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Embedded Systems

Special Lecture

By

N.SHANMUGASUNDARAM

Asst. Professor – ECE Department

Mahendra Engineering College

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What is an Embedded System?

Embedded system is a

Microcontroller based

Software driven

Reliable

Real time control system

Autonomous or Human interactive

Operating on diverse physical variables

In diverse environments

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DRIVES

What is an Embedded System?

Embedded system is a Hardware with Software embedded in it,

for a dedicated application.

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SMART Embedded Systems …

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SMART Embedded Systems …

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SMART Embedded Systems …

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HARDWARE Processor, RAM, ROM, ADC, DAC, Timers, Ports, etc.

APPLICATION SOFTWARE written in Assembly, C, C++, Java, etc.

RTOS (to supervise the Application Software) µC OS-II, Win CE, VxWorks, Embedded Linux, etc.

3 MAIN COMPONENTS of Embedded System

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• SMALL SCALE: 8/16 bit CPU, little H/w, less S/w complexity, No RTOS, Battery operated.

• MEDIUM SCALE: 16/32 bit µC or DSPs, Complex H/w & S/w design, RTOS Source code Engg tools, IDE.

• SOPHISTICATED: Configurable processors, Cutting edge applications, Highly complex H/w and S/w design,

CLASSIFICATION of Embedded Systems

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SKILLS for Embedded System Engineer

• HARDWARE:

µP / µC, DSPs, Memories, Peripheral devices, sensors, Computer architecture, Digital electronics, Electronic system design, Control system, Data communication.

• SOFTWARE:

IDE - Editor, Assemblers, Compilers, Linkers, Debuggers, Simulator. Programming languages - Assembly, C, C++, Java RTOS – Vxworks, Win CE, RTLinux, etc.

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COMPONENTS of Embedded System Hardware

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PROCESSORS for Embedded Systems

ALU

Control Unit

PROCESSOR

Types of Processor

• General Purpose Processor (µc, µP, DSP, EP,MP)

• Application Specific System Processor

• Multiprocessor system

• GPP/ASIP core with other hardware integrated in ASIC chip.

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OTHER HARDWARE for Embedded Systems

1. Power supply circuit

2. Memory - EPROM, RAM, EEPROM (flash), CACHE

3. I/O Ports - 8255 (PPI), 8251 (UART)

4. Timers - 8253

5. ADC / DAC - ADC0809, DAC0800

6. Display & Keyboard Controllers - 8279

7. Programmable Interrupt Controllers - 8259

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SOFTWARE Components in Embedded Systems

Programming Languages: 1. Machine code

2. Assembly language

3. High level languages ie., C, C++

Editor Simulator

Assembler Loader

Compiler Stethoscope

Linker Trace scope

Debugger IDE

Software Tools:

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Software Development Chain

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HARDWARE in Exemplary Embedded Systems

Processor Multi processor on a Chip

Bus Size 32

Architecture RISC

Cache Memory Yes

ROM 1 MB

EEPROM 32 KB

RAM 1 MB

I/O Ports KBD & Display ports

DAC & ADC Yes

Modulation / Demodulation Yes

DSP instructions Yes

MOBILE PHONE

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SOFTWARE in Exemplary Embedded Systems

Editor yes

Interpreter No

Assembler No

Cross Assembler No

Compiler yes

Locator yes

Simulator yes

Source code Engg tools yes

RTOS yes

IDE yes

Stethoscope yes

MOBILE PHONE

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Exemplary SOC for Mobile Phone

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Types of I/O Devices

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Structure of Serial Port

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Structure of Parallel Port

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BUSES for Communication

Buses

Serial Parallel

ISA, EISA, PCI, …I2C, CAN, USB, …

I2C : Bus for communication between multiple ICs.CAN: Bus used in automobiles with centrally controlled network.USB: Bus for communication between CPU and devices like mouse, etc.

ISA, EISA, PCI are standard buses for parallel communication used in PCs, computer network devices, etc.

