UNIT 7.
STUDY OF COMMERCIAL RTOS
OVERVIEW
Real time operating system
Overview of Linux
Linux Kernel
Architecure of RTLinux
RTLinux Modules
Semaphor & Mutex Management
Other RTOS
REAL-TIME OPERATING SYSTEM
A Real-time operating system is a multitasking
operating system intended for applications with fixed
deadlines.
Applications include-
some small embedded systems,
automobiles engine controllers,
industrial robots,
spacecraft,
industrial control
and some large-scale computing devices.
LINUX
In April 1991, Linus Torvards, a 21-year-old student
at the University of Helsinki, Finland started working
on some simple ideas for an operating system.
Linux is a Unix-like computer operating system
assembled under the model of free and open source
software development and distribution.
Linux was originally developed as a free operating
system for Intel x86-based personnel computers.
Linux since has been ported to more computed
hardware platforms than any other operating systems.
Linux also run on embedded systems. Such as
mobile phones, network routers, televisions.
KERNEL:
Kernel manages the tasks to achieve the desired
performance of the system .
To manage the tasks, the important requirements are
to schedule the tasks and to provide inter-task
communication facilities
to achieve these two requirements, kernel objects are
defined such as
Tasks
Mutexes
ISR’s
Events
Message boxes
Mailboxes
Pipes and timers
Kernel provide the memory management service,
time management services, interrupt handling
services and device management services.
LINUX KERNEL
ARCHITECTURE OF RTLINUX
RTLinux is a hard RTOS microkernel that runs the
entire Linux operating system as a fully preemptive
process.
It was developed by Victor Yodaiken, Michael
Barabanov and others at the New Mexico Institute of
Mining and Technology and then as a commercial
product at FSMLabs.
FSMLabs has two editions of RTLinux.
RTLinux pro and RTLinux free.
RTLinux pro is the priced edition and RTLinux is the
open source release.
RTLinux support hard real time applications,
Linux kernel has been modified by adding a layer of
software between the hardware and the Linux kernel.
The new layer, RTLinux layer has a separate task
scheduler. This task scheduler assigns lowest
priority to the standard Linux kernel.
Any task that has to met real-time constraints will run
under RTLinux.
Interrupts from Linux are disabled to achieve real-
time performance.
ARCHITECTURE OF RTLINUX KERNEL
DIFFERENCES BETWEEN THE LINUX AND RTLINUX:
Linux RTLinux
Linux is not a hard real RTLinux supports hard
time system. real-time applications.
The tasks, which do not Any task that has real-
have any time time constraints will run
constraints. under RTLinux.
In RTLinux location of the various files are:
RTLinux will be installed in the directory
/usr/rtlinux-xxx, where xxx is the version name.
/usr/rtlinux/include contains all the include files
necessary for development project.
/usr/doc/rtlinux/man contains the manual pages for
the RTLinux.
/usr/rtlinux/modules contains the core RTLinux
modules
RTLINUX MODULES
RTLinux programs are not created as stand-alone units,
they are created as modules, which are loaded into the
Linux kernel space.
The C source files are compiled into objects files using the
gcc command with the argument –c flag.
In the C file, the main() function gets replaced with the
following lines:
Int init_module();
Void cleanup_module();
Init_module is called when the module is first loaded into
the kernel.
This function returns 0 if the module is successfully loaded.
It returns a negative value in case of failure.
cleanup_module() is called When the module is loaded is
to be unloaded.
EXECUTING THE RTLINUX MODULES
In RTLinux load and stop user modules using the
RTLinux commands.
Using command, we can also obtain status information
about RTLinux modules.
The command syntax is:
$rtlinux start my_program
$rtlinux stop my_program
$rtlinux status my_program
CREATING RTLINUX POSIX THREADS
A real-time program generally consists of a number of
threads.
Each thread share a common address space .
Pthread_create() function is used to create a new real-
time thread.
The corresponding header file is
#include <pthread.h>
SEMAPHOR AND MUTEX MANAGEMENT IN RTLINUX
To achieve real-time performance, various POSIX
compliant API function calls are used.
These function calls are related to create and cancel
semaphores.
To implement mutex, we have to include the header file
<rtl_mutex.h> in the C program.
To cancel a thread, the system call is pthread_cancel.
OTHER REAL TIME OPERATING SYSTEMS
RTLinux – Monolithic kernel with loadable modules
QNX – Microkernel approach
VxWorks – Monolithic kernel
LynxOS – Microkernel
ARTS, Spring, KURT, RTAI, etc….
