EMBEDDED SYSTEM DESIGN UNIT I

EMBEDDED SYSTEM
An embedded system is an electronic/electro-mechanical system designed to perform a
specific function and is a combination of both hardware and firmware (software).
Every embedded system is unique, and the hardware as well as the firmware is highly
specialized to the application domain. Embedded systems are becoming an inevitable part of any
product or equipment in all fields including household appliances, telecommunications, medical
equipment, industrial control, consumer products, etc.

EMBEDDED SYSTEMS VS GENERAL COMPUTING SYSTEMS

Criteria General Purpose Computer Embedded System

Contents A system which is a combination of A system which is a combination of

a generic hardware and a General special purpose hardware and embedded
Purpose Operating System for OS/firmware for executing a specific set
executing a variety of applications. of applications

OS It contains a It may or not contain an

general purpose operating operating system for functioning.
system (GPOS).

Alterations Applications are alterable by the Applications are not-alterable by

user. the user.

Key factor Performance is key factor. Application specific requirements are

key factors.

Power More Less

Consumption

Response Time Not critical Critical for some applications

Execution Need not be deterministic Deterministic for certain types of ES

Like ‘Hard Real Time’ systems.

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HISTORY OF EMBEDDED SYSTEMS

Embedded systems were in existence even before the IT revolution. In the olden days,
embedded systems were built around the old vacuum tube and transistor technologies and the
embedded algorithm was developed in low level languages.

Advances in semiconductor and nano-technology and IT revolution gave way to the

development of miniature embedded systems. The first recognized modern embedded system is
the Apollo Guidance Computer (AGC) developed by the MIT Instrumentation Laboratory
for the lunar expedition.

They ran the inertial guidance systems of both the Command Module (CM) and the
Lunar Excursion Module (LEM). The Command Module was designed to encircle the moon
while the Lunar Module and its crew were designed to go down to the moon surface and land
there safely.

The first mass-produced embedded system was the guidance computer for the
Minuteman-I missile in 1961. It was the ‘Autonetics D-17’ guidance computer, built using
discrete transistor logic and a hard-disk for main memory.

The first integrated circuit was produced in September 1958 but computers using them
didn’t begin to appear until 1963. Some of their early uses were in embedded systems, notably
used by NASA for the Apollo Guidance Computer and by the US military in the Minuteman-II
intercontinental ballistic missile.

CLASSIFICATION OF EMBEDDED SYSTEMS

Some of the criteria used in the classification of embedded systems are as follows:

(1) Based on generation

(2) Complexity and performance requirements

(3) Based on deterministic behaviour

(4) Based on triggering.

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1. Classification Based on Generation

This classification is based on the order in which the embedded processing systems evolved from
the first version to where they are today. As per this criterion, embedded systems can be
classified into the following:

1. First Generation: The early embedded systems were built around 8-bit
microprocessors like 8085 and Z80, and 4-bit microcontrollers. Simple in hardware
circuits with firmware developed in Assembly code. Digital telephone keypads, stepper
motor control units etc. are examples of this.
2. Second Generation: These are embedded systems built around 16-bit
microprocessors and 8 or 16-bit microcontrollers, following the first generation
embedded systems. The instruction set for the second generation processors/controllers
were much more complex and powerful than the first generation processors / controllers.
Data Acquisition Systems, SCADA systems, etc. are examples of second generation
embedded systems.
3. Third Generation: With advances in processor technology, embedded system
developers started making use of powerful 32bit processors and 16bit microcontrollers
for their design. A new concept of application and domain specific processors/controllers
like Digital Signal Processors (DSP) and Application Specific Integrated Circuits
(ASICs) came into the picture. The instruction set of processors became more complex
and powerful and the concept of instruction pipelining also evolved. Embedded systems
spread its ground to areas like robotics, media, industrial process control, networking, etc.
4. Fourth Generation: The advent of System on Chips (SoC), reconfigurable
processors and multicore processors are bringing high performance, tight integration and
miniaturisation into the embedded device market. The SoC technique implements a total
system on a chip by integrating different functionalities with a processor core on an
integrated circuit. Smart phone devices, mobile internet devices (MIDs), etc. are
examples of fourth generation embedded systems.
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2. Classification Based on Complexity and Performance

According to this classification, embedded systems can be grouped into the following:

Small-Scale Embedded Systems

Embedded systems which are simple in application needs and where the performance
requirements are not time critical fall under this category. An electronic toy is a typical
example of a small-scale embedded system. Small-scale embedded systems are usually built
around low performance and low cost 8 or 16 bit microprocessors/microcontrollers. A small-
scale embedded system may or may not contain an operating system for its functioning.

