Unit - 1

Introduction to Embedded Systems

What is Embedded System?

An Electronic/Electro mechanical system which is designed to perform a specific

function and is a combination of both hardware and firmware (Software)

E.g. Electronic Toys, Mobile Handsets, Washing Machines, Air Conditioners, Automotive
Control Units, Set Top Box, DVD Player etc…

Embedded Systems are:

 Unique in character and behaviour

 With specialized hardware and software

Embedded Systems Vs General Computing Systems:

General Purpose Computing System Embedded System
A system which is a combination of generic A system which is a combination of special
hardware and General Purpose Operating purpose hardware and embedded OS for
System for executing a variety of executing a specific set of applications
applications
Contain a General Purpose Operating System May or may not contain an operating system
(GPOS) for functioning
Applications are alterable (programmable) by The firmware of the embedded system is pre-
user (It is possible for the end user to re- programmed and it is non-alterable by end-
install the Operating System, and add or user
remove user applications)
Performance is the key deciding factor on the Application specific requirements (like
selection of the system. Always „Faster is performance, power requirements, memory
Better‟ usage etc) are the key deciding factors
Less/not at all tailored towards reduced Highly tailored to take advantage of the
operating power requirements, options for power saving modes supported by hardware
different levels of power management. and Operating System
Response requirements are not time critical For certain category of embedded systems
like mission critical systems, the response
 time requirement is highly critical
Need not be deterministic in execution Execution behaviour is deterministic for
behaviour certain type of embedded systems like „Hard
Real Time‟ systems

History of Embedded Systems:

 First Recognized Modern Embedded System: Apollo Guidance Computer (AGC)
developed by Charles Stark Draper at the MIT Instrumentation Laboratory.
 It has two modules
 1.Command module(CM) 2.Lunar Excursion module(LEM)
 RAM size 256 , 1K ,2K words
 ROM size 4K,10K,36K words
 Clock frequency is 1.024MHz
 5000 ,3-input RTL NOR gates are used
 User interface is DSKY(display/Keyboard)
 First Mass Produced Embedded System: Autonetics D-17 Guidance computer for
Minuteman-I missile

Classification of Embedded Systems:

 Based on Generation
 Based on Complexity & Performance Requirements
 Based on deterministic behaviour
 Based on Triggering
1. Embedded Systems - Classification based on Generation
 First Generation: The early embedded systems built around 8-bit microprocessors
like 8085 and Z80 and 4-bit microcontrollers
 EX. stepper motor control units, Digital Telephone Keypads etc.
 Second Generation: Embedded Systems built around 16-bit microprocessors and 8
or 16-bit microcontrollers, following the first generation embedded systems.
 EX.SCADA, Data Acquisition Systems etc.
 Third Generation: Embedded Systems built around high performance 16/32 bit
Microprocessors/controllers, Application Specific Instruction set processors like
Digital Signal Processors (DSPs), and Application Specific Integrated Circuits
(ASICs).The instruction set is complex and powerful.
 EX. Robotics, industrial process control, networking etc.
 Fourth Generation: Embedded Systems built around System on Chips (SoC’s),
Reconfigurable processors and multicore processors. It brings high performance, tight
integration and miniaturization into the embedded device market
 EX Smart phone devices, MIDs etc.
2. Embedded Systems - Classification based on Complexity & Performance
 Small Scale: The embedded systems built around low performance and low cost 8
or 16 bit microprocessors/ microcontrollers. It is suitable for simple applications
and where performance is not time critical. It may or may not contain OS.
 Medium Scale: Embedded Systems built around medium performance, low cost
16 or 32 bit microprocessors / microcontrollers or DSPs. These are slightly
complex in hardware and firmware. It may contain GPOS/RTOS.
 Large Scale/Complex: Embedded Systems built around high performance 32 or
64 bit RISC processors/controllers, RSoC or multi-core processors and PLD. It
requires complex hardware and software. These system may contain multiple
processors/controllers and co-units/hardware accelerators for offloading the
processing requirements from the main processor. It contains RTOS for
scheduling, prioritization and management.
3. Embedded Systems - Classification Based on deterministic behaviour: It is applicable
for Real Time systems. The application/task execution behavior for an embedded system
can be either deterministic or non-deterministic.
 These are classified in to two types:
1. Soft Real time Systems: Missing a deadline may not be critical and can be tolerated to
a certain degree.
2. Hard Real time systems: Missing a program/task execution time deadline can have
catastrophic consequences (financial, human loss of life, etc.)
4. Embedded Systems - Classification Based on Triggering:
These are classified into two types
1. Event Triggered: Activities within the system (e.g., task run-times) are dynamic and
depend upon occurrence of different events.
2. Time triggered: Activities within the system follow a statically computed schedule
(i.e., they are allocated time slots during which they can take place) and thus by nature
are predictable.