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Types of TIMERS

Timers

HardwareTimer

Software Timer

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Structure of Hardware Timer

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Usage of TIMERS

1 Real Time Clock (RTC) for the system

2 Initiating an Event after a preset time delay

3 Initiating an Event after a comparison of preset times

4 Capturing the count value in timer on an event

5 Finding time interval between two events

6 Watchdog timer

7 Baud rate control for Serial communication

8 Scheduling of various tasks in RTOS

9 Time slicing of various tasks

10 Time division multiplexing

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Programming Embedded Systems in Assy & C

Assembly C, C++

1. Full use of processor specific

instructions.

1. Software development cycle is short

due to usage of functions, std library

functions, modular programming

approach, Top down design, etc.

2. Machine codes are Compact.2. Data type declarations make

programming easy.

3. Device driver code needs only

few assembly instructions.3. Type checking eliminates errors.

4. Usage of Control structures

like if-then, do-while, for, etc.

5. Portability to different hardware

and OS.

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Programming Embedded Systems using C++

Combines the advantage of OOPS, C & Assembly.

Special features: Data Encapsulation, inheritance, etc.

Advantages : Reusability of software components.

Disadvantages: Standard C++ programming makes code complex and lengthy, due to features like Templates, Multiple inheritance, Exception handling, Virtual base classes, Namespaces, etc.

Solution : Special version of C++ (Embedded C++) has provision for selective disabling of features.

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Phases of Software Development

1.Definition and Analysis of the System Requirement

a) Complete Specification of the System.

b) Specification of the data, functions, tasks,..

c) System behaviour

d) Constraints of Design

e) Human machine interaction

f) Expected life cycle

g) Validation criteria & time delivery schedule

2. DevelopmentThe process of software

Designing, Coding and Testing.

3. Support

a) Correction of bugs

b) Addition of extra functions as per changing

environment

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S/w development of Typical application (Automobiles)

Development of a Embedded system in a Car to monitor Instrument clusters, Engine performance, Automatic Gear box, Brakes, etc., the typical code will be as follows

Watch 1254

Recording data of usage / malfunction 168

Engine speed 399

Vehicle speed 557

Odometer 999

Wake-up / Sleep down 252

Fuel 376

Alarms 4781

Coolant Temperature 537

Light Control 1925

Automatic gear box 207

(Total 11643 LOC)

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Source Code Engineering tool

It is a tool for source code development, compiling, debugging and testing.

eg. SNiFF+ from WindRiver® Systems

Features of SNiFF+

• Comprehension, Navigation and Browsing

• Editing

• Configuring (selective disabling of C++ features)

• Compiling

• Debugging

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Code / Memory Optimization

It is a process of making the code compact and fitting into a small

memory space without affecting code performance.

Techniques for code optimization:

• Use of unsigned byte

• Avoiding std lib functions, when simple coding is possible.

• Usage of Assy code, when target processor is well known.

• Usage of Global Variable, when no chance for shared data problem.

• Reduce usage of frequent function calls.

• Usage of delete / free, to release the used memory.

• Disabling the used features of C++.

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Process / Tasks / Threads

Process : It is a sequentially running program with its state.

Task : An application consisting of tasks controlled by scheduling

mechanism of an OS.

Threads : Light weighted sub-process in application program,

controlled by process control entity.

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Function ISR Task

- Set of instructions for performing an actions.

- Called by Proc/Task/ISR.

- Each Fn has a context

- Provision for nested Function calls.

- ISR is independent

- Call from H/w & S/w.

- ISR has Priority.

- Each ISR has Context.

- Task is independent.

- Sync done by RTOS.

- Scheduler runs one

task at a time.

Comparison of Function / ISR / Task

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Inter Process Communication (IPC)

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Inter Process Communication (IPC)

IPC: Some information generated by a processes / tasks, by setting / resetting a flag / value, or generates an output so that it lets another process take note / use of it.

Types: 1) Signal

2) Semaphores (flags, mutex, resource key, counting)

3) Queues, Pipes or Mailbox (eg. LCD display in Mobile – Time, Ph No.)

4) Sockets (eg. COM port in PC to connect modem, port 80 – web server)

5) Remote Procedure Calls (RPC) – for distributed processes

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Shared Data Problem & its Solutions

Shared Data Problem: Conflict arising on a common variable due to usage by multiple tasks / processes on it.

