EMBEDDED-SYSTEMS DESIGN ENGINEERING.pptx

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
LECTURE NOTES
ON
EMBEDDED SYSTEMS
IV B. Tech I semester (R19)
Faculty Members
Gandhi Lakavath
Asst.Professor
EEE Dept

NEC EEE ES SYLLABUS
MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY
IV Year B.Tech. ECE-I Sem
CORE ELECTIVE – III
EMBEDDED SYSTEMS
DESIGN (R15A0424)
COURSE OBJECTIVES:
For embedded systems, the course will enable the students to:
1. Understand the basics of an embedded system.
2. Understand the typical components of an embedded system.
3. To understand different communication interfaces.
4. To learn the design process of embedded system
applications.
5. To understands the RTOS and inter-process communication.
UNIT-I INTRODUCTION TO EMBEDDED SYSTEMS
History of embedded systems, Classification of embedded systems based on generation and
complexity, Purpose of embedded systems, The embedded system design process-requirements,
specification, architecture design, designing hardware and software, components, system
integration, Applications of embedded systems, and characteristics of embedded systems.
UNIT-II TYPICAL EMBEDDED SYSTEM
Core of the embedded system-general purpose and domain specific processors, ASICs, PLDs,
COTs; Memory-ROM, RAM, memory according to the type of interface, memory shadowing,
memory selection for embedded systems, Sensors, actuators, I/O components: seven segment
LED, relay, piezo buzzer, push button switch, other sub-systems: reset circuit, brownout protection
circuit, oscillator circuit real time clock, watch dog timer.
UNIT-III COMMUNICATION INTERFACE
Onboard communication interfaces-I2C, SPI, CAN, parallel interface;
External communication interfaces-RS232 and RS485, USB, infrared, Bluetooth, Wi-Fi,
ZigBee, GPRS, GSM.
EEE Dept

NEC EEE ES SYLLABUS
UNIT-IV EMBEDDED FIRMWARE DESIGN AND DEVELOPMENT
Embedded firmware design approaches-super loop based approach, operating system based
approach; embedded firmware development languages-assembly language based development,
high level language based development.
UNIT-V RTOS BASED EMBEDDED SYSTEM DESIGN
Operating system basics, types of operating systems, tasks, process and threads, multiprocessing
and multitasking, task scheduling: non-pre-emptive and pre-emptive scheduling; task
communication-shared memory, message passing, Remote Procedure Call and Sockets, Task
Synchronization: Task Communication/ Synchronization Issues, Task Synchronization
Techniques
TEXT BOOKS:
1. Introduction to Embedded Systems - shibu k v, Mc Graw Hill Education.
2. Computers as Components –Wayne Wolf, Morgan Kaufmann (second edition).
REFERENCE BOOKS:
1. Embedded System Design -frank vahid, tony grivargis, john Wiley.
2. Embedded Systems- An integrated approach - Lyla b das, Pearson education 2012.
3. Embedded Systems – Raj Kamal, TMH
COURSE OUTCOMES:
Upon completion of this course, the students will be able to:
1. Understand the design process of an embedded system
2. Understand typical embedded System & its components
3. Understand embedded firmware design approaches
4. Learn the basics of OS and RTOS
EEE Dept

ESD UNIT-1 NOTES
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1. Introduction to Embedded Systems
What is Embedded System? (DEC2016, March-2017.)
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 behavior

With specialized hardware and software
Embedded Systems Vs General Computing Systems:
(March-2017)
General Purpose Computing System Embedded System
A system which is a combination of generic
hardware and General Purpose Operating System
for executing a variety of applications
A system which is a combination of special
purpose hardware and embedded OS for
executing a specific set of applications
Contain a General Purpose Operating System
(GPOS)
May or may not contain an operating system
for functioning
Applications are alterable (programmable) by
user (It is possible for the end user to re-install the
Operating System, and add or remove user
applications)
The firmware of the embedded system is
pre-programmed and it is non-alterable by
end-user
Performance is the key deciding factor on the
selection of the system. Always „Faster is Better‟
Application specific requirements
(like
performance, power requirements, memory
usage etc) are the key deciding factors
Less/not at all tailored towards reduced operating
power requirements, options for different levels
of power management.
Highly tailored to take advantage of the
power saving modes supported by hardware
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 behavior
Execution behavior is deterministic
for
certain type of embedded systems like „Hard
Real Time‟ systems
Gandhi Lakavath, EEE Page 2

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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 (March-2017)
Based on Complexity & Performance Requirements
Based on deterministic behavior
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.

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Fourth Generation: Embedded Systems built around System on Chips (SoC’s), Re-
configurable 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, prioritizationand management.
3.Embedded Systems - Classification Based on deterministic behavior: 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.

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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: (DEC2016)
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

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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)

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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.

Fig: Major levels of abstraction in the design process
Requirements:
Clearly, before we design a system, we must know what we are designing. The initial stages of the
design process capture this information for use in creating the architecture and components. We
generally proceed in two phases: First, we gather an informal description from the customers
known as requirements, and we refine the requirements into a specification that contains enough
information to begin designing the system architecture.
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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
EMBEDDED SYSTEM DESIGN PROCESS:
This section provides an overview of the embedded system design process aimed at two objectives.
First, it will give us an introduction to the various steps in embedded system design before we
delve into them in more detail. Second, it will allow us to consider the design methodology itself.
A design methodology is important for three reasons. First, it allows us to keep a scorecard on a
design to ensure that we have done everything we need to do, such as optimizing performance or
performing functional tests. Second, it allows us to develop computer-aided design tools.
Developing a single program that takes in a concept for an embedded system and emits a
completed design would be a daunting task, but by first breaking the process into manageable
steps, we can work on automating (or at least semi automating) the steps one at a time. Third, a
design methodology makes it much easier for members of a design team to communicate.
The below Figure summarizes the major steps in the embedded system design process. In this top–down
view, we start with the system requirements.

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Requirements may be functional or nonfunctional. We must of course capture the basic functions
of the embedded system, but functional description is often not sufficient. Typical nonfunctional
requirements include:
■Performance: The speed of the system is often a major consideration both for the usability
of the system and for its ultimate cost. As we have noted, performance may be a combination of
soft performance metrics such as approximate time to perform a user-level function and hard
deadlines by which a particular operation must be completed.
■Cost: The target cost or purchase price for the system is almost always a consideration. Cost
typically has two major components: manufacturing cost includes the cost of components and
assembly; nonrecurring engineering (NRE) costs include the personnel and other costs of
designing the system.
■Physical size and weight: The physical aspects of the final system can vary greatly
depending upon the application. An industrial control system for an assembly line may be
designed to fit into a standard-size rack with no strict limitations on weight. A handheld device
typically has tight requirements on both size and weight that can ripple through the entire system
design.
■Power consumption: Power, of course, is important in battery-powered systems and is
often important in other applications as well. Power can be specified in the requirements stage in
terms of battery life—the customer is unlikely to be able to describe the allowable wattage.
A sample requirements form that can be filled out at the start of the project. We can use the form
as a checklist in considering the basic characteristics of the system. Let’s consider the entries in
the form:
■Name: This is simple but helpful. Giving a name to the project not only simplifies talking
about it to other people but can also crystallize the purpose of the machine.
■Purpose: This should be a brief one- or two-line description of what the system is supposed
to do. If you can’t describe the essence of your system in one or two lines, chances are that you
don’t
understand it well enough.
■Inputs and outputs: These two entries are more complex than they seem. The inputs and
outputs to the system encompass a wealth of detail:
— Types of data: Analog electronic signals? Digital data? Mechanical inputs?
—Data characteristics: Periodically arriving data, such as digital
audio samples? Occasional user inputs? How many bits per data
element?
— Types of I/O devices: Buttons? Analog/digital converters? Video
displays?
■Functions: This is a more detailed description of what the system does. A good way to
approach this is to work from the inputs to the outputs: When the system receives an input, what
does it do? How do user interface inputs affect these functions? How do different functions
interact? Performance: Many embedded computing systems spend at least some time controlling
physical devices or processing data coming from the physical world. In most of these
cases, the computations must be performed within a certain time frame. It is essential that the
performance requirements be identified early
since they must be carefully measured during implementation to ensure that the system works
properly.
■ Manufacturing cost: This includes primarily the cost of the hardware components. Even if you
don’t know exactly how much you can afford to spend on system components, you should have
some idea of the eventual cost range. Cost has a substantial influence on architecture: A machine
that is meant to
sell at $10 most likely has a very different internal structure than a $100 system.
■Power: Similarly, you may have only a rough idea of how much power the system can
consume, but a little information can go a long way. Typically, the most important decision is

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whether the machine will be battery powered or plugged into the wall. Battery-powered machines
must be much more careful about how they spend energy.
■Physical size and weight: You should give some indication of the physical size of the
system to help guide certain architectural decisions. A desktop machine has much more flexibility
in the components used than, for example, a lapel mounted voice recorder.
GPS MODULE:
REQUIREMENTS FORM OF GPS MOVING MAP MODULE:
Name : GPS moving map
Purpose: Consumer-grade moving map for driving use
Inputs : Power button, two control buttons
Outputs : Back-lit LCD display 400 _ 600
Functions : Uses 5-receiver GPS system; three user-selectable resolutions;
always displays current latitude and longitude
Performance: Updates screen within 0.25 seconds upon movement
Manufacturing cost:$30
Power: 100mW
Physical size and weight: No more than 2” _ 6, ” 12 ounces
Specification
The specification is more precise—it serves as the contract between the customer and thearchitects.
As such, the specification must be carefully written so that it accurately reflects the customer’s
requirements and does so in a way that can be clearly followed during design.
The specification should be understandable enough so that someone can verify that it meets
system requirements and overall expectations of the customer.
A specification of the GPS system would include several components:
 Data received from the GPS satellite constellation.
 Map data.
 User interface.
 Operations that must be performed to satisfy customer requests.
 Background actions required to keep the system running, such as operating the GPS
receiver.

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Architecture Design
The specification does not say how the system does things, only what the system does. Describing
how the system implements those functions is the purpose of the architecture. The architecture is
a plan for the overall structure of the system that will be used later to design the components that
make up the architecture. The creation of the architecture is the first phase of what many designers
think of as design.
This block diagram is still quite abstract—we have not yet specified which operations will be
performed by software running on a CPU, what will be done by special-purpose hardware, and so
on. The diagram does, however, go a long way toward describing how to implement the functions
described in the specification. We clearly see, for example, that we need to search the topographic
database and to render (i.e., draw) the results for the display. We have chosen to separate those
functions so that we can potentially do them in parallel—performing rendering separately from
searching the database may help us update the screen more fluidly.
FIG: BLOCK DIAGRAM FOR THE MOVING MAP
The hardware block diagram clearly shows that we have one central CPU surrounded by memory
and I/O devices. In particular, we have chosen to use two memories: a frame buffer for the pixels
to be displayed and a separate program/data memory for general use by the CPU. The software
block diagram fairly closely follows the system block diagram, but we have added a timer to
control when we read the buttons on the user interface and render data onto the screen. To have a
truly complete architectural description, we require more detail, such as where units in the software
block diagram will be executed in the hardware block diagram and when operationswill be
performed in time.

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Fig : Hardware and software architectures for the moving map.
The architectural description tells us what components we need. The component design effort
builds those components in conformance to the architecture and specification. The components
will in general include both hardware—FPGAs, boards, and so on—and software modules. Some
of the components will be ready-made. The CPU, for example, will be a standard component in
almost all cases, as will memory chips and many other components .In the moving map, the GPS
receiver is a good example of a specialized component that will nonetheless be a predesigned,
standard component. We can also make use of standard software modules.
System Integration:
Only after the components are built do we have the satisfaction of putting them together and
seeing a working system. Of course, this phase usually consists of a lot more than just plugging
everything together and standing back. Bugs are typically found during system integration, and
good planning can help us find the bugs quickly. By building up the system in phases and
running properly chosen tests, we can often find bugs more easily. If we debug only a few
modules at a time, we are more likely to uncover the simple bugs and able to easily recognize
them. Only by fixing the simple bugs early will we be able to uncover the more complex or
obscure bugs that can be identified only by giving the system a hard workout

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Characteristics of Embedded systems: (DEC2016, March-2017)
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
11. 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.

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T,VINAYSIMHA REDDY, Dept. of ECE, MRCET
2. Reactive and Real Time:-
• E.S 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.
• E.S 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 behavior 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.

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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.(DEC16,March-2017)
Quality attributes can be classified as
I. Operational quality attributes
II. Non-operational quality attributes.
III.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.

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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 checkup.
• 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

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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 afirmware
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.
II. 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.
6. 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 behavior in the
system
• Debug-ability is two level process
• 1.Hardware level 2.software level
• 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.

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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.

ESD UNIT-1 NOTES
SUMMARY
1. An embedded system is an electronic/electromechanical system designed to perform a
specific function and is a combination of both hardware and firmware (software).
2. A general purpose computing system is a combination of generic hardware and general
purpose operating system for executing a variety of applications, whereas an embedded
3. System is a combination of special purpose hardware and embedded OS/firmware for
executing a specific set of applications.
4. Apollo Guidance Computer (AGC) is the first recognized modern embedded system and
Autonetics D-17, the guidance computer for the Minuteman-I missile, was the first mass
produced embedded system.
5. Based on the complexity and performance requirements, embedded systems are classified
into small-scale, medium-scale and large-scale/complex.
6. The presences of embedded system vary from simple electronic system toys to complex
flight and missile control systems.
7. Embedded systems are designed to serve the purpose of any one or combination of data
collection/storage/representation, data processing, monitoring, control or application
specific user interface.
8. Wearable devices refer to embedded systems which are incorporated into accessories and
apparels. It envisions the bonding of embedded technology in our day to day lives.
OBJECTIVE QUESTIONS
(b) Special Purpose
1. Embedded systems are
(a) General Purpose
2. Embedded system is
(a) An electronic
system
(b) A pure mechanical system
(c)An electro-mechanical system (d) (a) or (c)
3. Which of the following is not true about embedded systems?
(a)Built around specialized hardware (b) Always contain an operating
system (c)Execution behavior may be deterministic (d) All of these (e) none of these
4. Which of the following is not an example of small scale embedded system?
(a) Electronic Barbie doll
(c) Cell Phone
(b) Simple calculator
(d) Electronic toy car

ESD UNIT-1 NOTES
5. The first recognized modern embedded system is
(a) Apple computer
(c) Calculator
(b) Apollo Guidance Computer
(d) Radio navigation system
6. The first mass produced embedded system is
(a) Minuteman-I
(c) Autonetics D17
(b) Minuteman-II
(d) Apollo Guidance Computer
7. Which of the following is (are) an intended purpose of embedded systems?
(a) Data collection
(c) Data communication
(b) Data processing
(d) All of these (e) None of these
8. Which of the following is an example of an embedded system for data communication?
9
10. Which of the following is an example of an embedded system for signal processing?
(a) Apple iPOD
(c) both a and b
(b) Sandisk USB mass storage device
(d) None of these
Reference Text Books:-
1. Introduction to Embedded Systems – Shibu K.V Mc Graw Hill
2. Computers as Components –Wayne Wolf-morgan Kaufmann publications
(a) USB mass storage device (b) Network router (c) Digital camera
(d)Music player (e) All of these (f) None of these
. A digital multimeter is an example of embedded system for
(a) Data communication (b) Monitoring (c) Control
(d) All of these (e) None of these

IV ECE
EMBEDDED SYSTEM DESIGN
UNIT-II
TYPICAL EMBEDDED
SYSTEM
N.SURESH
Department of ECE

NEC EEE ES UNIT-2 Notes
ELEMENTS OF EMBEDDED SYSTEMS:
An embedded system is a combination of 3 things, Hardware Software Mechanical
Components and it is supposed to do one specific task only. A typical embedded system contains
a single chip controller which acts as the master brain of the system. Diagrammatically an
embedded system can be represented as follows:
FPGA/ASIC/DSP/SoC
Microprocessor/controller
Embedded
Firmware
Memory
Communication Interface
System
I/p Ports Core O/p Ports
(Sensors) (Actuators)
Other supporting
Integrated Circuits &
subsystems
Embedded System
Real World
Embedded systems are basically designed to regulate a physical variable (such Microwave
Oven) or to manipulate the state of some devices by sending some signals to the actuators or
devices connected to the output port system (such as temperature in Air Conditioner), in
response to the input signal provided by the end users or sensors which are connected to the
input ports. Hence the embedded systems can be viewed as a reactive system.

