrupt routine, do not
be confused. This has proven to be the most efficient way of initiating a task switch
from within an interrupt service routine.
If fast task-activation at the end of an interrupt service routine is not required,
OS_LeaveInterruptNoSwitch() can be used instead.

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14.5 Calling embOS routines from within an ISR

Before calling any embOS function from within an ISR, embOS has to be informed
that an interrupt service routine is running.

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14.5.1 Interrupts API function overview

Routine Description
OS_CallISR() Interrupt entry function.
Interrupt entry function supporting
OS_CallNestableISR()
estable interrupts.
Informs embOS that interrupt code is
OS_EnterInterrupt()
executing.
Informs embOS that the end of the inter-
OS_LeaveInterrupt() rupt routine has been reached; executes
task switching within ISR.
Informs embOS that the end of the inter-
OS_LeaveInterruptNoSwitch() rupt routine has been reached but does
not execute task switching within ISR.
Increments the interrupt disable counter
OS_IncDI()
(OS_DICnt) and disables interrupts.
Decrements the counter and enables
OS_DecRI()
interrupts if the counter reaches 0.
Disables interrupts. Does not change the
OS_DI()
interrupt disable counter.
OS_EI() Unconditionally enables Interrupt.
Restores the status of the interrupt flag,
OS_RestoreI()
based on the interrupt disable counter.
Re-enables interrupts and increments the
OS_EnterNestableInterrupt() embOS internal critical region counter,
thus disabling further task switches.
OS_LeaveNestableInterrupt() Disables further interrupts.
Disables further interrupts, informs
OS_LeaveNestableInterruptNoSwitch() embOS that the end of ISR is reached,
but does not perform a task switch.
Table 14.1: Interrupt API overview

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14.5.2 OS_CallISR()
Description
Entry function for use in an embOS interrupt handler. Nestable interrupts disabled.
Prototype
void OS_CallISR (void (*pRoutine)(void));

Parameter Description
pRoutine Pointer to a routine that should run on interrupt.
Table 14.2: OS_CallISR() parameter list

Additional Information
OS_CallISR() can be used as entry function in an embOS interrupt handler, when
the corresponding interrupt should not be interrupted by another embOS interrupt.
OS_CallISR() sets the interrupt priority of the CPU to the user definable ’fast’ inter-
rupt priority level, thus locking any other embOS interrupt.
Fast interrupts are not disabled.
Note: For some specific CPUs OS_CallISR() has to be used to call an interrupt
handler because OS_EnterInterrupt() / OS_LeaveInterrupt() may not be avail-
able.
Refer to the CPU specific manual.
Example
#pragma interrupt void OS_ISR_Tick(void) {
OS_CallISR(_IsrTickHandler);
}

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14.5.3 OS_CallNestableISR()
Description
Entry function for use in an embOS interrupt handler. Nestable interrupts enabled.
Prototype
void OS_CallNestableISR (void (*pRoutine)(void));

Parameter Description
pRoutine Pointer to a routine that should run on interrupt.
Table 14.3: OS_CallNestableISR() parameter list

Additional Information
OS_CallNestableISR() can be used as entry function in an embOS interrupt handler,
when interruption by higher prioritized embOS interrupts should be allowed.
OS_CallNestableISR() does not alter the interrupt priority of the CPU, thus keeping
all interrupts with higher priority enabled.
Note: For some specific CPUs OS_CallNestableISR() has to be used to call an
interrupt handler because OS_EnterNestableInterrupt() /
OS_LeaveNestableInterrupt() may not be available.
Refer to the CPU specific manual.
Example
#pragma interrupt void OS_ISR_Tick(void) {
OS_CallNestableISR(_IsrTickHandler);
}

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14.5.4 OS_EnterInterrupt()
Note: This function may not be available in all ports.
Description
Informs embOS that interrupt code is executing.
Prototype
void OS_EnterInterrupt (void);

Additional Information
If OS_EnterInterrupt() is used, it should be the first function to be called in the
interrupt handler. It must be used with either OS_LeaveInterrupt() or
OS_LeaveInterruptNoSwitch() as the last function called.
The use of this function has the following effects, it:
• disables task switches
• keeps interrupts in internal routines disabled.

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14.5.5 OS_LeaveInterrupt()
Note: This function may not be available in all ports.
Description
Informs embOS that the end of the interrupt routine has been reached; executes
task switching within ISR.
Prototype
void OS_LeaveInterrupt (void);

Additional Information
If OS_LeaveInterrupt() is used, it should be the last function to be called in the
interrupt handler. If the interrupt has caused a task switch, it will be executed
(unless the program which was interrupted was in a critical region).

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14.5.6 OS_LeaveInterruptNoSwitch()
Note: This function may not be available in all ports.
Description
Informs embOS that the end of the interrupt routine has been reached but does not
execute task switching within ISR.
Prototype
void OS_LeaveInterruptNoSwitch (void);

Additional Information
If OS_LeaveInterruptNoSwitch() is used, it should be the last function to be called
in the interrupt handler. If the interrupt has caused a task switch, it is not executed
from within the ISR, but at the next possible occasion. This will be the next call of an
embOS function or the scheduler interrupt if the program is not in a critical region.

14.5.7 Example using OS_EnterInterrupt()/OS_LeaveInterrupt()

Interrupt routine using OS_EnterInterrupt()/OS_LeaveInterrupt():

__interrupt void ISR_Timer(void) {

OS_EnterInterrupt();
OS_SignalEvent(1,&Task);/* Any functionality could be here */
OS_LeaveInterrupt();
}

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14.6 Enabling / disabling interrupts from C

During the execution of a task, maskable interrupts are normally enabled. In certain
sections of the program, however, it can be necessary to disable interrupts for short
periods of time to make a section of the program an atomic operation that cannot be
interrupted. An example would be the access to a global volatile variable of type long
on an 8/16-bit CPU. To make sure that the value does not change between the two or
more accesses that are needed, the interrupts have to be temporarily disabled:
Bad example:
volatile long lvar;

void routine (void) {

lvar ++;
}

The problem with disabling and re-enabling interrupts is that functions that disable/
enable the interrupt cannot be nested.
Your C compiler offers two intrinsic functions for enabling and disabling interrupts.
These functions can still be used, but it is recommended to use the functions that
embOS offers (to be precise, they only look like functions, but are macros in reality).
If you do not use these recommended embOS functions, you may run into a problem
if routines which require a portion of the code to run with disabled interrupts are
nested or call an OS routine.
We recommend disabling interrupts only for short periods of time, if possible. Also,
you should not call routines when interrupts are disabled, because this could lead to
long interrupt latency times (the longer interrupts are disabled, the higher the inter-
rupt latency). As long as you only call embOS functions with interrupts enabled, you
may also safely use the compiler-provided intrinsics to disable interrupts.

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14.6.1 OS_IncDI() / OS_DecRI()

The following functions are actually macros defined in RTOS.h, so they execute very
quickly and are very efficient. It is important that they are used as a pair: first
OS_IncDI(), then OS_DecRI().
OS_IncDI()
Short for Increment and Disable Interrupts. Increments the interrupt disable
counter (OS_DICnt) and disables interrupts.
OS_DecRI()
Short for Decrement and Restore Interrupts. Decrements the counter and
enables interrupts if the counter reaches 0.
Example
volatile long lvar;

void routine (void) {

OS_IncDI();
lvar ++;
OS_DecRI();
}

OS_IncDI() increments the interrupt disable counter which is used for the entire OS
and is therefore consistent with the rest of the program in that any routine can be
called and the interrupts will not be switched on before the matching OS_DecRI() has
been executed.
If you need to disable interrupts for a short moment only where no routine is called,
as in the example above, you could also use the pair OS_DI() and OS_RestoreI().
These are a bit more efficient because the interrupt disable counter OS_DICnt is not
modified twice, but only checked once. They have the disadvantage that they do not
work with routines because the status of OS_DICnt is not actually changed, and they
should therefore be used with great care. In case of doubt, use OS_IncDI() and
OS_DecRI().

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14.6.2 OS_DI() / OS_EI() / OS_RestoreI()

OS_DI()
Short for Disable Interrupts. Disables interrupts. Does not change the interrupt
disable counter.
OS_EI()
Short for Enable Interrupts. Refrain from using this function directly unless you are
sure that the interrupt enable count has the value zero, because it does not take the
interrupt disable counter into account.
OS_RestoreI()
Short for Restore Interrupts. Restores the status of the interrupt flag, based on the
interrupt disable counter.
Example
volatile long lvar;

void routine (void) {

OS_DI();
lvar++;
OS_RestoreI();
}

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14.7 Definitions of interrupt control macros (in RTOS.h)

#define OS_IncDI() { OS_ASSERT_DICnt(); OS_DI(); OS_DICnt++; }
#define OS_DecRI() { OS_ASSERT_DICnt(); if (--OS_DICnt==0) OS_EI(); }
#define OS_RestoreI() { OS_ASSERT_DICnt(); if (OS_DICnt==0) OS_EI(); }

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14.8 Nesting interrupt routines

By default, interrupts are disabled in an ISR because the CPU disables interrupts with
the execution of the interrupt handler. Re-enabling interrupts in an interrupt handler
allows the execution of further interrupts with equal or higher priority than that of
the current interrupt. These are known as nested interrupts, illustrated in the dia-
gram below:

Task ISR 1 ISR 2 ISR 3

Interrupt 1

Interrupt 2

Interrupt 3

Time

For applications requiring short interrupt latency, you may re-enable interrupts inside
an ISR by using OS_EnterNestableInterrupt() and OS_LeaveNestableInterrupt()
within the interrupt handler.
Nested interrupts can lead to problems that are difficult to track; therefore it is not
really recommended to enable interrupts within an interrupt handler. As it is impor-
tant that embOS keeps track of the status of the interrupt enable/disable flag, the
enabling and disabling of interrupts from within an ISR has to be done using the
functions that embOS offers for this purpose.
The routine OS_EnterNestableInterrupt() enables interrupts within an ISR and
prevents further task switches; OS_LeaveNestableInterrupt() disables interrupts
right before ending the interrupt routine again, thus restores the default condition.
Re-enabling interrupts will make it possible for an embOS scheduler interrupt to
shortly interrupt this ISR. In this case, embOS needs to know that another ISR is still
active and that it may not perform a task switch.

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14.8.1 OS_EnterNestableInterrupt()
Note: This function may not be available in all ports.
Description
Re-enables interrupts and increments the embOS internal critical region counter,
thus disabling further task switches.
Prototype
void OS_EnterNestableInterrupt (void);

Additional Information
This function should be the first call inside an interrupt handler when nested inter-
rupts are required. The function OS_EnterNestableInterrupt() is implemented as a
macro and offers the same functionality as OS_EnterInterrupt() in combination
with OS_DecRI(), but is more efficient, resulting in smaller and faster code.
Example
Refer to the example for OS_LeaveNestableInterrupt().

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14.8.2 OS_LeaveNestableInterrupt()
Note: This function may not be available in all ports.
Description
Disables further interrupts, then decrements the embOS internal critical region
count, thus re-enabling task switches if the counter has reached zero again.
Prototype
void OS_LeaveNestableInterrupt (void);

Additional Information
This function is the counterpart of OS_EnterNestableInterrupt(), and has to be the
last function call inside an interrupt handler when nested interrupts have earlier been
enabled by OS_EnterNestableInterrupt().
The function OS_LeaveNestableInterrupt() is implemented as a macro and offers
the same functionality as OS_LeaveInterrupt() in combination with OS_IncDI(),
but is more efficient, resulting in smaller and faster code.