Eg. Interrupt changing the subsequent bits while processing a 32 bit data on a 8-bit CPU.

Solutions: 1) Use of modifier “Volatile”

2) Use of “Re-entrant” functions

3) Putting shared variable in circular queues

4) Disabling interrupts on execution of Critical section

5) Using Semaphores

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Semaphore & its types

Types of Semaphores: 1) Single, 2) Multiple, 3) Mutex

4) P & V 5) Counting

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GOALS of Operating System

1. Facilitating easy sharing of resource as per schedule and allocation.

2. Facilitating easy implementation of application software.

3. Optimally scheduling the processes on one / more CPU.

4. Maximizing the system performance without any security breach.

5. Providing the management functions for Processes, tasks, etc.

6. Providing the management functions for Devices, Files, etc.

7. Providing easy interface and management functions for network & protocols.

8. Providing portability of application software on different hardware.

9. Providing interoperability of application on different networks.

10. Providing common set of interfaces.

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STRUCTURE of Operating System

Application Software

API

System Software(with functions other than in OS)

OS interface

OS

Hardware – OS

Interface

Hardware

Eg. Device driver for Multimedia device

Consists of KERNEL(Operated in User and Supervisory modes)

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KERNEL of Operating System

- OS is a middle layer between Application Software & Hardware.

- It consists of KERNEL and other functions not provided by Kernel.

- KERNEL is operated in Supervisory mode and Other functions are operated in User Mode.

KERNEL Services

Process Management Memory Management Inter Process Communication I/O management Interrupt Control Device drivers

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Process Management in OS

A. Process Creation: Initial and Subsequent process.

B. Management of Created process:

- Processing resource requests

- Allocation of Resources (through Message / system calls)

- Controlling of process through PCB.

- Scheduling and synchronization

Process management consists of

creation, activation, running, blocking, resumption, deactivation, deletion of processes.

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Memory Management in OS

A. Memory Allocation: at the time of creation of a new process / tasks.

B. Memory Management after allocation:

- Fixed block allocation

- Dynamic block allocation

- Dynamic page allocation

- Dynamic data memory allocation

- Dynamic address reallocation

- Multiprocessor memory allocation

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Device Management in OS

A. Manages Physical / Virtual devices (eg. Pipes & sockets).

B. Three standard approach to three types of device drivers

a) Programmed I/O poling

b) Interrupt driven through ISR

c) DMA

C. Functions of Device manager

It includes function like Device detection & addition, device allocation and registration, device sharing, device buffer management, device access management.

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File System Organization & Implementation

- File is a named entity stored on secondary storage device.

- It contains data in different formats.

- Both real and Virtual files (Pipe) are managed.

Functions to Organize Files in systematic way:

Open

Write

Read

Seek

Close

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Real Time Operating System (RTOS)

RTOS is an OS for Embedded system

for response time and event controlled processes.

RTOS Services:

• Basic OS functions - PM, RM, MM, DM, FSM, I/o, etc.

• RTOS main functions - RT task scheduling and latency control

• Time management - Time Allocation, time slicing & monitoring for efficiency.

• Predictability - Predicting time behaviour and initiation of task synchronization

• Priorities Management - Allocation and Inheritance

• IPC - Synchronization of Tasks using IPC.

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Why need RTOS?

Reasons for need of RTOS Occasions for NO need of RTOS

When efficient scheduling in needed for multitasks with time constraints.

Task synchronization is needed.

Interrupt latency Control is essential.

Small scale embedded system never use RTOS.

Instead of functions in RTOS, standard lib functions in C can be used.

eg. malloc(), free(),

fopen(), fclose(), etc.

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RTOS Task Scheduling Models

A. Control flow strategy

Complete control of i/p and o/ps. Co-operative scheduler adopts this

strategy. Worst case latencies are well defined.

B. Data flow strategy

Interrupt occurrences are predictable. Task control not deterministic.

Eg.network. (Packet arrival not predictable)

Pre-emptive scheduler adopts this strategy.

C. Control-data flow strategy

Task scheduler fns are designed with predefined time-out delays.

WC latency is deterministic, because the max delay is predefined.

