Introduction of

Embedded Systems
What is an embedded system?
A physical system that employs computer control for a specific purpose,
rather than for general-purpose computation.
 Embedded systems are application specific & single functioned; application is known
apriori, the programs are executed repeatedly.
 They generally have minimal or no user interface.
 Embedded Systems is a special purpose computer system/board, which covers all the
devices such as processor, memory, interface and control in single package or board to
perform only a specific application tasks.
 A “Short List” of Embedded Systems
 Anti-lock brakes Fingerprint identifiers
 Auto-focus cameras Home security systems
 Automatic teller machine Medical testing systems
 Automatic toll systems Modems
 Automatic transmission MPEG decoders
 Avionic systems Network cards
 Battery chargers Network switches/routers
 Camcorders Pagers
 Cell phones Photocopiers
 Cell-phone base stations Printers
 Cordless phones Scanners
 Cruise control Stereo systems
 Digital cameras TV
 Disk drives VCR
 Electronic card readers Video game controllers
 Electronic toys/games Video phones
 Fax machines Washers and dryers
 Embedded Systems
 Embedded systems
 information processing systems
embedded into a larger product
 Two types of computing
 Desktop – produced millions/year
 Embedded – billions/year
 Non-Embedded Systems
 PCs, servers, and notebooks
 The future of computing!
 Automobiles, entertainment,
communication, aviation, handheld
devices, military and medical
equipments.
Components of Embedded Systems
Components of Embedded Systems

 Analog components
- Sensors, controllers,…
 Digital components
- Processor, coprocessors
- Memories
- Controllers, busses
- ASIC: Application-Specific Integrated Circuit, a chip designed for a
particular application
 Converters – A/D, D/A, …
 Software
- Application programs
- Exception handlers
Hardware components of an Embedded
System
CPU: Microprocessor/ Microcontroller/DSP
• Non Volatile memory: EPROM, Flash
• Volatile memory: DRAM, SRAM
• System clocks: RTC circuitry, System clock
• Standard devices: I/O ports, peripherals,
• Custom devices: FPGA, PAL
• Communication devices and drivers: Ethernet, RS-232, USART
• Debug mechanism: Debug port, Watchdog timer, JTAG, ICE
• Buses for device networks: I2C, CAN, SPI, etc.
 Characteristics

 Application specific
- Optimize for cost, area, power, and performance
 Digital signal processing
- Signals are represented digitally
 Reactive
- Reacts to changes in the system’s environment
 Real-time
- Compute certain tasks before deadline
 Distributed, networked,…
Characteristics

 Reliability
- Probability of system working correctly at fixed time
 Maintainability
- Probability of system working correctly fixed time units after error
occurred
 Safety
- Not harmful for user
 Security
- Confidential and authentic communication
Essential Considerations

• Response Time -- Real Time Systems

• Area
• Cost
• Portability
• Low Power (Battery Life)
Fault Tolerance-continue operation despite
hardware and software faults
Processor Classifications

 Based on register size

-8 bit
-32 bit
 Processors can be classified as 8 bit/16 bit/32 bit /64 bit based on the size
of their internal registers.
• Typically, the data bus width equals the size of the data registers so that the
register data can be read/written in one read/write cycle.
Based on Endianness

- Big Endian
- Little Endian

- Big Endian
Eg: SPARC, power PC
Little Endian
Intel processors
• Configurable Processors
some processors can be configured during boot up process as big or little
endian. Eg: ARM processors
Based of instruction set

RISC
CISC

RISC
• Only load/store instructions use the external memory.
• All instructions are same size and fixed length.
• Number of instructions available are less compared to CISC.
• Typically has less pipeline stages than CISC.
Eg ARM processor.
Based of instruction set

 CISC
 Most instructions can operate directly on external memory.
• Hence require less number of registers.
• Instructions are of different sizes. Hence they take varied clock cycle to
decode and execute each instruction
• Pipeline stages take varied times and hence pipeline is not so efficient as
the RISC processors.
 More number of instructions since many complex operations are
implemented
Eg: Intel Pentium processors
Based on Bus Architecture