The control is achieved by processing the information coming from the sensors and user
interfaces and controlling some actuators that regulate the physical variable.
Keyboards, push button, switches, etc. are Examples of common user interface input devices
and LEDs, LCDs, Piezoelectric buzzers, etc examples for common user interface output
devices for a typical embedded system.The requirement of type of user interface changes from
application to application based on domain.
Some embedded systems do not require any manual intervention for their operation. They
automatically sense the input parameters from real world through sensors which are connected
at input port. The sensor information is passed to the processor after signal conditioning and
digitization. The core of the system performs some predefined operationson input data with
the help of embedded firmware in the system and sends some actuating signals to the actuator
connect connected to the output port of the system.
The memory of the system is responsible for holding the code (control algorithm and
other important configuration details). There are two types of memories are used in any
embedded system. Fixed memory (ROM) is used for storing code or program. The user
cannot change the firmware in this type of memory. The most common types of memories
used in embedded systems for control
algorithm storage are OTP,PROM,UVEPROM,EEPROM and FLASH
An embedded system without code (i.e. the control algorithm) implemented memory has all
the peripherals but is not capable of making decisions depending on the situational as wellas
real world changes.
Memory for implementing the code may be present on the processor or may be
implemented as a separate chip interfacing the processor
In a controller based embedded system, the controller may contain internal memory for
storing code such controllers are called Micro-controllers with on-chip ROM, eg. Atmel
AT89C51.

The Core of the Embedded Systems: The core of the embedded system falls into any one
of the following categories.

General Purpose and Domain Specific Processors
o Microprocessors
o Microcontrollers
o Digital Signal Processors

Programmable Logic Devices (PLDs)

Application Specific Integrated Circuits (ASICs)

Commercial off the shelf Components (COTS)
GENERAL PURPOSE AND DOMAIN SPECIFIC PROCESSOR:
Almost 80% of the embedded systems are processor/ controller based.
The processor may be microprocessor or a microcontroller or digital signal processor,
depending on the domain and application.
Microprocessor:
A silicon chip representing a Central Processing Unit (CPU), which is capable of
performing arithmetic as well as logical operations according to a pre-defined set of
Instructions, which is specific to the manufacturer
In general the CPU contains the Arithmetic and Logic Unit (ALU), Control Unit and
Working registers
Microprocessor is a dependant unit and it requires the combination of other hardware like
Memory, Timer Unit, and Interrupt Controller etc for proper functioning.
Intel claims the credit for developing the first Microprocessor unit Intel 4004, a 4 bit
processor which was released in Nov 1971
· Developers of microprocessors.
Intel – Intel 4004 – November 1971(4-bit)
Intel – Intel 4040.
Intel – Intel 8008 – April 1972.
Intel – Intel 8080 – April 1974(8-bit).
Motorola – Motorola 6800.
Intel – Intel 8085 – 1976.
Zilog - Z80 – July 1976

Microcontroller:

A highly integrated silicon chip containing a CPU, scratch pad RAM, Special and General
purpose Register Arrays, On Chip ROM/FLASH memory for program storage, Timer and
Interrupt control units and dedicated I/O ports
 Microcontrollers can be considered as a super set of Microprocessors
 Microcontroller can be general purpose (like Intel 8051, designed for generic applications
and domains) or application specific (Like Automotive AVR from Atmel Corporation.
Designed specifically for automotive applications)

Since a microcontroller contains all the necessary functional blocks for independent
working,
they found greater place in the embedded domain in place of microprocessors
 Microcontrollers are cheap, cost effective and are readily available in the market

Texas Instruments TMS 1000 is considered as the world s
‟ first microcontroller
Microprocessor Vs Microcontroller:
Microprocessor Microcontroller
A microcontroller is a highly integrated chip that
contains a CPU, scratch pad RAM, Special and
A silicon chip representing a Central Processing Unit
(CPU), which is capable of performing arithmetic as
well as logical operations according to a pre-defined set General purpose Register Arrays, On Chip
of Instructions ROM/FLASH memory for program storage, Timer
and Interrupt control units and dedicated I/O ports
It is a dependent unit. It requires the combination of
other chips like Timers, Program and data memory
chips, Interrupt controllers etc for functioning
It is a self contained unit and it doesn’t require
external Interrupt Controller, Timer, UART etc for
its functioning
Most of the time general purpose in design and Mostly application oriented or domain specific
operation
Doesn t
‟ contain a built in I/O port. The I/O Port
functionality needs to be implemented with the help of
external Programmable Peripheral Interface Chips like
Most of the processors contain multiple built-in I/O
ports which can be operated as a single 8 or 16 or 32
bit Port or as individual port pins
8255
Targeted for high end market where performance is
important
Targeted for embedded market where performance is
not so critical (At present this demarcation is invalid)
Includes lot of power saving features
Limited power saving options compared to
microcontrollers

General Purpose Processor (GPP) Vs Application Specific Instruction Set Processor (ASIP)

General Purpose Processor or GPP is a processor designed for general computational tasks
 GPPs are produced in large volumes and targeting the general market. Due to the high
volume production, the per unit cost for a chip is low compared to ASIC or other specific
ICs

A typical general purpose processor contains an Arithmetic and Logic Unit (ALU) and
Control Unit (CU)
 Application Specific Instruction Set processors (ASIPs) are processors with architecture
and instruction set optimized to specific domain/application requirements like Network
processing, Automotive, Telecom, media applications, digital signal processing, control
applications etc.

ASIPs fill the architectural spectrum between General Purpose Processors and
Application Specific Integrated Circuits (ASICs)

The need for an ASIP arises when the traditional general purpose processor are unable to meet
the increasing application needs
 Some Microcontrollers (like Automotive AVR, USB AVR from Atmel), System on Chips,
Digital Signal Processors etc are examples of Application Specific Instruction Set
Processors (ASIPs)

ASIPs incorporate a processor and on-chip peripherals, demanded by the application
requirement, program and data memory
Digital Signal Processors (DSPs):
Powerful special purpose 8/16/32 bit microprocessors designed specifically to meet the
computational demands and power constraints of today's embedded audio, video, and
communications applications
Digital Signal Processors are 2 to 3 times faster than the general purpose microprocessors
in signal processing applications
DSPs implement algorithms in hardware which speeds up the execution whereas general
purpose processors implement the algorithm in firmware and the speed of execution
depends primarily on the clock for the processors
DSP can be viewed as a microchip designed for performing high speed computational
operations for „addition ,
‟ „subtraction ,
‟ „multiplication‟ and „division‟

A typical Digital Signal Processor incorporates the following key units

Program Memory

Data Memory

Computational Engine

I/O Unit
Audio video signal processing, telecommunication and multimedia applications are
typical examples where DSP is employed
RISC V/s CISC Processors/Controllers:
RISC CISC
Lesser no. of instructions Greater no. of Instructions
Instruction Pipelining and increased execution Generally no instruction pipelining feature
speed
Orthogonal Instruction Set (Allows each instruction Non Orthogonal Instruction Set (All instructions
to operate on any register and use any addressing are not allowed to operate on any register and
mode) use any addressing mode. It is instruction
specific)
Operations are performed on registers only, the Operations are performed on registers or
only memory operations are load and store memory depending on the instruction
Large number of registers are available Limited no. of general purpose registers
Programmer needs to write more code to execute a . A programmer can achieve the desired
task since the instructions are simpler ones functionality with a single instruction which in
turn provides the effect of using more simpler
single instructions in RISC
Single, Fixed length Instructions Variable length Instructions
Less Silicon usage and pin count More silicon usage since more additional
decoder logic is required to implement the
complex instruction decoding.
With Harvard Architecture Can be Harvard or Von-Neumann Architecture

Microprocessors/controllers based on the Harvard architecture will have separate data bus
and instruction bus. This allows the data transfer and program fetching to occur
simultaneously on both buses
With Harvard architecture, the data memory can be read and written while the program
memory is being accessed. These separated data memory and code memory buses allow
one instruction to execute while the next instruction is fetched (“Pre-fetching”)
Single shared Bus
Harvard V/s Von-Neumann Processor/Controller Architecture:
Harvard V/s Von-Neumann Processor/Controller Architecture
The terms Harvard and Von-Neumann refers to the processor architecture design.
Microprocessors/controllers based on the
common bus for fetching both instructions
stored in a common main memory
Von-Neumann architecture shares a single
and data. Program instructions and data are
I/O CPU Memory
Program
CPU Data Memory
Memory
Harvard Architecture Von-Neumann Architecture
Separate buses for Instruction and Data fetching Single shared bus for Instruction and Data
fetching
Easier to Pipeline, so high performance can be Low performance Compared to Harvard
achieved Architecture
Comparatively high cost Cheaper
No memory alignment problems Allows self modifying codes†
Since data memory and program memory are Since data memory and program memory
stored physically in different locations, no are stored physically in same chip, chances
chances for accidental corruption of program for accidental corruption of program
memory memory

Big-endian V/s Little-endian processors:
 Endianness specifies the order in which the data is stored in the memory by processor
operations in a multi byte system (Processors whose word size is greater than one byte).
Suppose the word length is two byte then data can be stored in memory in two different
ways
Higher order of data byte at the higher memory and lower order of data byte at
location just below the higher memory
Lower order of data byte at the higher memory and higher order of data byte
at location just below the higher memory

Little-endian means the lower-order byte of the data is stored in memory at the
lowest address, and the higher-order byte at the highest address. (The little end comes
first)

Big-endian means the higher-order byte of the data is stored in memory at the lowest
address, and the lower-order byte at the highest address. (The big end comes first.)

Load Store Operation & Instruction Pipelining:
The RISC processor instruction set is orthogonal and it operates on registers. The memory access
related operations are performed by the special instructions load and store. If the operand is
specified as memory location, the content of it is loaded to a register using the load instruction.
The instruction store stores data from a specified register to a specified memory location
Instruction Pipelining
The conventional instruction execution by the processor follows the fetch-decode-
execute sequence
The „fetch‟ part fetches the instruction from program memory or code memory and the
decode part decodes the instruction to generate the necessary control signals
The execute stage reads the operands, perform ALU operations and stores the result.
In conventional program execution, the fetch and decode operations are performed
in sequence

During the decode operation the memory address bus is available and if it possible to
effectively utilize it for an instruction fetch, the processing speed can be increased
In its simplest form instruction pipelining refers to the overlapped execution of
instructions
Application Specific Integrated Circuit (ASIC):
A microchip designed to perform a specific or unique application. It is used as replacement
to conventional general purpose logic chips.
ASIC integrates several functions into a single chip and thereby reduces the system
development cost
Most of the ASICs are proprietary products. As a single chip, ASIC consumes very small
area in the total system and thereby helps in the design of smaller systems with high
capabilities/functionalities.
ASICs can be pre-fabricated for a special application or it can be custom fabricated by
using the components from a re-usable „building block‟ library of components for a
particular customer application
Fabrication of ASICs requires a non-refundable initial investment (Non Recurring
Engineering (NRE) charges) for the process technology and configuration expenses
If the Non-Recurring Engineering Charges (NRE) is born by a third party and the
Application Specific Integrated Circuit (ASIC) is made openly available in the market,the
ASIC is referred as Application Specific Standard Product (ASSP)
The ASSP is marketed to multiple customers just as a general-purpose product , but to a
smaller number of customers since it is for a specific application.

Some ASICs are proprietary products , the developers are not interested in revealing the
internal details.
Programmable Logic Devices (PLDs):
 Logic devices provide specific functions, including device-to-device interfacing, data
communication, signal processing, data display, timing and control operations, and almost
every other function a system must perform.
 Logic devices can be classified into two broad categories - Fixed and Programmable. The
circuits in a fixed logic device are permanent, they perform one function or set of functions
- once manufactured, they cannot be changed

Programmable logic devices (PLDs) offer customers a wide range of logic capacity,
features, speed, and voltage characteristics - and these devices can be re-configured to
perform any number of functions at any time
 Designers can use inexpensive software tools to quickly develop, simulate, and test their
logic designs in PLD based design. The design can be quickly programmed into a device,
and immediately tested in a live circuit

PLDs are based on re-writable memory technology and the device is reprogrammed to
change the design
Programmable Logic Devices (PLDs) – CPLDs and FPGA
Field Programmable Gate Arrays (FPGAs) and Complex Programmable Logic Devices
(CPLDs) are the two major types of programmable logic devices
FPGA:
FPGA is an IC designed to be configured by a designer after manufacturing.
FPGAs offer the highest amount of logic density, the most features, and the highest
performance.
Logic gate is Medium to high density ranging from 1K to 500K system gates

These advanced FPGA devices also offer features such as built-in hardwired processors
(such as the IBM Power PC), substantial amounts of memory, clock management systems,
and support for many of the latest, very fast device-to-device signaling technologies
Figure: FPGA Architecture
These advanced FPGA devices also offer features such as built-in hardwired processors,
substantial amounts of memory, clock management systems, and support for many of the
latest, very fast device-to-device signaling technologies.
FPGAs are used in a wide variety of applications ranging from data processing and
storage, to instrumentation, telecommunications, and digital signal processing
CPLD:

A complex programmable logic device (CPLD) is a programmable logic device with
complexity between that of PALs and FPGAs, and architectural features of both.
CPLDs, by contrast, offer much smaller amounts of logic - up to about 10,000 gates.
CPLDs offer very predictable timing characteristics and are therefore ideal for critical
control applications.

MRCET ECE ES UNIT-2 Notes
CPLDs such as the Xilinx CoolRunner series also require extremely low amounts of
power and are very inexpensive, making them ideal for cost-sensitive, battery-operated,
portable applications such as mobile phones and digital handheld assistants.
ADVANTAGES OF PLDs:
• PLDs offer customer much more flexibility during design cycle
• PLDSs do not require long lead times for prototype or production-the PLDs are already
on a distributor s
‟ self and ready for shipment
• PLDs do not require customers to pay for large NRE costs and purchase expensive mask
sets
• PLDs allow customers to order just the number of parts required when they need them.
allowing them to control inventory.
• PLDs are reprogrammable even after a piece of equipment is shipped to a customer.
• The manufacturers able to add new features or upgrade the PLD based products that are
in the field by uploading new programming file
Commercial off the Shelf Component (COTS):
A Commercial off-the-shelf (COTS) product is one which is used „as-is‟
COTS products are designed in such a way to provide easy integration and
interoperability with existing system components

Typical examples for the COTS hardware unit are Remote Controlled Toy Car control unit
including the RF Circuitry part, High performance, high frequency microwave electronics
(2 to 200 GHz), High bandwidth analog-to-digital converters, Devices and components for
operation at very high temperatures, Electro-optic IR imaging arrays, UV/IR Detectors etc
A COTS component in turn contains a General Purpose Processor (GPP) or Application
Specific Instruction Set Processor (ASIP) or Application Specific Integrated Chip
(ASIC)/Application Specific Standard Product (ASSP) or Programmable Logic Device
(PLD)
The major advantage of using COTS is that they are readily available in the market,
cheap and a developer can cut down his/her development time to a great extend.
There is no need to design the module yourself and write the firmware .
Everything will be readily supplied by the COTs manufacturer.

The major problem faced by the end-user is that there are no operational and
manufacturing standards.
The major drawback of using COTs component in embedded design is that the
manufacturer may withdraw the product or discontinue the production of the COTs at any
time if rapid change in technology
This problem adversely affect a commercial manufacturer of the embedded system which
makes use of the specific COTs
Memory:
Memory is an important part of an embedded system. The memory used in embedded
system can be either Program Storage Memory (ROM) or Data memory (RAM)
Certain Embedded processors/controllers contain built in program memory and data
memory and this memory is known as on-chip memory
Certain Embedded processors/controllers do not contain sufficient memory inside the
chip and requires external memory called off-chip memory or external memory.
Memory – Program Storage Memory:
 Stores the program instructions

Retains its contents even after the power to it is turned off. It is generally known as
Non volatile storage memory

Depending on the fabrication, erasing and programming techniques they are classified
into

FLASH Code Memory
(ROM)
NVRAM
PROM Masked ROM
(OTP) (MROM) EPROM EEPROM
1. Masked ROM (MROM):
One-time programmable memory.
Uses hardwired technology for storing data.
The device is factory programmed by masking and metallization process according to
the data provided by the end user.
The primary advantage of MROM is low cost for high volume
production. MROM is the least expensive type of solid state memory.
Different mechanisms are used for the masking process of the ROM, like
 Creation of an enhancement or depletion mode transistor through
channel implant

By creating the memory cell either using a standard transistor or a high
threshold transistor.

