《信息科学类专业英语》课件第16章

Lesson16EmbeddedSystems:aPrimer

(第十六课嵌入式系统：初级)

Vocabulary(词汇)ImportantSentences(重点句)Multiple-choiceQuestion(多选题)

Problems(问题)

GeoffreyBessinisamarketmanagerforIBMRational ’ssoftwarequalityproducts.Afrequentlecturerwithsales,marketing,andproductmanagementexperience,Geoffrey’sentirecareerwithRationalandIBMhasbeendedicatedtohelpingcustomersimprovetheirskillswhiledeliveringbetterqualityapplicationsinlesstime.

Intheworldofsoftwaredevelopment,theindustrycanbedividedintothreelargesectors:embeddedsystems/network-connecteddevices,infrastructure,ande-businesssystems.

Woulditsurpriseyoutoknowthatbothofthefirsttwosectors(infrastructuresandembeddedsystems/network-connecteddevices)relyheavilyonembeddedsystemtechnology?It’strue.Buthowimportantarethey,really?Well,ifyou’veevercalledsomeoneonyourcellphone,youhaveanembeddedsystemtothank.Ifyou’veeverdrivenacarorlandedsafelyinanairplane,thankembeddedsystems.ThesamegoesforusingyourPersonalDigitalAssistant(PDA),benefitingfromcomplexmedicalequipment,orconsumingelectricityfromyourlocalpowercompany.Embeddedsystemsareeverywhere.

Impressive?Soarethenumbers.Everyyear,morethanabilliondollarsarespentonthetechnologyandknow-hownecessarytomakeallofthesesystemsareality.

Embeddedsystemshaveavocabularyandgrammaralltheirown.Ifyouarenewtoembeddedsystems,thisprimerwillgiveyouusefulbackgroundandabasicunderstandingoftheunderlyingconcepts.1WhatisanEmbeddedSystem?

Toughquestion,really.Thereisnooneanswer.Iaskedatleastahalfdozenindustryexpertsandgotasmanyanswers.Infact,itwassohardtopindownadefinitionthatIalmoststartedthinking“embeddedsystem”wasjustanothertermfor“software”.Nevertheless,there’sonefactaboutembeddedsystemsthatalltheexpertsdoseemtoagreeon:

Anembeddedsystemisanysoftwaresystemthatmustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.[1]

Whatismeantbyplatform?Onthedevelopmentside,platformtypicallyreferstoanoperatingsystemcapableofhostingsoftwaredevelopment,suchasWindows,Solaris,HP,etc.Onthetargetside,thewordplatformreferstothedevicesonwhichtheembeddedsystemwillbedeployed.[2]

OKthen,whythedesignconstraint?Whyaren’tembeddedtargetscapableofhostingsoftwaredevelopment?Becausethesetargetsareoptimizedforperformanceand/orsimplicity,theylacktheequipmentnecessaryfordevelopment(suchaskeyboards,monitors,networking,etc.).Ingeneral,developmentfortheembeddedenvironmentisreferredtoas“cross-platformdevelopment.”[3]2EmbeddedSystemPerformance

Toreiterate,targetplatforms,theactualembeddeddevicesandsystemsthemselves,areoptimizedforperformanceand/orsimplicity.Whatdowemeanbyperformance?Ifyouthinkitmeansthetargethastobeextremelyfast,thenyou’reonlypartiallycorrect.Formostembeddedsystems,amaximallyacceptableprocesstimeisrigidlyobserved,butthattimeneednotbesuperfast—justfastenoughforthesysteminquestion.Considertheairplane:Howmuchtimeisacceptablebetweenachangeinexternalatmosphericconditionsandtheappropriatealterationmadebytheautopilot?Perhapsthereactionneednotbelightningquick,butitcertainlycan'tbesluggish.

Andhowaboutsimplicity?Dependingontheresponsibilityoftheembeddedsystem,small,inexpensive,low-powermicrochipsareviableandpreferableoptionstomorebulkyalternatives.[4]Didyouknowthatthereismorecomputationalpowerinamodern-dayautomobilethantherewasintheApollo13moonlander?Canyouimaginethecostandsizeoftoday’sautomobilesiftheirembeddedsystemswerecomplexandbulky?

Sowhat’stheoverallresponsibilityofanembeddedsystem?Again,Ifoundtheexpertscouldagreeonthisstatement:

Theobjectiveofanembeddedsystemistoexecuteasfastasnecessaryinanasynchronousworldusingthesmallestamountofcodeandwiththehighestlevelofpredictability.(Note:Predictabilityistheembeddedworld’stermforreliability.)