Major Application Areas of Embedded Systems:

 Consumer Electronics: Camcorders, Cameras etc.

 Household Appliances: Television, DVD players, washing machine, Fridge,
Microwave Oven etc.
 Home Automation and Security Systems: Air conditioners, sprinklers, Intruder
detection alarms, Closed Circuit Television Cameras, Fire alarms etc.
 Automotive Industry: Anti-lock breaking systems (ABS), Engine Control, Ignition
Systems, Automatic Navigation Systems etc.
 Telecom: Cellular Telephones, Telephone switches, Handset Multimedia Applications
etc.
 Computer Peripherals: Printers, Scanners, Fax machines etc.
 Computer Networking Systems: Network Routers, Switches, Hubs, Firewalls etc.
 Health Care: Different Kinds of Scanners, EEG, ECG Machines etc.
 Measurement & Instrumentation: Digital multi meters, Digital CROs, Logic
Analyzers PLC systems etc.
 Banking & Retail: Automatic Teller Machines (ATM) and Currency counters, Point
of Sales (POS)
 Card Readers: Barcode, Smart Card Readers, Hand held Devices etc.
Purpose of Embedded Systems:

Each Embedded Systems is designed to serve the purpose of any one or a combination of the
following tasks.

o Data Collection/Storage/Representation
o Data Communication
o Data (Signal) Processing
o Monitoring
o Control
o Application Specific User Interface

1. Data Collection/Storage/Representation:-
 Performs acquisition of data from the external world.
 The collected data can be either analog or digital
 Data collection is usually done for storage, analysis, manipulation and
transmission
 The collected data may be stored directly in the system or may be transmitted
to some other systems or it may be processed by the system or it may be
deleted instantly after giving a meaningful representation
2. Data Communication:-

 Embedded Data communication systems are deployed in applications ranging

from complex satellite communication systems to simple home networking
systems
 Embedded Data communication systems are dedicated for data
communication.
 The data communication can happen through a wired interface (like Ethernet,
RS-232C/USB/IEEE1394 etc) or wireless interface (like Wi-Fi, GSM,/GPRS,
Bluetooth, ZigBee etc).
 Network hubs, Routers, switches, Modems etc are typical examples for
dedicated data transmission embedded systems.
3. Data (Signal) Processing:-
  Embedded systems with Signal processing functionalities are employed in
applications demanding signal processing like Speech coding, synthesis,
audio video codec, transmission applications etc.
 Computational intensive systems
 Employs Digital Signal Processors (DSPs)

4. Monitoring:-

 Embedded systems coming under this category are specifically designed for
monitoring purpose.
 They are used for determining the state of some variables using input sensors.
 They cannot impose control over variables.
 Electro Cardiogram (ECG) machine for monitoring the heart beat of a patient
is a typical example for this.
 The sensors used in ECG are the different Electrodes connected to the
patient‟s body.
 Measuring instruments like Digital CRO, Digital Multi meter, Logic Analyzer
etc used in Control & Instrumentation applications are also examples of
embedded systems for monitoring purpose
5. Control:-