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14.8.3 OS_LeaveNestableInterruptNoSwitch()
Note: This function may not be available in all ports.
Description
Disables further interrupts, informs embOS that the end of the ISR is reached, but
does not perform a task switch.
Prototype
void OS_LeaveNestableInterruptNoSwitch (void);

Additional Information
If OS_LeaveNestableInterruptNoSwitch() is used, it should be the last function to
be called in the interrupt handler. If the interrupt has caused a task switch, it is not
executed from within the ISR, but at the next possible occasion. This will be the next
call of an embOS function or the scheduler interrupt if the program is not in a critical
region.
Example
__interrupt void ISR_Timer(void) {
OS_EnterNestableInterrupt(); /* Enable interrupts, but disable task switch*/
/*
* Any code legal for interrupt-routines can be placed here
*/
IntHandler();
OS_LeaveNestableInterrupt(); /* Disable interrupts, allow task switch */
}

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14.9 Non-maskable interrupts (NMIs)

embOS performs atomic operations by disabling interrupts. However, a non-maskable
interrupt (NMI) cannot be disabled, meaning it can interrupt these atomic operations.
Therefore, NMIs should be used with great care and may under no circumstances call
any embOS routines.

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Chapter 15

Critical Regions

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Critical regions are program sections during which the scheduler is switched off,
meaning that no task switch and no execution of software timers are allowed except
in situations where the active task has to wait. Effectively, preemptions are switched
off.
A typical example for a critical region would be the execution of a program section
that handles a time-critical hardware access (for example writing multiple bytes into
an EEPROM where the bytes have to be written in a certain amount of time), or a
section that writes data into global variables used by a different task and therefore
needs to make sure the data is consistent.
A critical region can be defined anywhere during the execution of a task. Critical
regions can be nested; the scheduler will be switched on again after the outermost
loop is left. Interrupts are still legal in a critical region. Software timers and inter-
rupts are executed as critical regions anyhow, so it does not hurt but does not do any
good either to declare them as such. If a task switch becomes due during the execu-
tion of a critical region, it will be performed right after the region is left.

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15.1 Critical regions API function overview

Routine Description
OS_EnterRegion() Indicates to the OS the beginning of a critical region.
OS_LeaveRegion() Indicates to the OS the end of a critical region.
Table 15.1: Critical regions API overview

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15.1.1 OS_EnterRegion()
Description
Indicates to the OS the beginning of a critical region.
Prototype
void OS_EnterRegion (void);

Additional Information
OS_EnterRegion() is not actually a function but a macro. However, it behaves very
much like a function but is much more efficient. Using the macro indicates to embOS
the beginning of a critical region. A critical region counter (OS_RegionCnt), which is 0
by default, is incremented so that the routine can be nested. The counter will be dec-
remented by a call to the routine OS_LeaveRegion(). If this counter reaches 0 again,
the critical region ends. Interrupts are not disabled using OS_EnterRegion(); how-
ever, disabling interrupts will disable preemptive task switches.
Example
void SubRoutine(void) {
OS_EnterRegion();
/* this code will not be interrupted by the OS */
OS_LeaveRegion();
}

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15.1.2 OS_LeaveRegion()
Description
Indicates to the OS the end of a critical region.
Prototype
void OS_LeaveRegion (void);

Additional Information
OS_LeaveRegion() is not actually a function but a macro. However, it behaves very
much like a function but is much more efficient. Usage of the macro indicates to
embOS the end of a critical region. A critical region counter (OS_RegionCnt), which is
0 by default, is decremented. If this counter reaches 0 again, the critical region ends.
Example
Refer to the example for OS_EnterRegion().

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 223

Chapter 16

Time measurement

embOS supports 2 types of time measurement:

• Low resolution (using a time variable)
• High resolution (using a hardware timer)
Both are explained in this chapter.

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Overview
embOS supports two basic types of run-time measurement which may be used for
calculating the execution time of any section of user code. Low-resolution measure-
ments use a time base of ticks, while high-resolution measurements are based on a
time unit called a cycle. The length of a cycle depends on the timer clock frequency.

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16.1 Low-resolution measurement

The system time variable OS_Time is measured in ticks, or ms. The low-resolution
functions OS_GetTime() and OS_GetTime32() are used for returning the current con-
tents of this variable. The basic idea behind low-resolution measurement is quite
simple: The system time is returned once before the section of code to be timed and
once after, and the first value is subtracted from the second to obtain the time it took
for the code to execute.
The term low-resolution is used because the time values returned are measured in
completed ticks. Consider the following: with a normal tick of 1 ms, the variable
OS_Time is incremented with every tick-interrupt, or once every ms. This means that
the actual system time can potentially be more than what a low-resolution function
will return (for example, if an interrupt actually occurs at 1.4 ticks, the system will
still have measured only 1 tick as having elapsed). The problem becomes even
greater with runtime measurement, because the system time must be measured
twice. Each measurement can potentially be up to 1 tick less than the actual time, so
the difference between two measurements could theoretically be inaccurate by up to
two ticks.
The following diagram illustrates how low-resolution measurement works. We can see
that the section of code actually begins at 0.5 ms and ends at 5.2 ms, which means
that its actual execution time is (5.2 - 0.5) = 4.7 ms. However with a tick of 1 ms,
the first call to OS_GetTime() returns 0, and the second call returns 5. The measured
execution time of the code would therefore result in (5 - 0) = 5 ms.

OS_GetTime() => 0 OS_GetTime() => 5

Code to be timed

OS_Time 0.5 ms 5.2 ms

0 ms 1 ms 2 ms 3 ms 4 ms 5 ms 6 ms

For many applications, low-resolution measurement may be fully sufficient for your
needs. In some cases, it may be more desirable than high-resolution measurement
due to its ease of use and faster computation time.

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16.2 Low-resolution measurement API function over-

view
Routine Description
OS_GetTime() Returns the current system time in ticks.
Returns the current system time in ticks as a 32-bit
OS_GetTime32()
value.
Table 16.1: Low-resolution measurement API overview

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16.2.1 OS_GetTime()
Description
Returns the current system time in ticks.
Prototype
int OS_GetTime (void);

Return value
The system variable OS_Time as a 16- or 32-bit integer value.
Additional Information
This function returns the system time as a 16-bit value on 8/16-bit CPUs, and as a
32-bit value on 32-bit CPUs. The OS_Time variable is a 32-bit value. Therefore, if the
return value is 32-bit, it is simply the entire contents of the OS_Time variable. If the
return value is 16-bit, it is the lower 16 bits of the OS_Time variable.

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16.2.2 OS_GetTime32()
Description
Returns the current system time in ticks as a 32-bit value.
Prototype
U32 OS_GetTime32 (void);

Return value
The system variable OS_Time as a 32-bit integer value.
Additional Information
This function always returns the system time as a 32-bit value. Because the OS_Time
variable is also a 32-bit value, the return value is simply the entire contents of the
OS_Time variable.

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16.3 High-resolution measurement

High-resolution measurement uses the same routines as those used in profiling
builds of embOS, allowing for fine-tuning of time measurement. While system resolu-
tion depends on the CPU used, it is typically about 1 µs, making high-resolution mea-
surement about 1000 times more accurate than low-resolution calculations.
Instead of measuring the number of completed ticks at a given time, an internal
count is kept of the number of cycles that have been completed. Look at the illustra-
tion below, which measures the execution time of the same code used in the low-res-
olution calculation. For this example, we assume that the CPU has a timer running at
10 MHz and is counting up. The number of cycles per tick is therefore (10 MHz / 1
kHz) = 10,000. This means that with each tick-interrupt, the timer restarts at 0 and
counts up to 10,000.

OS_GetTime() => 0 OS_GetTime() => 5

Code to be timed

OS_Time 0.5 ms 5.2 ms

0 ms 1 ms 2 ms 3 ms 4 ms 5 ms 6 ms

The call to OS_Timing_Start() calculates the starting value at 5,000 cycles, while
the call to OS_Timing_End() calculates the ending value at 52,000 cycles (both val-
ues are kept track of internally). The measured execution time of the code in this
example would therefore be (52,000 - 5,000) = 47,000 cycles, which corresponds to
4.7 ms.
Although the function OS_Timing_GetCycles() may be used for returning the execu-
tion time in cycles as above, it is typically more common to use the function
OS_Timing_Getus(), which returns the value in microseconds (µs). In the above
example, the return value would be 4,700 µs.
Data structure
All high-resolution routines take as parameter a pointer to a data structure of type
OS_TIMING, defined as follows:

#define OS_TIMING OS_U32

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16.4 High-resolution measurement API function over-

view
Routine Description
OS_TimingStart() Marks the beginning of a code section to be timed.
OS_TimingEnd() Marks the end of a code section to be timed.
Returns the execution time of the code between
OS_Timing_Getus() OS_Timing_Start() and OS_Timing_End() in microsec-
onds.
Returns the execution time of the code between
OS_Timing_GetCycles()
OS_Timing_Start() and OS_Timing_End() in cycles.
Table 16.2: High-resolution measurement API overview

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16.4.1 OS_Timing_Start()
Description
Marks the beginning of a section of code to be timed.
Prototype
void OS_Timing_Start (OS_TIMING* pCycle);

Parameter Description
pCycle Pointer to a data structure of type OS_TIMING.
Table 16.3: OS_TimingStart() parameter list

Additional Information
This function must be used with OS_Timing_End().

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16.4.2 OS_Timing_End()
Description
Marks the end of a section of code to be timed.
Prototype
void OS_Timing_End (OS_TIMING* pCycle);

Parameter Description
pCycle Pointer to a data structure of type OS_TIMING.
Table 16.4: OS_TimingEnd() parameter list

Additional Information
This function must be used with OS_Timing_Start().

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16.4.3 OS_Timing_Getus()
Description
Returns the execution time of the code between OS_Timing_Start() and
OS_Timing_End() in microseconds.
Prototype
OS_U32 OS_Timing_Getus (OS_TIMING* pCycle);

Parameter Description
pCycle Pointer to a data structure of type OS_TIMING.
Table 16.5: OS_Timing_Getus() parameter list

Additional Information
The execution time in microseconds (µs) as a 32-bit integer value.

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16.4.4 OS_Timing_GetCycles()
Description
Returns the execution time of the code between OS_Timing_Start() and
OS_Timing_End() in cycles.
Prototype
OS_U32 OS_Timing_GetCycles (OS_TIMING* pCycle);

Parameter Description
pCycle Pointer to a data structure of type OS_TIMING.
Table 16.6: OS_Timing_GetCycles() parameter list

Return value
The execution time in cycles as a 32-bit integer.
Additional Information
Cycle length depends on the timer clock frequency.

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16.5 Example
The following sample demonstrates the use of low-resolution and high-resolution
measurement to return the execution time of a section of code:

/**********************************************************
* SEGGER MICROCONTROLLER SYSTEME GmbH
* Solutions for real time microcontroller applications
***********************************************************
File : SampleHiRes.c
Purpose : Demonstration of embOS Hires Timer
--------------END-OF-HEADER------------------------------*/

#include "RTOS.H"
#include <stdio.h>

OS_STACKPTR int Stack[1000]; /* Task stacks */

OS_TASK TCB; /* Task-control-blocks */

volatile int Dummy;

void UserCode(void) {
for (Dummy=0; Dummy < 11000; Dummy++); /* Burn some time */
}

/*
* Measure the execution time with low resolution and return it in ms (ticks)
*/
int BenchmarkLoRes(void) {
int t;
t = OS_GetTime();
UserCode(); /* Execute the user code to be benchmarked */
t = OS_GetTime() - t;
return t;
}

/*
* Measure the execution time with hi resolution and return it in us
*/
OS_U32 BenchmarkHiRes(void) {
OS_U32 t;
OS_Timing_Start(&t);
UserCode(); /* Execute the user code to be benchmarked */
OS_Timing_End(&t);
return OS_Timing_Getus(&t);
}

void Task(void) {
int tLo;
OS_U32 tHi;
char ac[80];
while (1) {
tLo = BenchmarkLoRes();
tHi = BenchmarkHiRes();
sprintf(ac, "LoRes: %d ms\n", tLo);
OS_SendString(ac);
sprintf(ac, "HiRes: %d us\n", tHi);
OS_SendString(ac);
}
}

/**********************************************************
*
* main
*
**********************************************************/

void main(void) {
OS_InitKern(); /* Initialize OS */
OS_InitHW(); /* Initialize Hardware for OS */
/* You need to create at least one task here ! */
OS_CREATETASK(&TCB, "HP Task", Task, 100, Stack);
OS_Start(); /* Start multitasking */
}

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The output of the sample is as follows:

LoRes: 7 ms
HiRes: 6641 us
LoRes: 7 ms
HiRes: 6641 us
LoRes: 6 ms

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Chapter 17

System variables

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The system variables are described here for a deeper understanding of how the OS
works and to make debugging easier.
Note: Do not change the value of any system variables.
These variables are accessible and are not declared constant, but they should only be
altered by functions of embOS. However, some of these variables can be very useful,
especially the time variables.