In the high threshold mode, the supply voltage required to turn ON the transistor
is above the normal ROM IC operating voltage.

This ensures that the transistor is always off and the memory cell stores always
logic 0.
The limitation with MROM based firmware storage is the inability to modify the
device firmware against firmware upgrades.
The MROM is permanent in bit storage, it is not possible to alter the bit
information

2. Programmable Read Only Memory (PROM) / (OTP) :
It is not pre-programmed by the manufacturer
The end user is responsible for Programming these devices.
PROM/OTP has nichrome or polysilicon wires arranged in a matrix, these wires can be
functionally viewed as fuses.
It is programmed by a PROM programmer which selectively burns the fuses according to
the bit pattern to be stored.
Fuses which are not blown/burned represents a logic “1” where as fuses which are
blown/burned represents a logic “0”.The default state is logic “1”.
OTP is widely used for commercial production of embedded systems whose proto-typed
versions are proven and the code is finalized.
It is a low cost solution for commercial production.
OTPs cannot be reprogrammed.
3. Erasable Programmable Read Only Memory
(EPROM):
Erasable Programmable Read Only (EPROM) memory gives the flexibility to re-program
the same chip.
During development phase , code is subject to continuous changes and using an OTP is not
economical.
EPROM stores the bit information by charging the floating gate of an FET
Bit information is stored by using an EPROM Programmer, which applies high voltage to
charge the floating gate
EPROM contains a quartz crystal window for erasing the stored information. If the
window is exposed to Ultra violet rays for a fixed duration, the entire memory will be
erased
Even though the EPROM chip is flexible in terms of re-programmability, it needs to be
taken out of the circuit board and needs to be put in a UV eraser device for 20 to 30
minutes

4. Electrically Erasable Programmable Read Only Memory (EEPROM):
Erasable Programmable Read Only (EPROM) memory gives the flexibility to re-program
the same chip using electrical signals
The information contained in the EEPROM memory can be altered by using electrical
signals at the register/Byte level
They can be erased and reprogrammed within the circuit
These chips include a chip erase mode and in this mode they can be erased in a few
milliseconds
It provides greater flexibility for system design
The only limitation is their capacity is limited when compared with the standard ROM (A
few kilobytes).
5. Program Storage Memory – FLASH
FLASH memory is a variation of EEPROM technology.
FALSH is the latest ROM technology and is the most popular ROM technology used in
today s
‟ embedded designs
It combines the re-programmability of EEPROM and the high capacity of standard
ROMs
FLASH memory is organized as sectors (blocks) or pages
FLASH memory stores information in an array of floating gate MOSFET
transistors
The erasing of memory can be done at sector level or page level without affecting the
other sectors or pages
Each sector/page should be erased before re-programming
The typical erasable capacity of FLASH is of the order of a few 1000 cycles.
Read-Write Memory/Random Access Memory (RAM)
 RAM is the data memory or working memory of the controller/processor

RAM is volatile, meaning when the power is turned off, all the contents are destroyed

 RAM is a direct access memory, meaning we can access the desired memory location
directly without the need for traversing through the entire memory locations to reach the
desired memory position (i.e. Random Access of memory location)
Read/Write
Memory (RAM)
NVRAM
SRAM
DRAM
1. Static RAM (SRAM):
 Static RAM stores data in the form of Voltage.

They are made up of flip-
flops

In typical implementation, an SRAM cell (bit) is realized
using 6 transistors (or 6 MOSFETs).

Four of the transistors are used for building the latch (flip-flop)
part of the memory cell and 2 for controlling the access.
 Static RAM is the fastest form of RAM available.

SRAM is fast in operation due to its resistive networking and switching capabilities
2. Dynamic RAM (DRAM)

Dynamic RAM stores data in the form of charge. They are made up of MOS transistor
gates

The advantages of DRAM are its high density and low cost compared
to SRAM
 The disadvantage is that since the information is stored as charge it
gets leaked off with time and to prevent this they need to be
refreshed periodically

Special circuits called DRAM controllers are used for the refreshing operation. The
refresh operation is done periodically in milliseconds interval

SRAM Vs DRAM:
SRAM Cell DRAM Cell
Made up of 6 CMOS transistors (MOSFET) Made up of a MOSFET and a capacitor
Doesn t
‟ Require refreshing Requires refreshing
Low capacity (Less dense) High Capacity (Highly dense)
More expensive Less Expensive
Fast in operation. Typical access time is 10ns Slow in operation due to refresh
requirements. Typical access time is 60ns.
Write operation is faster than read operation.
3. Non Volatile RAM (NVRAM):
 Random access memory with battery backup

It contains Static RAM based memory and a minute battery for providing supply to
the
memory in the absence of external power supply
 The memory and battery are packed together in a single package


NVRAM is used for the non volatile storage of results of operations or for setting up of flags
etc
The life span of NVRAM is expected to be around 10 years

DS1744 from Maxim/Dallas is an example for 32KB NVRAM
Memory selection for Embedded Systems:
• Selection of suitable memory is very much essential step in high performance applications,
because the challenges and limitations of the system performance are often decided upon
the type of memory architecture.
• Systems memory requirement depend primarily on the nature of the application that is
planned to run on the system.
• Memory performance and capacity requirement for low cost systems are small, whereas
memory throughput can be the most critical requirement in a complex, high performance
system.

• Following are the factors that are to be considered while selecting the memory devices,

Speed

Data storage size and capacity

Bus width

Power consumption

Cost
Embedded system requirements:
 Program memory for holding control algorithm or embedded OS and the
applications designed to run on top of OS.
 Data memory for holding variables and temporary data during task execution.

Memory for holding non-volatile data which are modifiable by the application.
The memory requirement for an embedded system in terms of RAM (SRAM/DRAM) and
ROM (EEPROM/FLASH/NVRAM) is solely dependent on the type of the embedded
system and applications for which it is designed.
There is no hard and fast rule for calculating the memory requirements.
Lot of factors need to be considered for selecting the type and size of memory for
embedded system.
Example: Design of Embedded based electronic Toy.
SOC or microcontroller can be selected based type(RAM &ROM) and size of on-chip
memory for the design of embedded system.
If on-chip memory is not sufficient then how much external memory need to be
interfaced.
If the ES design is RTOS based ,the RTOS requires certain amount of RAM for its
execution and ROM for storing RTOS Image.
The RTOS suppliers gives amount of run time RAM requirements and program memory
requirements for the RTOS.
Additional memory is required for executing user tasks and user applications.

On a safer side, always add a buffer value to the total estimated RAM and ROM
requirements.
A smart phone device with windows OS is typical example for embedded device requires
say 512MB RAM and 1GB ROM are minimum requirements for running the mobile
device.
And additional RAM &ROM memory is required for running user applications.
So estimate the memory requirements for install and run the user applications without
facing memory space.
Memory can be selected based on size of the memory ,data bus and address bus size of
the processor/controller.
Memory chips are available in standard sizes like 512 bytes,1KB,2KB ,4KB,8KB,16 KB
….1MB etc.
FLASH memory is the popular choice for ROM in embedded applications .
It is powerful and cost-effective solid state storage technology for mobile electronic
devices and other consumer applications.
Flash memory available in two major variants
1. NAND FLASH 2. NOR FLASH
NAND FLASH is a high density low cost non-volatile storage memory.
NOR FLASH is less dense and slightly expensive but supports Execute in place(XIP).
The XIP technology allows the execution of code memory from ROM itself without the
need for copying it to the RAM.
The EEPROM is available as either serial interface or parallel interface chip.
If the processor/controller of the device supports serial interface and the amount of data to
write and read to and from the device (Serial EEPROM) is less.
The serial EEPROM saves the address space of the total system.
The memory capacity of the serial EEPROM is expressed in bits or Kilobits.

Industrial grade memory chips are used in certain embedded devices may be operated at
extreme environmental conditions like high temperature.
Sensors & Actuators:
• Embedded system is in constant interaction with the real world
• Controlling/monitoring functions executed by the embedded system is achieved in
accordance with the changes happening to the Real World.
• The changes in the system environment or variables are detected by the sensors
connected to the input port of the embedded system.
• If the embedded system is designed for any controlling purpose, the system will produce
some changes in controlling variable to bring the controlled variable to the desired value.
• It is achieved through an actuator connected to the out port of the embedded system.
Sensor:
A transducer device which converts energy from one form to another for any
measurement or control purpose. Sensors acts as input device
Eg. Hall Effect Sensor which measures the distance between the cushion and magnet in
the Smart Running shoes from adidas
Example: IR, humidity , PIR(passive infra red) , ultrasonic , piezoelectric , smoke
sensors

Actuator:
A form of transducer device (mechanical or
electrical) which converts signals to
corresponding physical action (motion).
Actuator acts as an output device
Eg. Micro motor actuator which adjusts the
position of the cushioning element in the
Smart Running shoes from adidas

The I/O Subsystem:

The I/O subsystem of the embedded system facilitates the interaction of the
embedded system with external world

The interaction happens through the sensors and actuators connected to the
Input and output ports respectively of the embedded system

The sensors may not be directly interfaced to the Input ports, instead they
may be interfaced through signal conditioning and translating systems
like ADC, Optocouplers etc
1. I/O Devices - Light Emitting Diode (LED):
Light Emitting Diode (LED) is an output device for visual
Vcc
indication in any embedded system
R
LED can be used as an indicator for the status of various signals
or situations.
Typical examples are indicating the presence of power conditions
GND
like „Device ON ,
‟ „Battery low‟ or „Charging of battery for
‟ a
battery operated handheld embedded devices
LED is a p-n junction diode and it contains an anode and a cathode.
For proper functioning of the LED, the anode of it should be connected to +ve terminal
of the supply voltage and cathode to the –ve terminal of supply voltage
The current flowing through the LED must limited to a value below the maximum
current that it can conduct.
A resister is used in series between the power supply and the resistor to limit the current
through the LED
2. I/O Devices – 7-Segment LED Display
The 7 – segment LED display is an output device for displaying alpha numeric
characters
It contains 8 light-emitting diode (LED) segments arranged in a special form. Out of the
8 LED segments, 7 are used for displaying alpha numeric characters

The LED segments are named A to G and the decimal point LED segment is named
as DP
The LED Segments A to G and DP should be lit accordingly to display numbers and
characters
The 7 – segment LED displays are available in two different configurations, namely;
Common anode and Common cathode
In the Common anode configuration, the anodes of the 8 segments are connected
commonly whereas in the Common cathode configuration, the 8 LED segments share a
common cathode line
Based on the configuration of the 7 – segment LED unit, the LED segment anode or
cathode is connected to the Port of the processor/controller in the order „A‟ segment to the
Least significant port Pin and DP segment to the most significant Port Pin.
The current flow through each of the LED segments should be limited to the maximum
value supported by the LED display unit
Anode
DP
DPGF ED C B A
Common Cathode LED Display
GFEDCB A
Common Anode LED Display Cathode
The typical value for the current falls within the range of 20mA
The current through each segment can be limited by connecting a current limiting resistor
to the anode or cathode of each segment
3. I/O Devices – Optocoupler
Optocoupler is a solid state device to isolate two parts of a circuit.
Optocoupler combines an LED and a photo-transistor in a single housing (package)

In electronic circuits, optocoupler is used for suppressing interference in data
communication, circuit isolation, High voltage separation, simultaneous separation and
intensification signal etc Vcc
O/p interface
Optocouplers can be used in either input circuits or in output circuits
4. I/O Devices – Stepper Motor:
Stepper motor is an electro mechanical device which generates discrete
displacement (motion) in response to dc electrical signals
It differs from the normal dc motor in its operation. The dc motor produces
continuous rotation on applying dc voltage whereas a stepper motor produces discrete
rotation in response to the dc voltage applied to it
Stepper motors are widely used in industrial embedded
applications, consumer electronic products and robotics
control systems
The paper feed mechanism of a printer/fax makes use
of stepper motors for its functioning.
Based on the coil winding arrangements, a two phase
stepper motor is classified into

Unipolar

Bipolar
A
M
C
B D
GND
GND
LED AT89C51 LED
I/p interface Port Pin
Port Pin
Photo-transistor Photo-transistor
Opto-Coupler
IC MCT2M
Microcontroller Opto-Coupler
IC MCT2M

 Unipolar: A unipolar stepper motor contains two windings per phase. The direction of
rotation (clockwise or anticlockwise) of a stepper motor is controlled by changing the
direction of current flow. Current in one direction flows through one coil and in the
opposite direction flows through the other coil. It is easy to shift the direction of rotation
by just switching the terminals to which the coils are connected
 Bipolar: A bipolar stepper motor contains single winding per phase. For reversing the
motor rotation the current flow through the windings is reversed dynamically. It requires
complex circuitry for current flow reversal
5. The I/O Subsystem – I/O Devices – Relay:

An electro mechanical device which acts as dynamic path selectors for signals and power.

The „Relay‟ unit contains a relay coil made up of insulated wire on a metal core and a
metal armature with one or more contacts.
„Relay‟ works on electromagnetic principle.


When a voltage is applied to the relay coil, current flows through the coil, which in
turn generates a magnetic field.
CoilR
elay
C
oi
l
R
el
a
y
Coil
Relay
Single Pole Single Single Pole Single Single Pole Double
Throw Normally Throw Normally Throw
Open Closed

The magnetic field attracts the armature core and moves the contact point.

The movement of the contact point changes the power/signal flow path.

The Relay is normally controlled using a relay driver circuit connected to the port pin of
the processor/controller

A transistor can be used as the relay driver. The transistor can be selected depending on
the relay driving current requirements.

6. The I/O Subsystem – I/O Devices -Piezo Buzzer:
• It is a piezoelectric device for generating audio indications in embedded applications.
• A Piezo buzzer contains a piezoelectric diaphragm which produces audible sound in
response to the voltage applied to it.
• Piezoelectric buzzers are available in two types
1.Self-driving 2.External driving
• Self-driving contains are the necessary components to
generate sound at a predefined tone.
• External driving piezo Buzzers supports the
generation of different tones.
• The tone can be varied by applying a variable pulse
train to the piezoelectric buzzer.
• A Piezo Buzzer can be directly interfaced to the port
pin of the processor/Controller.
7. The I/O Subsystem – I/O Devices – Push button
switch:

Push Button switch is an input device.

Push button switch comes in two configurations, namely „Push to
Make‟ and „Push to Break‟

The switch is normally in the open state and it makes a circuit contact
when it is pushed or pressed in the „Push to Make‟ configuration.

is
In the „Push to Break‟ configuration, the switch
normally in the closed state and it breaks the
circuit contact when it is pushed or pressed

The push button stays in the „closed‟ (For Push
to Make type) or „open‟ (For Push to Break
type) state as long as it is kept in the pushed
state and it breaks/makes the circuit
connectionwhen it is released.
Push button is used for generating a momentary
pulse


Text Book:-

NEC EEE ESD UNIT-3 NOTES
IV YEAR ECE (R15)
UNIT-III
COMMUNICATION INTERFACE
N.SURESH
Department of ECE
Gandhi Lakavath, EEE. Page 1

Communication Interface:
• Communication interface is essential for communicating with various subsystems of the
embedded system and with the external world
• The communication interface can be viewed in two different perspectives; namely;
1. Device/board level communication interface (Onboard Communication Interface)
2. Product level communication interface (External Communication Interface)
3. Device/board level communication interface (Onboard Communication Interface):
The communication channel which interconnects the various components within an
embedded product is referred as Device/board level communication interface (Onboard
Communication Interface)
 Examples: Serial interfaces like I2C, SPI, UART, 1-Wire etc and Parallel bus interface
2. Product level communication interface (External Communication Interface):
The „Product level communication interface‟ (External Communication Interface) is
responsible for data transfer between the embedded system and other devices or modules. The
external communication interface can be either wired media or wireless media and it can be a
serial or parallel interface.
 Examples for wireless communication interface: Infrared (IR), Bluetooth (BT), Wireless
LAN (Wi-Fi), Radio Frequency waves (RF), GPRS etc.
 Examples for wired interfaces: RS-232C/RS-422/RS 485, USB, Ethernet (TCP-IP), IEEE
1394 port, Parallel port etc.

