1. EMBEDDED SYSTEMS * Embedded systems need to be highly
By reliable. Once in a while pressing ALT-
CTRL-DEL is OK on your desktop, but
Pravellika you cannot afford to reset your
embedded system.
Keerthi Priyanka * Some embedded systems have to
operate in extreme environmental
ABSTRACT conditions such as very high
temperatures and humidity.
An embedded system can be defined as a An embedded systems is a computing
computing device that does a specific that does not a specific job . Both the
focused job. Appliances such as the air- hardware and software in an embedded
conditioned, VCD player, DVD player, system are optimized for that specific
printer , fax , mobile phone etc , are job.
examples of embedded systems. Each of
these appliances will have a processor
and special hardware to meet the specific Nearly 99 percent of the processors
requirement of the application along manufactured end up in embedded
with the embedded software that is systems. The embedded system maarket
executed by the processor for meeting is one of the heighest growth areas as
that specific requirement. these systems are used in very market
The embedded software is also called segment consumer electronics , office
‘FIRMWARE’ automation, industrial automation,
biomedical engineering , wireless
Embedded systems are characterized by communication ,data communication ,
some special features. telecommunication , transportation ,
* Embedded systems do a very specific military and so on.
task, they cannot be programmed to do Here we have different application areas
different things. .
* Embedded systems have very limited those are .
resources , particularly the memory.
Generally , they do not have secondary
storage devices such as the CDROM or EMBEDDED
the floppy disk.
* Embedded systems have to work SYSTEMS
against some deadlines. A specific job
has to be completed within a specific Nearly 99 percent of the processors
time. In some embedded systems, called manufactured end up in embedded
real time systems, the deadlines are systems. The embedded system maarket
stringent. Missing a deadline may cause is one of the heighest growth areas as
a catastrophe-loss of life or damage to these systems are used in very market
property. segment consumer electronics , office
* Embedded systems are constrained for automation, industrial automation,
power. As many embedded systems biomedical engineering , wireless
operate through a battery , the power communication ,data communication ,
consumption has to be very low .

2. telecommunication , transportation ,
military and so on. Industrial automation:
Here we have different application areas Today a lot of industries use embedded
. systems
those are . for process control . These include
pharmasutical , cement , sugar , oil
Here we have different application areas exploration , nuclear energy , electricity
. generation and transmission . The
those are . embedded systems for industrial use are
*. Consumer appliances. designed to carry out specific tasks such
*. Office automation. as monitoring the temperature ,
*. Industrial automation. pressure , humidity, voltage , current etc.
*. Medical electronics. and then take appropriate action based
*. Computer networking. on the monitored levels to control other
*. Telecommunication. devices or to send information to a
*. Wireless technologies. centralized monitoring station. In
*. Instrumentation. hazardous industrial environment ,
*. Security. where human presence
*. Finance. has to be avoided , robots are used ,
which are
Consumer appliances: programmed to do specific jobs. The
robots are now becoming very powerful
At home we use a number of embedded and carry out many intresting and
systems which include digital camera, complicated tasks such as hardware
digital diary, assembly.
DVD player, electronic toys, microwave
oven, remote controls for TV and air-
conditioner, Medical electronics ::
VCD player, video game console , video Almost every medical equipments in the
recorders etc. Today’s high-tech car has hospital is an embedded system . These
about 20 embedded systems for equipments include diagnostic aids such
transmission control, engine spark as ECG,EEG ,blood pressure measuring
control, air-conditioning, navigation etc. devices , x-ray scanners;
Even wristwatches arenow becoming equipment used in blood analysis ,
embedded systems. The palmtopps are radiation , colonoscopy , endoscopy etc.
powerful embedded systems using Developments in medical electronics
which we can carry out many general- have paved way for more accurate
purpose tasks such as playing games and diagnosis of diseases
word processing . .
Overview of embedded system
Office automation: architecture ::
Equipment used in blood analysis ,
The office automation products using radiation , colonoscopy , endoscopy etc.
embedded systems are copying Developments in medical electronics
machine , fax machine , key telephone , have paved way for more accurate
printer , scanner etc. diagnosis of diseases.

3. Overview of embedded system For applications involving complex
architecture :: processing,
it is advisable to have an operating
Every embedded system consists of system. In such a case , you need to
custom-built hardware built around a integrate the application software with
central processing unit. the operating and then transfer the entire
software on to the memory chip. Once
the software is transferred to the memory
chip, the software will continue to run
for a long time and you don’t need to
reload new software.
Now let us see the details of the various
building blocks of the hardware of an
embedded system.
* CPU
*Memory
*Output devices
*Communication interfaces
*Application-specific circuitry.
This hardware also contains memory
chips onto which the software is loaded.
The software
residing on the memory chip is also
called the firmware.The embedded
system architecture can be represented
as a layered architecture as shown
above.The operating system runs above
the hardware and the application
software runs above the operating
system. The same architecture is
applicable to any computer including a
desktop computer. However , ther are
significant differences .It is not
compulsory to have an operating system
Communication interfaces :
in every embedded system.
For small appliances such as remote
The embedded systems may need to
control units , air-conditioners ,toys etc.,
interact with other embedded systems or
there is no need for an operating system
they may have to transmit data to a
and you can write only the software
desktop.To facilitate this , the embedded
specific to that application.

