《信息科學類專業(yè)英語》課件第16章

Lesson16EmbeddedSystems:aPrimer

(第十六課嵌入式系統(tǒng)：初級)

Vocabulary(詞匯)ImportantSentences(重點句)Multiple-choiceQuestion(多選題)

Problems(問題)

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,內含的,嵌入式。

2.?infrastructuresn.基建,配套結構,基本建設。

3.?impressiveadj.給人印象深刻的,感人的。

4.?pindown把……固定住;使動彈不得,迫使作出決定,采取行動。

5.?reiterate?vt.反復地說,重申。Vocabulary

6.?autopilot?n.自動駕駛儀。

7.?asynchronous?adj.異步的。

8.?unpredictable?adj.無法預言的，不可預測的。

9.?piston?n.活塞。

10.?RTOS(Real-TimeOperatingSystem)實時操作系統(tǒng)。

11.?PDAabbrPersonalDigitalAssistant個人數(shù)字助理,即掌上型電腦。

[1]Anembeddedsystemisanysoftwaresystemthatmustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.

嵌入式系統(tǒng)是一種設計平臺與運行平臺不同的軟件系統(tǒng)。deploy，部署，調遣，展開，配置。本句子的主框架是：Aissomethingthat(description).即“嵌入式系統(tǒng)是一種軟件系統(tǒng)”，什么樣的軟件系統(tǒng)呢？這種軟件系統(tǒng)mustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.ImportantSentences

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

平臺是什么？對于開發(fā)者來說，平臺指的是一種操作系統(tǒng)，能進行軟件的開發(fā)工作，例如Windows、Solaris、HP操作系統(tǒng)等。對目標機來說，平臺指的是一種設備，嵌入式軟件能運行于其上。本句子的結構是：“Whatismeantbyplatform?Onthedevelopmentside,…Onthetargetside,…”什么是平臺？對于開發(fā)者來說……對于目標機來說……。

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

為什么基于目標機的開發(fā)會受到限制？為什么嵌入式目標機不能用來開發(fā)嵌入式軟件呢？為達到高性能或簡潔性，目標機都進行過優(yōu)化。它們缺乏開發(fā)所必需的設備(例如鍵盤、顯示器、網絡等)。一般而言，嵌入式開發(fā)被稱為“跨平臺開發(fā)”。本句提出兩個問題，Because引導兩個并列句對其進行解釋。

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

為什么要簡潔化？考慮到嵌入式系統(tǒng)的性能，體積小、廉價、低功耗的微處理器芯片是比龐大的設備更可行、更合適的選擇。本句的主框架是：DependingonA,BareviableandpreferableoptionstoC，考慮到A、B是比C更可行、更合適的選擇。

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

隨著對功能需求的增加，或需要建立優(yōu)先級，在嵌入式系統(tǒng)中加入一些決策機制將顯得尤為重要。最先進的系統(tǒng)實際上有一個微小的、精簡的操作系統(tǒng)在運行，這是在32位或64位處理器上執(zhí)行的。這就是所謂的實時操作系統(tǒng)(RTOS)。兩個并列的現(xiàn)在分詞短語runningtheshow(掌管一切)和executingona32-bitor64-bitprocessor修飾operatingsystem。

(1)?Thefourdescriptionsbelow,whicharetoilluminateembeddedsystem？()

A.?Mustbedevelopedinacross-developmentenvironment.

B.?Implementfunctionsthatprovideanelementofcontrolinanasynchronousworld.

C.?Thesystemwillperformancebetterifit’