Medium-Scale Embedded Systems

Embedded systems which are slightly complex in hardware and firmware (software)
requirements fall under this category. Medium-scale embedded systems are usually built around
medium performance, low cost 16 or 32 bit microprocessors/microcontrollers or digital signal
processors. They usually contain an embedded operating system (either general purpose or real
time operating system) for functioning.

Large-Scale Embedded Systems/Complex Systems

Embedded systems which involve highly complex hardware and firmware requirements fall
under this category. They are employed in mission critical applications demanding high
performance. Such systems are commonly built around high performance 32 or 64 bit RISC
processors/controllers or Reconfigurable System on Chip (RSoC) or multi-core processors and
programmable logic devices. They may contain multiple processors/controllers and co-
units/hardware accelerators for offloading the processing requirements from the main processor
of the system.

3. Based on deterministic behaviour

The classification based on deterministic system behaviour is applicable for ‘Real Time’
systems. The application/task execution behaviour for an embedded system can be deterministic
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or non- deterministic. Based on the execution behaviour, Real Time embedded systems are
classified into Hard and Soft.
4. Based on triggering
Embedded Systems which are ‘Reactive’ in nature (Like process control systems in industrial
control applications) can be classified based on the trigger. Reactive systems can be either event
triggered or time triggered.

MAJOR APPLICATION AREAS OF EMBEDDED SYSTEMS

The application areas and the products in the embedded domain are countless.

1. Consumer electronics: Camcorders, cameras, etc.

2. Household appliances: Television, DVD players, washing machine, fridge, microwave

oven, etc.

3. Home automation and security systems: Air conditioners, sprinklers, intruder detection
alarms, closed circuit television cameras, fire alarms, etc.

4. Automotive industry: Anti-lock breaking systems (ABS), engine control, ignition

systems, automatic navigation systems, etc.

5. Telecom: Cellular telephones, telephone switches, handset multimedia applications, etc.

6. Computer peripherals: Printers, scanners, fax machines, etc.

7. Computer Networking systems: Network routers, switches,

hubs, firewalls, etc.

8. Healthcare: Different kinds of scanners, EEG, ECG machines etc.

9. Measurement & Instrumentation: Digital multi meters, digital CROs, logic analyzers
PLC systems, etc.

10. Banking & Retail: Automatic teller machines (ATM) and currency counters, point of
sales (POS).

11. Card Readers: Barcode, smart card readers, hand held devices, etc.
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PURPOSE OF EMBEDDED SYSTEMS

Each embedded system is designed to serve the purpose of any one or a combination of the
following tasks:

1. Data collection/Storage/Representation

2. Data Communication

3. Data (signal) processing

4. Monitoring

5. Control

6. Application specific user interface

1. Data Collection/Storage/Representation

 Embedded systems designed for the purpose of data collection performs acquisition of
data from the external world.
 Data collection is usually done for storage, analysis, manipulation and transmission.
 Data can be either analog (continuous) or digital (discrete).
 Embedded systems with analog data capturing techniques collect data directly in the
form of analog signal whereas embedded systems with digital data collection mechanism
converts the analog signal to the digital signal using analog to digital (A/D) converters
and then collects the binary equivalent of the analog data.
 If the data is digital, it can be directly captured without any additional interface by digital
embedded systems.
 A digital camera is a typical example of an embedded system with data
collection/storage/representation of data.
 Images are captured and the captured image may be stored within the memory of the
camera. The captured image can also be presented to the user through a graphic LCD
unit.
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2. Data Communication

 Embedded data communication systems are deployed in applications from complex

satellite communication systems to simple home networking systems.
 The transmission is achieved either by a wire-line medium or by a wire-less medium.
 Data can either be transmitted by analog means or by digital means.
 The data collecting embedded terminal itself can incorporate data communication units
like Wireless modules (Bluetooth, ZigBee, Wi-Fi, EDGE, GPRS, etc.) or wire-line
modules (RS-232C, USB, TCP/IP, PS2,etc).
 Network hubs, routers, switches, etc. are typical examples of 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.
 A digital hearing aid is a typical example of an embedded system employing data
processing.
 Digital hearing aid improves the hearing capacity of hearing impaired persons.

4. Monitoring
 Almost all embedded products coming under the medical domain are with monitoring
functions only.
 Electro cardiogram machine (ECG) is intended to do the monitoring of the heartbeat of a
patient but it cannot impose control over the heartbeat.
 Other examples with monitoring function are digital CRO, digital multimeters, and logic
analyzers.

5. Control

 A system with control functionality contains both sensors and actuators.