Von Neumann Architecture

Harvard Architecture
Von Neumann

 A Von-Neumann Machine Architecture provides one data path (bus) for

both instruction and data
• As a result, the CPU can either be fetching an instruction from memory, or
read/writing data to it
• Other than less complexity of hardware, it allows for using a single,
sequential memory.
• Today’s processing speeds vastly outpace memory access times, and we
employ a very fast but small amount of memory (cache) local to the
processor
Harvard

 Harvard Architecture refers to a memory structure where the processor is

connected to two different memory banks via two sets of buses
• This is to provide the processor with two distinct data paths, one for instruction
and one for data
• Through this scheme, the CPU can read both an instruction and data from the
respective memory banks at the same time
• This inherent independence increases the throughput of the machine by
enabling it to always prefetch the next instruction
• The cost of such a system is complexity in hardware
Commonly used in DSPs
 Modern processors employ a Harvard Architecture to read from two instruction
and data caches, when at the same time using a Von-Neumann Architecture
to access external memory
Based on Functionality

General purpose Processors

Special purpose Processors- DSP, Network

General purpose processors:

 All the regular processors

Special purpose processors:

 Digital Signal Processors
 DSP processors are microprocessors designed for efficient mathematical
manipulation of digital signals.
 They are optimized for doing intense addition and multiplication
operations.
Based on Functionality

 Network Processors
Used in routers. Multiple processors are pipelined to process the network
packets in a optimal way.
 Each processor processes multiple packets concurrently in multiple
threads.
Eg : IXP1200 from Intel
Traditional Design Challenges

 Low cost  Mixed digital/analog

requirements
 Light weight
 Shrinking time-to-
 Reliability
market
 Low power
 Short product lifetime
 Portable
 Real-time processing
 Complexity
 Inherent concurrency
 Ease of use
 HW/SW co-design
Recent Design Challenges

 Design complexity
 Ultra low power
- Highly adaptive
- Active power management (voltage scaling, etc.)
- Alternative energy source (solar, etc.)
 Internet aware
- Incorporate RF (radio frequency) technologies
- Networking capabilities
* Larger OS, middleware, etc.
* Understanding of many/changing protocols
 Verification
 Security
Block Diagram of an Embedded
Parallel
To external Processor I/O ports
memory core

Serial
I/O ports

Internal
memory
Counter/Timer

A-to-D conv ersion D-to-A conv ersion

Processor
Figure 9.3. A block diagram of an embedded processor.
Design Issues

 Cost
 I/O capability
 Size
 Power consumption
 On-Chip memory
 Performance
 Software
 Instruction set
 Development tools
 Testability and reliability
Various types of Memory

DRAM: Dynamic Random Access Memory

 very dense (1 transistor per bit) and inexpensive
 requires refresh and often not the fastest access times
 often used for main memories
SRAM: Static Random Access Memory
 fast and no refresh required
 not so dense and not so cheap
 often used for caches
Various types of Memory

ROM: Read-Only Memory

 often used for bootstrapping
 All ROM devices can retain data and programs forever, even during
power failure.

PROM: Programmable ROM

 Once programmed, its contents cannot be changed.
 One time programmable.
Various types of Memory

EPROM: Erasable-and-programmable ROM

 EPROM can be erased and programmed repeatedly.

 Essential part of software development and testing.
Hybrid Devices
 hybrid memories can be written as desired, like RAM, but maintained their contents
without electrical power, just like ROM
 two of hybrid devices – EEPROM and Flash are ROM devices used to store code.
 third hybrid device – NVRAM, is modified version of SRAM.
 EEPROMs are electrically erasable and programmable
Various types of Memory

Flash memory
 high density, low cost, nonvolatile, fast and electrically erasable.
 Flash devices can be erased one sector at a time.
 sector sizes range from 256 bytes to 16 KB

NVRAM
 usually SRAM with a battery backup when power is turned on, operates
just like SRAM when power is turned off, NVRAM draws power from battery
to retain its data
The Embedded Software Development
Process
The Tools

 Compiler: Translates human readable code into assembly language or

opcodes for a particular processor. Produces an object file.

 Assembler: Translates assembly language into opcodes. Also produces an

object file.

 Linker: Organizes the object files, necessary libraries, and other data and
produces a relocatable file.
The Tools

 Relocatable file: an object file that holds code and data suitable for linking
with other object files to create an executable or a shared object file. In
other word, you can say that relocatable file is a foundation for creating
executables and libraries.

