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INTRODUCTION TO EMBEDDED SYSTEMSEach day, our lives become more dependent on 'embedded systems',

digital information technology that is embedded in our environment. Thisincludes not only safety-critical applications such as automotive devicesand controls, railways, aircraft, aerospace and medical devices, but alsocommunications, 'mobile worlds' and 'e-worlds', the 'smart' home, clothes,factories etc. All of these have wide-ranging impacts on society, includingsecurity, privacy and modes of working and living. More than 98% of processors applied today are in embedded systems, and are no longer visible to the customer as 'computers' in the ordinary sense. Newprocessors and methods of processing, sensors, actuators,communications and infrastructures are 'enablers' for this very pervasivecomputing .

Embedded systems are generally defined as special purpose

computer-systems designed to perform one or more dedicated functions,usually with real-time constraints, and have computer hardware andsoftware embedded as parts of a complete device or system, they rangefrom simple portable devices to sophisticated multiboard stationarysystems.

The term “computer” usually conjures up in the minds of many peoplethe image of a mainframe, a minicomputer, a PC, a workstation or a laptopcomputer. However, computers have always been embedded into all sortsof everyday items from automobiles and planes to TVs, in-houseentertainment centers and toasters. These are usually called embeddedcomputers or embedded systems, and actually account for more than 90%of all the world’s manufactured processors. In general, users of embeddedsystems see a specialized function (such as a High-Definition TV) and donot directly think of the computer embedded within the system. Suchembedded computers are gaining importance as an increasing number of systems use embedded processors, RAM, disk drives, and networks.Embedded systems range in size from simple toasters and mini-robots tolarge-scale systems deployed in process control, manufacturing, power generation, defense systems, telecommunication systems, automotivesystems, air traffic control, avionics, video-on-demand and videoconferencing systems. Embedded systems also differ from their conventional PC or workstation cousins in several ways. Embeddedsystems are typically used over long periods of time, will not (or cannot) beprogrammed or maintained by its end-users, an often face significantlydifferent design constraints such as limited memory, low cost, strictperformance guarantees, fail-safe operation, low power, reliability andguaranteed real-time behavior. These embedded systems often use simple

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executives (OS kernels) or real-time operating systems with typically smallfootprints, support for real-time scheduling and no hard drives. Manyembedded systems also interact with their physical environment using avariety of sensors and/or actuators.

Certain operating systems or language platforms are tailored for theembedded market, such as Embedded Java and Windows XP Embedded.However, some low-end consumer products use very inexpensivemicroprocessors and limited storage, with the application and operatingsystem both part of a single program. The program is written permanentlyinto the system's memory in this case, rather than being loaded into RAM(random access memory) like programs on a personal computer.

An embedded computer is frequently a computer that is implementedfor a particular purpose. In contrast, an average PC computer usuallyserves a number of purposes: checking email, surfing the internet, listeningto music, word processing, etc... However, embedded systems usually onlyhave a single task, or a very small number of related tasks that they areprogrammed to perform.

Every home has several examples of embedded computers. Anyappliance that has a digital clock, for instance, has a small embeddedmicrocontroller that performs no other task than to display the clock.Modern cars have embedded computers onboard that control such things

as ignition timing and anti-lock brakes using input from a number of different sensors.Embedded computers rarely have a generic interface, however. Even

if embedded systems have a keypad and an LCD display, they are rarelycapable of using many different types of input or output. An example of anembedded system with I/O capability is a security alarm with an LCD statusdisplay, and a keypad for entering a password.In general, an Embedded System:

• Is a system built to perform its duty, completely or partially

independent of human intervention.• Is specially designed to perform a few tasks in the most efficient way.• Interacts with physical elements in our environment, viz. controlling

and driving a motor, sensing temperature, etc.An embedded system can be defined as a control system or computer

system designed to perform a specific task. Common examples of

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embedded systems include MP3 players, navigation systems on aircraftand intruder alarm systems. An embedded system can also be defined as asingle purpose computer.

Most embedded systems are time critical applications meaning that the

embedded system is working in an environment where timing is veryimportant: the results of an operation are only relevant if they take place ina specific time frame. An autopilot in an aircraft is a time critical embeddedsystem. If the autopilot detects that the plane for some reason is going intoa stall then it should take steps to correct this within milliseconds or therewould be catastrophic results.What are Embedded Systems Used For?

The uses of embedded systems are virtually limitless, because everyday new products are introduced to the market that utilize embedded

computers in novel ways. In recent years, hardware such asmicroprocessors, microcontrollers, and FPGA chips have become muchcheaper. So when implementing a new form of control, it's wiser to just buythe generic chip and write your own custom software for it. Producing acustom-made chip to handle a particular task or set of tasks costs far moretime and money. Many embedded computers even come with extensivelibraries, so that "writing your own software" becomes a very trivial taskindeed.

From an implementation viewpoint, there is a major differencebetween a computer and an embedded system. Embedded systems areoften required to provide Real-Time response. A Real-Time system isdefined as a system whose correctness depends on the timeliness of itsresponse. Examples of such systems are flight control systems of anaircraft, sensor systems in nuclear reactors and power plants. For thesesystems, delay in response is a fatal error. A more relaxed version of Real- Time Systems , is the one where timely response with small delays isacceptable. Example of such a system would be the Scheduling DisplaySystem on the railway platforms. In technical terminology, Real-TimeSystems can be classified as:

•

Hard Real-Time Systems - systems with severe constraints on thetimeliness of the response.• Soft Real-Time Systems - systems which tolerate small variations in

response times.• Hybrid Real-Time Systems - systems which exhibit both hard and

soft constraints on its performance.

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