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 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 the
input variable.
 Air conditioner system used in our home to control the room temperature to a specified
limit is a typical example for ES for CONTROL purpose.

6. Applications specific user interface

 Buttons, switches, keypad, lights, speakers, display units, etc. are application-specific
user interfaces.
 Mobile phone is an example of application specific user interface.
 In mobile phone the user interface is provided through the keypad, graphic LCD module,
system speaker, vibration alert, etc.

CHARACTERISTICS OF AN EMBEDDED SYSTEM

Unlike general purpose computing systems, embedded systems possess certain specific
characteristics and these characteristics are unique to each embedded system. Some of the
important characteristics of an embedded system are as follows:

(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

1. Application and Domain Specific

 An embedded system is designed for a specific purpose only.

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 It will not do any other task.

 Ex. Air conditioners embedded control unit, it cannot replace microwave oven…
 Ex. A washing machine can only wash, it cannot cook.
 Because the embedded control units of microwave oven and air conditioner are
specifically designed to perform certain specific tasks.
 Certain embedded systems are specific to a domain: ex. A hearing aid is an application
that belongs to the domain of signal processing and telecom with another control unit
designed to serve another domain like consumer electronics.

2. Reactive and Real Time

 Certain embedded systems are designed to react to the events that occur in the nearby
environment. These events also occur real-time.
 Ex. Flight control systems, Antilock Brake Systems (ABS), etc. are examples of Real
Time systems
 Ex. An air conditioner adjusts its mechanical parts as soon as it gets a signal from its
sensors to increase or decrease the temperature when the user operates it using a
remote control.
 An embedded system uses Sensors to take inputs and has actuators to bring out the
required functionality.

3. Operation in Harsh Environment

 Certain embedded systems are designed to operate in harsh environments like a dusty
one or a high temperature zone or an area subject to vibrations and shock or very high
temperature of the deserts or very low temperature of the mountains or extreme rains.
 These embedded systems have to be capable of sustaining the environmental
conditions it is designed to operate in.

4. Distributed
 The term distributed means that embedded systems may be a part of a larger system.
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 These components are independent of each other but have to work together for the
larger system to function properly
 Ex. Automatic Teller Machine (ATM) contains a card reader embedded unit,
responsible for reading and validating the user’s ATM card, transaction unit for
performing transactions, a currency counter for dispatching/vending currency to the
authorized person and a printer unit for printing the transaction details.
 This can visualize these as independent embedded systems. But they work together to
achieve a common goal.

5. Small Size and Weight

 An embedded system that is compact in size and has light weight will be desirable or
more popular than one that is bulky and heavy.
 Ex. Currently available cell phones. The cell phones that have the maximum features are
popular but also their size and weight is an important characteristic.

6. Power Concerns
 It is desirable that the power utilization and heat dissipation of any embedded system
be low.
 If more heat is dissipated then additional units like heat sinks or cooling fans need to be
added to the circuit.
 Ex. The production of highamount of heat demands cooling requirements like
cooling fans which in turn occupies additional space and make the system bulky.
Nowadays ultra low power components are available in the market.
 Select the design according to the low power components like low dropout regulators,
and controllers/processors with power saving modes.
 Also power management is a critical constraint in battery operated application.
 The more the power consumption the less is the battery life.
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Quality Attributes of Embedded Systems

 Quality attributes are the non-functional requirements that need to be documented properly
in any system design.

 If the quality attributes are more concrete and measurable, it will give a positive impact
on the system development process and the end product.

 The various quality attributes that needs to be addressed in any embedded system
development are broadly classified into two, namely

1. Operational Quality Attributes

2. Non-Operational Quality Attributes

1. 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. The important quality
attributes coming under this category are listed below:

a. Response

b. Throughput

c. Reliability

d. Maintainability

e. Security

f. safety

a. Response
 Response is a measure of quickness of the system.
 It gives you an idea about how fast your system is tracking the input variables.
 Most of the embedded system demand fast response which should be real-time.
 Ex. An embedded system deployed in flight control application should respond
in a Real Time manner.
 Any response delay in the system will create potential damages to the safety of
the flight as well as the passengers.
 It is not necessary that all embedded systems should be Real Time in response.
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 For example, the response time requirement for an electronic toy is not at all
time-critical.
b. Throughput
 Throughput deals with the efficiency of system.
 It can be defined as rate of production or process of a defined process over a
stated period of time.
 The rates can be expressed in terms of units of products, batches produced, or
any other meaningful measurements.
 In case of card reader like the ones used in buses, throughput means how many
transactions the Reader can perform in a minute or hour or day.
 Throughput is generally measured in terms of ‘Benchmark’. A ‘Benchmark’ is a
reference point by which something can be measured.
 Benchmark can be a set of performance criteria that a product is expected to
meet or a standard product that can be used for comparing other products of
the same product line.
c. Reliability
 Reliability is a measure of how much percentage you rely upon the proper
functioning of the system or what is the % susceptibility of the system to failure.
 Mean Time between Failures (MTBF) and Mean Time To Repair (MTTR)
are the terms used in defining 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 an embedded system with critical application need, it should be of the order
of minutes.
d. Maintainability
 Maintainability deals with support and maintenance to the end user or client in
case of technical issues and product failures or on the basis of a routine system
checkup.
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 Reliability and maintainability are considered as two complementary