1. Device/board level or On board communication interfaces: The
Communication channel which interconnects the various components within an embedded product
is referred as Device/board level communication interface (Onboard Communication Interface)
These are classified into
1. I2C (Inter Integrated Circuit) Bus
2. SPI (Serial Peripheral Interface) Bus
3. UART (Universal Asynchronous Receiver Transmitter)
4. 1-Wires Interface
5. Parallel Interface
1 I2C (Inter Integrated Circuit) Bus:
Inter Integrated Circuit Bus (I2C - Pronounced „I square C )
‟ is a synchronous bi-directional half
duplex (one-directional communication at a given point of time) two wire serial interface bus.The
concept of I2C bus was developed by „Philips Semiconductors in the
‟ early 1980 s.
‟ Theoriginal
intention of I2C was to provide an easy way of connection between a
microprocessor/microcontroller system and the peripheral chips in Television sets.

The I2C bus is comprised of two bus lines, namely; Serial Clock – SCL and Serial Data – SDA.
SCL line is responsible for generating synchronization clock pulses and SDA is responsible
for transmitting the serial data across devices.I2C bus is a shared bus system to which many
number of I2C devices can be connected. Devices connected to the I2C bus can act as either
„Master‟ device or „Slave‟ device.
The „Master‟ device is responsible for controlling the communication by
initiating/terminating data transfer, sending data and generating necessary synchronization clock
pulses.

Slave devices wait for the commands from the master and respond upon receiving the
commands. Master and „Slave‟ devices can act as either transmitter or receiver. Regardless
whether a master is acting as transmitter or receiver, the synchronization clock signal is generated
by the „Master‟ device only.I2C supports multi masters on the same bus.
The sequence of operation for communicating with an I2C slave device is:
1. Master device pulls the clock line (SCL) of the bus to „HIGH‟
2. Master device pulls the data line (SDA) „LOW ,
‟ when the SCL line is at logic
„HIGH‟ (This is the „Start‟ condition for data transfer)
3. Master sends the address (7 bit or 10 bit wide) of the „Slave‟ device to which it wants to
communicate, over the SDA line.
4. Clock pulses are generated at the SCL line for synchronizing the bit reception by the
slave device.
5. The MSB of the data is always transmitted first.
6. The data in the bus is valid during the „HIGH‟ period of the clock signal
7. In normal data transfer, the data line only changes state when the clock is low.
8. Master waits for the acknowledgement bit from the slave device whose address is sent on
the bus along with the Read/Write operation command.

9. Slave devices connected to the bus compares the address received with the address
assigned to them
10. The Slave device with the address requested by the master device responds by sending an
acknowledge bit (Bit value =1) over the SDA line
11. Upon receiving the acknowledge bit, master sends the 8bit data to the slave device over
SDA line, if the requested operation is „Write to device .
‟
12. If the requested operation is „Read from device ,
‟ the slave device sends data to the
master over the SDA line.
13. Master waits for the acknowledgement bit from the device upon byte transfer complete
for a write operation and sends an acknowledge bit to the slave device for a read operation
14. Master terminates the transfer by pulling the SDA line „HIGH‟ when the clock line SCL
is at logic „HIGH‟ (Indicating the „STOP‟ condition).

1.2 Serial Peripheral Interface (SPI) Bus:
The Serial Peripheral Interface Bus (SPI) is a synchronous bi-directional full duplex four wire
serial interface bus. The concept of SPI is introduced by Motorola.SPI is a single master multi-
slave system.

It is possible to have a system where more than one SPI device can be master, provided
the condition only one master device is active at any given point of time, is satisfied.
 SPI is used to send data between Microcontrollers and small peripherals such as shift
registers, sensors, and SD cards.
SPI requires four signal lines for communication. They are:
Master Out Slave In (MOSI): Signal line carrying the data from master to slave device. It is
also known as Slave Input/Slave Data In (SI/SDI)
Master In Slave Out (MISO): Signal line carrying the data from slave to master device. It is
also known as Slave Output (SO/SDO)

Serial Clock (SCLK): Signal line carrying the clock signals
Slave Select (SS): Signal line for slave device select. It is an active low signal.
The master device is responsible for generating the clock signal.
Master device selects the required slave device by asserting the corresponding slave devices
slave select signal „LOW .
‟
 The data out line (MISO) of all the slave devices when not selected floats at high impedance
state
 The serial data transmission through SPI Bus is fully configurable.
 SPI devices contain certain set of registers for holding these configurations.
 The Serial Peripheral Control Register holds the various configuration parameters like
master/slave selection for the device, baudrate selection for communication, clock
signal control etc.
 The status register holds the status of various conditions for transmission and reception.SPI
works on the principle of „Shift Register .
‟
 The master and slave devices contain a special shift register for the data to transmit or
receive.
 The size of the shift register is device dependent. Normally it is a multiple of 8.
 During transmission from the master to slave, the data in the master s
‟ shift register is
shifted out to the MOSI pin and it enters the shift register of the slave device through the
MOSI pin of the slave device.

 At the same time the shifted out data bit from the slave device’s shift register enters the
shift register of the master device through MISO pin
I2C V/S SPI:

1-wire interface (protocol)
1- Wire is a device communications bus system designed by Dallas Semiconductor Corp. that
provides low-speed data, signaling, and power over a single conductor.
1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used
to communicate with small inexpensive devices such as digital thermometers and weather
instruments.
One distinctive feature of the bus is the possibility of using only two wires: data and
ground. To accomplish this, 1-Wire devices include an 800 pF capacitor to store charge, and to
power the device during periods when the data line isactive
There is always one master in overall charge, which may be a PC or a microcontroller.
The
master initiates activity on the bus, simplifying the avoidance of collisions on the bus.
Protocols are built into the software to detect collisions. After a collision, the master retries the
required communication.
Many devices can share the same bus. Each device on the bus has a unique 64-bit serial
number. The least significant byte of the serial number is an 8-bit number that tells the type of the
device. The most significant byte is a standard (for the 1-wire bus) 8-bit CRC.
The master starts a transmission with a reset pulse, which pulls the wire to 0 volts for at
least 480 µs. This resets every slave device on the bus. After that, any slave device, if present,
shows that it exists with a "presence" pulse: it holds the bus low for at least 60 µs after the master
releases the
bus.

To send a "1", the bus master sends a very brief (1– 15 µs) low pulse. To send a "0", the
master sends a 60 µs low pulse.When receiving data, the master start sends a 1–15-µs 0-volt pulse
to slave each bit. If the transmitting does unit wants to send a "1", it to the nothing, and the bus
goes transmitting pulled-up voltage. If the "0", it pulls slave wants to send the data line to ground
for 60 µs.
PARALLEL COMMUNICATION:
In data transmission, parallel communication is a method of conveying multiple binary
digits (bits) simultaneously. It contrasts with communication. The communication channel is the
number of electrical conductors used at the physical layer to convey bits.
Parallel communication implies more than one such conductor. For example, an 8-bit
parallel channel will convey eight bits (or a byte) simultaneously, whereas a serial channel would
convey those same bits sequentially, one at a time. Parallel communication is and always has been
widely used within integrated circuits, in peripheral buses, and in memory devices such as RAM.
2. Product level communication interface (External
Communication
Interface): The Product level communication interface‟ (External Communication Interface) is
responsible for data transfer between the embedded system and other devices or modules
It is classified into two types
1. Wired communication interface
2. Wireless communication interface:
1. Wired communication interface: Wired communication interface is an interface used to
transfer information over a wired network.

It is classified into following types.
1. RS-232C/RS-422/RS 485
2. USB
RS-232C:
 RS-232 C (Recommended Standard number 232, revision C from the Electronic Industry
Association) is a legacy, full duplex, wired, asynchronous serial communication interface
 RS-232 extends the UART communication signals for external data communication.
 UART uses the standard TTL/CMOS logic (Logic „High‟ corresponds to bit value 1 and
Logic „LOW‟ corresponds to bit value 0) for bit transmission whereas RS232 use the EIA
standard for bit transmission.
 As per EIA standard, a logic „0‟ is represented with voltage between +3 and +25V and a
logic „1‟ is represented with voltage between -3 and -25V.
 In EIA standard, logic „0‟ is known as „Space‟ and logic „1‟ as „Mark .
‟
The RS232 interface define various handshaking and control signals for communication
apart from the „Transmit‟ and „Receive‟ signal lines for data communication

RS-232 supports two different types of connectors, namely; DB-9: 9-Pin connector and DB-25:
25-Pin connector.
Fig: DB-25:25-Pin connector.
Fig: DB-9:9-Pin connector.


RS-232 is a point-to-point communication interface and the devices involved in RS-232
communication are called „Data Terminal Equipment (DTE)‟ and „Data Communication
Equipment (DCE) .
‟

If no data flow control is required, only TXD and RXD signal lines and ground line (GND)
are required for data transmission and reception.

The RXD pin of DCE should be connected to the TXD pin of DTE and vice versa for proper
data transmission.

If hardware data flow control is required for serial transmission, various control signal lines of
the RS-232 connection are used appropriately.

The control signals are implemented mainly for modem communication and some of them may
be irrelevant for other type of devices.

The Request to Send (RTS) and Clear To Send (CTS) signals co-ordinate the communication
between DTE and DCE.

Whenever the DTE has a data to send, it activates the RTS line and if the DCE is ready to
accept the data, it activates the CTS line.

The Data Terminal Ready (DTR) signal is activated by DTE when it is ready to accept data.

The Data Set Ready (DSR) is activated by DCE when it is ready for establishing a
communication link.

DTR should be in the activated state before the activation of DSR.

The Data Carrier Detect (DCD) is used by the DCE to indicate the DTE that a good signal is

being received.


Ring Indicator (RI) is a modem specific signal line for indicating an incoming call on the
telephone line.

As per the EIA standard RS-232 C supports baudrates up to 20Kbps (Upper limit 19.2Kbps).

The commonly used baudrates by devices are 300bps, 1200bps, 2400bps, 9600bps,
11.52Kbps and 19.2Kbps.

The maximum operating distance supported in RS-232 communication is 50 feet at the
highest supported baudrate.

Embedded devices contain a UART for serial communication and they generate signal levels
conforming to TTL/CMOS logic.

A level translator IC like MAX 232 from Maxim Dallas semiconductor is used for converting
the signal lines from the UART to RS-232 signal lines for communication.

On the receiving side the received data is converted back to digital logic level by a converter
IC.

Converter chips contain converters for both transmitter and receiver.

RS-232 uses single ended data transfer and supports only point-to-point communication and
not suitable for multi-drop communication.
USB (UNIVERSAL SERIAL BUS):
 External Bus Standard.
 Allows connection of peripheral devices.
 Connects Devices such as keyboards, mice, scanners, printers, joysticks, audio
devices, disks.
 Facilitates transfers of data at 480 (USB 2.0 only), 12 or 1.5 Mb/s (mega-
bits/second).
 Developed by a Special Interest Group including Intel, Microsoft, Compact, DEC,
IBM, Northern Telecom and NEC originally in 1994.
 Low-Speed: 10 – 100 kb/s
 1.5 Mb/s signaling bit rate

 Full-Speed: 500 kb/s – 10 Mb/s 12 Mb/s signaling bit rate
 High-Speed: 400 Mb/s

NEC EEE
 480 Mb/s signaling bit rate
 NRZI with bit stuffing used
 SYNC field present for every packet
ESD UNIT-3 NOTES
 There exist two pre-defined connectors in any USB system - Series “A” and Series “B”
Connectors.
 Series “A” cable: Connects USB devices to a hub port.
 Series “B” cable: Connects detachable devices (hot- swappable)
Bus Topology:
 Connects computer to peripheral devices.
 Ultimately intended to replace parallel and serial ports
 Tiered Star Topology
 All devices are linked to a common point referred to as the root hub.
7
Specification allows for up to 127 (2 -1) different devices.
 Four wire cable serves as interconnect of system - power, ground and two differential
signaling lines.
 USB is a polled bus-all transactions are initiated by host.


USB HOST: Device that controls entire system usually a PC of some form. Processes data
arriving to and from the USB port.
USB HUB: Tests for new devices and maintains status information of child devices.Serve as
repeaters, boosting strength of up and downstream signals. Electrically isolates devices from one
another - allowing an expanded number of devices.
2.Wireless communication interface : Wireless communication interface is an interface used to
transmission of information over a distance without help of wires, cables or any other forms of
electrical conductors.
They are basically classified into following types
1.
2.
3.
4.
Infrared
Bluetooth
Wi-Fi
Zigbee
5. GPRS
INFRARED:
Infrared is a certain region in the light spectrum
Ranges from .7µ to 1000µ or .1mm
Broken into near, mid, and far infrared
One step up on the light spectrum from visible
light
Measure of heat
Most of the thermal radiation emitted by objects near room temperature is infrared. Infrared
radiation is used in industrial, scientific, and medical applications. Night-vision devices using
active near-infrared illumination allow people or animals to be observed without the observer
being detected.

IR transmission:
The transmitter of an IR LED inside its circuit, which emits infrared light for every electric pulse
given to it. This pulse is generated as a button on the remote is pressed, thus completing the
circuit, providing bias to the LED.
The LED on being biased emits light of the wavelength of 940nm as a series of pulses,
corresponding to the button pressed. However since along with the IR LED many other sources
of infrared light such as us human beings, light bulbs, sun, etc, the transmitted information can be
interfered. A solution to this problem is by modulation. The transmitted signal is modulated using
a carrier frequency of 38 KHz (or any other frequency between 36 to 46 KHz). The IR LED is
made to oscillate at this frequency for the time duration of the pulse. The information or the light
signals are pulse width modulated and are contained in the 38 KHz frequency.
IR supports data rates ranging from 9600bits/second to 16Mbps
Serial infrared: 9600bps to 115.2 kbps
Medium infrared: 0.576Mbps to 1.152 Mbps
Fast infrared: 4Mbps
BLUETOOTH:
Bluetooth is a wireless technology standard for short distances (using short-wavelength UHF
band from 2.4 to 2.485 GHz)for exchanging data over radio waves in the ISM and mobile
devices, and building personal area networks (PANs).Invented by telecom vendor Ericsson in
1994, it was originally conceived as a wireless alternative to RS- 232 data cables.

Bluetooth uses a radio technology called frequency- hopping spread spectrum. Bluetooth
divides transmitted data into packets, and transmits each packet on one of 79 designated
Bluetooth channels. Each channel has a bandwidth of 1 MHz. It usually performs 800 hops per
second, with Adaptive Frequency-Hopping (AFH) enabled
Originally, Gaussian frequency-shift keying (GFSK) modulation was the only modulation
scheme available. Since the introduction of Bluetooth 2.0+EDR, π/4-DQPSK (Differential
Quadrature Phase Shift Keying) and 8DPSK modulation may also be used between compatible
devices. Bluetooth is a packet-based protocol with a master- slave structure. One master may
communicate with up to seven slaves in a piconet. All devices share the master's clock. Packet
exchange is based on the basic clock, defined by the master, which ticks at312.5 µs intervals.
A master BR/EDR Bluetooth device can communicate with a maximum of seven devices
in a piconet (an ad-hoc computer network using Bluetooth technology), though not all devices
reach this maximum. The devices can switch roles, by agreement, and the slave can become the
master (for example, a headset initiating a connection to a phone necessarily begins as master—
as initiator of the connection—but may subsequently operate as slave).
Wi-Fi:
 Wi-Fi is the name of a popular wireless networking technology that uses radio waves to
provide wireless high-speed Internet and network connections
 Wi-Fi follows the IEEE 802.11 standard
 Wi-Fi is intended for network communication and it supports Internet Protocol (IP) based
communication
 Wi-Fi based communications require an intermediate agent called Wi-Fi router/Wireless
Access point to manage the communications.
 The Wi-Fi router is responsible for restricting the access to a network, assigning IP address
to devices on the network, routing data packets to the intended devices on the network.