 Embedded systems with control functionalities are used for imposing control
over some variables according to the changes in input variables.
 Embedded system with control functionality contains both sensors and
actuators.
 Sensors are connected to the input port for capturing the changes in
environmental variable or measuring variable.
 The actuators connected to the output port are controlled according to the
changes in input variable to put an impact on the controlling variable to bring
the controlled variable to the specified range.
 Air conditioner for controlling room temperature is a typical example for
embedded system with „Control‟ functionality.
 Air conditioner contains a room temperature sensing element (sensor) which
may be a thermistor and a handheld unit for setting up (feeding) the desired
temperature.
 The air compressor unit acts as the actuator. The compressor is controlled
according to the current room temperature and the desired temperature set by
the end user.
 6. Application Specific User Interface:-

 Embedded systems which are designed for a specific application.

 Contains Application Specific User interface (rather than general standard UI )
like key board, Display units etc.
 Aimed at a specific target group of users.
 Mobile handsets, Control units in industrial applications etc are examples

Characteristics of Embedded systems:

Embedded systems possess certain specific characteristics and these are unique to each
embedded system.

1. Application and domain specific

2. Reactive and Real Time
3. Operates in harsh environments
4. Distributed
5. Small Size and weight
6. Power concerns
7. Single-functioned
8. Complex functionality
9. Tightly-constrained
10. Safety-critical
1. Application and Domain Specific:-
 Each E.S has certain functions to perform and they are developed in such a manner
to do the intended functions only.
 They cannot be used for any other purpose.
 Ex – The embedded control units of the microwave oven cannot be replaced with
AC‟S embedded control unit because the embedded control units of microwave
oven and AC are specifically designed to perform certain specific tasks.
2. Reactive and Real Time:-
 Embedded Systems are in constant interaction with the real world through sensors
and user-defined input devices which are connected to the input port of the system.
 Any changes in the real world are captured by the sensors or input devices in real
time and the control algorithm running inside the unit reacts in a designed manner
to bring the controlled output variables to the desired level.
 Embedded Systems produce changes in output in response to the changes in the
input, so they are referred as reactive systems.
 Real Time system operation means the timing behaviour of the system should be
deterministic ie the system should respond to requests in a known amount of time.
 Example – E.S which are mission critical like flight control systems, Antilock
Brake Systems (ABS) etc are Real Time systems.
3. Operates in Harsh Environment :–
 The design of E.S should take care of the operating conditions of the area where
the system is going to implement.
 Ex – If the system needs to be deployed in a high temperature zone, then all the
components used in the system should be of high temperature grade.
 Also proper shock absorption techniques should be provided to systems which are
going to be commissioned in places subject to high shock.
4. Distributed: –
 It means that embedded systems may be a part of a larger system.
 Many numbers of such distributed embedded systems form a single large
embedded control unit.
 Ex – Automatic vending machine. It contains a card reader, a vending unit etc.
Each of them are independent embedded units but they work together to perform
the overall vending function.
5. Small Size and Weight:-
 Product aesthetics (size, weight, shape, style, etc) is an important factor in
choosing a product.
 It is convenient to handle a compact device than a bulky product.
6. Power Concerns:-
 Power management is another important factor that needs to be considered in
designing embedded systems.
 E.S should be designed in such a way as to minimize the heat dissipation by the
system.
7. Single-functioned:- Dedicated to perform a single function.
8. Complex functionality: - We have to run sophisticated algorithms or multiple algorithms
in some applications.
9. Tightly-constrained:- Low cost, low power, small, fast, etc.
10. Safety-critical:- Must not endanger human life and the environment.

Quality Attributes of Embedded System: Quality attributes are the non-functional

requirements that need to be documented properly in any system design.

Quality attributes can be classified as:

A. Operational quality attributes

B. Non-operational quality attributes.
A. Operational Quality Attributes: The operational quality attributes represent the
relevant quality attributes related to the embedded system when it is in the operational
mode or online mode.
Operational Quality Attributes are:
1. Response :-
 It is the measure of quickness of the system.
 It tells how fast the system is tracking the changes in input variables.
 Most of the E.S demands fast response which should be almost real-
time.