disciplines. A more reliable system means a system with less corrective
maintainability requirements and vice versa.
 Maintainability can be classified into two types:
1. Scheduled or Periodic Maintenance (Preventive Maintenance)
 An inkjet printer uses ink cartridges, which are consumable components and as
per the printer manufacturer the end use should replace the cartridge after each
‘n’ number of printouts to get quality prints.
2. Maintenance to Unexpected Failures (Corrective Maintenance)
 If the paper feeding part of the printer fails the printer fails to print and it requires
immediate repairs to rectify this problem.
 Hence it is obvious that maintainability is simply an indication of the
availability of the product for use. In any embedd
embedded
ed system design, the ideal
value for availability is expressed as

Where Ai=Availability in the ideal condition, MTBF=Mean Time between Failures, and
MTTR= Mean Time to Repair

e. Security
 ‘Confidentially’, ‘Integrity’, and ‘Availability’ are three major measures of
information security.
 ‘Confidentially’ deals with the protection of data and application from
unauthorized disclosure
disclosure.
 ‘Integrity’ deals with the protection of data and application from unauthorized
modification.
 ‘Availability’ deals with protection of data and application from unauthorized
users.
 Certain embedded systems have to make sure they conform to the security
measures.
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 Ex. An electronic safety Deposit Locker can be used only with a pin number like
a password.

f. Safety
 Safety deals with the possible damages that can happen to the operators, public
and the environment due to the breakdown of an embedded system or due to the
emission of radioactive or hazardous materials from the embedded products.
 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 the damages to an acceptable level.

2. Non Operational Attributes

 The quality attributes that needs to be addressed for the product ‘not’ on the
basic of operational aspects are grouped under this category. The important
quality attributes coming under this category are listed below:

i. Testability & Debug-ability

ii. Evolvability

iii. Portability

iv. Time to prototype and market

v. Per unit and total cost

i. Testability & Debug-ability

 Testability deals with how easily one can test his/her design, application and by
which means he/she can test it.
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 For an embedded product, testability is applicable to both the embedded

hardware and firmware.
 Debug-ability is a means of debugging the product as such for figuring out the
probable sources that create unexpected behavior in the total system.
 Debug-ability has two aspects in the embedded system development context,
namely, hardware level debugging and firmware level debugging.
 Hardware debugging is used for figuring out the issues created by hardware
problems whereas firmware debugging is employed to figure out the probable
errors that appear as a result of flaws in the firmware.

ii. Evolvability

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

 Evolvability is referred as the non-heritable variation.
 For an embedded system, the quality attribute ‘Evolvability’ refers to the ease
with which the embedded product (including firmware and hardware) can be
modified to take advantage of new firmware or hardware technologies.

iii. Portability

 Portability is a measure of ‘system independence’.

 An embedded product can be called portable if it is capable of functioning in
various environments, target processors/controllers and embedded operating
systems.
 A standard embedded product should always be flexible and portable.

iv. Time-to-Prototype and Market

 Time-to-market is the time elapsed between the conceptualization of a product

and the time at which the product is ready for selling (for commercial product) or
use (for non-commercial products).
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 The commercial embedded product market is highly competitive and time to

market the product is a critical factor in the success of a commercial embedded
product.
 Product prototyping helps a lot in reducing time-to-market

v. Per Unit Cost and Revenue

 Cost is a factor which is closely monitored by both end user (those who buy the
product) and product manufacturer (those who build the product).
 Cost is a highly sensitive factor for commercial products.
 Proper market study and cost benefit analysis should be carried out before taking
decision on the per unit cost of the embedded product.
 When the product is introduced in the market, for the initial period the sales and
revenue will be low.
 There won’t be much competition when the product sales and revenue increase.
 During the maturing phase, the growth will be steady and revenue reaches highest
point and at retirement time there will be a drop in sales volume.

Product life cycle (PLC) curve