 Wi-Fi enabled devices contain a wireless adaptor for transmitting and receiving data in the
form of radio signals through an antenna.
 Wi-Fi operates at 2.4GHZ or 5GHZ of radio spectrum and they co-exist with other ISM
band devices like Bluetooth.
 A Wi-Fi network is identified with a Service Set Identifier (SSID). A Wi-Fi device can
connect to a network by selecting the SSID of the network and by providing the
credentials
if the network is security enabled
 Wi-Fi networks implements different security mechanisms for authentication and data
transfer.
 Wireless Equivalency Protocol (WEP), Wireless Protected Access (WPA) etc are some of
the security mechanisms supported by Wi-Fi networks in data communication.
ZIGBEE:
Zigbee is an IEEE 802.15.4-based specification for a suite of high- level communication protocols
used to create personal area networks with small, low-power digital radios, such as for home
automation, medical device data collection, and other low-power low-bandwidth needs, designed
for small scale projects which need wireless connection.Hence, zigbee is a low-power, low data
rate, and close proximity (i.e., personal area) wireless ad hoc network.The technology

defined by the zigbee specification is intended to be simpler and less expensive than other
wireless personal area networks (WPANs), such as Bluetooth or Wi-Fi . Applications include
wireless light switches, electrical meters with in-home-displays, traffic management systems, and
other consumer and industrial equipment that require short-range low- rate wireless data transfer.
Its low power consumption limits transmission distances to 10– 100 meters line-of-sight,
depending on power output and environmental characteristics. Zigbee devices can transmit data
over long distances by passing data through a mesh network of intermediate devices to reach
more distant ones.
Zigbee Coordinator: The zigbee coordinator acts as the root of the zigbee network. The ZC is
responsible for initiating the Zigbee network and it has the capability to store information about
the network.
Zigbee Router: Responsible for passing information from device to another device or to another
ZR.
Zigbee end device:End device containing zigbee functionality for data communication. It can talk
only with a ZR or ZC and doesn’t have the capability to act as a mediator for transferring data
from one device to another.
Zigbee supports an operating distance of up to 100 metres at a data rate of 20 to 250 Kbps.

General Packet Radio Service(GPRS):
General Packet Radio Service (GPRS) is a packet oriented mobile data service on the 2G and 3
G cellular communication system's global system for mobile communications (GSM).GPRS was
originally standardized by European Telecommunications Standards Institute (ETSI) GPRS usage
is typically charged based on volume of data transferred, contrasting with circuit switched data,
which is usually billed per minute of connection time. Sometimes billing time is broken down to
every third of a minute. Usage above the bundle cap is charged per megabyte, speed limited, or
disallowed.
Services offered:
 GPRS extends the GSM Packet circuit switched data capabilities and makes the
following services possible:
 SMS messaging and broadcasting
 "Always on" internet access
 Multimedia messaging service (MMS)
 Push-to-talk over cellular (PoC)
 Instant messaging and presence-wireless village Internet applications for smart devices
through wireless application protocol (WAP).
 Point-to-point (P2P) service: inter-networking with the Internet (IP).
 Point-to-multipoint (P2M) service]: point-to- multipoint multicast and point-to-multipoint
group calls.
Text Book:-

UNIT-4
EMBEDDED FIRMWARE DESIGN &
DEVELOPMENT
Gandhi Lakavath,
Department of EEE

Embedded Systems Unit-4 Notes
Embedded Firmware
Introduction:
The control algorithm (Program instructions) and or the configuration
settings that an embedded system developer dumps into the code (Program)
memory of the embedded system
It is an un-avoidable part of an embedded system.
The embedded firmware can be developed in various methods like
o Write the program in high level languages like Embedded C/C++
using an Integrated Development Environment (The IDE
will contain an editor, compiler, linker, debugger, simulator
etc. IDEs are differentfor different family of processors/controllers.
o Write the program in Assembly Language using the Instructions
Supported by your application’s target
processor/controller
Embedded Firmware Design & Development:
The embedded firmware is responsible for controlling the various
peripherals of the embedded hardware and generating response in
accordance with the functional requirements of the product.
The embedded firmware is the master brain of the embedded system.
The embedded firmware imparts intelligence to an Embedded
system. It is a onetime process and it can happen at any stage.
The product starts functioning properly once the intelligence imparted to
the product by embedding the firmware in the hardware.
The product will continue serving the assigned task till hardware
breakdown occurs or a corruption in embedded firmware.
In case of hardware breakdown , the damaged component may need to be
replaced and for firmware corruptions the firmware should be re-loaded, to
bring back the embedded product to the normal functioning.

The embedded firmware is usually stored in a permanent memory (ROM)
and it is non alterable by end users.
Designing Embedded firmware requires understanding of the particular
embedded product hardware, like various component interfacing, memory
map details, I/O port details, configuration and register details of various
hardware chips used and some programming language (either low level
Assembly Language or High level language like C/C++ or a combination of
the two)
The embedded firmware development process starts with the conversion
of the firmware requirements into a program model using various
modeling tools.
The firmware design approaches for embedded product is purely
dependent on the complexity of the functions to be performed and speed
of operation required.
There exist two basic approaches for the design and implementation
of embedded firmware, namely;
 The Super loop based approach
 The Embedded Operating System based approach
The decision on which approach needs to be adopted for firmware
development is purely dependent on the complexity and system
requirements
1. Embedded firmware Design Approaches – The Super loop:
The Super loop based firmware development approach is Suitable for
applications that are not time critical and where the response time is not so
important (Embedded systems where missing deadlines are acceptable).

It is very similar to a conventional procedural programming where the
code is executed task by task
The tasks are executed in a never ending loop.
The task listed on top on the program code is executed first and the tasks
just below the top are executed after completing the first task
A typical super loop implementation will look like:
1. Configure the common parameters and perform initialization
for various hardware components memory, registers
etc.
2. Start the first task and execute it
3. Execute the second task
4. Execute the next task
5. :
6. :
7. Execute the last defined task
8. Jump back to the first task and follow the same flow.
The ‘C’ program code for the super loop is given
below void main ()
{
Configurations ();
Initializations ();
while (1)
{
Task 1 ();
Task 2 ();
:

:
Task n ();
}
}
Pros:
Doesn’t require an Operating System for task scheduling and monitoring
and free from OS related overheads
Simple and straight forward
design Reduced memory footprint
Cons:
Non Real time in execution behavior (As the number of tasks increases the
frequency at which a task gets CPU time for execution also increases)
Any issues in any task execution may affect the functioning of the product
(This can be effectively tackled by using Watch Dog Timers for task
execution monitoring)
Enhancements:
 Combine Super loop based technique with interrupts
 Execute the tasks (like keyboard handling) which require Real time
attention as Interrupt Service routines.
2. Embedded firmware Design Approaches – Embedded OS based Approach:
The embedded device contains an Embedded Operating System which
can be one of:
 A Real Time Operating System (RTOS)
 A Customized General Purpose Operating System (GPOS)

The Embedded OS is responsible for scheduling the execution of user
tasks and the allocation of system resources among multiple tasks
It Involves lot of OS related overheads apart from managing and
executing user defined tasks
Microsoft® Windows XP Embedded is an example of GPOS for embedded
devices
Point of Sale (PoS) terminals, Gaming Stations, Tablet PCs etc are
examples of embedded devices running on embedded GPOSs
‘Windows CE’, ‘Windows Mobile’,‘QNX’, ‘VxWorks’, ‘ThreadX’,
‘MicroC/OS-II’, ‘Embedded Linux’, ‘Symbian’ etc are examples of RTOSs
employed in Embedded Product development
Mobile Phones, PDAs, Flight Control Systems etc are examples of
embedded devices that runs on RTOSs
Embedded firmware Development Languages/Options
Assembly Language
High Level
Language
o Subset of C
(Embedded C)
o Subset of C++
(Embedded C+
+)
o Any other high
level language
with supported
Cross-compiler
Mix of Assembly &
High level Language
o Mixing High
Level Language

1. Embedded firmware Development Languages/Options
– Assembly Language
‘Assembly Language’ is the human readable
notation of ‘machine language’
‘Machine language’ is a processor understandable language
Machine language is a binary representation and it consists of 1s and 0s
Assembly language and machine languages are
processor/controller dependent
An Assembly language program written for one processor/controller family
will not work with others
Assembly language programming is the process of writing processor specific
machine code in mnemonic form, converting the mnemonics into actual
processor instructions (machine language) and associated data using an
assembler
The general format of an assembly language instruction is an Opcode
followed by Operands
The Opcode tells the processor/controller what to do and the
Operandsprovide the data and information required to perform the action
specified by the opcode
It is not necessary that all opcode should have Operands following them.
Some of the Opcode implicitly contains the operand and in such situation
no operand is required. The operand may be a single operand, dual operand
or more
The 8051 Assembly Instruction
MOV A, #30
Moves decimal value 30 to the 8051 Accumulator register. Here MOV A is the
Opcode and 30 is the operand (single operand). The same instruction when written
in machine language will look like

01110100 00011110
The first 8 bit binary value 01110100 represents the opcode MOV A and the
second 8 bit binary value 00011110 represents the operand 30.
Assembly language instructions are written one per line
A machine code program consists of a sequence of assembly language
instructions, where each statement contains a mnemonic (Opcode +
Operand)
Each line of an assembly language program is split into four fields as:
LABEL OPCODE OPERAND
COMMENTS
LABEL is an optional field. A ‘LABEL’ is an identifier used extensively in
programs to reduce the reliance on programmers for remembering where
data or code is located. LABEL is commonly used for representing
A memory location, address of a program, sub-routine, code portion etc.
 The maximum length of a label differs between assemblers.
Assemblers insist strict formats for labeling. Labels are always
suffixed by a colon and begin with a valid character. Labels can
contain number from 0 to 9 and special character _ (underscore).
;###############################################################
; SUBROUTINE FOR GENERATING DELAY
; DELAY PARAMETR PASSED THROUGH REGISTER R1
; RETURN VALUE NONE,REGISTERS USED: R0, R1
;###############################################################
##### DELAY: MOV R0, #255 ; Load Register R0 with 255
DJNZ R1, DELAY; Decrement R1 and loop till
R1= 0 RET
; Return to calling
program

 The symbol ; represents the start of a comment. Assembler ignores
the text in a line after the ; symbol while assembling the program
 DELAY is a label for representing the start address of the
memory location where the piece of code is located in code
memory
 The above piece of code can be executed by giving the label DELAY
as part of the instruction. E.g. LCALL DELAY; LMP DELAY
2. Assembly Language – Source File to Hex File Translation:
The Assembly language program written in assembly code is saved as
.asm (Assembly file) file or a .src (source) file or a format supported
by the assembler
Similar to ‘C’ and other high level language programming, it is
possibleto have multiple source files called modules in assembly
language programming. Each module is represented by a ‘.asm’ or ‘.src’
file or the assembler supported file format similar to the ‘.c’ files in C
programming
The software utility called ‘Assembler’ performs the translation
of assembly code to machine code
The assemblers for different family of target machines are different. A51
Macro Assembler from Keil software is a popular assembler for the 8051
family micro controller
Figure 5: Assembly Language to machine language conversion
process

Each source file can be assembled separately to examine the syntax
errors and incorrect assembly instructions
Assembling of each source file generates a corresponding object file. The
object file does not contain the absolute address of where the generated
code needs to be placed (a re-locatable code) on the program memory
The software program called linker/locater is responsible for assigning
absolute address to object files during the linking process
The Absolute object file created from the object files corresponding to
different source code modules contain information about the address
where each instruction needs to be placed in code memory
A software utility called ‘Object to Hex file converter’ translates
the absolute object file to corresponding hex file (binary file)
Advantages:
 1.Efficient Code Memory & Data Memory Usage (Memory
Optimization):
 The developer is well aware of the target processor architecture and
memory organization, so optimized code can be written for
performing operations.
 This leads to less utilization of code memory and efficient
utilization of data memory.
 2.High Performance:
 Optimized code not only improves the code memory usage but
also improves the total system performance.
 Through effective assembly coding, optimum performance can
be achieved for target processor.
 3.Low level Hardware Access:
 Most of the code for low level programming like accessing external
device specific registers from OS kernel ,device drivers, and low level
interrupt routines, etc are making use of direct assembly coding.

4.Code Reverse Engineering:
 It is the process of understanding the technology behind a product by
extracting the information from the finished product.
 It can easily be converted into assembly code using a dis-
assembler program for the target machine.
Drawbacks:
1.High Development time:
 The developer takes lot of time to study about architecture ,memory
organization, addressing modes and instruction set of target
processor/controller.
 More lines of assembly code is required for performing a simple
action.
2.Developer dependency:
 There is no common written rule for developing assembly language
based applications.
3.Non portable:
 Target applications written in assembly instructions are valid only for
that particular family of processors and cannot be re-used for another
target processors/controllers.
 If the target processor/controller changes, a complete re-writing of the
application using assembly language for new targetprocessor/controller
is required.
2. Embedded firmware Development Languages/Options – High Level
Language
The embedded firmware is written in any high level language like C, C++
A software utility called ‘cross-compiler’ converts the high level language to
target processor specific machine code

 The cross-compilation of each module generates a corresponding object
file. The object file does not contain the absolute address of where the
generated code needs to be placed (a re-locatable code) on the program
memory
 The software program called linker/locater is responsible for assigning
absolute address to object files during the linking process
 The Absolute object file created from the object files corresponding to
different source code modules contain information about the
address where each instruction needs to be placed in code
memory
 A software utility called ‘Object to Hex file converter’ translates the
absolute object file to corresponding hex file (binary file)
Embedded firmware Development Languages/Options – High Level
Language – Source File to Hex File Translation
Machine Code
(Hex File)
Figure 6: High level language to machine language conversion
process
Library Files
Source File 1
(.c /.c++ etc)
(Module-1)
Module
Cross-compiler
Object File 1
Source File 2
(.c /.c++ etc)
(Module-2)
Module
Cross-compiler
Object File 2
Object to Hex File
Converter
Absolute Object File
Linker/
Locator

Advantages:
Reduced Development time: Developer requires less or little
knowledge on internal hardware details and architecture of the target
processor/Controller.
Developer independency: The syntax used by most of the high
level languages are universal and a program written high level can
easily understand by a second person knowing the syntax of the
language
Portability: An Application written in high level language
for particular target processor /controller can be easily be
converted to another target processor/controller specific application
with little or less effort
Drawbacks:
• The cross compilers may not be efficient in generating the optimized
target processor specific instructions.
• Target images created by such compilers may be messy and non-
optimized in terms of performance as well as code size.
• The investment required for high level language based development
tools (IDE) is high compared to Assembly Language
based firmware development tools.
Embedded firmware Development Languages/Options – Mixing of
Assembly Language with High Level Language
Embedded firmware development may require the mixing of
Assembly Language with high level language or vice versa.
Interrupt handling, Source code is already available in high
level languageAssembly Language etc are examples

High Level language and low level language can be mixed in three different
ways
 Mixing Assembly Language with High level language like ‘C’
 Mixing High level language like ‘C’ with Assembly Language
 In line Assembly
The passing of parameters and return values between the high level and low
level language is cross-compiler specific
1. Mixing Assembly Language with High level
language like ‘C’ (Assembly Language with ‘C’):
Assembly routines are mixed with ‘C’ in situations where the entire program is
written in ‘C’ and the cross compiler in use do not have built in support for
implementing certain features like ISR.
If the programmer wants to take advantage of the speed and optimized code
offered by the machine code generated by hand written assembly rather than
cross compiler generated machine code.
For accessing certain low level hardware ,the timing specifications may be
very critical and cross compiler generated machine code may not be able to
offer the required time specifications accurately.
Writing the hardware/peripheral access routine in processor/controller
specific assembly language and invoking it from ‘C’ is the most advised
method.
Mixing ‘C’ and assembly is little complicated.
The programmer must be aware of how to pass parameters from the ‘C’
routine to assembly and values returned from assembly routine to ‘C’ and
how Assembly routine is invoked from the ‘C’ code.

Passing parameter to the assembly routine and returning values from the
assembly routine to the caller ‘C’ function and the method of invoking the
assembly routine from ‘C’ code is cross compiler dependent.
There is no universal written rule for purpose.
We can get this information from documentation of the cross compiler.
Different cross compilers implement these features in different
ways depending on GPRs and memory supported by target
processor/controller
2. Mixing High level language like ‘C’
with Assembly Language (‘C’ with Assembly Language)
The source code is already available in assembly language and routinewritten in
a high level language needs to be included to the existing code.
The entire source code is planned in Assembly code for various reasons like
optimized code, optimal performance, efficient code memory utilization and
proven expertise in handling the assembly.
The functions written in ‘C’ use parameter passing to the function and returns
values to the calling functions.
The programmer must be aware of how parameters are passed to the function
and how values returned from the function and how function is invoked
from the assembly language environment.
Passing parameter to the function and returning values from the function using
CPU registers , stack memory and fixed memory.
Its implementation is cross compiler dependent and varies across compilers.