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17.1 Time variables

17.1.1 OS_Time
Description
This is the time variable which contains the current system time in ticks (usually
equivalent to ms).
Prototyp
extern volatile OS_I32 OS_Time;

Additional Information
The time variable has a resolution of one time unit, which is normally 1/1000 sec
(1 ms) and is normally the time between two successive calls to the embOS interrupt
handler. Instead of accessing this variable directly, use OS_GetTime() or
OS_GetTime32() as explained in the Chapter Time measurement on page 223.

17.1.2 OS_TimeDex
Basically, for internal use only. Contains the time at which the next task switch or
timer activation is due. If ((int)(OS_Time - OS_TimeDex)) >= 0, the task list and
timer list will be checked for a task or timer to activate. After activation, OS_TimeDex
will be assigned the time stamp of the next task or timer to be activated.

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17.2 OS internal variables and data-structures

embOS internal variables are not explained here as they are in no way required to
use embOS. Your application should not rely on any of the internal variables, as only
the documented API functions are guaranteed to remain unchanged in future
versions of embOS.
Important
Do not alter any system variables.

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Chapter 18

System tick

This chapter explains the concept of the system tick, generated by a hardware timer
and all options available for it.

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Overview
Typically a hardware timer generates periodic interrupts used as a time base. embOS
offers tick handlers with different functionality as well as a way to call a hook func-
tion from within the system tick handler.
The hardware timer will normally be initialized in the OS_InitHW() function which is
delivered with the BSP.
The BSP also includes the interrupt handler which will be called by the hardware
timer interrupt. This interrupt handler has to call one of the embOS system tick han-
dler functions which are explained in this chapter.

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18.1 Tickhandler
Routine Description
OS_HandleTick() Standard embOS tick handler.
OS_HandleTick_Ex() Extended embOS tick handler.
Table 18.1: Tickhandlers

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18.1.1 OS_HandleTick()
Description
The default embOS timer tick handler which is typically called by the hardware timer
interrupt handler.
Prototype
void OS_HandleTick (void);

Additional Information
The embOS tick handler must not be called by the application, it has to be called
from an interrupt handler.
OS_EnterInterrupt(), or OS_EnterNestableInterrupt() has to be called, before
calling the embOS tick handler
Example
/* Example of a timer interrupt handler */
__interrupt void OS_ISR_Tick(void) {
OS_EnterNestableInterrupt();
OS_HandleTick();
OS_LeaveNestableInterrupt();
}

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18.1.2 OS_HandleTick_Ex()
Description
An alternate tick handler which may be used instead of the standard tick handler. It
can be used in situations where the basic timer-interrupt interval (tick) is a multiple
of 1 ms and the time values used as parameter for delays still should use 1 ms as the
time base.
Prototype
void OS_HandleTick_Ex (void);

Additional Information
The embOS tick handler must not be called by the application, it has to be called
from an interrupt handler.
OS_EnterInterrupt(), or OS_EnterNestableInterrupt() has to be called, before
calling the embOS tick handler.
OS_HandleTick_Ex() incremets the embOS internal time variable by an amount
which is stored in the variable OS_IntMSInc which has to be initialized accordingly.
Example
/* Example of a timer interrupt handler using OS_HandleTick_Ex */
__interrupt void OS_ISR_Tick(void) {
OS_EnterNestableInterrupt();
OS_HandleTick_Ex();
OS_LeaveNestableInterrupt();
}

Assuming the hardware timer runs at a frequency of 500Hz, thus interrupting the
system every 2ms, the embOS internal variable OS_IntMSInc should be initialized
with a value of two.
This should be done during OS_IntHW(), before the embOS timer is started.

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18.2 Hooking into the system tick

Routine Description
OS_AddTickHook() Adds a tick hook handler.
OS_RemoveTickHook() Removes a tick hook handler.
Table 18.2: Tick hook functions API

There are various situations in which it can be desireable to call a function from the
tick handler. Some examples are:
• Watchdog update
• Periodic status check
• Periodic I/O update
The same functionality can be achieved with a high-priority task or a software timer
with 1 tick period time.
Advantage of using a hook function
Using a hook function is much faster than performing a task switch or activating a
software timer, because the hook function is directly called from the embOS timer
interrupt handler.

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18.2.1 OS_AddTickHook()
Description
Adds a tick hook handler.
Prototype
void OS_AddTickHook (OS_TICK_HOOK* pHook,
OS_TICK_HOOK_ROUTINE * pfUser);

Parameter Description
pHook Pointer to a structure of OS_TICK_HOOK.
pfUser Pointer to an OS_TICK_HOOK_ROUTINE function.
Table 18.3: OS_AddTickHook() parameter list

Additional Information
The hook function is called driectly from the interrupt handler.
The function therefore should execute as fast as possible.
The function called by the tick hook must not re-enable interrupts.

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18.2.2 OS_RemoveTickHook()
Description
Removes a tick hook handler.
Prototype
void OS_RemoveTickHook (OS_TICK_HOOK* pHook);

Parameter Description
pHook Pointer to a structure of OS_TICK_HOOK.
Table 18.4: OS_RemoveTickHook() parameter list

Additional Information
The function may be called to dynamically remove a tick hook function which was
installed by a call of OS_AddTickHook().

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Chapter 19

Configuration of target system

(BSP)

This chapter explains the target system specific parts of embOS, also called BSP
(board support package).
If the system is up and running on your target system, there is no need to read this
chapter.

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250 CHAPTER 19 Configuration of target system (BSP)

Overview
You do not have to configure anything to get started with embOS. The start project
supplied will execute on your system. Small changes in the configuration will be nec-
essary at a later point for system frequency or for the UART used for communication
with the optional embOSView.
The file RTOSInit.c is provided in source code and can be modified to match your
target hardware needs. It is compiled and linked with your application program.

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19.1 Hardware-specific routines

Routine Description
Initializes the hardware timer used for generating inter-
rupts. embOS needs a timer-interrupt to determine when
OS_InitHW() to activate tasks that wait for the expiration of a delay,
when to call a software timer, and to keep the time vari-
able up-to-date.
The idle loop is always executed whenever no other task
OS_Idle()
(and no interrupt service routine) is ready for execution.
Reads the timestamp in cycles. Cycle length depends on
OS_GetTime_Cycles() the system. This function is used for system information
sent to embOSView.
OS_ConvertCycles2us() Converts cycles into µs (used with profiling only).
Initializes communication for embOSView
OS_COM_Init()
(used with embOSView only).
The embOS timer-interrupt handler. When using a differ-
OS_ISR_Tick()
ent timer, always check the specified interrupt vector.
Rx Interrupt service handler for embOSView
OS_ISR_rx()
(used with embOSView only).
Tx Interrupt service handler for embOSView
OS_ISR_tx()
(used with embOSView only).
Send 1 byte via a UART (used with embOSView only).
OS_COM_Send1()
Do not call this function from your application.
Table 19.1: Hardware specific routines

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19.2 Configuration defines

For most embedded systems, configuration is done by simply modifying the following
defines, located at the top of the RTOSInit.c file:

Define Description
System frequency (in Hz).
OS_FSYS
Example: 20000000 for 20MHz.
Selection of UART to be used with embOSView
OS_UART
(-1 will disable communication),
OS_BAUDRATE Selection of baudrate for communication with embOSView.
Table 19.2: Configuration defines overview

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19.3 How to change settings

The only file which you may need to change is RTOSInit.c. This file contains all
hardware-specific routines. The one exception is that some ports of embOS require
an additional interrupt vector table file (details can be found in the CPU & Compiler
Specifics manual of embOS documentation).

19.3.1 Setting the system frequency OS_FSYS

Relevant defines
OS_FSYS
Relevant routines
OS_ConvertCycles2us() (used with profiling only)
For most systems it should be sufficient to change the OS_FSYS define at the top of
RTOSInit.c. When using profiling, certain values may require a change in
OS_ConvertCycles2us(). The RTOSInit.c file contains more information about in
which cases this is necessary and what needs to be done.

19.3.2 Using a different timer to generate the tick-interrupts for

embOS
Relevant routines
OS_ InitHW()
embOS usually generates 1 interrupt per ms, making the timer-interrupt, or tick,
normally equal to 1 ms. This is done by a timer initialized in the routine
OS_InitHW(). If you have to use a different timer for your application, you must
modify OS_InitHW() to initialize the appropriate timer. For details about initialization,
read the comments in RTOSInit.c.

19.3.3 Using a different UART or baudrate for embOSView

Relevant defines
OS_UART
OS_BAUDRATE
Relevant routines:
OS_COM_Init()
OS_COM_Send1()
OS_ISR_rx()
OS_ISR_tx()
In some cases, this is done by simply changing the define OS_UART. Refer to the con-
tents of the RTOSInit.c file for more information about which UARTS that are sup-
ported for your CPU.

19.3.4 Changing the tick frequency

Relevant defines
OS_FSYS
As noted above, embOS usually generates 1 interrupt per ms. OS_FSYS defines the
clock frequency of your system in Hz (times per second). The value of OS_FSYS is
used for calculating the desired reload counter value for the system timer for 1000
interrupts/sec. The interrupt frequency is therefore normally 1 kHz.
Different (lower or higher) interrupt rates are possible. If you choose an interrupt
frequency different from 1 kHz, the value of the time variable OS_Time will no longer
be equivalent to multiples of 1 ms. However, if you use a multiple of 1 ms as tick

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time, the basic time unit can be made 1 ms by using the (optional) configuration
macro OS_CONFIG() (see µbelow). The basic time unit does not have to be 1 ms; it
might just as well be 100 µs or 10 ms or any other value. For most applications, 1 ms
is an appropriate value.

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19.4 STOP / HALT / IDLE modes

Most CPUs support power-saving STOP, HALT, or IDLE modes. Using these types of
modes is one possible way to save power consumption during idle times. As long as
the timer-interrupt will wake up the system with every embOS tick, or as long as
other interrupts will activate tasks, these modes may be used for saving power con-
sumption.
If required, you may modify the OS_Idle() routine, which is part of the hardware-
dependant module RTOSInit.c, to switch the CPU to power-saving mode during idle
times. Refer to the CPU & Compiler Specifics manual of embOS documentation for
details about your processor.

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Chapter 20

embOSView: Profiling and analyz-

ing

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20.1 Overview
embOSView displays the state of a running application using embOS. A serial
interface (UART) is normally used for communication with the target. The hardware-
dependent routines and defines and defines available for communication with
embOSView are located in RTOSInit.c. This file has to be configured properly. For
details on how to configure this file, refer the CPU & Compiler Specifics manual of
embOS documentation. The embOSView utility is shipped as embOSView.exe with
embOS and runs under Windows 9x / NT / 2000. The latest version is available on
our website at www.segger.com

embOSView is a very helpful tool for analysis of the running target application.