4. systems ar provided with one or a few frequent recharging of the battery, the
communication interfaces such as power consumption of the embedded
RS422. system has to be very low . To reduce
Universal serial bus(USB) etc. power consumption such hardware
components should be used that
consume less power .Besides ,emphasis
Specalities of embedded systems:: should be on reducing the components
count of the hardware.
As compare to desktop computers , Cost:
workstations or mainframes , embedded For embedded systems used in safety
systems have many specialities. applications of a nuclear plant or in a
Developers need to keep these spacecraft, cost may not be a very
specialities in mind while disigning important factor . However , for
embedded systems . embedded systems used in consumer
Reliability: electronics or offfice automation , the
When we use a desktop , sometimes the cost is of utmost importance. Suppose
system you designed a toy in which the
‘hangs’ and we need to reset the electronics will cost 20 us $.
computer .Generally , this does not cause
any problem .However , this is not the
case with th embedded systems used in
mission-critical applications. They must
work with high reliability.
Reliability is of paramount inportance in
embedded systems .They should contnue
to work for thousnads of hours without
break. Many embedded systems used in
industrial control are inaccessible. Embedded system
Performance:
Many embedded systems have time
constraints .
For instance , in a process control system
, a constraint can be : “ if the
temperature exceeds 40 degrees , open a
value within 10 ms.
The system must meet such deadlines .If
the deadlines are missed it may result in
a catastrophe . You can imagine the
damage that can be done if such
deadlines are not met in a safety system
of a nuclear plant .
Power consumption: A router, an example of an embedded
Most of the embedded systems operate system. Labelled parts include a
through a battery. To reduce the battery microprocessor (4), RAM (6), and flash
drain and avoid memory (7).

5. An embedded system is a special- • 5 See also
purpose system in which the computer is
completely encapsulated by the device it • 6 External links
controls. Unlike a general-purpose
computer, such as a personal computer,
an embedded system performs pre- Examples of embedded
defined tasks, usually with very specific systems
requirements. Since the system is
dedicated to a specific task, design • automatic teller machines
engineers can optimize it, reducing the (ATMs)
size and cost of the product. Embedded • avionics, such as inertial
systems are often mass-produced, so the guidance systems, flight control
cost savings may be multipled by hardware/software and other
millions of items. integrated systems in aircraft and
Handheld computers or PDAs are missiles
generally considered embedded devices • cellular telephones and telephone
because of the nature of their hardware switches
design, even though they are more • computer equipment such as
expandable in software terms. This line routers and printers
of definition continues to blur as devices • engine controllers and antilock
expand. brake controllers for automobiles
Contents • home automation products, like
thermostats, air conditioners,
• 1 Examples of embedded systems sprinklers, and security
• 2 History monitoring systems
• 3 Characteristics • handheld calculators
o 3.1 User interfaces • household appliances, including
o 3.2 CPU Platform microwave ovens, washing
o 3.3 Tools machines, television sets, DVD
o 3.4 Debugging players/recorders
o 3.5 Start-up • medical equipment
o 3.6 Self-Test • handheld computers
o 3.7 Reliability regimes • videogame consoles
• 4 Embedded software
architectures History
o 4.1 Simple control loop
o 4.2 Nonpreemptive
multitasking
o 4.3 Preemptive
multitasking
o 4.4 Microkernels and
Exokernels
o 4.5 Monolithic Kernels
o 4.6 Exotic custom
operating systems

6. The Apollo Guidance Computer, the first use of embedded systems became
recognizably modern embedded system. feasible.
source: The Computer History Museum As the cost of a microcontroller fell
The first recognizably modern embedded below $1, it became feasible to replace
system was the Apollo Guidance expensive analog components such as
Computer, developed by Charles Stark potentiometers and variable capacitors
Draper at the MIT Instrumentation with digital electronics controlled by a
Laboratory. Each flight to the moon had small microcontroller. By the end of the
two. They ran the inertial guidance 80s, embedded systems were the norm
systems of both the command module rather than the exception for almost all
and LEM. electronics devices, a trend which has
At the project's inception, the Apollo continued since.
guidance computer was considered the
riskiest item in the Apollo project. The
use of the then new monolithic
integrated circuits, to reduce the size and
weight, increased this risk. Characteristics
The first mass-produced embedded
system was the Autonetics D-17 Embedded systems are designed to do
guidance computer for the Minuteman some specific task, rather than be a
missile, released in 1961. It was built general-purpose computer for multiple
from discrete transistor logic and had a tasks. Some also have real-time
hard disk for main memory. When the performance constraints that must be
Minuteman II went into production in met, for reason such as safety and
1966, the D-17 was replaced with a new usability; others may have low or no
computer that was the first high-volume performance requirements, allowing the
use of integrated circuits. This program system hardware to be simplified to
alone reduced prices on quad nand gate reduce costs.
ICs from $1000/each to $3/each, For high volume systems such as
permitting their use in commercial portable music players or mobile phones,
products. minimizing cost is usually the primary
Since these early applications in the design consideration. Engineers typically
1960s, where cost was no object, select hardware that is just “good
embedded systems have come down in enough” to implement the necessary
price. There has also been an enormous functions. For example, a digital set-top
rise in processing power and box for satellite television has to process
functionality. For example the first large amounts of data every second, but
microprocessor was the Intel 4004, most of the processing is done by
which found its way into calculators and custom integrated circuits. The
other small systems, but required embedded CPU "sets up" this process,
external memory and support chips. By and displays menu graphics, etc. for the
the mid-1980s, most of the previously set-top's look and feel.
external system components had been For low-volume or prototype embedded
integrated into the same chip as the systems, personal computer hardware
processor, resulting in integrated circuits can be used, by limiting the programs or
called microcontrollers, and widespread