Howcouldthisevenbepossible?Bydefinition,inanasynchronousworld,inputsareunpredictable;insuchaworldthereisnosuchthingasareliable,dependable,predictableenvironment!

Tounderstand,thinkintermsofyourcar:everytimeapistonintheengineexpands,yourcarhastomeasuretemperatureandpressuretodecidehowmuchgasolineandairtoinjectintothecylinderbeforethenextcompression.Ifyoudriveyourcarat130mphonadesertedhighway,itwillforceyourcar’sembeddedcomputertomakethatdecisionthousandsoftimespersecondbecauseyourcarwillberunningat6000rpm.Everyreadingwillsupplydifferentvaluesthatrequiredifferentdecisions.Butyourembeddedcomputerwillletyouenjoythat130mphridebecausethesystemitselfisverypredictable,veryreliable.Itwillevenstopyouwhentheengineistoohotorthecarisoutofgas.Andithadbetterbepredictableandreliable—youwouldn’twanttorebootyourcarwhilebreakingthesoundbarrier,wouldyou?

Okay,let’sreview.Wenowunderstandthatembeddedsystems:

Mustbedevelopedinacross-developmentenvironment;

Implementfunctionsthatprovideanelementofcontrolinanasynchronousworld;

Usethesmallestamountofcodetoachievethegreatestnecessaryspeedanddegreeofpredictabilitypossible.3TargetPlatforms

Forthesimplesttargetplatforms—platformsthatareinexpensiveandconsumeminimalpower—allfunctionsareconsideredequallyimportant,sothesystemhasnorecognitionofpriority.FunctionsaretypicallywritteninCandthen“burned”intosomeReadOnlyMemoryonan8-bitor16-bitmicroprocessor.Thereisnooperatingsystemandperhaps0.5KofRandomAccessMemoryforsomeminoruse.It’sinformationin,informationout.Lightningquick.(Thebitsizejustreferstotheamountofmemoryaccessedbytheprocessor.Allmemoryisdividedintolittlestoragebinswithindividualaddresses.Themorebitssupportedbyaprocessor,themoreaddressesthatcanbespecified.)

Astheneedforfeaturesincreasesand/orastheneedtoestablishprioritiesarises,itbecomesmoreimportanttohavesomesortofdecision-makingmechanismbepartoftheembeddedsystem.Themostadvancedsystemsactuallyhaveatiny,streamlinedoperatingsystemrunningtheshow,executingona32-bitor64-bitprocessor.ThisiscalledaReal-TimeOperatingSystem(RTOS).[5]

AnRTOSrunsyourPDA.Morethanonethingmaybehappeningatthesametimeonthisdevice,anditisthejoboftheRTOStodirecttraffic.Butwhyreal-time?Here’swhatmyexpertshadtosay:

Intheembeddedindustry,“real-time”isusedtorefertoasystemthatmustcomputearesult,basedoncertaininputs,inlessthanamaximallyacceptabletime—i.e.,itmustrespondinrealtime.

Thefactis,real-timeresponseisnotalwaysnecessaryinanembeddedsystem.Nevertheless,withintheindustry,thetermreal-timehasbecomealmostsynonymouswithembeddedsystem.4EmbeddedSystemCertification

Embeddedsystemsassociatedwithsafetyandmission-criticalapplicationstypicallyhaveextremelyrigorouscertificationstandards.Forexample,allinternationalaviationadministrationsdisallowtheuseofanewembeddedsystemwithinairplanesuntilthatsystemhasbeendevelopedandtestedwiththetechniquesandmethodsdefinedwithinadocumentlabeledDO-178B.Criticaltothiswell-definedprocessisaninsistenceonexposingandtestingcode,baseduponcodecoverageuptothelevelofcompletenesssoftwaredevelopersrefertoasMC-DC(ModifiedConditions—DecisionConditions).

Sohowdoyoutestandcertifysuchcriticalembeddedsystems?Yourtestingtoolsetmust:

Executeitstestsdirectlyonthetargetsystem.

Supportallpotentialdevelopmentplatformsanddevelopmenttools.

Accommodate,andnotinterferewith,thepotentiallylimitedmemoryandprocesspowerofthetargetsystem.

Enableeverythingfromunittesting(i.e.,testingoffunctions,classes,tasks)tooverallsystemtesting.

ProvidecodecoveragemetricsuptotherigorousMC-DCstandard.