Ex – Flight control application.

2. Throughput :-
 It deals with the efficiency of a system.
 It can be defined as the rate of production or operation of a defined
process over a stated period of time.
 The rates can be expressed in terms of products, batches produced or
any other meaningful measurements.
 Ex – In case of card reader throughput means how many transactions
the reader can perform in a minute or in an hour or in a day.
 Throughput is generally measured in terms of “Benchmark”.
 A Benchmark is a reference point by which something can be
measured.
3. Reliability :-
 It is a measure of how much we can rely upon the proper functioning
of the system.
 Mean Time Between Failure (MTBF) and Mean Time To Repair
(MTTR) are the terms used in determining system reliability.
 MTBF gives the frequency of failures in hours/weeks/months.
 MTTR specifies how long the system is allowed to be out of order
following a failure.
 For embedded system with critical application need, it should be of the
order of minutes.
4. Maintainability:-
  It deals with support and maintenance to the end user or client in case
of technical issues and product failure or on the basis of a routine
system check-up.
 Reliability and maintainability are complementary to each other.
 A more reliable system means a system with less corrective
maintainability requirements and vice versa.
 Maintainability can be broadly classified into two categories
1. Scheduled or Periodic maintenance (Preventive maintenance)
2. Corrective maintenance to unexpected failures.

5. Security:-
 Confidentiality, Integrity and availability are the three major measures
of information security.
 Confidentiality deals with protection of data and application from
unauthorized disclosure.
 Integrity deals with the protection of data and application from
unauthorized modification.
 Availability deals with protection of data and application from
unauthorized users.
6. Safety :-
 Safety deals with the possible damages that can happen to the operator,
public and the environment due to the breakdown of an Embedded
System.
 The breakdown of an embedded system may occur due to a hardware
failure or a firmware failure.
 Safety analysis is a must in product engineering to evaluate the
anticipated damages and determine the best course of action to bring
down the consequences of damage to an acceptable level.
B. Non-Operational Quality Attributes: The quality attributes that needs to be
addressed for the product not on the basis of operational aspects are grouped under
this category.
1. Testability and Debug-ability:-
  Testability deals with how easily one can test the design, application
and by which means it can be done.
 For an E.S testability is applicable to both the embedded hardware and
firmware.
 Embedded hardware testing ensures that the peripherals and total
hardware functions in the desired manner, whereas firmware testing
ensures that the firmware is functioning in the expected way.
 Debug-ability is a means of debugging the product from unexpected
behaviour in the system.
 Debug-ability is two level process
1. Hardware level: It is used for finding the issues created by
hardware problems.
2. software level: It is employed for finding the errors created by the
flaws in the software

2. Evolvability :-

 It is a term which is closely related to Biology.

 It is referred as the non-heritable variation.
 For an embedded system evolvability refers to the ease with which the
embedded product can be modified to take advantage of new firmware
or hardware technologies.

3. Portability:-

 It is the measure of system independence.

 An embedded product is said to be portable if the product is capable of
functioning in various environments, target processors and embedded
operating systems.
 „Porting‟ represents the migration of embedded firmware written for
one target processor to a different target processor.

4. Time-to-Prototype and Market:-

 It is the time elapsed between the conceptualization of a product and

the time at which the product is ready for selling.
  The commercial embedded product market is highly competitive and
time to market the product is critical factor in the success of
commercial embedded product.
 There may be multiple players in embedded industry who develop
products of the same category (like mobile phone)

5. per Unit Cost and Revenue:-

 Cost is a factor which is closely monitored by both end user and

product manufacturer.
 Cost is highly sensitive factor for commercial products.
 Any failure to position the cost of a commercial product at a nominal
rate may lead to the failure of the product in the market.
 Proper market study and cost benefit analysis should be carried out
before taking a decision on the per-unit cost of the embedded product.
 The ultimate aim of the product is to generate marginal profit so the
budget and total cost should be properly balanced to provide a marginal
profit.