3.In line Assembly:
• Inline assembly is another technique for inserting the target
processor/controller specific assembly instructions at any location of
source code written in high level language ‘C’
• Inline Assembly avoids the delay in calling an assembly routine from a ‘C’
code.
• Special keywords are used to indicate the start and end of Assembly
instructions
• E.g #pragma asm
Mov A,#13H
#pragma ensasm
• Keil C51 uses the keywords #pragma asm and #pragma endasm to indicate
a block of code written in assembly.
Text Books:
2. Embedded System Design-Raj Kamal TMH

ES Unit-5 Notes
UNIT-V
RTOS Based Embedded System
Design
N.SURESH
Department of ECE

resources and
available to
the system
makes them
the user
ES Unit-5 Notes
Operating System Basics:
 The Operating System acts as a bridge between the user applications/tasks
and the underlying system resources through a set of system functionalities
and services
 OSmanages
applications/tasks on a need basis
 The primary functions of an Operating system is
 Make the system convenient to use
 Organize and manage the system resources efficiently andcorrectly
Figure 1: The Architecture of Operating System
K
e
r
n
e
l
S
e
r
v
i
c
e
s

ES Unit-5 Notes
The Kernel:
 The kernel is the core of the operating system
 It is responsible for managing the system resources and the
communication among the hardware and other system services
 Kernel acts as the abstraction layer between system resources and
user applications
 Kernel contains a set of system libraries and services.
 For a general purpose OS, the kernel contains different services like
 Process Management
 Primary Memory Management
 File System management
 I/O System (Device) Management
 Secondary Storage Management
 Protection
 Time management
 Interrupt Handling
Kernel Space and User Space:
 The program code corresponding to the kernel applications/services are kept
in a contiguous area (OS dependent) of primary (working) memory and is
protected from the un-authorized access by user programs/applications
 The memory space at which the kernel code is located is known as
‘Kernel Space’

ES Unit-5 Notes
 All user applications are loaded to a specific area of primary memory and
this memory area is referred as ‘User Space’
 The partitioning of memory into kernel and user space is purely Operating
System dependent
 An operating system with virtual memory support, loads the user
applications into its corresponding virtual memory space with demand
paging technique
 Most of the operating systems keep the kernel application code in main
memory and it is not swapped out into the secondary memory
Monolithic Kernel:
 All kernel services run in the kernel space
 All kernel modules run within the same memory space under a single
kernel thread
 The tight internal integration of kernel modules in monolithic
kernel architecture allows the effective
utilization of the low-level features of
the underlying
system
 The major drawback of monolithic
kernel is that any error or failure in
any one of the kernel modules leads
tothe crashing of the entire
kernel application
 LINUX, SOLARIS, MS-DOS kernels
are examples of monolithic kernel
Applications
Monolithic kernel with all
operating system services
running in kernel space
Figure 2: The Monolithic Kernel Model

ES Unit-5 Notes
Microkernel
 The microkernel design incorporates only the essential set of
Operating System services into the kernel
 Rest of the Operating System services are implemented in programs
known as ‘Servers’ which runs in user space
 The kernel design is highly
modular provides OS-neutral
abstraction.
 Memory management,
process
Servers (kernel
services running
in user space)
Applications
management, timer systems and
interrupt handlers are examples of
essential services, which forms the
part of the microkernel
Microkernel with essential
services like memory
management, process
management, timer systemetc...
Figure 3: The Microkernel Model
 QNX, Minix 3 kernels are examples for microkernel.
Benefits of Microkernel:
1. Robustness: If a problem is encountered in any services in server can
reconfigured and re-started without the need for re-starting the
entire OS.
2. Configurability: Any services , which run as ‘server’ application can be
changed without need to restart the whole system.
Types of Operating Systems:
Depending on the type of kernel and kernel services, purpose and
type of
computing systems where the OS is deployed and the responsiveness to
applications, Operating Systems are classified into
3. General Purpose Operating System (GPOS):
4. Real Time Purpose Operating System (RTOS):

ES Unit-5 Notes
1. General Purpose Operating System (GPOS):
 Operating Systems, which are deployed in general computing systems
 The kernel is more generalized and contains all the required services
to execute generic applications
 Need not be deterministic in execution behavior
 May inject random delays into application software and thus cause
slow responsiveness of an application at unexpected times
 Usually deployed in computing systems where deterministic behavior is
not an important criterion
 Personal Computer/Desktop system is a typical example for a systemwhere
GPOSs are deployed.
 Windows XP/MS-DOS etc are examples of General Purpose Operating
System
2. Real Time Purpose Operating System (RTOS):
 Operating Systems, which are deployed in embedded systems
demanding real-time response
 Deterministic in execution behavior. Consumes only known amount oftime
for kernel applications
 Implements scheduling policies for executing the highest
priority task/application always
 Implements policies and rules concerning time-critical allocation of
a system’s resources
 Windows CE, QNX, VxWorks , MicroC/OS-II etc are examples of Real
Time Operating Systems (RTOS)

ES Unit-5 Notes
The Real Time Kernel: The kernel of a Real Time Operating System is referred
as Real Time kernel. In complement to the conventional OS kernel, the Real
Time kernel is highly specialized and it contains only the minimal set of services
required for running the user applications/tasks. The basic functions of a Real
Timekernel are
a) Task/Process management
b) Task/Process scheduling
c) Task/Process synchronization
d) Error/Exception handling
e) Memory Management
f) Interrupt handling
g) Time management
 Real Time Kernel Task/Process Management: Deals with setting up the
memory space for the tasks, loading the task’s code into the memory space,
allocating system resources, setting up a Task Control Block (TCB) for the task
and task/process termination/deletion. A Task Control Block (TCB) is used for
holding the information corresponding to a task. TCB usually contains the
following set of information
 Task ID: Task Identification Number
 Task State: The current state of the task. (E.g. State= ‘Ready’ for a
task which is ready to execute)
 Task Type: Task type. Indicates what is the type for this task. The task can
be a hard real time or soft real time or background task.
 Task Priority: Task priority (E.g. Task priority =1 for task with priority =
1)
 Task Context Pointer: Context pointer. Pointer for context saving

ES Unit-5 Notes
 Task Memory Pointers: Pointers to the code memory, data memory and
stack memory for the task
 Task System Resource Pointers: Pointers to system resources (semaphores,
mutex etc) used by the task
 Task Pointers: Pointers to other TCBs (TCBs for preceding, next
and waiting tasks)
 Other Parameters Other relevant task parameters
The parameters and implementation of the TCB is kernel dependent. The TCB
parameters vary across different kernels, based on the task management
implementation
 Task/Process Scheduling: Deals with sharing the CPU among various
tasks/processes. A kernel application called ‘Scheduler’ handles the task
scheduling. Scheduler is nothing but an algorithm implementation, which
performs the efficient and optimal scheduling of tasks to provide a deterministic
behavior.
Task/Process Synchronization: Deals with synchronizing the concurrent access
of a resource, which is shared across multiple tasks and thecommunication
between various tasks.
Error/Exception handling: Deals with registering and handling the errors
occurred/exceptions raised during the execution of tasks. Insufficient memory,
timeouts, deadlocks, deadline missing, bus error, divide by zero, unknown
instruction execution etc, are examples of errors/exceptions. Errors/Exceptions
can happen at the kernel level services or at task level. Deadlock is an example
for kernel level exception, whereas timeout is an example for a task level
exception. The OS kernel gives the information about the error in the form of a
system call (API).

ES Unit-5 Notes
Memory Management:
 The memory management function of an RTOS kernel is slightly
different compared to the General Purpose Operating Systems
 The memory allocation time increases depending on the size of the block
of memory needs to be allocated and the state of the allocated memory
block (initialized memory block consumes more allocation time than un-
initialized memory block)
 Since predictable timing and deterministic behavior are the primary
focus for an RTOS, RTOS achieves this by compromising the
effectiveness of memory allocation
 RTOS generally uses ‘block’ based memory allocation technique, instead
of the usual dynamic memory allocation techniques used by the GPOS.
 RTOS kernel uses blocks of fixed size of dynamic memory and the block
is allocated for a task on a need basis. The blocks are stored in a ‘Free
buffer Queue’.
 Most of the RTOS kernels allow tasks to access any of the memory
blocks without any memory protection to achieve predictable timing
and avoid the timing overheads
 RTOS kernels assume that the whole design is proven correct and
protection is unnecessary. Some commercial RTOS kernels allow
memory protection as optional and the kernel enters a fail-safe mode
when an illegal memory access occurs
 The memory management function of an RTOS kernel is slightly
different compared to the General Purpose Operating Systems
 A few RTOS kernels implement Virtual Memory concept for memory
allocation if the system supports secondary memory storage (like HDD
and FLASH memory).

ES Unit-5 Notes
 In the ‘block’ based memory allocation, a block of fixed memory is
always allocated for tasks on need basis and it is taken as a unit. Hence,
there will not be any memory fragmentation issues.
 The memory allocation can be implemented as constant functions and
thereby it consumes fixed amount of time for memory allocation. This
leaves the deterministic behavior of the RTOS kernel untouched.
Interrupt Handling:
 Interrupts inform the processor that an external device or an associated
task requires immediate attention of the CPU.
 Interrupts can be either Synchronous or Asynchronous.
 Interrupts which occurs in sync with the currently executing task is
known as Synchronous interrupts. Usually the software interrupts fall
under the Synchronous Interrupt category. Divide by zero, memory
segmentation error etc are examples of Synchronous interrupts.
 For synchronous interrupts, the interrupt handler runs in the same context
of the interrupting task.
 Asynchronous interrupts are interrupts, which occurs at any point of
execution of any task, and are not in sync with the currently executing
task.
 The interrupts generated by external devices (by asserting the Interrupt
line of the processor/controller to which the interrupt line of the device is
connected) connected to the processor/controller, timer overflow
interrupts, serial data reception/ transmission interrupts etc are
examples for asynchronous interrupts.
 For asynchronous interrupts, the interrupt handler is usually written as
separate task (Depends on OS Kernel implementation) and it runs in a

ES Unit-5 Notes
different context. Hence, a context switch happens while handling
the asynchronous interrupts.
 Priority levels can be assigned to the interrupts and each interrupts can be
enabled or disabled individually.
 Most of the RTOS kernel implements ‘Nested Interrupts’ architecture.
Interrupt nesting allows the pre-emption (interruption) of an Interrupt
Service Routine (ISR), servicing an interrupt, by a higher priority
interrupt.
Time Management:
 Interrupts inform the processor that an external device or an associated
task requires immediate attention of the CPU.
 Accurate time management is essential for providing precise time
reference for all applications
 The time reference to kernel is provided by a high-resolution Real Time
Clock (RTC) hardware chip (hardware timer)
 The hardware timer is programmed to interrupt the processor/controller
at a fixed rate. This timer interrupt is referred as ‘Timer tick’
 The ‘Timer tick’ is taken as the timing reference by the kernel. The
‘Timer tick’ interval may vary depending on the hardware timer.
Usually the ‘Timer tick’ varies in the microseconds range
 The time parameters for tasks are expressed as the multiples of
the‘Timer tick’
 The System time is updated based on the ‘Timer tick’
 If the System time register is 32 bits wide and the ‘Timer tick’ interval is
1microsecond, the System time register will reset in
232 * 10-6/ (24 * 60 * 60) = 49700 Days =~ 0.0497 Days = 1.19 Hours

ES Unit-5 Notes
If the ‘Timer tick’ interval is 1 millisecond, the System time register
will reset in
232 * 10-3 / (24 * 60 * 60) = 497 Days = 49.7 Days =~ 50 Days
The ‘Timer tick’ interrupt is handled by the ‘Timer Interrupt’ handler of kernel.
The ‘Timer tick’ interrupt can be utilized for implementing the following
actions.
 Save the current context (Context of the currently executing task)
 Increment the System time register by one. Generate timing error and reset
the System time register if the timer tick count is greater than the maximum
range available for System time register
 Update the timers implemented in kernel (Increment or decrement the timer
registers for each timer depending on the count direction setting for each
register. Increment registers with count direction setting = ‘count up’ and
decrement registers with count direction setting = ‘count down’)
 Activate the periodic tasks, which are in the idle state
 Invoke the scheduler and schedule the tasks again based on the scheduling
algorithm
 Delete all the terminated tasks and their associated data structures (TCBs)
 Load the context for the first task in the ready queue. Due to the re-
scheduling, the ready task might be changed to a new one from the task,
which was preempted by the ‘Timer Interrupt’ task

ES Unit-5 Notes
Hard Real-time System:
 A Real Time Operating Systems which strictly adheres to the timing
constraints for a task
 A Hard Real Time system must meet the deadlines for a task without any
slippage
 Missing any deadline may produce catastrophic results for Hard Real
Time Systems, including permanent data lose and irrecoverable damages
to the system/users
 Emphasize on the principle ‘A late answer is a wrong answer’
 Air bag control systems and Anti-lock Brake Systems (ABS) of vehicles
are typical examples of Hard Real Time Systems
 As a rule of thumb, Hard Real Time Systems does not implement the
virtual memory model for handling the memory. This eliminates
thedelay in swapping in and out the code corresponding to the task to and
from the primary memory
 The presence of Human in the loop (HITL) for tasks introduces un-
expected delays in the task execution. Most of the Hard Real
TimeSystems are automatic and does not contain a ‘human in the loop’
 Soft Real-time System:
Real Time Operating Systems that does not guarantee meeting
deadlines, but, offer the best effort to meet the deadline
Missing deadlines for tasks are acceptable if the frequency of
deadline missing is within the compliance limit of the Quality of
Service(QoS)
A Soft Real Time system emphasizes on the principle ‘A late answer is
an acceptable answer, but it could have done bit faster’
Soft Real Time systems most often have a ‘human in the loop (HITL)’

ES Unit-5 Notes
Automatic Teller Machine (ATM) is a typical example of Soft Real Time
System. If the ATM takes a few seconds more than the ideal operation
time, nothing fatal happens.
An audio video play back system is another example of Soft Real Time
system. No potential damage arises if a sample comes late by fraction of a
second, for play back.
Tasks, Processes & Threads :
 In the Operating System context, a task is defined as the program in
execution and the related information maintained by the Operating
system for the program
 Task is also known as ‘Job’ in the operating systemcontext
 A program or part of it in execution is also called a ‘Process’
 The terms ‘Task’, ‘job’ and ‘Process’ refer to the same entity in the
Operating System context and most often they are usedinterchangeably
 A process requires various system resources like CPU for executing the
process, memory for storing the code corresponding to the process and
associated variables, I/O devices for information exchange etc
The structure of a Processes
 The concept of ‘Process’ leads to concurrent execution (pseudo parallelism)
of tasks and thereby the efficient utilization of the CPU and other
system resources
 Concurrent execution is achieved through the sharing of CPU among the
processes.
 A process mimics a processor in properties and holds a set of registers,
process status, a Program Counter (PC) to point to the next executable
instruction of the process, a stack for holding the local variables
associated with the process and the code corresponding to the
process

ES Unit-5 Notes
Process
 A process, which inherits all
the properties of the
CPU, can be
considered as a virtual
processor, awaiting its turn
to have its
properties switched into
the physical
processor
Figure: 4 Structure of a Process
 When the process gets its turn, its registers and Program counter
register becomes mapped to the physical registers of the CPU
Memory organization of Processes:
 The memory occupied by the process is
segregated into three regions namely;
Stack memory, Data memory and Code
memory
 The ‘Stack’ memory holds all
temporarydata such as variables local to the
process
 Data memory holds all global data for the
process
 The code memory contains the program
code (instructions) corresponding to the
process
Stack Memory
Stack memory grows
downwards
Data memory grows
upwards
Data Memory
Code Memory
Fig: 5 Memory organization of a Process
Stack
(Stack Pointer)
Working Registers
Status Registers
Program Counter (PC)
Code Memory
corresponding to
the Process

ES Unit-5 Notes
 On loading a process into the main memory, a specific area of memory is
allocated for the process
 The stack memory usually starts at the highest memory address from the
memory area allocated for the process (Depending on the OS kernel
implementation)
Process States & State Transition
 The creation of a process to its termination is not a single step operation
 The process traverses through a series of states during its transition from the
newly created state to the terminated state
 The cycle through which a process changes its state from ‘newly created’ to
‘execution completed’ is known as ‘Process Life Cycle’. The various states
through which a process traverses through during a Process Life Cycle
indicates the current status of the process with respect to time and also
provides information on what it is allowed to do next
Process States & State Transition:
 Created State: The state at which a process is being created is referred as
‘Created State’. The Operating System recognizes a process in the
‘Created State’ but no resources are allocated to the process
 Ready State: The state, where a process is incepted into the memory and
awaiting the processor time for execution, is known as ‘Ready State’.
At this stage, the process is placed in the ‘Ready list’ queue maintained by
the OS
 Running State: The state where in the source code instructions
corresponding to the process is being executed is called ‘Running
State’. Running state is the state at which the process execution
happens