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20.2 Task list window

embOSView shows the state of every created task of the target application in the
Task list window. The information shown depends on the library used in your
application.

Item Description Builds

Prio Current priority of task. All

Task ID, which is the address of the task control

Id All
block.

Name Name assigned during creation. All

Current state of task (ready, executing, delay,

Status All
reson for suspension).

Data Depends on status. All

Timeout Time of next activation. All

Stack Used stack size/max. stack size/stack location. S, SP, D, DP, DT

CPULoad Percentage CPU load caused by task. SP, DP, DT

Context
Number of activations since reset. SP, DP, DT
Switches
Table 20.1: Task list window overview

The Task list window is helpful in analysis of stack usage and CPU load for every
running task.

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20.3 System variables window

embOSView shows the actual state of major system variables in the System vari-
ables window. The information shown also depends on the library used in your
application:

Item Description Builds

OS_VERSION Current version of embOS. All

CPU Target CPU and compiler. All

LibMode Library mode used for target application. All

OS_Time Current system time in timer ticks. All

OS_NUM_TASKS Current number of defined tasks. All

OS_Status Current error code (or O.K.). All

OS_pActiveTask Active task that should be running. SP, D, DP, DT

OS_pCurrentTask Actual currently running task. SP, D, DP, DT

Used size/max. size/location of system

SysStack SP, DP, DT
stack.

Used size/max. size/location of interrupt

IntStack SP, DP, DT
stack.

Current count/maximum size and current

TraceBuffer All trace builds
state of trace buffer.
Table 20.2: System variables window overview

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20.4 Sharing the SIO for terminal I/O

The serial input/output (SIO) used by embOSView may also be used by the
application at the same time for both input and output. This can be very helpful.
Terminal input is often used as keyboard input, where terminal output may be used
for outputting debug messages. Input and output is done via the Terminal window,
which can be shown by selecting View/Terminal from the menu.
To ensure communication via the Terminal window in parallel with the viewer
functions, the application uses the function OS_SendString() for sending a string to
the Terminal window and the function OS_SetRxCallback() to hook a recep-
tion routine that receives one byte.

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20.4.1 Shared SIO API function overview

Routine Description
OS_SendString() Sends a string over SIO to the Terminal window.
Sets a callback hook to a routine for receiving one char-
OS_SetRxCallback()
acter.
Table 20.3: Shared SIO API overview

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20.4.2 OS_SendString()
Description
Sends a string over SIO to the Terminal window.
Prototype
void OS_SendString (const char* s);

Parameter Description
Pointer to a zero-terminated string that should be sent to the
s
Terminal window.
Table 20.4: OS_SendString() parameter list

Additional Information
This function uses OS_COM_Send1() which is defined in RTOSInit.c.

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20.4.3 OS_SetRxCallback()
Description
Sets a callback hook to a routine for receiving one character.
Prototype
typedef void OS_RX_CALLBACK (OS_U8 Data)
OS_RX_CALLBACK* OS_SetRxCallback (OS_RX_CALLBACK* cb);

Parameter Description
Pointer to the application routine that should be called when one
cb
character is received over the serial interface.
Table 20.5: OS_SetRxCallback() parameter list

Return value
OS_RX_CALLBACK* as described above. This is the pointer to the callback function that
was hooked before the call.
Additional Information
The user function is called from embOS. The received character is passed as parame-
ter. See the example below.
Example
void GUI_X_OnRx(OS_U8 Data); /* Callback ... called from Rx-interrupt */

void GUI_X_Init(void) {
OS_SetRxCallback( &GUI_X_OnRx);
}

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20.5 Using the API trace

embOS versions 3.06 or higher contain a trace feature for API calls. This requires the
use of the trace build libraries in the target application.
The trace build libraries implement a buffer for 100 trace entries. Tracing of API calls
can be started and stopped from embOSView via the Trace menu, or from within the
application by using the functions OS_TraceEnable() and OS_TraceDiasable().
Individual filters may be defined to determine which API calls should be traced for
different tasks or from within interrupt or timer routines.
Once the trace is started, the API calls are recorded in the trace buffer, which is peri-
odically read by embOSView. The result is shown in the Trace window:

Every entry in the Trace list is recorded with the actual system time. In case of
calls or events from tasks, the task ID (TaskId) and task name (TaskName) (lim-
ited to 15 characters) are also recorded. Parameters of API calls are recorded if pos-
sible, and are shown as part of the APIName column. In the example above, this
can be seen with OS_Delay(3). Once the trace buffer is full, trace is automatically
stopped. The Trace list and buffer can be cleared from embOSView.
Setting up trace from embOSView
Three different kinds of trace filters are defined for tracing. These filters can be set
up from embOSView via the menu Options/Setup/Trace.
Filter 0 is not task-specific and records all specified events regardless of the task. As
the Idle loop is not a task, calls from within the idle loop are not traced.
Filter 1 is specific for interrupt service routines, software timers and all calls that
occur outside a running task. These calls may come from the idle loop or during
startup when no task is running.
Filters 2 to 4 allow trace of API calls from named tasks.

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To enable or disable a filter, simply check or uncheck the corresponding checkboxes

labeled Filter 4 Enable to Filter 0 Enable.
For any of these five filters, individual API functions can be enabled or disabled by
checking or unchecking the corresponding checkboxes in the list. To speed up the
process, there are two buttons available:
• Select all - enables trace of all API functions for the currently enabled (checked)
filters.
• Deselect all - disables trace of all API functions for the currently enabled
(checked) filters.
Filter 2, Filter 3, and Filter 4 allow tracing of task-specific API calls. A task name
can therefore be specified for each of these filters. In the example above, Filter 4 is
configured to trace calls of OS_Delay() from the task called MainTask. After the set-
tings are saved (via the Apply or OK button), the new settings are sent to the target
application.

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20.6 Trace filter setup functions

Tracing of API or user function calls can be started or stopped from embOSView. By
default, trace is initially disabled in an application program. It may be very helpful to
control the recording of trace events directly from the application, using the following
functions.

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20.7 Trace filter API functions

Routine Description
OS_TraceEnable() Enables tracing of filtered API calls.
OS_TraceDisable() Disables tracing of API and user function calls.
Sets up Filter 0 (any task), enables tracing of all API
OS_TraceEnableAll()
calls and then enables the trace function.
Sets up Filter 0 (any task), disables tracing of all
OS_TraceDisableAll()
API calls and also disables trace.
Sets the specified ID value in Filter 0 (any task),
OS_TraceEnableId() thus enabling trace of the specified function, but
does not start trace.
Resets the specified ID value in Filter 0 (any task),
OS_TraceDisableId() thus disabling trace of the specified function, but
does not stop trace.
Sets the specified ID value in the specified trace fil-
OS_TraceEnableFilterId() ter, thus enabling trace of the specified function,
but does not start trace.
Resets the specified ID value in the specified trace
OS_TraceDisableFilterId() filter, thus disabling trace of the specified function,
but does not stop trace.
Table 20.6: Trace filter API overview

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20.7.1 OS_TraceEnable()
Description
Enables tracing of filtered API calls.
Prototype
void OS_TraceEnable (void);

Additional Information
The trace filter conditions should have been set up before calling this function. This
functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.2 OS_TraceDisable()
Description
Disables tracing of API and user function calls.
Prototype
void OS_TraceDisable (void);

Additional Information
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.3 OS_TraceEnableAll()
Description
Sets up Filter 0 (any task), enables tracing of all API calls and then enables the trace
function.
Prototype
void OS_TraceEnableAll (void);

Additional Information
The trace filter conditions of all the other trace filters are not affected.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.4 OS_TraceDisableAll()
Description
Sets up Filter 0 (any task), disables tracing of all API calls and also disables trace.
Prototype
void OS_TraceDisableAll (void);

Additional Information
The trace filter conditions of all the other trace filters are not affected, but tracing is
stopped.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.5 OS_TraceEnableId()
Description
Sets the specified ID value in Filter 0 (any task), thus enabling trace of the specified
function, but does not start trace.
Prototype
void OS_TraceEnableId (OS_U8 Id);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
Table 20.7: OS_TraceEnabled() parameter list

Additional Information
To enable trace of a specific embOS API function, you must use the correct Id value.
These values are defined as symbolic constants in RTOS.h.
This function may also enable trace of your own functions.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.6 OS_TraceDisableId()
Description
Resets the specified ID value in Filter 0 (any task), thus disabling trace of the speci-
fied function, but does not stop trace.
Prototype
void OS_TraceDisableId (OS_U8 Id);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
Table 20.8: OS_TraceDisabledId() parameter list

Additional Information
To disable trace of a specific embOS API function, you must use the correct Id value.
These values are defined as symbolic constants in RTOS.h.
This function may also be used for disabling trace of your own functions.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.7 OS_TraceEnableFilterId()
Description
Sets the specified ID value in the specified trace filter, thus enabling trace of the
specified function, but does not start trace.
Prototype
void OS_TraceEnableFilterId (OS_U8 FilterIndex,
OS_U8 Id)

Parameter Description
Index of the filter that should be affected:
FilterIndex 0 <= FilterIndex <= 4
0 affects Filter 0 (any task) and so on.
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
Table 20.9: OS_TraceEnabledFilterId() parameter list

Additional Information
To enable trace of a specific embOS API function, you must use the correct Id value.
These values are defined as symbolic constants in RTOS.h.
This function may also be used for enabling trace of your own functions.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.7.8 OS_TraceDisableFilterId()
Description
Resets the specified ID value in the specified trace filter, thus disabling trace of the
specified function, but does not stop trace.
Prototype
void OS_TraceDisableFilterId (OS_U8 FilterIndex,
OS_U8 Id)

Parameter Description
Index of the filter that should be affected:
FilterIndex 0 <= FilterIndex <= 4
0 affects Filter 0 (any task) and so on.
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
Table 20.10: OS_TraceDisableFilterId() parameter list

Additional Information
To disable trace of a specific embOS API function, you must use the correct Id value.
These values are defined as symbolic constants in RTOS.h.
This function may also be used for disabling trace of your own functions.
This functionality is available in trace builds only. In non-trace builds, the API call is
removed by the preprocessor.

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20.8 Trace record functions

The following functions are used for writing (recording) data into the trace buffer. As
long as only embOS API calls should be recorded, these functions are used internally
by the trace build libraries. If, for some reason, you want to trace your own functions
with your own parameters, you may call one of these routines.

All of these functions have the following points in common:

• To record data, trace must be enabled.
• An ID value in the range from 100 to 127 must be used as the Id parameter. ID
values from 0 to 99 are internally reserved for embOS.
• The events specified as Id have to be enabled in any of the trace filters.
• Active system time and the current task are automatically recorded together with
the specified event.

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20.9 Trace record API function overview

Routine Description
Writes an entry identified only by its ID into the trace
OS_TraceVoid()
buffer.
Writes an entry with ID and a pointer as parameter into
OS_TracePtr()
the trace buffer.
Writes an entry with ID and an integer as parameter into
OS_TraceData()
the trace buffer.
Writes an entry with ID, an integer, and a pointer as
OS_TraceDataPtr()
parameter into the trace buffer.
Writes an entry with ID, a 32-bit unsigned integer, and a
OS_TraceU32Ptr()
pointer as parameter into the trace buffer.
Table 20.11: Trace record API overview

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20.9.1 OS_TraceVoid()
Description
Writes an entry identified only by its ID into the trace buffer.
Prototype
void OS_TraceVoid (OS_U8 Id);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
Table 20.12: OS_TraceVoid() parameter list

Additional Information
This functionality is available in trace builds only, and the API call is not removed by
the preprocessor.