 Locator: Takes the relocatable file and information about the memory of
the system and produces an executable file.(By the way: gcc takes care
of all of these functions at once)
The Tools: Embedded System
Specifics

 All of the tools run on the host computer, not the embedded computer.
 Compiler
 Assembler
 Linker
 Locator

 Another alternative is to add a real-time operating system or embedded

operating system, which may have DSP capabilities like DSP nano RTOS.
The Tools: Embedded System
Specifics

Cross Compiler
 A compiler that generates machine language for a different type of
computer than the one the compiler is running in.
Cross-compiling doesn’t guarantee correct target code due to (e.g.,
differences in word sizes, instruction sizes, variable declarations, library
functions)
Cross Assembler
 An assembler that generates machine language for a different type of
computer than the one the assembler is running in. It is used to develop
programs for computers on a chip or microprocessors
 used in specialized applications that are either too small or are otherwise
incapable of handling the development software.
Moving the program onto the
embedded system
 Remember, the program is written (and possibly run in an emulator) on a
host computer, but it still needs to get onto the embedded system.
 Methods:
 Build/burn the program into the hardware (firmware or other flash
memory)
 Bootloader: a bootloader resides on the embedded system and facilitates
loading programs onto the system.
 Debug Monitor: The debug monitor is a more robust program on an
embedded system that helps with debugging, and can include a
bootloader as well.
Debugging

 Debugging embedded systems can be facilitated with a Debug Monitor,

or through a remote debugger on the host computer. A serial link is
normally set up.

 Emulators can be used to test the system without utilizing the actual
hardware

 A complete emulator provides a simulation of all aspects of the hardware,

allowing all of it to be controlled and modified, and allowing debugging
on a normal PC.
Debugging

 An in-circuit debugger (ICD), a hardware device that connects to the

microprocessor via a JTAG or Nexus interface. This allows the operation of
the microprocessor to be controlled externally, but is typically restricted to
specific debugging capabilities in the processor
 An in-circuit emulator (ICE) is a hardware device used to debug the
software of an embedded system. An in-circuit emulator replaces the
microprocessor with a simulated equivalent, providing full control over all
aspects of the microprocessor.
 In-circuit emulation can also refer to the use of hardware emulation,
when the emulator is plugged into a system (not always embedded) in
place of a yet-to-be-built chip (not always a processor). These in-circuit
emulators provide a way to run the system with "live" data while still
allowing relatively good debugging capabilities.
Debugging

 Software Simulators allow the programmer to debug completely on the

host system, which can be quicker .
 When it comes down to it, an oscilloscope and a multimeter can be your
best friend for debugging.
Device Drivers

 Device
Any peripheral such as a graphics display, disk driver, terminal, or printer is a
device. A device is usually considered to be a piece of hardware that you
can connect to your computer system and that you wish to manipulate by
sending commands and data.
Device Drivers

Three Classes of Device

 Character Devices
ex: Key board, mouse, monitor, printer, Tape, etc.,
 Block Devices
Ex: CD-ROM, floppy, Hard disk, etc.,
 Network Interfaces
ex: Ethernet card, etc.,
Device Drivers

 The OS interacts with devices through a program known as “Device Driver”

 A device driver is a specific type of computer software developed to
allow interaction with hardware devices. Typically this constitutes an
interface for communicating with the device, through the specific
computer bus or communications subsystem that the hardware is
connected to, providing commands to and/or receiving data from the
device, and on the other end, the requisite interfaces to the operating
system and software applications
Device Drivers

 Structure of Device Driver is OS specific

• Some RTOS allow device drivers to be installed and removed dynamically.
 Statically linked driver, whose object code is linked with the kernel. The
code of such device driver is physically contained in the kernel and
therefore loaded in memory when the system boots.
 Dynamically linked driver, whose object code is NOT linked with the
kernel. The code of such device driver is NOT contained in the kernel, and
the device driver is loaded and unloaded as and when required.
Real time in operating systems

“The ability of the operating system to provide a required level of service in a

bounded response time.”
Who are the Embedded OS players

 Wind River Systems

– VxWorks
– pSOS
 Mentor Graphics
– Nucleus
 Palm Computing
– PalmOS
 Symbian
– SymbianOS