何少华计算机专业英语论文Word格式文档下载.docx
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何少华计算机专业英语论文Word格式文档下载.docx
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班级:
软件09K2
姓名:
何少华
学号:
0919*******
ABSTRACT
Weintroduceatextbookthatstrivestoidentifyandintro-ducethedurableintellectualideasofembeddedsystemsasatechnologyandasasubjectofstudy.Theemphasisisonmodeling,design,andanalysisofcyber-physicalsystems,whichintegratecomputing,networking,andphysicalpro-cesses.Thebookisintendedforstudentsattheadvancedundergraduatelevelortheintroductorygraduatelevel,andforpracticingengineersandcomputerscientistswhowishtounderstandtheengineeringprinciplesofembeddedsys-tems.Itisalsoanexperimentinpublishing.Thebookisavailablefreeinelectronicform,intheformofPDFfilede-signedspecificallyforon-linereading.Specifically,thelay-outisoptimizedformedium-sizedscreens,particularlytheiPadandforthcomingtablets.Extensiveuseofhyperlinksandcolorenhancetheonlinereadingexperience.Aprintversionwillbeavailablethroughaprint-on-demandservice,enablingrapidevolutionandimmediatecorrectionoferrors.Seehttp:
//LeeSeshia.org.
1.INTRODUCTION
Themostvisibleuseofcomputersandsoftwareispro-cessinginformationforhumanconsumption.Weusethemtowritebooks(liketheonepresentedhere),searchforinfor-mationontheweb,communicateviaemail,andkeeptrackoffinancialdata.Thevastmajorityofcomputersinuse,however,aremuchlessvisible.Theyruntheengine,brakes,seatbelts,airbag,andaudiosysteminyourcar.Theydigi-tallyencodeyourvoiceandconstructaradiosignaltosenditfromyourcellphonetoabasestation.Theycontrolyourmicrowaveoven,refrigerator,anddishwasher.Theyrunprintersrangingfromdesktopinkjetprinterstolargeindustrialhigh-volumeprinters.Theycommandrobotsonafactoryfloor,powergenerationinapowerplant,processesinachemicalplant,andtrafficlightsinacity.Theysearchformicrobesinbiologicalsamples,constructimagesoftheinsideofahumanbody,andmeasurevitalsigns.Theypro-cessradiosignalsfromspacelookingforsupernovaeandforextraterrestrialintelligence.Theybringtoystolife,enablingthemtoreacttohumantouchandtosounds.Theycontrolaircraftandtrains.Theselessvisiblecomputersarecalledembeddedsystems,andthesoftwaretheyruniscalledembeddedsoftware.
Despitethiswidespreadprevalenceofembeddedsystems,computersciencehas,throughoutitsrelativelyshorthistory,focusedprimarilyoninformationprocessing.Onlyrecentlyhaveembeddedsystemsreceivedmuchattentionfromre-searchers.Andonlyrecentlyhasthecommunityrecognizedthattheengineeringtechniquesrequiredtodesignandana-lyzethesesystemsaredistinct.Althoughembeddedsystemshavebeeninusesincethe1970s,formostoftheirhistorytheywereseensimplyassmallcomputers.Theprincipalen-gineeringproblemwasunderstoodtobeoneofcopingwithlimitedresources(limitedprocessingpower,limitedenergysources,smallmemories,etc.).Assuch,theengineeringchallengewastooptimizethedesigns.Sincealldesignsben-efitfromoptimization,thedisciplinewasnotdistinctfromanythingelseincomputerscience.Itjusthadtobemoreaggressiveaboutapplyingthesameoptimizationtechniques.Recently,thecommunityhascometounderstandthattheprincipalchallengesinembeddedsystemsstemfromtheirinteractionwithphysicalprocesses,andnotfromtheirlim-itedresources.Thetermcyber-physicalsystems(CPS)wascoinedbyHelenGillattheNationalScienceFounda-tionintheU.S.torefertotheintegrationofcomputationwithphysicalprocesses.InCPS,embeddedcomputersandnetworksmonitorandcontrolthephysicalprocesses,usuallywithfeedbackloopswherephysicalprocessesaffectcompu-tationsandviceversa.Thedesignofsuchsystems,there-fore,requiresunderstandingthejointdynamicsofcomput-ers,software,networks,andphysicalprocesses.Itisthisstudyofjointdynamicsthatsetsthisdisciplineapart.WhenstudyingCPS,certainkeyproblemsemergethat
arerareinso-calledgeneral-purposecomputing.Forexam-ple,ingeneral-purposesoftware,thetimeittakestoperformataskisaperformanceissue,notacorrectnessissue.Itisnotincorrecttotakelongertoperformatask.Itismerelylessconvenientandthereforelessvaluable.InCPS,thetimeittakestoperformataskmaybecriticaltocorrectfunc-tioningofthesystem.Inthephysicalworld,asopposedtothecyberworld,thepassageoftimeisinexorable.