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20.9.2 OS_TracePtr()
Description
Writes an entry with ID and a pointer as parameter into the trace buffer.
Prototype
void OS_TracePtr (OS_U8 Id,
void* p);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
p Any void pointer that should be recorded as parameter.
Table 20.13: OS_TracePtr() parameter list

Additional Information
The pointer passed as parameter will be displayed in the trace list window of
embOSView. This functionality is available in trace builds only. In non-trace builds,
the API call is removed by the preprocessor.

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20.9.3 OS_TraceData()
Description
Writes an entry with ID and an integer as parameter into the trace buffer.
Prototype
void OS_TraceData (OS_U8 Id,
int v);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
v Any integer value that should be recorded as parameter.
Table 20.14: OS_TraceData() parameter list

Additional Information
The value passed as parameter will be displayed in the trace list window of
embOSView.This functionality is available in trace builds only. In non-trace builds,
the API call is removed by the preprocessor.

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20.9.4 OS_TraceDataPtr()
Description
Writes an entry with ID, an integer, and a pointer as parameter into the trace buffer.
Prototype
void OS_TraceDataPtr (OS_U8 Id,
int v,
void* p);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
v Any integer value that should be recorded as parameter.
p Any void pointer that should be recorded as parameter.
Table 20.15: OS_TraceDataPtr() parameter list

Additional Information
The values passed as parameters will be displayed in the trace list window of embOS-
View. This functionality is available in trace builds only. In non-trace builds, the API
call is removed by the preprocessor.

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20.9.5 OS_TraceU32Ptr()
Description
Writes an entry with ID, a 32-bit unsigned integer, and a pointer as parameter into
the trace buffer.
Prototype
void OS_TraceU32Ptr (OS_U8 Id,
OS_U32 p0,
void* p1);

Parameter Description
ID value of API call that should be enabled for trace:
Id 0 <= Id <= 127
Values from 0 to 99 are reserved for embOS.
p0 Any unsigned 32-bit value that should be recorded as parameter.
p1 Any void pointer that should be recorded as parameter.
Table 20.16: OS_TraceU32Ptr() parameter list

Additional Information
This function may be used for recording two pointers. The values passed as parame-
ters will be displayed in the trace list window of embOSView. This functionality is
available in trace builds only. In non-trace builds, the API call is removed by the pre-
processor.

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20.10 Application-controlled trace example

As described in the previous section, the user application can enable and set up the
trace conditions without a connection or command from embOSView. The trace
record functions can also be called from any user function to write data into the trace
buffer, using ID numbers from 100 to 127.
Controlling trace from the application can be very helpful for tracing API and user
functions just after starting the application, when the communication to embOSView
is not yet available or when the embOSView setup is not complete.
The example below shows how a trace filter can be set up by the application. The
function OS_TraceEnableID() sets the trace filter 0 which affects calls from any
running task. Therefore, the first call to SetState() in the example would not be
traced because there is no task running at that moment. The additional filter setup
routine OS_TraceEnableFilterId() is called with filter 1, which results in tracing
calls from outside running tasks.
Example code
#include "RTOS.h"

#ifndef OS_TRACE_FROM_START
#define OS_TRACE_FROM_START 1
#endif

/* Application specific trace id numbers */

#define APP_TRACE_ID_SETSTATE 100

char MainState;

/* Sample of application routine with trace */

void SetState(char* pState, char Value) {

#if OS_TRACE
OS_TraceDataPtr(APP_TRACE_ID_SETSTATE, Value, pState);
#endif
* pState = Value;
}

/* Sample main routine, that enables and setup API and function call trace
from start */
void main(void) {
OS_InitKern();
OS_InitHW();
#if (OS_TRACE && OS_TRACE_FROM_START)
/* OS_TRACE is defined in trace builds of the library */
OS_TraceDisableAll(); /* Disable all API trace calls */
OS_TraceEnableId(APP_TRACE_ID_SETSTATE); /* User trace */
OS_TraceEnableFilterId(APP_TRACE_ID_SETSTATE); /* User trace */
OS_TraceEnable();
#endif

/* Application specific initilisation */

SetState(&MainState, 1);
OS_CREATETASK(&TCBMain, "MainTask", MainTask, PRIO_MAIN, MainStack);
OS_Start(); /* Start multitasking -> MainTask() */
}

By default, embOSView lists all user function traces in the trace list window as Rou-
tine, followed by the specified ID and two parameters as hexadecimal values. The
example above would result in the following:

Routine100(0xabcd, 0x01)

where 0xabcd is the pointer address and 0x01 is the parameter recorded from
OS_TraceDataPtr().

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20.11 User-defined functions

To use the built-in trace (available in trace builds of embOS) for application program
user functions, embOSView can be customized. This customization is done in the
setup file embOS.ini.
This setup file is parsed at the startup of embOSView. It is optional; you will not see
an error message if it cannot be found.
To enable trace setup for user functions, embOSView needs to know an ID number,
the function name and the type of two optional parameters that can be traced. The
format is explained in the following sample embOS.ini file:
Example code
# File: embOS.ini
#
# embOSView Setup file
#
# embOSView loads this file at startup. It has to reside in the same
# directory as the execuatble itself.
#
# Note: The file is not required to run embOSView. You will not get
# an error message if it is not found. However, you will get an error message
# if the contents of the file are invalid.

#
# Define add. API functions.
# Syntax: API( <Index>, <Routinename> [parameters])
# Index: Integer, between 100 and 127
# Routinename: Identifier for the routine. Should be no more than 32 characters
# parameters: Optional paramters. A max. of 2 parameters can be specified.
# Valid parameters are:
# int
# ptr
# Every parameter has to be preceeded by a colon.
#
API( 100, "Routine100")
API( 101, "Routine101", int)
API( 102, "Routine102", int, ptr)

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Chapter 21

Debugging

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21.1 Runtime errors

Some error conditions can be detected during runtime. These are:
• Usage of uninitialized data structures
• Invalid pointers
• Unused resource that has not been used by this task before
• OS_LeaveRegion() called more often than OS_EnterRegion()
• Stack overflow (this feature is not available for some processors)
Which runtime errors that can be detected depend on how much checking is per-
formed. Unfortunately, additional checking costs memory and speed (it is not that
significant, but there is a difference). If embOS detects a runtime error, it calls the
following routine:

void OS_Error(int ErrCode);

This routine is shipped as source code as part of the module OS_Error.c. It simply
disables further task switches and then, after re-enabling interrupts, loops forever as
follows:
Example
/*
Run time error reaction
*/
void OS_Error(int ErrCode) {
OS_EnterRegion(); /* Avoid further task switches */
OS_DICnt =0; /* Allow interrupts so we can communicate */
OS_EI();
OS_Status = ErrCode;
while (OS_Status);
}

If you are using embOSView, you can see the value and meaning of OS_Status in the
system variable window.
When using an emulator, you should set a breakpoint at the beginning of this routine
or simply stop the program after a failure. The error code is passed to the function as
parameter.
You can modify the routine to accommodate your own hardware; this could mean
that your target hardware sets an error-indicating LED or shows a little message on
the display.
Note: When modifying the OS_Error() routine, the first statement needs
to be the disabling of scheduler via OS_EnterRegion(); the last statement
needs to be the infinite loop.
If you look at the OS_Error() routine, you will see that it is more complicated than
necessary. The actual error code is assigned to the global variable OS_Status. The
program then waits for this variable to be reset. Simply reset this variable to 0 using
your in circuit-emulator, and you can easily step back to the program sequence
causing the problem. Most of the time, looking at this part of the program will make
the problem clear.

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21.2 List of error codes

Value Define Explanation
Index value out of bounds during inter-
100 OS_ERR_ISR_INDEX rupt controller initilization or interrupt
installation.
Default interrupt handler called, but
101 OS_ERR_ISR_VECTOR
interrupt vector not initialized.
120 OS_ERR_STACK Stack overflow or invalid stack.
121 OS_ERR_CSEMA_OVERFLOW Counting semaphore overflow.
Task control block invalid, not initial-
128 OS_ERR_INV_TASK
ized or overwritten.
Timer control block invalid, not initial-
129 OS_ERR_INV_TIMER
ized or overwritten.
Mailbox control block invalid, not ini-
130 OS_ERR_INV_MAILBOX
tialized or overwritten.
Control block for counting semaphore
132 OS_ERR_INV_CSEMA
invalid, not initialized or overwritten.
Control block for resource semaphore
133 OS_ERR_INV_RSEMA
invalid, not initialized or overwritten.
One of the following 1-byte mailbox
functions has been used on a multi-
byte mailbox:
135 OS_ERR_MAILBOX_NOT1 OS_PutMail1()
OS_PutMailCond1
()OS_GetMail1()
OS_GetMailCond1().
OS_DeleteMB() was called on a mail-
136 OS_ERR_MAILBOX_DELETE
box with waiting tasks.
OS_DeleteCSema() was called on a
137 OS_ERR_CSEMA_DELETE counting semaphore with waiting
tasks.
OS_DeleteRSema() was called on a
138 OS_ERR_RSEMA_DELETE resource semaphore which is claimed
by a task.
The mailbox is not in the list of mail-
boxes as expected. Possible reasons
140 OS_ERR_MAILBOX_NOT_IN_LIST
may be that one mailbox data struc-
ture was overwritten.
142 OS_ERR_TASKLIST_CORRUPT The OS internal tasklist is destroyed.
OS_Unuse() has been called before
150 OS_ERR_UNUSE_BEFORE_USE
OS_Use().
OS_ERR_LEAVEREGION_BEFORE_ENTE OS_LeaveRegion() has been called
151
RREGION before OS_EnterRegion().
152 OS_ERR_LEAVEINT Error in OS_LeaveInterrupt().
The interrupt disable counter
(OS_DICnt) is out of range (0-15). The
counter is affected by the following API
calls:
153 OS_ERR_DICNT
OS_IncDI()
OS_DecRI()
OS_EnterInterrupt()
OS_LeaveInterrupt()
OS_Delay() or OS_DelayUntil() called
154 OS_ERR_INTERRUPT_DISABLED from inside a critical region with inter-
rupts disabled.
Table 21.1: Error code list

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Value Define Explanation

OS_Unuse() has been called from a
156 OS_ERR_RESOURCE_OWNER
task which does not own the resource.
Illegal function call in an interrupt ser-
vice routine:A routine that may not be
160 OS_ERR_ILLEGAL_IN_ISR
called from within an ISR has been
called from within an ISR.
Illegal function call in an interrupt ser-
vice routine:A routine that may not be
161 OS_ERR_ILLEGAL_IN_TIMER
called from within a software timer
has been called from within a timer.
embOS timer tick handler or UART han-
162 OS_ERR_ILLEGAL_OUT_ISR dler for embOSView was called without
a call of OS_EnterInterrupt().
Task control block has been initialized
170 OS_ERR_2USE_TASK
by calling a create function twice.
Timer control block has been initialized
171 OS_ERR_2USE_TIMER
by calling a create function twice.
Mailbox control block has been initial-
172 OS_ERR_2USE_MAILBOX
ized by calling a create function twice.
Binary semaphore has been initialized
173 OS_ERR_2USE_BSEMA
by calling a create function twice.
Counting semaphore has been initial-
174 OS_ERR_2USE_CSEMA
ized by calling a create function twice.
Resource semaphore has been initial-
175 OS_ERR_2USE_RSEMA
ized by calling a create function twice.
Fixed size memory pool has been ini-
176 OS_ERR_2USE_MEMF tialized by calling a create function
twice.
OS_Rx interrupt handler for embOS-
180 OS_ERR_NESTED_RX_INT View is nested. Disable nestable inter-
rupts.
Fixed size memory block control struc-
190 OS_ERR_MEMF_INV
ture not created before use.
Pointer to memory block does not
191 OS_ERR_MEMF_INV_PTR
belong to memory pool on Release
Pointer to memory block is already free
192 OS_ERR_MEMF_PTR_FREE when calling OS_MEMF_Release(). Pos-
sibly, same pointer was released twice.
OS_MEMF_Release() was called for a
memory pool, that had no memory
193 OS_ERR_MEMF_RELEASE
block allocated (all available blocks
were already free before).
OS_MEMF_Create() was called with a
194 OS_ERR_POOLADDR memory pool base address which is not
located at a word aligned base address
OS_MEMF_Create() was called with a
195 OS_ERR_BLOCKSIZE data block size which is not a multiple
of processors word size.
Nested call of OS_Suspend() exceeded
200 OS_ERR_SUSPEND_TOO_OFTEN
OS_MAX_SUSPEND_CNT
OS_Resume() called on a task that was
201 OS_ERR_RESUME_BEFORE_SUSPEND
not suspended.
Table 21.1: Error code list (Continued)

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Value Define Explanation

OS_CreateTask() was called with a
task priority which is already assigned
202 OS_ERR_TASK_PRIORITY to another task. This error can only
occur when embOS was compiled with-
out round robin support.
An OS_EVENT object was used before it
210 OS_ERR_EVENT_INVALID
was created.
211 OS_ERR_2USE_EVENTOBJ An OS_EVENT object was created twice.
An OS_EVENT object was deleted with
212 OS_ERR_EVENT_DELETE
waiting tasks
Table 21.1: Error code list (Continued)

The latest version of the defined error table is part of the comment just before the
OS_Error() function declaration in the source file OS_Error.c.