Cyclic Co-op Schd, Pre-emp Schd, Fixed time Schd, Dynamic RT Schd uses this strategy.

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Co-operative Round robin Scheduling

Other Types of Co-operative scheduling: i) using ordered list.

ii) using time slicing with timers

Dis-advantages: Longer execution time of a low priority task makes a higher priority task wait until it finishes.

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Pre-emptive Scheduling

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Other Scheduling techniques and Critical Section

Critical Section: It is an important portion of a task, which should not be blocked as it uses a shared variable.

Here, Pre-emptive scheduling leads to conflict.

Other Scheduling Techniques: 1) Fixed real time scheduling of Tasks

2) Probabilistic timed Petrinets

3) Multi Thread Graphs (MTG)

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RTOS - Real Time Operating System

A Real-Time Operating System (RTOS) is an operating system (OS) intended for real-time applications in Embedded systems.

A key characteristic of real-time operating systems is the level of its consistency concerning the amount of time it takes to accept and complete an application's task.

A real-time OS has an advanced algorithm for scheduling.

Key factors in an real-time OS are a minimal interrupt latency and a minimal thread switching latency.

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Basic functions of RTOS

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Need for Tested RTOS

While designing a complex embedded systems, we need a tested bug free codes for the following.

• Multiple task functions in C or C++.

• Real time clock based software timers (RTCSWT).

• Software for Co-operative scheduler.

• Software for a Pre-emptive scheduler.

• Device drivers and Device managers.

• Functions for Inter Process Communications.

• Network functions

• Error handling functions and exception handling functions.

• Testing and System debugging software.

A readily available RTOS package provides the above functions and a lot of time is saved for coding the same.

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Options in RTOS

Options for

RTOS

Own RTOSLinux BasedRTOS

µC/ OS-II(Freeware)

PSoSVxWorksNucleusWin CE

Palm OS

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µC/OS-II (MUCOS)

µC/OS-II is Free Open-source RTOS designed by Jean J. Labrosse in 1992.

µC/OS-II is intended for Non-commercial use.

µC/OS-II codes are in C and few CPU specific modules are in ASSY.

µC/OS-II code Port on MANY Processors that are commonly used in ES design.

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Features of µC/OS-II

µC/OS-II is a Scalable OS. µC/OS-II uses Pre-emptive Scheduler (for multitasking). µC/OS-II has System level functions. µC/OS-II has Task service functions. µC/OS-II has Task delay functions. µC/OS-II has Memory allocation functions. µC/OS-II has IPC functions. µC/OS-II has Semaphore, Queue, Mailbox functions.

when OS or OS_ used as prefix, it denotes a function / variable

is a µC/OS-II function or variable.

Eg. OSTaskCreate() ---→ µC/OS-II function for TASK CREATION.

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Source code files of µC/OS-II

A. Processor dependent source files

Os_cpu.h Processor definition header file

Os_cfg.h Kernel building configuration file

Os_tick.c C file for ISR and RTOS timers

Os_cpu_c.c Processor C codes file

Os_cpu-a.s12 Assy code for task switching functions (68HC12)

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Source code files of µC/OS-II (contd..)

Ucos.ii.h MUCOS header file

Ucos.ii.c MUCOS header file

Os_core.c For RTOS core

Os_time.c For RTOS timer

Os_task.c For RTOS task related functions

Os_mem.c For Memory partitioning

Os_sem.c For Semaphore related functions

Os_q.c For Queue related functions

B. Processor independent source files

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RTOS System level functions

The System level functions are

void OSInit (void) At the beginning prior to OSStart()

void OSStart (void) After OSInit() and task creating functions

void OSTickInit (void) To initialize System timer ticks

void OSIntEnter (void) Just after the start of ISR codes

Void OSIntExit (void) before return form the ISR codes

OS_ENTER_CRITICAL Macro to disable all interrupts

OS_EXIT_CRITICAL Macro to enable all interrupts

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Task Service functions

These functions are used to create task, suspend and resume, and time setting and retrieving functions.

