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 environmentalABSTRACT conditions such as very high temperatures and humidity.An embedded system can be defined as a An embedded systems is a computingcomputing device that does a specific that does not a specific job . Both thefocused job. Appliances such as the air- hardware and software in an embeddedconditioned, VCD player, DVD player, system are optimized for that specificprinter , fax , mobile phone etc , are job.examples of embedded systems. Each ofthese appliances will have a processorand special hardware to meet the specific Nearly 99 percent of the processorsrequirement of the application along manufactured end up in embeddedwith the embedded software that is systems. The embedded system maarketexecuted by the processor for meeting is one of the heighest growth areas asthat specific requirement. these systems are used in very marketThe embedded software is also called segment consumer electronics , office‘FIRMWARE’ automation, industrial automation, biomedical engineering , wirelessEmbedded 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 areasdifferent things. .* Embedded systems have very limited those are .resources , particularly the memory.Generally , they do not have secondarystorage devices such as the CDROM or EMBEDDEDthe floppy disk.* Embedded systems have to work SYSTEMSagainst some deadlines. A specific jobhas to be completed within a specific Nearly 99 percent of the processorstime. In some embedded systems, called manufactured end up in embeddedreal time systems, the deadlines are systems. The embedded system maarketstringent. Missing a deadline may cause is one of the heighest growth areas asa catastrophe-loss of life or damage to these systems are used in very marketproperty. segment consumer electronics , office* Embedded systems are constrained for automation, industrial automation,power. As many embedded systems biomedical engineering , wirelessoperate through a battery , the power communication ,data communication ,consumption has to be very low .
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 , oilHere 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 andsystems which include digital camera, complicated tasks such as hardwaredigital diary, assembly.DVD player, electronic toys, microwaveoven, remote controls for TV and air-conditioner, Medical electronics ::VCD player, video game console , video Almost every medical equipments in therecorders etc. Today’s high-tech car has hospital is an embedded system . Theseabout 20 embedded systems for equipments include diagnostic aids suchtransmission control, engine spark as ECG,EEG ,blood pressure measuringcontrol, 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 electronicswhich we can carry out many general- have paved way for more accuratepurpose tasks such as playing games and diagnosis of diseasesword processing . . Overview of embedded systemOffice automation: architecture :: Equipment used in blood analysis ,The office automation products using radiation , colonoscopy , endoscopy etc.embedded systems are copying Developments in medical electronicsmachine , fax machine , key telephone , have paved way for more accurateprinter , scanner etc. diagnosis of diseases.
Overview of embedded system For applications involving complexarchitecture :: processing, it is advisable to have an operatingEvery embedded system consists of system. In such a case , you need tocustom-built hardware built around a integrate the application software withcentral 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 memorychips onto which the software is loaded.The softwareresiding on the memory chip is alsocalled the firmware.The embeddedsystem architecture can be representedas a layered architecture as shownabove.The operating system runs abovethe hardware and the applicationsoftware runs above the operatingsystem. The same architecture isapplicable to any computer including adesktop computer. However , ther aresignificant differences .It is notcompulsory to have an operating system Communication interfaces :in every embedded system.For small appliances such as remote The embedded systems may need tocontrol units , air-conditioners ,toys etc., interact with other embedded systems orthere is no need for an operating system they may have to transmit data to aand you can write only the software desktop.To facilitate this , the embeddedspecific to that application.
systems ar provided with one or a few frequent recharging of the battery, thecommunication interfaces such as power consumption of the embeddedRS422. system has to be very low . To reduceUniversal serial bus(USB) etc. power consumption such hardware components should be used that consume less power .Besides ,emphasisSpecalities 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 safetysystems have many specialities. applications of a nuclear plant or in aDevelopers need to keep these spacecraft, cost may not be a veryspecialities in mind while disigning important factor . However , forembedded systems . embedded systems used in consumerReliability: electronics or offfice automation , theWhen we use a desktop , sometimes the cost is of utmost importance. Supposesystem you designed a toy in which the‘hangs’ and we need to reset the electronics will cost 20 us $.computer .Generally , this does not causeany problem .However , this is not thecase with th embedded systems used inmission-critical applications. They mustwork with high reliability.Reliability is of paramount inportance inembedded systems .They should contnueto work for thousnads of hours withoutbreak. Many embedded systems used inindustrial control are inaccessible. Embedded systemPerformance:Many embedded systems have timeconstraints .For instance , in a process control system, a constraint can be : “ if thetemperature exceeds 40 degrees , open avalue within 10 ms.The system must meet such deadlines .Ifthe deadlines are missed it may result ina catastrophe . You can imagine thedamage that can be done if suchdeadlines are not met in a safety systemof a nuclear plant .Power consumption: A router, an example of an embeddedMost of the embedded systems operate system. Labelled parts include athrough a battery. To reduce the battery microprocessor (4), RAM (6), and flashdrain and avoid memory (7).