WiththeadditionofRationalTestRealTime,Rationalcannowsupplyatoolsetthatmeetsalltherequirementsonthislist.Ofcourse,notallembeddedsystemsmustmeetsuchrigorouscertificationstandards,buttestingtoolsthatcanmeetastrictcertificationstandardcaneasilyaccommodatesimpler,lessrestricted,embeddedsystems.

That’sit!Nowthatyouknowthebasicsaboutembeddedsystems,youcanunderstandwhatthebigfussisabout.FutureRationalEdgearticleswillprovideinformationabouthowtoapplythetoolsRationalsuppliestodevelopandtestembeddedsystems,sostaytuned!

1. embeddedadj.植入的,深入的,内含的,嵌入式。

2. infrastructuresn.基建,配套结构,基本建设。

3. impressiveadj.给人印象深刻的,感人的。

4. pindown把……固定住;使动弹不得,迫使作出决定,采取行动。

5. reiterate vt.反复地说,重申。Vocabulary

6. autopilot n.自动驾驶仪。

7. asynchronous adj.异步的。

8. unpredictable adj.无法预言的，不可预测的。

9. piston n.活塞。

10. RTOS(Real-TimeOperatingSystem)实时操作系统。

11. PDAabbrPersonalDigitalAssistant个人数字助理,即掌上型电脑。

[1]Anembeddedsystemisanysoftwaresystemthatmustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.

嵌入式系统是一种设计平台与运行平台不同的软件系统。deploy，部署，调遣，展开，配置。本句子的主框架是：Aissomethingthat(description).即“嵌入式系统是一种软件系统”，什么样的软件系统呢？这种软件系统mustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.ImportantSentences

[2]Whatismeantbyplatform?Onthedevelopmentside,platformtypicallyreferstoanoperatingsystemcapableofhostingsoftwaredevelopment,suchasWindows,Solaris,HP,etc.Onthetargetside,thewordplatformreferstothedevicesonwhichtheembeddedsystemwillbedeployed.

平台是什么？对于开发者来说，平台指的是一种操作系统，能进行软件的开发工作，例如Windows、Solaris、HP操作系统等。对目标机来说，平台指的是一种设备，嵌入式软件能运行于其上。本句子的结构是：“Whatismeantbyplatform?Onthedevelopmentside,…Onthetargetside,…”什么是平台？对于开发者来说……对于目标机来说……。

[3]Whythedesignconstraint?Whyaren’tembeddedtargetscapableofhostingsoftwaredevelopment?Becausethesetargetsareoptimizedforperformanceand/orsimplicity,theylacktheequipmentnecessaryfordevelopment(suchaskeyboards,monitors,networking,etc.).Ingeneral,developmentfortheembeddedenvironmentisreferredtoas“cross-platformdevelopment.”

为什么基于目标机的开发会受到限制？为什么嵌入式目标机不能用来开发嵌入式软件呢？为达到高性能或简洁性，目标机都进行过优化。它们缺乏开发所必需的设备(例如键盘、显示器、网络等)。一般而言，嵌入式开发被称为“跨平台开发”。本句提出两个问题，Because引导两个并列句对其进行解释。

[4]Andhowaboutsimplicity?Dependingontheresponsibilityoftheembeddedsystem,small,inexpensive,low-powermicrochipsareviableandpreferableoptionstomorebulkyalternatives.

为什么要简洁化？考虑到嵌入式系统的性能，体积小、廉价、低功耗的微处理器芯片是比庞大的设备更可行、更合适的选择。本句的主框架是：DependingonA,BareviableandpreferableoptionstoC，考虑到A、B是比C更可行、更合适的选择。

[5]Astheneedforfeaturesincreasesand/orastheneedtoestablishprioritiesarises,itbecomesmoreimportanttohavesomesortofdecision-makingmechanismbepartoftheembeddedsystem.Themostadvancedsystemsactuallyhaveatiny,streamlinedoperatingsystemrunningtheshow,executingona32-bitor64-bitprocessor.ThisiscalledaReal-TimeOperatingSystem(RTOS).

随着对功能需求的增加，或需要建立优先级，在嵌入式系统中加入一些决策机制将显得尤为重要。最先进的系统实际上有一个微小的、精简的操作系统在运行，这是在32位或64位处理器上执行的。这就是所谓的实时操作系统(RTOS)。两个并列的现在分词短语runningtheshow(掌管一切)和executingona32-bitor64-bitprocessor修饰operatingsystem。

(1) Thefourdescriptionsbelow,whicharetoilluminateembeddedsystem？()

A. Mustbedevelopedinacross-developmentenvironment.

B. Implementfunctionsthatprovideanelementofcontrolinanasynchronousworld.

C. Thesystemwillperformancebetterifit’