ES Unit-5 Notes
 . Blocked State/Wait State: Refers
to a state where a running process is
temporarily suspended
execution and does
not
from
have
immediate access to resources. The
blocked state might have invoked by
various conditions like- the process
enters a wait state for an event to
occur (E.g. Waiting for user inputs
such as keyboard input) or waiting
for getting access to a shared
resource like semaphore, mutex etc
Blocked
Created
Incepted into
memory
Ready
Running
Execution Completion
Completed
Figure 6.Process states and State
transition
 Completed State: A state where the process completes its execution
 The transition of a process from one state to another is known as
‘Statetransition’
 When a process changes its state from Ready to running or from
running toblocked or terminated or from blocked to running, the CPU
allocation for the process may alsochange
Threads
 A thread is the primitive that can execute code
 A thread is a single sequential flow of control within a process
 ‘Thread’ is also known as lightweight process
 A process can have many threads of execution
Scheduled
for
Execution
Interrupted
or
Preempted

ES Unit-5 Notes
 Different threads, which are part of a
process, share the same address space;
meaning they share the data memory,
code memory and heap memory area
 Threads maintain their own thread status
(CPU register values), Program Counter
(PC) and stack
Figure 7 Memory organization of process and its associated Threads
The Concept of multithreading
Use of multiple threads to execute a process brings the following
advantage.
 Better memory utilization.
Multiple threads of the same
process share the address
spacefor data memory. This also
reduces the complexity of
inter thread communication
since variables can be shared
across thethreads.
 Since the process is split
into different threads,
when one thread enters a
wait state, the
CPU can be utilized by other
Task/Process
Code Memory
Data Memory
Stack Stack Stack
Registers Registers Registers
Thread 1
void main (void)
{
//Create child
thread 1
CreateThread(NULL,
1000,(LPTHREAD_STA
RT_ROUTINE)
ChildThread1,NULL,
0, &dwThreadID);
//Create child
thread 2
CreateThread(NULL,
1000,(LPTHREAD_STA
RT_ROUTINE)
ChildThread2,NULL,
0, &dwThreadID);
}
Thread 2
int ChildThread1
(void)
{
//Do something
}
Thread 3
int ChildThread2
(void)
{
//Do something
}
Figure 8 Process with multi-threads
 threads of the process that do not require the event, which the other thread
is waiting, for processing. This speeds up the execution of the process.
 Efficient CPU utilization. The CPU is engaged all time.

ES Unit-5 Notes
Thread V/s Process
Thread Process
Thread is a single unit of execution and is part
of process.
Process is a program in execution and contains
one or more threads.
A thread does not have its own data memory
and heap memory. It shares the data memory
and heap memory with other threads of the
same process.
Process has its own code memory, data memory
and stack memory.
A thread cannot live independently; it lives
within the process.
A process contains at least one thread.
There can be multiple threads in a process.The
first thread (main thread) calls the main
function and occupies the start of the stack
memory of the process.
Threads within a process share the code, data
and heap memory. Each thread holds separate
memory area for stack (shares the total stack
memory of the process).
Threads are very inexpensive to create Processes are very expensive to create. Involves
many OS overhead.
Context switching is inexpensive and fast Context switching is complex and involves lot of
OS overhead and is comparatively slower.
If a thread expires, its stack is reclaimed by the
process.
If a process dies, the resources allocated to it are
reclaimed by the OS and all the associated
threads of the process also dies.
Advantages of Threads:
1. Better memory utilization: Multiple threads of the same process share the
address space for data memory. This also reduces the complexity of
inter thread communication since variables can be shared across the threads.
2. Efficient CPU utilization: The CPU is engaged all time.

ES Unit-5 Notes
3. Speeds up the execution of the process: The process is split into different
threads, when one thread enters a wait state, the CPU can be utilized by
other threads of the process that do not require the event, which the other
thread is waiting, for processing.
Multiprocessing & Multitasking
 The ability to execute multiple processes simultaneously is referred as
multiprocessing
 Systems which are capable of performing multiprocessing are known as
multiprocessor systems
 Multiprocessor systems possess multiple CPUs and can execute multiple
processes simultaneously
 The ability of the Operating System to have multiple programs in memory,
which are ready for execution, is referred as multiprogramming
 Multitasking refers to the ability of an operating system to hold multiple
processes in memory and switch the processor (CPU) from executing one
process to another process
 Multitasking involves ‘Context switching’, ‘Context saving’ and ‘Context
retrieval’
 Context switching refers to the switching of execution context from task to
other
 When a task/process switching happens, the current context of execution
should be saved to (Context saving) retrieve it at a later point of time when
the CPU executes the process, which is interrupted currently due to
execution switching
 During context switching, the context of the task to be executed is retrieved
from the saved context list. This is known as Context retrieval

ES Unit-5 Notes
Multitasking – Context Switching:
Process
2
Process
1
Idle
Figure 9 Context Switching
 Multiprogramming: The ability of the Operating System to have multiple
programs in memory, which are ready for execution, is referred
as multiprogramming.
Types of Multitasking :
Depending on how the task/process execution switching act is
implemented, multitasking can is classified into
Running
Idle
Waits in ‘Ready’ Queue
Running
dy’ Queue
Running
Idle
due to
‘Context
Switching’
due to
‘Context
Switching’
Processes
Execution
switches
to
Process
2
(Interrupt
or
System
Call)
1.
Save
Current
context
into
PCB0
2.
Perform
other
OS
operations
related
to
‘Context
Switching’
3.
Reload
Context
for
Process
2
from
PCB1
Execution
switches
to
Process
1
(Interrupt
or
System
Call)
1.
Save
Current
context
into
PCB1
2.
Perform
other
OS
operations
related
to
‘Context
Switching’
3.
Reload
Context
for
Process
1
from
PCB0

ES Unit-5 Notes
• Co-operative Multitasking: Co-operative multitasking is the most primitive
form of multitasking in which a task/process gets a chance to execute
only when the currently executing task/process voluntarily relinquishes the
CPU. In this method, any task/process can avail the CPU as much time as it
wants. Since this type of implementation involves the mercy of the tasks
each other for getting the CPU time for execution, it is known as
co-operative multitasking. If the currently executing task is non-
cooperative, the other tasks may have to wait for a long time to get
the CPU
• Preemptive Multitasking: Preemptive multitasking ensures that every
task/process gets a chance to execute. When and how much time a
process gets is dependent on the implementation of the preemptive
scheduling. As the name indicates, in preemptive multitasking, the
currently running task/process is preempted to give a chance to
other tasks/process to execute. The preemption of task may be
based on time slots or task/processpriority
• Non-preemptive Multitasking: The process/task, which is currently given the
CPU time, is allowed to execute until it terminates (enters the
‘Completed’ state) or enters the ‘Blocked/Wait’ state, waiting for
an I/O. The co- operative and non-preemptive multitasking differs
in their behavior when they are in the ‘Blocked/Wait’ state. In co-operative
multitasking, the currently executing process/task need not relinquish the CPU
when it enters the ‘Blocked/Wait’ sate, waiting for an I/O, or a shared
resource access or anevent to occur whereas in non-preemptive
multitasking the currently executing task relinquishes the CPU when
it waits for an I/O.
Task Scheduling:
 In a multitasking system, there should be some mechanism in place to share
the CPU among the different tasks and to decide which process/task is to be
executed at a given point of time
 Determining which task/process is to be executed at a given point of time is
known as task/process scheduling

ES Unit-5 Notes
 Task scheduling forms the basis of multitasking
 Scheduling policies forms the guidelines for determining which task is to be
executed when
 The scheduling policies are implemented in an algorithm and it is run by the
kernel as a service
 The kernel service/application, which implements the scheduling algorithm,
is known as ‘Scheduler’
 The task scheduling policy can be pre-emptive, non-preemptive or co-
operative
 Depending on the scheduling policy the process scheduling decision may
take place when a process switches its state to
 ‘Ready’ state from ‘Running’ state
 ‘Blocked/Wait’ state from ‘Running’ state
 ‘Ready’ state from ‘Blocked/Wait’ state
 ‘Completed’ state
Task Scheduling - Scheduler Selection:
The selection of a scheduling criteria/algorithm should consider
• CPU Utilization: The scheduling algorithm should always make the CPU
utilization high. CPU utilization is a direct measure of how much percentage
of the CPU is being utilized.
• Throughput: This gives an indication of the number of processes executed
per unit of time. The throughput for a good scheduler should always be
higher.
• Turnaround Time: It is the amount of time taken by a process for
completing its execution. It includes the time spent by the process for
waiting for the main memory, time spent in the ready queue, time spent on
completing the
I/O operations, and the time spent in execution. The turnaround time should
be a minimum for a good schedulingalgorithm.

oce
ES Unit-5 Notes
• Waiting Time: It is the amount of time spent by a process in the ‘Ready’
queue waiting to get the CPU time for execution. The waiting time should
be minimal for a good scheduling algorithm.
• Response Time: It is the time elapsed between the submission of a process
and the first response. For a good scheduling algorithm, the response time
should be as least as possible.
Task Scheduling - Queues
The various queues maintained by OS in association with CPU scheduling are
• Job Queue: Job queue contains all the processes in the system
• Ready Queue: Contains all the processes, which are ready for execution and
waiting for CPU to get their turn for execution. The Ready queue is empty
when there is no process ready for running.
• Device Queue: Contains the set of processes, which are waiting for an I/O
device
Task Scheduling – Task transition through various Queues
Process
Figure 10. Process TranDe
sv
iic
te
iQ
ou
neue
through various
queues
CPU
Run Process
to
Completion
Process n
Resource
Request
By
Process
Process 1
Scheduler
Admitted
Job Queue
Process 1
Move
Pr
ss
to
‘De
Queue’
vice
Ready Queue
to ‘Ready’ queue Process
Move preempted process
Move I/O C ompleted
Process to ‘R eady’
queue
Device
Manage
r
Process Process 1
Process 2
To summarize, a good scheduling algorithm has high CPU utilization, minimum
Turn Around Time (TAT), maximum throughput and least response time.

ES Unit-5 Notes
Non-preemptive scheduling – First Come First Served (FCFS)/First In
First Out (FIFO) Scheduling:
 Allocates CPU time to the processes based on the order in which they
enters the ‘Ready’ queue
 The first entered process is serviced first
 It is same as any real world application where queue systems are used;
E.g. Ticketing
Drawbacks:
 Favors monopoly of process. A process, which does not contain any
I/O operation, continues its execution until it finishes its task
 In general, FCFS favors CPU bound processes and I/O bound
processes may
have to wait until the completion of CPU bound process, if the currently
executing process is a CPU bound process. This leads to poor device
utilization.
 The average waiting time is not minimal for FCFS scheduling algorithm
EXAMPLE: Three processes with process IDs P1, P2, P3 with estimated
completion time 10, 5, 7 milliseconds respectively enters the ready queue together
in the order P1, P2, P3. Calculate the waiting time and Turn Around Time (TAT)
for each process and the Average waiting time and Turn Around Time (Assuming
there is no I/O waiting for the processes).
Solution: The sequence of execution of the processes by the CPU is represented as
0 10 15 22
10 5 7

ES Unit-5 Notes
Assuming the CPU is readily available at the time of arrival of P1, P1 starts
executing without any waiting in the ‘Ready’ queue. Hence the waiting time for
P1 is zero.
Waiting Time for P1 = 0 ms (P1 starts executing first)
Waiting Time for P2 = 10 ms (P2 starts executing after completing P1)
Waiting Time for P3 = 15 ms (P3 starts executing after completing P1 and
P2) Average waiting time = (Waiting time for all processes) / No. of
Processes
= (Waiting time for (P1+P2+P3)) / 3
= (0+10+15)/3 = 25/3 = 8.33 milliseconds
Turn Around Time (TAT) for P1 = 10 ms (Time spent in Ready Queue +
Execution
Time)
Turn Around Time (TAT) for P2 = 15 ms (-Do-)
Turn Around Time (TAT) for P3 = 22 ms (-
Do-)
Average Turn Around Time= (Turn Around
Time for all processes) / No. of
P
r
o
c
e
s
s
e
s
= (Turn Around
Time for
(P1+P2+P3)) / 3
= (10+15+22)/3 =

ES Unit-5 Notes
 LCFS scheduling is also known as Last In First Out (LIFO) where the
process, which is put last into the ‘Ready’ queue, is serviced first
Drawbacks:
 Favors monopoly of process. A process, which does not contain any I/O
operation, continues its execution until it finishes its task
 In general, LCFS favors CPU bound processes and I/O bound processes may
have to wait until the completion of CPU bound process, if the currently
executing process is a CPU bound process. This leads to poor device
utilization.
 The average waiting time is not minimal for LCFS scheduling algorithm
completion time 10, 5, 7 milliseconds respectively enters the ready queue together
in the order P1, P2, P3 (Assume only P1 is present in the ‘Ready’ queue when the
scheduler picks up it and P2, P3 entered ‘Ready’ queue after that). Now a new
process P4 with estimated completion time 6ms enters the ‘Ready’ queue after 5ms
of scheduling P1. Calculate the waiting time and Turn Around Time (TAT) for
each process and the Average waiting time and Turn Around Time (Assumingthere
is no I/O waiting for the processes).Assume all the processes contain only CPU
operation and no I/O operations are involved.
Solution: Initially there is only P1 available in the Ready queue and the
scheduling sequence will be P1, P3, P2. P4 enters the queue during the
execution of P1 and becomes the last process entered the ‘Ready’ queue. Now
the order of execution changes to P1, P4, P3, and P2 as given below.

ES Unit-5 Notes
P1 P4 P3 P2
0 10 16 23 28
10 6 7 5
The waiting time for all the processes are given as
Waiting Time for P1 = 0 ms (P1 starts executing
first)
Waiting Time for P4 = 5 ms (P4 starts executing after completing P1. But P4
arrived after 5ms of execution of P1. Hence its waiting time = Execution start
time – Arrival Time = 10-5 = 5)
Waiting Time for P3 = 16 ms (P3 starts executing after completing P1 and P4)
Waiting Time for P2 = 23 ms (P2 starts executing after completing P1, P4 and
P3) Average waiting time = (Waiting time for all processes) / No. of Processes
= (Waiting time for (P1+P4+P3+P2)) / 4
= (0 + 5 + 16 + 23)/4 = 44/4
= 11 milliseconds
Turn Around Time (TAT) for P1 = 10 ms (Time spent in Ready Queue + Execution Time)
Execution Time = (Execution Start Time – Arrival
Time) + Estimated Execution Time = (10-5) + 6 = 5 +
6)
Turn Around Time (TAT) for P3 = 23 ms
(Time spent in Ready Queue + Execution Time)
(Time spent in Ready Queue + Execution Time)
Average Turn Around Time = (Turn Around Time for all processes) / No. of Processes
= (Turn Around Time for (P1+P4+P3+P2)) / 4
= (10+11+23+28)/4 = 72/4
= 18 milliseconds

ES Unit-5 Notes
Non-preemptive scheduling – Shortest Job First (SJF) Scheduling.
 Allocates CPU time to the processes based on the execution completion
time for tasks
 The average waiting time for a given set of processes is minimal in SJF
scheduling
 Optimal compared to other non-preemptive scheduling like FCFS
Drawbacks:
 A process whose estimated execution completion time is high may not get a
chance to execute if more and more processes with least estimated execution
time enters the ‘Ready’ queue before the process with longest estimated
execution time starts its execution
 May lead to the ‘Starvation’ of processes with high estimated completion
time
 Difficult to know in advance the next shortest process in the ‘Ready’ queue
for scheduling since new processes with different estimated execution time
keep entering the ‘Ready’ queue at any point of time.
Non-preemptive scheduling – Priority based Scheduling
 A priority, which is unique or same is associated with each task
 The priority of a task is expressed in different ways, like a priority number,
the time required to complete the execution etc.
 In number based priority assignment the priority is a number ranging from 0
to the maximum priority supported by the OS. The maximum level
ofpriority is OS dependent.
 Windows CE supports 256 levels of priority (0 to 255 priority numbers,
with 0 being the highest priority)

ES Unit-5 Notes
 The priority is assigned to the task on creating it. It can also be changed
dynamically (If the Operating System supports this feature)
 The non-preemptive priority based scheduler sorts the ‘Ready’ queue based
on the priority and picks the process with the highest level of priority for
execution
completion time 10, 5, 7 milliseconds and priorities 0, 3, 2 (0- highest priority, 3
lowest priority) respectively enters the ready queue together. Calculate the waiting
time and Turn Around Time (TAT) for each process and the Average waiting time
and Turn Around Time (Assuming there is no I/O waiting for the processes) in
priority based scheduling algorithm.
Solution: The scheduler sorts the ‘Ready’ queue based on the priority and
schedules the process with the highest priority (P1 with priority number 0) first
andthe next high priority process (P3 with priority number 2) as second and so on.
Theorder in which the processes are scheduled for execution is represented as
P1 P3 P2
0 10 17 22
5
10
7
Waiting Time for P1 = 0 ms (P1 starts executing
first)
Waiting Time for P3 = 10 ms (P3 starts executing after completing P1)
Average waiting time = (Waiting time for all processes) / No. of Processes

ES Unit-5 Notes
= (0+10+17)/3 = 27/3
= 9 milliseconds
(-Do-)
(-Do-)
Average Turn Around Time= (Turn Around Time for all processes) / No. of Processes
= (Turn Around Time for (P1+P3+P2)) / 3
= (10+17+22)/3 = 49/3
= 16.33 milliseconds
Drawbacks:
 Similar to SJF scheduling algorithm, non-preemptive priority based
algorithm also possess the drawback of ‘Starvation’ where a process whose
priority is low may not get a chance to execute if more and more processes
with higher priorities enter the ‘Ready’ queue before the process with lower
priority starts its execution.
 ‘Starvation’ can be effectively tackled in priority based non-preemptive
scheduling by dynamically raising the priority of the low priority
task/process which is under starvation (waiting in the ready queue for a
longer time for getting the CPU time)
 The technique of gradually raising the priority of processes which are
waiting in the ‘Ready’ queue as time progresses, for preventing
‘Starvation’,is known as ‘Aging’.