7. by replacing the operating system with a On larger screens, a touch-screen or
real-time operating system. screen-edge soft buttons also provides
The software written for embedded good flexibility while minimising space
systems is often called firmware, and is used. The advantage of this system is
stored in ROM or Flash memory chips that the meaning of the buttons can
rather than a disk drive. It often runs change with the screen, and selection
with limited hardware resources: small can be very close to the natural behavior
or no keyboard, screen, and little RAM of pointing at what's desired.
memory. The rise of the World Wide Web has
Embedded systems reside in machines given embedded designers another quite
that are expected to run continuously for different option, by providing a web
years without errors, and in some cases page interface over a network
recover by themselves if an error occurs. connection. This avoids the cost of a
Therefore the Software is usually sophisticated display, yet provides
developed and tested more carefully than complex input and display capabilities
that for Personal computers, and when needed, on another computer.
unreliable mechanical moving parts such
as Disk drives, switches or buttons are
avoided. Recovery from errors may be CPU Platform
achieved with techniques such as a
watchdog timer that resets the computer There are many different CPU
unless the software periodically notifies architectures used in embedded designs
the watchdog. such as ARM, MIPS, Coldfire/68k,
PowerPC, X86, PIC, 8051, Atmel AVR,
Renesas H8, SH, V850, FR-V, M32R
etc. This in contrast to the desktop
computer market, which is currently
User interfaces limited to just a few competing
architectures.
Embedded systems range from no user PC/104 is a typical base for small, low-
interface at all - dedicated only to one volume embedded and ruggedized
task - to full user Interfaces similar to system design. These often use DOS,
desktop operating systems in devices Linux, NetBSD, or an embedded real-
such as PDAs. In between are devices time operating system such as QNX or
with small character- or digit-only Inferno.
displays and a few buttons. Therefore A common configuration for very-high-
usability considerations vary widely. volume embedded systems is the system
One approach widely used in embedded on a chip, an application-specific
systems without sophisticated displays, integrated circuit, for which the CPU
uses a few buttons to control a menu was purchased as intellectual property to
system, with some for movement and add to the IC's design. A related scheme
some for adjustments. On such devices is to use a field-programmable gate
simple, obvious, and low-cost array, and program it with all the logic,
approaches like red-yellow-green lights including the CPU.
(mirroring traffic lights) are common.

8. Tools
As for other software, embedded system Debugging
designers use compilers, assemblers, and
debuggers to develop embedded system Embedded Debugging may be
software. However, they may also use performed at different levels, depending
some more specific tools: on the facilities available, ranging from
• An in-circuit emulator (ICE) is a assembly- or source-level debugging
hardware device that replaces or with an in-circuit emulator, to output
plugs into the microprocessor, from serial debug ports, to an emulated
and provides facilities to quickly environment running on a personal
load and debug experimental computer.
code in the system. As the complexity of embedded systems
• Utilities to add a checksum or grows, higher level tools and operating
CRC to a program, so the systems are migrating into machinery
embedded system can check if where it makes sense. For example,
the program is valid cellphones, personal digital assistants
• For systems using digital signal and other consumer computers often
processing, developers may use a need significant software that is
math workbench such as purchased or provided by a person other
MathCad or Mathematica to than the manufacturer of the electronics.
simulate the mathematics. In these systems, an open programming
• Custom compilers and linkers environment such as Linux, NetBSD,
may be used to improve OSGi or Embedded Java is required so
optimisation for the particular that the third-party software provider can
hardware. sell to a large market.
• An embedded system may have Most such open environments have a
its own special language or reference design that runs on a PC.
design tool, or add enhancements Much of the software for such systems
to an existing language. can be developed on a conventional PC.
However, the porting of the open
Software tools can come from several environment to the specialized
sources: electronics, and the development of the
• Software companies that device drivers for the electronics are
specialize in the embedded usually still the responsibility of a classic
market embedded software engineer. In some
• Ported from the GNU software cases, the engineer works for the
development tools (see cross integrated circuit manufacturer, but there
compiler) is still such a person somewhere.
• Sometimes, development tools
for a personal computer can be
used if the embedded processor Start-up
is a close relative to a common
PC processor All embedded systems have start-up
code. Usually it sets up the electronics,
runs a self-test, and then starts the