An embedded system is a special- • 5 See alsopurpose system in which the computer iscompletely encapsulated by the device it • 6 External linkscontrols. Unlike a general-purposecomputer, such as a personal computer,an embedded system performs pre- Examples of embeddeddefined tasks, usually with very specific systemsrequirements. Since the system isdedicated to a specific task, design • automatic teller machinesengineers can optimize it, reducing the (ATMs)size and cost of the product. Embedded • avionics, such as inertialsystems are often mass-produced, so the guidance systems, flight controlcost savings may be multipled by hardware/software and othermillions of items. integrated systems in aircraft andHandheld computers or PDAs are missilesgenerally considered embedded devices • cellular telephones and telephonebecause of the nature of their hardware switchesdesign, even though they are more • computer equipment such asexpandable in software terms. This line routers and printersof definition continues to blur as devices • engine controllers and antilockexpand. brake controllers for automobilesContents • 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
The Apollo Guidance Computer, the first use of embedded systems becamerecognizably modern embedded system. feasible.source: The Computer History Museum As the cost of a microcontroller fellThe first recognizably modern embedded below $1, it became feasible to replacesystem was the Apollo Guidance expensive analog components such asComputer, developed by Charles Stark potentiometers and variable capacitorsDraper at the MIT Instrumentation with digital electronics controlled by aLaboratory. Each flight to the moon had small microcontroller. By the end of thetwo. They ran the inertial guidance 80s, embedded systems were the normsystems of both the command module rather than the exception for almost alland LEM. electronics devices, a trend which hasAt the projects inception, the Apollo continued since.guidance computer was considered theriskiest item in the Apollo project. Theuse of the then new monolithicintegrated circuits, to reduce the size andweight, increased this risk. CharacteristicsThe first mass-produced embeddedsystem was the Autonetics D-17 Embedded systems are designed to doguidance computer for the Minuteman some specific task, rather than be amissile, released in 1961. It was built general-purpose computer for multiplefrom discrete transistor logic and had a tasks. Some also have real-timehard disk for main memory. When the performance constraints that must beMinuteman II went into production in met, for reason such as safety and1966, the D-17 was replaced with a new usability; others may have low or nocomputer that was the first high-volume performance requirements, allowing theuse of integrated circuits. This program system hardware to be simplified toalone reduced prices on quad nand gate reduce costs.ICs from $1000/each to $3/each, For high volume systems such aspermitting their use in commercial portable music players or mobile phones,products. minimizing cost is usually the primarySince these early applications in the design consideration. Engineers typically1960s, where cost was no object, select hardware that is just “goodembedded systems have come down in enough” to implement the necessaryprice. There has also been an enormous functions. For example, a digital set-toprise in processing power and box for satellite television has to processfunctionality. For example the first large amounts of data every second, butmicroprocessor was the Intel 4004, most of the processing is done bywhich found its way into calculators and custom integrated circuits. Theother small systems, but required embedded CPU "sets up" this process,external memory and support chips. By and displays menu graphics, etc. for thethe mid-1980s, most of the previously set-tops look and feel.external system components had been For low-volume or prototype embeddedintegrated into the same chip as the systems, personal computer hardwareprocessor, resulting in integrated circuits can be used, by limiting the programs orcalled microcontrollers, and widespread
by replacing the operating system with a On larger screens, a touch-screen orreal-time operating system. screen-edge soft buttons also providesThe software written for embedded good flexibility while minimising spacesystems is often called firmware, and is used. The advantage of this system isstored in ROM or Flash memory chips that the meaning of the buttons canrather than a disk drive. It often runs change with the screen, and selectionwith limited hardware resources: small can be very close to the natural behavioror no keyboard, screen, and little RAM of pointing at whats desired.memory. The rise of the World Wide Web hasEmbedded systems reside in machines given embedded designers another quitethat are expected to run continuously for different option, by providing a webyears without errors, and in some cases page interface over a networkrecover by themselves if an error occurs. connection. This avoids the cost of aTherefore the Software is usually sophisticated display, yet providesdeveloped and tested more carefully than complex input and display capabilitiesthat for Personal computers, and when needed, on another computer.unreliable mechanical moving parts suchas Disk drives, switches or buttons areavoided. Recovery from errors may be CPU Platformachieved with techniques such as awatchdog timer that resets the computer There are many different CPUunless the software periodically notifies architectures used in embedded designsthe 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 currentlyUser 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 ruggedizedtask - 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 orwith 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 systemOne approach widely used in embedded on a chip, an application-specificsystems without sophisticated displays, integrated circuit, for which the CPUuses a few buttons to control a menu was purchased as intellectual property tosystem, with some for movement and add to the ICs design. A related schemesome for adjustments. On such devices is to use a field-programmable gatesimple, 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.
ToolsAs for other software, embedded system Debuggingdesigners use compilers, assemblers, anddebuggers to develop embedded system Embedded Debugging may besoftware. However, they may also use performed at different levels, dependingsome 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 openSoftware tools can come from several environment to the specializedsources: 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