unsigned byte OSTaskCreate (…) Must call before running a task

unsigned byte OSTaskSuspend (..) Called for blocking a task

unsigned byte OSTaskResume (..) Called for resuming a blocked task

void OSTimeset (..) When system time is to be set

Unsigned int OSTimeGet (void) Find present count when time is read

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Time Delay functions

MUCOS Time delay functions for the tasks are

void OSTimeDly (…) To delay a task by count-1 value

unsigned byte OSTimeDlyResume (…) To resume a task after a preset delay

void OSTimeDlyHMSM (…) Time delay to block a task

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Memory related functions

MUCOS memory related functions for the tasks are

OSMem *OSMemCreate (…) To create and initialize memory partition

void *OSMemGet (..) To find the pointer of memory control block

unsigned byte OSMemQuery (..)To find pointers of memory blocks

and data structures

unsigned byte OSMemPut (…) To return a pointer of memory block

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Semaphore related functions

When a semaphore created by OS and used a resource acquiring key, it must be initialized with “1” to indicate the resource is available.

MUCOS Semaphore related functions for the tasks are

OS_Event OSSemCreate (…) To create and initialize a semaphore

void OSSemPend (..) To check whether a semaphore is pending

unsigned short OSSemAccept (..) To check whether SemVal > 0

unsigned byte OSSemPost (…)If SemVal = 0 or more, increments, and makes a semaphore again not pending.

unsigned byte OSSemQuery (…) To get semaphore information

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Other functions

Apart from the previous said functions, MUCOS has functions related to

• Mailbox

• Queue

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Automatic Chocolate Vending Machine (ACVM)

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Applications

Medical instrumentation Military applications Aerospace research Robotics Consumer Electronics Industrial Applications Automobiles Telecommunication

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Breakthrough in Embedded System Designs

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According to analyst firm, the embedded system opportunity is expected to touch

• US$ 360 billion (in terms of devices)

• US$ 36 billion (up from the existing US$ 2 billion).

Experts also predict that there will be a ten-fold increase in the number of people employed in the embedded systems industry,

from the current 60,000 professionals to over six lakh people by 2015.

- Source: NASSCOM

Market Potential for Embedded Systems

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Embedded Systems Companies in Bangalore

SadhanasoftClick Technologies (I) Pvt. Ltd.

Nihar Infoway Ltd. Infobahn (India) Pvt. Ltd.

Vision Comptech Integrators Ltd

Datamation Consultants Pvt. Ltd. Koenig Solutions Pvt. Ltd. Convergent Communication

s (India) Pvt. Ltd.

Optimal Infotech Pvt. Ltd. Compucom Software Ltd. Surya Soft-Tech Ltd Kale Consultants Ltd

Datamation Consultants Pvt. Ltd.

Surya Soft-Tech Ltd Mphasis-BFL Ltd Rhombus Technologies Pvt. Ltd.

Mphasis-BFL Ltd Global Automation ( Kale Consultants Ltd MindEdge Solutions

Karishma Software Ltd. Parsec Technologies (India) Ltd.

Binary Semantics Ltd. Netmumbai

Virgosys Software Pvt. Ltd. Polaris Software Lab Ltd Cybersol Technologies Pvt Ltd

SolutionNet India Pvt. Ltd.

IQura Technologies Pvt. Ltd.

SDI Infotech Pvt. Ltd. Datum Technologys (India) Ltd

Gateway WebSystems Pvt. Ltd.

Worldwide Infotech Inc. Java Softech Pvt. Ltd. Binary Semantics Ltd. Learnet India Ltd.

Intrepid Solutions Private Ltd

Global Software Initiatives Pvt. Ltd.

Webspectrum Software Pvt. Ltd.

KPIT Infosystems Ltd

iBilt Technologies Ltd iTech Workshop Pvt. Ltd. Datum Technologys (India) Ltd

Perfect E Com Solution Pvt Ltd.

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References

1. Rajkamal, Embedded Systems Architecture, Programming and Design, TMH, First reprint Oct. 2003

2. David E.Simon, An Embedded Software Primer, Pearson Education Asia, First Indian Reprint 2000.

3. www.embedded.com

4. www.micrcontroller.com

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Thank You

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Thank Youfor your PATIENCE.