ES Unit-5 Notes
Preemptive scheduling:
 Employed in systems, which implements preemptive multitasking model
 Every task in the ‘Ready’ queue gets a chance to execute. When and how
often each process gets a chance to execute (gets the CPU time) is
dependenton the type of preemptive scheduling algorithm used for
scheduling the processes
 The scheduler can preempt (stop temporarily) the currently executing
task/process and select another task from the ‘Ready’ queue forexecution
 When to pre-empt a task and which task is to be picked up from the ‘Ready’
queue for execution after preempting the current task is purely dependent on
the scheduling algorithm
 A task which is preempted by the scheduler is moved to the ‘Ready’ queue.
The act of moving a ‘Running’ process/task into the ‘Ready’ queue by the
scheduler, without the processes requesting for it is known as‘Preemption’
 Time-based preemption and priority-based preemption are the two important
approaches adopted in preemptive scheduling
Preemptive scheduling – Preemptive SJF Scheduling/ Shortest Remaining
Time (SRT):
 The non preemptive SJF scheduling algorithm sorts the ‘Ready’ queue only
after the current process completes execution or enters wait state, whereas
the preemptive SJF scheduling algorithm sorts the ‘Ready’ queue when a
new process enters the ‘Ready’ queue and checks whether the
executiontime of the new process is shorter than the remaining of the
total estimated execution time of the currently executing process
 If the execution time of the new process is less, the currently executing
process is preempted and the new process is scheduled for execution

ES Unit-5 Notes
 Always compares the execution completion time (ie the remaining
execution time for the new process) of a new process entered the ‘Ready’
queue with the remaining time for completion of the currently executing
process and schedules the process with shortest remaining time for
execution.
completion time 10, 5, 7 milliseconds respectively enters the ready queue together.
A new process P4 with estimated completion time 2ms enters the ‘Ready’ queue
after 2ms. Assume all the processes contain only CPU operation and no I/O
operations are involved.
Solution: At the beginning, there are only three processes (P1, P2 and P3)
available in the ‘Ready’ queue and the SRT scheduler picks up the process with
theShortest remaining time for execution completion (In this example P2 with
remaining time 5ms) for scheduling. Now process P4 with estimated execution
completion time 2ms enters the ‘Ready’ queue after 2ms of start of execution of
P2. The processes are re- scheduled for execution in the following order
P2 P4 P2 P3 P1
7 14 24
0 2
4
2 2
3 7 10
Waiting Time for P2 = 0 ms + (4 -2) ms = 2ms (P2 starts executing first and
is
interrupted by P4 and has to wait till the completion
of P4 to get the next CPU slot)
Waiting Time for P4 = 0 ms (P4 starts executing by preempting P2 since the
execution time for completion of P4 (2ms) is less
than that of the Remaining time for execution
completion of P2 (Here it is 3ms))

ES Unit-5 Notes
Waiting Time for P1 = 14 ms (P1 starts executing after completing P4, P2 and P3)
Average waiting time = (Waiting time for all the processes) / No. of Processes
= (0 + 2 + 7 + 14)/4 = 23/4
= 5.75 milliseconds
Turn Around Time (TAT) for P2 = 7 ms (Time spent in Ready Queue + Execution
Time)
(Time spent in Ready Queue + Execution Time = (Execution Start Time – Arrival
Time) + Estimated Execution Time = (2-2) + 2)
(Time spent in Ready Queue +
Execution Time)
Execution Time)
Average Turn Around Time = (Turn Around Time for all the processes) / No. of
Processes
= (7+2+14+24)/4 = 47/4
Preemptive scheduling – Round Robin (RR)
Scheduling:
Execution Switch
Process 1
Execution Switch
 Each process in the ‘Ready’ queue
is executed for a pre-defined time slot.
Process 4 Process 2
 The execution starts with picking up the first
process in the ‘Ready’ queue. It is executed for a
pre-defined time
Execution Switch
Process 3
Execution Switch

ES Unit-5 Notes
Figure 11 Round Robin Scheduling

ES Unit-5 Notes
 When the pre-defined time elapses or the process completes (before the pre-
defined time slice), the next process in the ‘Ready’ queue is selected for
execution.
 This is repeated for all the processes in the ‘Ready’ queue
 Once each process in the ‘Ready’ queue is executed for the pre-defined time
period, the scheduler comes back and picks the first process in the ‘Ready’
queue again for execution.
 Round Robin scheduling is similar to the FCFS scheduling and the only
difference is that a time slice based preemption is added to switch the
execution between the processes in the ‘Ready’ queue
completion time 6, 4, 2 milliseconds respectively, enters the ready queue together
in the order P1, P2, P3. Calculate the waiting time and Turn Around Time (TAT)
for each process and the Average waiting time and Turn Around Time (Assuming
there is no I/O waiting for the processes) in RR algorithm with Time slice= 2ms.
Solution: The scheduler sorts the ‘Ready’ queue based on the FCFS policy and
picks up the first process P1 from the ‘Ready’ queue and executes it for the time
slice 2ms. When the time slice is expired, P1 is preempted and P2 is scheduled for
execution. The Time slice expires after 2ms of execution of P2. Now P2 is
preempted and P3 is picked up for execution. P3 completes its execution within
thetime slice and the scheduler picks P1 again for execution for the next time
slice. This procedure is repeated till all the processes are serviced. The order in
which theprocesses are scheduled for execution is represented as
P1 P2 P3 P1 P2 P1
0 2 4 6 8 10 12
2 2 2 2 2 2

ES Unit-5 Notes
Waiting Time for P1 = 0 + (6-2) + (10-8) = 0+4+2= 6ms (P1 starts executing first
and waits for two time slices to get execution back
and again 1 time slice for getting CPU time)
Waiting Time for P2 = (2-0) + (8-4) = 2+4 = 6ms (P2 starts executing after P1
executes for 1 time slice and waits for two
time slices to get the CPU time)
Waiting Time for P3 = (4 -0) = 4ms (P3 starts executing after completing the
first time slices for P1 and P2 and completes its execution in a single time slice.)
Average waiting time = (Waiting time for all the processes) / No. of
Processes
= (6+6+4)/3 = 16/3
= 5.33 milliseconds
Average Turn Around Time = (Turn Around Time for all the processes) / No. of
Processes
= (Turn Around Time for (P1+P2+P3)) / 3
= (12+10+6)/3 = 28/3
= 9.33 milliseconds.

ES Unit-5 Notes
Preemptive scheduling – Priority based Scheduling
 Same as that of the non-preemptive priority based scheduling except for the
switching of execution between tasks
 In preemptive priority based scheduling, any high priority process entering
the ‘Ready’ queue is immediately scheduled for execution whereas in the
non- preemptive scheduling any high priority process entering the ‘Ready’
queue is scheduled only after the currently executing process completes its
execution or only when it voluntarily releases the CPU
 The priority of a task/process in preemptive priority based scheduling is
indicated in the same way as that of the mechanisms adopted for non-
preemptive multitasking.
completion time 10, 5, 7 milliseconds and priorities 1, 3, 2 (0- highest priority, 3
lowest priority) respectively enters the ready queue together. A new process P4
with estimated completion time 6ms and priority 0 enters the ‘Ready’ queue after
5ms of start of execution of P1. Assume all the processes contain only CPU
operation and no I/O operations are involved.
Solution: At the beginning, there are only three processes (P1, P2 and P3)
available in the ‘Ready’ queue and the scheduler picks up the process with the
highest priority (In this example P1 with priority 1) for scheduling. Now process
P4 with estimated execution completion time 6ms and priority 0 enters the ‘Ready’
queue after 5ms of start of execution of P1. The processes are re-scheduled
for execution in the following order
P1 P4 P1 P3 P2
0 5 11 16
5 6 5 7
23 28
5

ES Unit-5 Notes
Waiting Time for P1 = 0 + (11-5) = 0+6 =6 ms (P1 starts executing first and gets
Preempted by P4 after 5ms and again gets the CPU
time after completion of P4)
Waiting Time for P4 = 0 ms (P4 starts executing immediately on entering the
‘Ready’ queue, by preempting P1)
Waiting Time for P2 = 23 ms (P2 starts executing after completing P1, P4 and P3)
Average waiting time = (Waiting time for all the processes) / No. of Processes
= (6 + 0 + 16 + 23)/4 = 45/4
Turn Around Time (TAT) for P4 = 6ms (Time spent in Ready Queue + Execution Time
= (Execution Start Time – Arrival Time) + Estimated Execution Time = (5-5) + 6 = 0 + 6)
Average Turn Around Time= (Turn Around Time for all the processes) / No. of Processes
= (16+6+23+28)/4 = 73/4

ES Unit-5 Notes
How to chose RTOS:
The decision of an RTOS for an embedded design is very critical.
A lot of factors need to be analyzed carefully before making a decision
on the selection of an RTOS.
These factors can be either
1. Functional
2. Non-functional requirements.
3. Functional Requirements:
1. Processor support:
It is not necessary that all RTOS’s support all kinds of processor
architectures.
It is essential to ensure the processor support by the RTOS
2. Memory Requirements:
• The RTOS requires ROM memory for holding the OS files and it
is normally stored in a non-volatile memory like FLASH.
OS also requires working memory RAM for loading the OS
service.
Since embedded systems are memory constrained, it is essential to
evaluate the minimal RAM and ROM requirements for the OS under
consideration.
3.Real-Time Capabilities:
It is not mandatory that the OS for all embedded systems need to be
Real- Time and all embedded OS’s are ‘Real-Time’ in behavior.
The Task/process scheduling policies plays an important role in the
Real- Time behavior of an OS.

ES Unit-5 Notes
3. Kernel and Interrupt Latency:
The kernel of the OS may disable interrupts while executing certain
services and it may lead to interrupt latency.
For an embedded system whose response requirements are high, this
latency should be minimal.
5.Inter process Communication (IPC) and Task Synchronization:
The implementation of IPC and Synchronization is OS kernel dependent.
6. Modularization Support:
Most of the OS’s provide a bunch of features.
It is very useful if the OS supports modularization where in which the
developer can choose the essential modules and re-compile the OS image
for functioning.
7.Support for Networking and Communication:
The OS kernel may provide stack implementation and driver support for
a bunch of communication interfaces and networking.
Ensure that the OS under consideration provides support for all
the interfaces required by the embedded product.
8. Development Language Support:
Certain OS’s include the run time libraries required for running
applications written in languages like JAVA and C++.
The OS may include these components as built-in component, if not ,
check the availability of the same from a third party.

ES Unit-5 Notes
2. Non-Functional Requirements:
1. Custom Developed or Off the Shelf:
It is possible to go for the complete development of an OS suiting the
embedded system needs or use an off the shelf, readily availableOS.
It may be possible to build the required features by customizing an
open source OS.
The decision on which to select is purely dependent on the development
cost, licensing fees for the OS, development time and availability of
skilled resources.
2. Cost:
The total cost for developing or buying the OS and maintaining it in terms
of commercial product and custom build needs to be evaluated before
taking a decision on the selection of OS.
3. Development and Debugging tools Availability:
The availability of development and debugging tools is a critical decision
making factor in the selection of an OS for embedded design.
Certain OS’s may be superior in performance, but the availability of tools
for supporting the development may be limited.
4. Ease of Use:
How easy it is to use a commercial RTOS is another important feature that
needs to be considered in the RTOS selection.
5. After Sales:
For a commercial embedded RTOS, after sales in the form of e-mail, on-call
services etc. for bug fixes, critical patch updates and support for production
issues etc. should be analyzed thoroughly.

ES Unit-5 Notes
Device Drivers:
• Device driver is a piece of software that acts as a bridge between
the operating system and the hardware
• The user applications talk to the OS kernel for all necessary
information exchange including communication with the hardware
peripherals
• The architecture of the OS kernel will not allow direct device access
from the user application
• All the device related access should flow through the OS kernel and the
OS kernel routes it to the concerned hardware peripheral
• OS Provides interfaces in the form of Application Programming
Interfaces (APIs) for accessing the hardware
• The device driver abstracts the hardware from user applications
Operating S
y
s
t
e
m Services
(Kernel)
Device Drivers
Hardware

ES Unit-5 Notes
• Device drivers are responsible for initiating and managing
the communication with the hardware peripherals
• Drivers which comes as part of the Operating system image is known
as ‘built-in drivers’ or ‘onboard’ drivers. Eg. NAND FLASH driver
• Drivers which needs to be installed on the fly for communicating with add-
on devices are known as ‘Installable drivers’
• For installable drivers, the driver is loaded on a need basis when the
device is present and it is unloaded when the device is removed/detached
• The ‘Device Manager service of the OS kernel is responsible for
loading and unloading the driver, managing the driver etc.
• The underlying implementation of device driver is OS kernel dependent
• The driver communicates with the kernel is dependent on the OS
structure and implementation.
• Device drivers can run on either user space or kernel space
• Device drivers which run in user space are known as user mode drivers
and the drivers which run in kernel space are known as kernel modedrivers
• User mode drivers are safer than kernel mode drivers
• If an error or exception occurs in a user mode driver, it won’t affect
the services of the kernel
• If an exception occurs in the kernel mode driver, it may lead to the
kernel crash
• The way how a device driver is written and how the interrupts are handled
in it are Operating system and target hardware specific.
• The device driver implements the following:
• Device (Hardware) Initialization and Interrupt configuration

ES Unit-5 Notes
• Interrupt handling and processing
• Client interfacing (Interfacing with user applications)
• The basic Interrupt configuration involves the following.
• Set the interrupt type (Edge Triggered (Rising/Falling) or Level
Triggered (Low or High)), enable the interrupts and set the interrupt
priorities.
• The processor identifies an interrupt through IRQ.
• IRQs are generated by the Interrupt Controller.
• Register an Interrupt Service Routine (ISR) with an Interrupt Request
(IRQ).
• When an interrupt occurs, depending on its priority, it is serviced and
the corresponding ISR is invoked
• The processing part of an interrupt is handled in an ISR
• The whole interrupt processing can be done by the ISR itself or by
invoking an Interrupt Service Thread (IST)
• The IST performs interrupt processing on behalf of the ISR
• It is always advised to use an IST for interrupt processing, to make the
ISR compact and short
Reference Books:
2. Embedded System Design-Raj Kamal TMH

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