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Chapter 22

Performance and resource usage

This chapter covers the performance and resource usage of embOS. It explains how
to benchmark embOS and contains information about the memory requirements in
typical systems which can be used to obtain sufficient estimates for most target sys-
tems.

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22.1 Introduction
High performance combined with low resource usage has always been a major design
consideration. embOS runs on 8/16/32-bit CPUs. Depending on which features are
being used, even single-chip systems with less than 2 Kbytes ROM and 1 Kbyte RAM
can be supported by embOS. The actual performance and resource usage depends on
many factors (CPU, compiler, memory model, optimization, configuration, etc.).

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22.2 Memory requirements

The memory requirements of embOS (RAM and ROM) differs depending on the used
features of the library. The following table shows the memory requirements for the
different modules.

Module Memory type Memory requirements

embOS kernel ROM 1100 - 1600 bytes *

embOS kernel RAM 18 - 25 bytes *

Mailbox RAM 9 - 15 bytes *

Binary and counting semaphores RAM 3 bytes

Recource semaphore RAM 4 - 5 bytes *

Timer RAM 9 - 11 bytes *

Event RAM 0 bytes

Table 22.1: embOS memory requirements

* Depends on CPU, compiler, and library model used

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22.3 Performance
The following section shows how to benchmark embOS with the supplied example
programs.

22.4 Benchmarking
embOS is designed to perform fast context switches. This section describes two dif-
ferent methods to calculate the execution time of a context switch from a task with
lower priority to a task with a higher priority.
The first method uses port pins and requires an oscilloscope. The second method
uses the high-resolution measurement functions. Example programs for both meth-
ods are supplied in the \Sample directory of your embOS shipment.
Segger uses these programs to benchmark the embOS performance. You can use
these examples to evaluate the benchmark results. Note, that the actual perfor-
mance depends on many factors (CPU, clock speed, toolchain, memory model, opti-
mization, configuration, etc.).
The following table gives an overview about the variations of the context switch time
depending on the memory type and the CPU mode:

Target OS version Memory CPU mode Time

ATMEL
3.50b Flash Thumb 7.562us
AT91SAM7S256

ATMEL
3.50b Flash ARM 7.875us
AT91SAM7S256

ATMEL
3.50b RAM ARM 5.896us
AT91SAM7S256

ATMEL
3.50b RAM Thumb 6.187us
AT91SAM7S256
Table 22.2: embOS context switch times

All named example performance values in the following section are determined with
the following system configuration:
ATMEL AT91SAM7S256 running with 48 MHz clock speed. All sources are compiled
with IAR Embedded Workbench version 4.40A using thumb or arm mode with high
optimization level.

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22.4.1 Measurement with port pins and oscilloscope

The example file MeasureCST_Scope.c uses the LED.c module to set and clear a port
pin. This allows measuring the context switch time with an oscilloscope.
The following source code is excerpt from MeasureCST_Scope.c:

#include "RTOS.h"
#include "LED.h"

static OS_STACKPTR int StackHP[128], StackLP[128]; // Task stacks

static OS_TASK TCBHP, TCBLP; // Task-control-blocks

/*********************************************************************
*
* HPTask
*/
static void HPTask(void) {
while (1) {
OS_Suspend(NULL); // Suspend high priority task
LED_ClrLED0(); // Stop measurement
}
}

/*********************************************************************
*
* LPTask
*/
static void LPTask(void) {
while (1) {
OS_Delay(100); // Syncronize to tick to avoid jitter
//
// Display measurement overhead
//
LED_SetLED0();
LED_ClrLED0();
//
// Perform measurement
//
LED_SetLED0(); // Start measurement
OS_Resume(&TCBHP); // Resume high priority task to force task switch
}
}

/*********************************************************************
*
* main
*/
int main(void) {
OS_IncDI(); // Initially disable interrupts
OS_InitKern(); // Initialize OS
OS_InitHW(); // Initialize Hardware for OS
LED_Init(); // Initialize LED ports
OS_CREATETASK(&TCBHP, "HP Task", HPTask, 100, StackHP);
OS_CREATETASK(&TCBLP, "LP Task", LPTask, 99, StackLP);
OS_Start(); // Start multitasking
return 0;
}

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22.4.1.1 Oscilloscope analysis

The context switch time is the time between switching the LED on and off. If the LED
is switched on with an active high signal, the context switch time is the time between
rising and falling edge of the signal. If the LED is switched on with an active low sig-
nal, the signal polarity is reversed.
The real context switch time is shorter, because the signal also contains the overhead
of switching the LED on and off. The time of this overhead is also displayed on the
oscilloscope as a small peak right before the task switch time display and has to be
subtracted from the displayed context switch time. The picture below shows a simpli-
fied oscilloscope signal with an active-low LED signal (low means LED is illuminated).
There are switching points to determine:
• A = LED is switched on for overhead measurement
• B = LED is switched off for overhead measurement
• C = LED is switched on right before context switch in low-prio task
• D = LED is switched off right after context switch in high-prio task
The time needed to switch the LED on and off in subroutines is marked as time tAB.
The time needed for a complete context switch including the time needed to switch
the LED on and off in subroutines is marked as time tCD.
The context switching time t CS is calculated as follows:
t CS = tCD - tAB
Voltage [V]

A B C D

tAB tCD

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22.4.1.2 Example measurements AT91SAM7S, ARM code in RAM

Task switching time has been measured with the pararmeters listed below:
embOS Version V3.50b
Application program: MeasureCST_Scope.c
Hardware: AT91SAM7S256 processor with 48MHz
Program is executing in RAM
ARM mode is used
Compiler used: IAR V4.40A
CPU frequency (fCPU): 47.9232MHz
CPU clock cycle (t Cycle): t Cycle = 1 / f CPU = 1 / 47.9232MHz = 20,866ns

Measuring tAB and tCD

tAB is measured as 312ns.

The number of cycles calcu-
lates as follows:
Cycles AB = t AB / tCycle
=312ns / 20.866ns
= 14.952Cycles
=> 15Cycles

tCD is measured as 6217.6ns.

The number of cycles calcu-
lates as follows:
Cycles CD = t CD / t Cycle
= 6217.6ns / 20.866ns
= 297.977Cycles
=> 298Cycles

Resulting context switching time and number of cycles

The time which is required for the pure context switch is:
t CS = tCD - tAB = 298Cycles - 15Cycles = 283Cycles
=> 283Cycles (5.9us @48MHz).

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22.4.1.3 Example measurements AT91SAM7S, Thumb code in FLASH

Task switching time has been measured with the pararmeters listed below:
embOS Version V3.50b
Application program: MeasureCST_Scope.c
Hardware: AT91SAM7S256 processor with 48MHz
Program is executing in FLASH
Thumb mode is used
Compiler used: IAR V4.40A
CPU frequency (f CPU): 47.9232MHz
CPU clock cycle (tCycle): t Cycle = 1 / f CPU = 1 / 47.9232MHz = 20,866ns

Measuring tAB and tCD

tAB is measured as 436.8ns.

The number of cycles calcu-
lates as follows:
Cycles AB = t AB / t Cycle
=436.8ns / 20.866ns
= 20.933Cycles
=> 21Cycles

tCD is measured as 8012ns.

The number of cycles calcu-
lates as follows:
Cycles CD = t CD / t Cycle
= 8012ns / 20.866ns
= 383.973Cycles
=> 384Cycles

Resulting context switching time and number of cycles

The time which is required for the pure context switch is:
t CS = tCD - tAB = 384Cycles - 21Cycles = 363Cycles
=> 363Cycles (7.56us @48MHz).

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22.4.1.4 Measurement with high-resolution timer

The context switch time may be measured with the high-resolution timer. Refer to
section High-resolution measurement on page 229 for detailed information about the
embOS high-resolution measurement.
The example MeasureCST_HRTimer_embOSView.c uses a high resolution timer to
measure the context switch time from a low priority task to a high priority task and
displays the results on embOSView.

#include "RTOS.h"
#include "stdio.h"

static OS_STACKPTR int StackHP[128], StackLP[128]; // Task stacks

static OS_TASK TCBHP, TCBLP; // Task-control-blocks
static OS_U32 _Time; // Timer values

/*********************************************************************
*
* HPTask
*/
static void HPTask(void) {
while (1) {
OS_Suspend(NULL); // Suspend high priority task
OS_Timing_End(&_Time); // Stop measurement
}
}

/*********************************************************************
*
* LPTask
*/
static void LPTask(void) {
char acBuffer[100]; // Output buffer
OS_U32 MeasureOverhead; // Time for Measure Overhead
OS_U32 v;

//
// Measure Overhead for time measurement so we can take
// this into account by subtracting it
//
OS_Timing_Start(&MeasureOverhead);
OS_Timing_End(&MeasureOverhead);
//
// Perform measurements in endless loop
//
while (1) {
OS_Delay(100); // Sync. to tick to avoid jitter
OS_Timing_Start(&_Time); // Start measurement
OS_Resume(&TCBHP); // Resume high priority task to force task switch
v = OS_Timing_GetCycles(&_Time) - OS_Timing_GetCycles(&MeasureOverhead);
v = OS_ConvertCycles2us(1000 * v); // Convert cycles to nano-seconds
sprintf(acBuffer, "Context switch time: %u.%.3u usec\r", v / 1000, v % 1000);
OS_SendString(acBuffer);
}
}

The example program calculates and subtracts the measurement overhead itself, so
there is no need to do this. The results will be transmitted to embOSView, so the
example runs on every target that supports UART communication to embOSView.
The example program MeasureCST_HRTimer_Printf.c is equal to the example pro-
gram MeasureCST_HRTimer_embOSView.c but displays the results with the printf()
function for those debuggers which support terminal output emulation.

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Chapter 23

Supported development tools

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304 CHAPTER 23 Supported development tools

embOS has been developed with and for a specific C compiler version for the selected
target processor. Check the file RELEASE.HTML for details. It works with the specified
C compiler only, because other compilers may use different calling conventions
(incompatible object file formats) and therefore might be incompatible. However, if
you prefer to use a different C compiler, contact us and we will do our best to satisfy
your needs in the shortest possible time.
Reentrance
All routines that can be used from different tasks at the same time have to be fully
reentrant. A routine is in use from the moment it is called until it returns or the task
that has called it is terminated.
All routines supplied with your real-time operating system are fully reentrant. If for
some reason you need to have non-reentrant routines in your program that can be
used from more than one task, it is recommended to use a resource semaphore to
avoid this kind of problem.
C routines and reentrance
Normally, the C compiler generates code that is fully reentrant. However, the com-
piler may have options that force it to generate non-reentrant code. It is recom-
mended not to use these options, although it is possible to do so under certain
circumstances.
Assembly routines and reentrance
As long as assembly functions access local variables and parameters only, they are
fully reentrant. Everything else has to be thought about carefully.

