《信息科學(xué)類專業(yè)英語(yǔ)》課件第16章

Lesson16EmbeddedSystems:aPrimer

(第十六課嵌入式系統(tǒng)：初級(jí))

Vocabulary(詞匯)ImportantSentences(重點(diǎn)句)Multiple-choiceQuestion(多選題)

Problems(問(wèn)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(nèi)含的,嵌入式。

2.?infrastructuresn.基建,配套結(jié)構(gòu),基本建設(shè)。

3.?impressiveadj.給人印象深刻的,感人的。

4.?pindown把……固定住;使動(dòng)彈不得,迫使作出決定,采取行動(dòng)。

5.?reiterate?vt.反復(fù)地說(shuō),重申。Vocabulary

6.?autopilot?n.自動(dòng)駕駛儀。

7.?asynchronous?adj.異步的。

8.?unpredictable?adj.無(wú)法預(yù)言的，不可預(yù)測(cè)的。

9.?piston?n.活塞。

10.?RTOS(Real-TimeOperatingSystem)實(shí)時(shí)操作系統(tǒng)。

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

[1]Anembeddedsystemisanysoftwaresystemthatmustbedesignedonaplatformdifferentfromtheplatformonwhichthesystemisintendedtobedeployed.

嵌入式系統(tǒng)是一種設(shè)計(jì)平臺(tái)與運(yùn)行平臺(tái)不同的軟件系統(tǒng)。deploy，部署，調(diào)遣，展開(kāi)，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(tái)是什么？對(duì)于開(kāi)發(fā)者來(lái)說(shuō)，平臺(tái)指的是一種操作系統(tǒng)，能進(jìn)行軟件的開(kāi)發(fā)工作，例如Windows、Solaris、HP操作系統(tǒng)等。對(duì)目標(biāo)機(jī)來(lái)說(shuō)，平臺(tái)指的是一種設(shè)備，嵌入式軟件能運(yùn)行于其上。本句子的結(jié)構(gòu)是：“Whatismeantbyplatform?Onthedevelopmentside,…Onthetargetside,…”什么是平臺(tái)？對(duì)于開(kāi)發(fā)者來(lái)說(shuō)……對(duì)于目標(biāo)機(jī)來(lái)說(shuō)……。

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

為什么基于目標(biāo)機(jī)的開(kāi)發(fā)會(huì)受到限制？為什么嵌入式目標(biāo)機(jī)不能用來(lái)開(kāi)發(fā)嵌入式軟件呢？為達(dá)到高性能或簡(jiǎn)潔性，目標(biāo)機(jī)都進(jìn)行過(guò)優(yōu)化。它們?nèi)狈﹂_(kāi)發(fā)所必需的設(shè)備(例如鍵盤、顯示器、網(wǎng)絡(luò)等)。一般而言，嵌入式開(kāi)發(fā)被稱為“跨平臺(tái)開(kāi)發(fā)”。本句提出兩個(gè)問(wèn)題，Because引導(dǎo)兩個(gè)并列句對(duì)其進(jìn)行解釋。

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

為什么要簡(jiǎn)潔化？考慮到嵌入式系統(tǒng)的性能，體積小、廉價(jià)、低功耗的微處理器芯片是比龐大的設(shè)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(duì)功能需求的增加，或需要建立優(yōu)先級(jí)，在嵌入式系統(tǒng)中加入一些決策機(jī)制將顯得尤為重要。最先進(jìn)的系統(tǒng)實(shí)際上有一個(gè)微小的、精簡(jiǎn)的操作系統(tǒng)在運(yùn)行，這是在32位或64位處理器上執(zhí)行的。這就是所謂的實(shí)時(shí)操作系統(tǒng)(RTOS)。兩個(gè)并列的現(xiàn)在分詞短語(yǔ)runningtheshow(掌管一切)和executingona32-bitor64-bitprocessor修飾operatingsystem。

(1)?Thefourdescriptionsbelow,whicharetoilluminateembeddedsystem？()

A.?Mustbedevelopedinacross-developmentenvironment.

B.?Implementfunctionsthatprovideanelementofcontrolinanasynchronousworld.

C.?Thesystemwillperformancebetterifit’