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Chapter 24

Limitations

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306 CHAPTER 24 Limitations

The following limitations exist for embOS:

Max. no. of tasks: limited by available RAM only

Max. no. of priorities: 255
Max. no. of semaphores: limited by available RAM only
Max. no. of mailboxes: limited by available RAM only
Max. no. of queues: limited by available RAM only
Max. size. of queues: limited by available RAM only
Max. no. of timers limited by available RAM only
Task specific Event flags : 8 bits / task

We appreciate your feedback regarding possible additional functions and we will do

our best to implement these functions if they fit into the concept.
Do not hesitate to contact us. If you need to make changes to embOS, the full source
code is available.

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Chapter 25

Source code of kernel and library

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308 CHAPTER 25 Source code of kernel and library

embOS is available in two versions:

1. Object version: Object code + hardware initialization source.
2. Full source version: Complete source code.
Because this document describes the object version, the internal data structures are
not explained in detail. The object version offers the full functionality of embOS
including all supported memory models of the compiler, the debug libraries as
described and the source code for idle task and hardware initialization. However, the
object version does not allow source-level debugging of the library routines and the
kernel.
The full source version gives you the ultimate options: embOS can be recompiled for
different data sizes; different compile options give you full control of the generated
code, making it possible to optimize the system for versatility or minimum memory
requirements. You can debug the entire system and even modify it for new memory
models or other CPUs.
The source code distribution of embOS contains the following additional files:
• The CPU folder contains all CPU and compiler specific source code and header
files used for building the embOS libraries. It also contains the sample start
project, workspace, and source files for the embOS demo project delivered in the
Start folder. Normally, you should not modify any of the files in the CPU folder.
• The GenOSSrc folder contains all embOS sources and a batch file used for compil-
ing all of them in batch mode as described in the following section.

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25.1 Building embOS libraries

The embOS libraries can only be built if you have purchased a source code version of
embOS.
In the root path of embOS, you will find a DOS batch file PREP.BAT, which needs to
be modified to match the installation directory of your C compiler. Once this is done,
you can call the batch file M.BAT to build all embOS libraries for your CPU.
Note: Rebuilding the embOS libraries using the M.bat file will delete and
rebuild the entire Start folder. If you made any modifications or built own
projects in the Start folder, make a copy of your start folder before rebuild-
ing embOS.
The build process should run without any error or warning message. If the build
process reports any problem, check the following:
• Are you using the same compiler version as mentioned in the file RELEASE.HTML?
• Can you compile a simple test file after running PREP.BAT and does it really use
the compiler version you have specified?
• Is there anything mentioned about possible compiler warnings in the
RELEASE.HTML?
If you still have a problem, let us know.
The whole build process is controlled with a few amount of batch files which are
located in the root directory of your source code distribution:
• Prep.bat: Sets up the environment for the compiler, assembler, and linker.
Ensure, that this file sets the path and additional include directories which are
needed for your compiler. Normally, this batch file is the only one which might
have to be modified to build the embOS libraries. Normally, this file is called from
M.bat during the build process of all libraries.
• Clean.bat: Deletes the whole output of the embOS library build process. It is
called automatically during the build process, before new libraries are generated.
Normally it deletes the Start folder. Therefore, be careful not to call this batch
file accidentally. Normally, this file is called initially by M.bat during the build
process of all libraries.
• cc.bat: This batch file calls the compiler and is used for compiling one embOS
source file without debug information output. Most compiler options are defined
in this file and should normally not be modified. For your purposes, you might
activate debug output and may also modify the optimization level. All modifica-
tions should be done with care. Normally, this file is called from the embOS inter-
nal batch file CC_OS.bat and can not be called directly.
• ccd.bat: This batch file calls the compiler and is used for compiling OS_Global.c
which contains all global variables. All compiler settings are equal to those used
in cc.bat, except debug output is activated to enable debugging of global vari-
ables when using embOS libraries. Normally, this file is called from the embOS
internal batch file CC_OS.bat and can not be called directly.
• asm.bat: This batch file calls the assembler and is used for assembling the
assembly part of embOS which normally contains the task switch functionality.
Normally this file is called from the embOS internal batch file CC_OS.bat and can
not be called directly.
• MakeH.bat: Builds the embOS header file RTOS.h which is composed from the
CPU/compiler-specific part OS_Chip.h and the generic part OS_RAW.h. Normally,
RTOS.h is output in the subfolder Start\Inc.
• M1.bat: This batch file is called from M.bat and is used for building one specific
embOS library, it can not be called directly.
• M.bat: This batch file has to be called to generate all embOS libraries. It initially
calls Clean.bat and therefore deletes the whole Start folder. The generated
libraries are then placed in a new Start folder which contains start projects,
libraries, header, and sample start programs.

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25.2 Major compile time switches

Many features of embOS may be modified by compile-time switches. All of them are
predefined to reasonable values in the distribution of embOS. The compile-time
switches must not be changed in RTOS.h. When the compile-time switches should be
modified to alter any of the embOS features, the modification has to be done in
OS_RAW.h or has to be passed as parameters during the library build process. embOS
sources have to be recompiled and RTOS.h has to be rebuilt with the modified
switches.

25.2.1 OS_RR_SUPPORTED
This switch defines whether round robin scheduling algorithm is supported. All
embOS versions enable round robin scheduling by default. If you never use round
robin scheduling and all of your tasks run on different individual priorities, you may
disable round robin scheduling by defining this switch to 0. This will save RAM and
ROM and will also speed up the task-switching process. Ensure that none of your
tasks ever run on the same priority when you disable round robin scheduling. This
compile time switch must not be modified in RTOS.h. It has to be modified in
OS_RAW.h before embOS libraries are rebuilt.

25.2.2 OS_SUPPORT_CLEANUP_ON_TERMINATE
This compile time switch is new since version 3.26 of embOS. If enabled, it allows
termination of tasks which are claiming resource semaphores or are suspended on
any synchronization object.
Note: By default, this switch is activated for 16- and 32-bit CPUs.
For 8-bit CPUs it is disabled.
Even though the overhead is minimal and execution time is not affected significantly,
you may define this switch to zero when you do not terminate tasks in your applica-
tion, or if your application ensures, that tasks are never suspended on any synchro-
nization object or claim any resource semaphores when they are terminated.
Disabling this switch will save some RAM in the task control structure and will also
speed up the wait functions for synchronization objects.
When using an 8-bit CPU, you have to enable this switch (define it to be unequal to
0) to enable termination of tasks which are suspended on synchronization objects or
claim resource semaphores.
This compile time switch must not be modified in RTOS.h. It can only be modified in
OS_RAW.h or has to be passed as define during the build process when embOS librar-
ies are rebuilt.

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Chapter 26

Additional modules

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312 CHAPTER 26 Additional modules

26.1 Keyboard manager: KEYMAN.C

Keyboard driver module supplied in C. It serves both as an example and as a module
that can actually be used in your application. The module can be used in most
applications with only little changes to the hardware-specific portion. It needs to be
initialized on startup and creates a task that checks the keyboard 50 times per
second.
Changes required for your hardware
void ReadKeys(void);

Example of how to implement into your program

void main(void) {
OS_InitKern(); /* Initialize OS (should be first !) */
OS_InitHW(); /* Initialize Hardware for OS (see RtosInit.c)*/
/* You need to create at least one task here ! */
OS_CREATETASK(&TCB0, "HP Task", Task0, 100, Stack0); /* Create Task0*/
OS_CREATETASK(&TCB1, "LP Task", Task1, 50, Stack1); / *Create Task1*/
InitKeyMan(); /* Initialize keyboard manager */
OS_Start();
}

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26.2 Additional libraries and modules

For all embOS-compatible real-time operating systems, there are additional libraries
and modules available. However, these modules can also be used without embOS or
with a different operating system. Because these libraries are written in ANSI C, they
can be used on any target CPU for which an ANSI C compiler exists. In general, these
modules are highly optimized for both low memory consumption (especially in RAM)
and high speed.
The modules can be scaled for optimum performance at minimum memory consump-
tion using compile-time switches. Unused portions of the modules are not even com-
piled; your program stays lean and fast.

emWin The complete solution for graphical LCDs.

A fully scaleable graphical user interface featuring:
• different fonts (from 4*6 to 16*32)
• line drawing, bitmap drawing
• advanced drawing (for example circles)
• display routines for strings, dec/hex/bin values, mul-
tiple windows
• ultra-fast, yet still very compact (typically between 8
and 20 Kbytes ROM)
Everything you need for graphic displays!
Any LCD * Any LCD controller * Any CPU
Both monochrome and color versions available, as well as bit-
mapconverter, font converter, PC simulation and viewer. Check
out our website!

emLoad Boot-loader software

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314 CHAPTER 26 Additional modules

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 315

Chapter 27

FAQ (frequently asked questions)

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316 CHAPTER 27 FAQ (frequently asked questions)

Q: Can I implement different priority scheduling algorithms ?

A: Yes, the system is fully dynamic, which means that task priorities can be changed
while the system is running (using OS_SetPriority()). This feature can be used
for changing priorities in a way so that basically every desired algorithm can be
implemented. One way would be to have a task control task with a priority higher
than that of all other tasks that dynamically changes priorities. Normally, the
priority-controlled round-robin algorithm is perfect for real-time applications.
Q: Can I use a different interrupt source for embOS ?
A: Yes, any periodical signal can be used, that is any internal timer, but it could also
be an external signal.
Q: What interrupt priorities can I use for the interrupts my program uses?
A: Any.

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Chapter 28

Glossary

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318 CHAPTER 28 Glossary

Active task Only one task can execute at any given time. The task that is
currently executing is called the active task.

A scheduling system in which each task is allowed to run until

Cooperative
it gives up the CPU; an ISR can make a higher priority task
multitasking
ready, but the interrupted task will be returned to and finished
first.

Counting sema- A type of semaphore that keeps track of multiple resources.

phore Used when a task must wait for something that can be sig-
naled more than once.

CPU Central Processing Unit. The "brain" of a microcontroller; the

part of a processor that carries out instructions.

A section of code which must be executed without interrup-

Critical region
tion.

Event A message sent to a single, specified task that something has

occurred. The task then becomes ready.

Interrupt Service Routine. The routine is called automatically

ISR
by the processor when an interrupt is acknowledged. ISRs
must preserve the entire context of a task (all registers).

A data buffer managed by the RTOS, used for sending mes-

Mailbox
sages to a task or interrupt handler.

An item of data (sent to a mailbox, queue, or other container

Message
for data).

The execution of multiple software routines independently of

Multitasking
one another. The OS divides the processor's time so that the
different routines (tasks) appear to be happening simulta-
neously.

NMI Non-Maskable Interrupt. An interrupt that cannot be masked

(disabled) by software. Example: Watchdog timer-interrupt.

Preemptive multi- A scheduling system in which the highest priority task that is
tasking ready will always be executed. If an ISR makes a higher prior-
ity task ready, that task will be executed before the inter-
rupted task is returned to.

Processor Short for microprocessor. The CPU core of a controller

Priority The relative importance of one task to another. Every task in

an RTOS has a priority.

A situation in which a high priority task is delayed while it

Priority inversion
waits for access to a shared resource which is in use by a
lower priority task. The lower priority task temporarily gets
the highest priority until it releases the resource.

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 319

Like a mailbox, but used for sending larger messages, or mes-

Queue
sages of individual size, to a task or an interrupt handler.

Anything in the computer system with limited availability (for

Resource
example memory, timers, computation time). Essentially, any-
thing used by a task.

Resource sema-
A type of semaphore used for managing resources by ensuring
phore
that only one task has access to a resource at a time.

RTOS Real-time Operating System.

Scheduler The program section of an RTOS that selects the active task,
based on which tasks are ready to run, their relative priorities,
and the scheduling system being used.

Semaphore A data structure used for synchronizing tasks.

A data structure which calls a user-specified routine after a

Software timer
specified delay.

An area of memory with LIFO storage of parameters, auto-

Stack
matic variables, return addresses, and other information that
needs to be maintained across function calls. In multitasking
systems, each task normally has its own stack.

Superloop A program that runs in an infinite loop and uses no real-time

kernel. ISRs are used for real-time parts of the software.

A program running on a processor. A multitasking system

Task
allows multiple tasks to execute independently from one
another.

Tick The OS timer interrupt. Usually equals 1 ms.

Timeslice The time (number of ticks) for which a task will be executed
until a round-robin task change may occur.

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 321

Index

A I
Additional modules ............................ 311 Internal data-structures ......................240
Interrupt control macros .....................210
B Interrupt level .................................... 21
Interrupt service routines .............. 21, 194
Baudrate for embOSView .................... 253
Interrupts ..................................193–215
enabling/disabling ............................207
C interrupt handler .............................199
C startup ............................................30 ISR ..................................................194
Compiler .......................................... 304
Configuration defines ......................... 252 K
Configuration, of embOS .......241, 249–255
Counting Semaphores ..........................97 Keyboard manager .............................312
Critical regions ......................24, 217–221 KEYMAN.C .........................................312

D L
Libraries, building ..............................309
Debug version, of embOS .....................32
Limitations, of embOS ........................305
Debugging ................................. 287–291
error codes ..................................... 289
runtime errors ................................ 288 M
Development tools ............................. 303 Mailboxes ............................. 26, 111–128
basics ............................................113
E single-byte .....................................115
Measurement ....................................225
embOS
high-resolution ................................229
building libraries of .......................... 309
low-resolution .................................225
different builds of ..............................32
Memory management
features of .......................................17
fixed block size ................................167
embOS features ..................................17
heap memory ..................................163
embOS profiling ..................................32
Memory pools .............................167–181
embOSView ............................... 257–285
Multitasking systems ........................... 22
API trace ........................................ 265
cooperative multitasking .................... 22
overview ........................................ 258
preemptives multitasking ................... 23
SIO ............................................... 261
system variables window .................. 260
task list window .............................. 259 N
trace filter setup functions ................ 267 Nesting interrupts ..............................211
trace record functions ...................... 277 Non-maskable interrupts .....................215
emLoad ............................................ 313
emWin ............................................. 313 O
Error codes ....................................... 289
OS_AddTickHook() .............................247
Events ..................................26, 141–162
OS_BAUDRATE ..................................252
OS_CallISR() .....................................202

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322 Index

OS_CallNestableISR() ........................ 203 OS_GetTimerValue() ............................ 70

OS_ClearEvents() .............................. 150 OS_GetTimerValueEx() ......................... 81
OS_ClearMB() ................................... 126 OS_HandleTick() ............................... 244
OS_COM_Init() ................................. 251 OS_HandleTick_Ex() .......................... 245
OS_COM_Send1() ............................. 251 OS_Idle() .................................. 251, 255
OS_ConvertCycles2us() ...................... 251 OS_IncDI() ....................................... 208
OS_CREATECSEMA() .......................... 100 OS_InitHW() ..................................... 251
OS_CreateCSema() ........................... 101 OS_ISR_rx() ..................................... 251
OS_CREATEMB() ............................... 117 OS_ISR_Tick() .................................. 251
OS_CREATERSEMA() ............................ 89 OS_ISR_tx() ..................................... 251
OS_CREATETASK() .............................. 36 OS_IsTask() ........................................ 50
OS_CreateTask() ................................. 37 OS_LeaveInterrupt() ................... 205–206
OS_CREATETASK_EX() ......................... 39 OS_LeaveInterruptNoSwitch() ............. 206
OS_CreateTaskEx() .............................. 40 OS_LeaveNestableInterrupt() .............. 213
OS_CREATETIMER() ............................. 62 OS_LeaveNestableInterruptNoSwitch() . 214
OS_CreateTimer() ............................... 63 OS_LeaveRegion() ............................. 221
OS_CREATETIMER_EX() ....................... 73 OS_malloc() ..................................... 165
OS_CreateTimerEx() ............................ 74 OS_MEMF_Alloc() .............................. 172
OS_CSemaRequest() ......................... 106 OS_MEMF_AllocTimed() ...................... 173
OS_DecRI() ...................................... 208 OS_MEMF_Create() ............................ 170
OS_Delay() ........................................ 41 OS_MEMF_Delete() ............................ 171
OS_DelayUntil() .................................. 42 OS_MEMF_FreeBlock() ....................... 176
OS_DeleteCSema() ........................... 109 OS_MEMF_GetBlockSize() ................... 178
OS_DeleteMB() ................................. 128 OS_MEMF_GetMaxUsed() ................... 180
OS_DeleteTimer() ............................... 68 OS_MEMF_GetNumBlocks() ................. 177
OS_DeleteTimerEx() ............................ 79 OS_MEMF_GetNumFreeBlocks() ........... 179
OS_DI() ........................................... 209 OS_MEMF_IsInPool() ......................... 181
OS_EI() ........................................... 209 OS_MEMF_Release() .......................... 175
OS_EnterInterrupt() ................... 204, 206 OS_MEMF_Request() .......................... 174
OS_EnterNestableInterrupt() .............. 212 OS_PutMail() .................................... 118
OS_EnterRegion() ............................. 220 OS_PutMail1() ................................... 118
OS_EVENT_Create() .......................... 154 OS_PutMailCond() ............................. 119
OS_EVENT_Delete() .......................... 162 OS_PutMailCond1() ............................ 119
OS_EVENT_Get() .............................. 161 OS_PutMailFront() ............................. 120
OS_EVENT_Pulse() ............................ 160 OS_PutMailFront1() ........................... 120
OS_EVENT_Reset() ............................ 159 OS_PutMailFrontCond() ...................... 121
OS_EVENT_Set() ............................... 157 OS_PutMailFrontCond1() .................... 121
OS_EVENT_Wait() ............................. 155 OS_Q_Clear() ................................... 139
OS_EVENT_WaitTimed() ..................... 156 OS_Q_Create() ................................. 133
OS_ExtendTaskContext() ...................... 43 OS_Q_GetMessageCnt() ..................... 140
OS_free() ......................................... 165 OS_Q_GetPtr() .................................. 135
OS_FSYS .......................................... 252 OS_Q_GetPtrCond() ........................... 136
OS_GetCSemaValue() ................. 107–108 OS_Q_GetPtrTimed() ......................... 137
OS_GetEventsOccurred() .................... 149 OS_Q_Purge() ................................... 138
OS_GetMail() .................................... 122 OS_Q_Put() ...................................... 134
OS_GetMail1() .................................. 122 OS_realloc() ..................................... 165
OS_GetMailCond() ............................. 123 OS_RemoveTickHook() ....................... 248
OS_GetMailCond1() ........................... 123 OS_Request() ..................................... 93
OS_GetMailTimed() ........................... 124 OS_RestoreI() ................................... 209
OS_GetMessageCnt() ......................... 127 OS_Resume() ..................................... 51
OS_GetpCurrentTask() ......................... 46 OS_RetriggerTimer() ............................ 66
OS_GetpCurrentTimer() ..................72, 83 OS_RetriggerTimerEx() ........................ 77
OS_GetPriority() ................................. 47 OS_SendString() ............................... 263
OS_GetResourceOwner ........................ 95 OS_SetPriority() .................................. 52
OS_GetSemaValue() ............................ 94 OS_SetRxCallback() ........................... 264
OS_GetStackBase() ........................... 189 OS_SetTaskName() .............................. 53
OS_GetStackSize() ............................ 190 OS_SetTimerPeriod() ........................... 67
OS_GetStackSpace() ......................... 191 OS_SetTimerPeriodEx() ........................ 78
OS_GetStackUsed() ........................... 192 OS_SetTimeSlice() ............................... 54
OS_GetTaskID() .................................. 49 OS_SignalCSema() ..................... 102–103
OS_GetTime() .................................. 227 OS_SignalEvent() .............................. 148
OS_GetTime_Cycles() ........................ 251 OS_StartTimer() .................................. 64
OS_GetTime32() ............................... 228 OS_StartTimerEx() .............................. 75
OS_GetTimerPeriod() ........................... 69 OS_StopTimer() .................................. 65
OS_GetTimerPeriodEx() ....................... 80 OS_StopTimerEx() ............................... 76
OS_GetTimerStatus() .......................... 71 OS_Suspend() .................................... 55
OS_GetTimerStatusEx() ....................... 82 OS_Terminate() ................................... 56

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 Index 323

OS_Time .......................................... 239 T

OS_TimeDex ..................................... 239 Task communication ............................ 26
OS_Timing_End() .............................. 232 Task control block .......................... 27, 34
OS_Timing_GetCycles() ...................... 234 Task routines ................................. 33–58
OS_Timing_Getus() ........................... 233 Tasks ................................................. 20
OS_Timing_Start() ............................. 231 communication ................................. 26
OS_TraceData() ................................. 281 global variables ................................ 26
OS_TraceDataPtr() ............................. 282 multitasking systems ........................ 22
OS_TraceDisable() ............................. 270 single-task systems .......................... 21
OS_TraceDisableAll() .......................... 272 status ............................................. 29
OS_TraceDisableFilterId() ................... 276 superloop ........................................ 21
OS_TraceDisableId() .......................... 274 switching ......................................... 27
OS_TraceEnable() .............................. 269 TCB ................................................... 27
OS_TraceEnableAll() ........................... 271 Time measurement .....................223–236
OS_TraceEnableFilterId() .................... 275 Time variables ...................................239
OS_TraceEnableId() ........................... 273
OS_TracePtr() ................................... 280
OS_TraceU32Ptr() .............................. 283 U
OS_TraceVoid() ................................. 279 UART ................................................258
OS_UART .......................................... 252 UART, for embOS ...............................253
OS_Unuse() ........................................92
OS_USE() ...........................................90 V
OS_WaitCSema() ............................... 104 Vector table file .................................253
OS_WaitCSemaTimed() ...................... 105
OS_WaitEvent() ................................. 144
OS_WaitEventTimed() ........................ 146
OS_WaitMail() ................................... 125
OS_WaitSingleEvent() ........................ 145
OS_WaitSingleEventTimed() ................ 147
OS_WakeTask() ...................................57

P
Preemptive multitasking .......................23
Priority ...............................................24
Priority inversion .................................25
Profiling ..............................................32

Q
Queues ................................26, 129–140

R
Reentrance ....................................... 304
Release version, of embOS ....................32
Resource semaphores ..........................85
Round-robin ........................................24
RTOSInit.c configuration ..................... 250
Runtime errors .................................. 288

S
Scheduler ...........................................24
Semaphores ........................................26
Counting ...................................97–109
Resource .................................... 85–96
Software timer .............................. 59–72
Software timers API overview ................61
Stack ...................................27, 183–192
Stack pointer ......................................27
Stacks
switching ..........................................28
Superloop ...........................................21
Switching stacks ..................................28
Syntax, conventions used ...................... 7
System variables ........................ 237–240

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324 Index

User & reference guide for embOS © 2008 SEGGER Microcontroller GmbH & Co. KG