InCPS,moreover,manythingshappenatonce.Physi-calprocessesarecompositionsofmanythingsgoingonatonce,unlikesoftwareprocesses,whicharedeeplyrootedinsequentialsteps.AbelsonandSussman[1]describecomput-ingas“proceduralepistemology,”knowledgethroughpro-cedure.Inthephysicalworld,bycontrast,processesarerarelyprocedural.Physicalprocessesarecompositionsofmanyconcurrentprocesses.Measuringandcontrollingthedynamicsoftheseprocessesbyorchestratingactionsthatinfluencetheprocessesarethemaintasksofembeddedsys-tems.Consequently,concurrencyisintrinsicinCPS.Manyofthetechnicalchallengesindesigningandanalyzingem-beddedsoftwarestemfromtheneedtobridgeanintrinsi-callysequentialsemanticswithanintrinsicallyconcurrentphysicalworld.
Today,gettingcomputerstoworktogetherwithphysi-calprocessesrequirestechnicallyintricate,low-leveldesign.Embeddedsoftwaredesignersareforcedtostrugglewithinterruptcontrollers,memoryarchitectures,assembly-levelprogramming(toexploitspecializedinstructionsortopre-ciselycontroltiming),devicedriverdesign,networkinter-faces,andschedulingstrategies,ratherthanfocusingonspecifyingdesiredbehavior.Thesheermassandcomplex-ityofthesetechnologiestemptsustofocusanintroductorycourseonmasteringthem.Butabetterintroductorycoursewouldfocusonhowtomodelanddesignthejointdynamicsofsoftware,networks,andphysicalprocesses.Suchacoursewouldpresentthetechnologiesonlyastoday’s(ratherprim-itive)meansofaccomplishingthosejointdynamics.Thebookpresentedhereisourattemptatatextbookforsuchacourse.
2.RELATEDBOOKS
Mosttextsonembeddedsystemsfocusonthecollectionoftechnologiesneededtogetcomputerstointeractwithphys-icalsystems[2,3,4,9,14,16,19,22,23].Othersfocusonadaptationsofcomputer-sciencetechniques(likeprogram-minglanguages,operatingsystems,networking,etc.)todealingwithtechnicalproblemsinembeddedsystems[5,6,18].Whiletheseimplementationtechnologiesare(to-day)necessaryforsystemdesignerstogetembeddedsys-temsworking,theydonotformtheintellectualcoreofthediscipline.Theintellectualcoreisinsteadinmodelsandab-stractionsthatconjoincomputationandphysicaldynamics.Afewtextbooksoffereffortsinthisdirection.Jantsch[8]focusesonconcurrentmodelsofcomputation,Marwedel[12]focusesonmodelsofsoftwareandhardwarebehavior,andSriramandBhattacharyya[20]focusondataflowmodelsofsignalprocessingbehaviorandtheirmappingontopro-grammableDSPs.Theseareexcellentstartingpoints.Mod-elsandconcurrency(suchasdataflow)andabstractmodelsofsoftware(suchasStatecharts)provideabetterstartingpointthanimperativeprogramminglanguages(likeC),interruptsandthreads,andarchitecturalannoyancesthatadesignermustworkaround(likecaches).Thesetexts,how-ever,arenotsuitableforanintroductorycourse.Theyareeithertoospecializedortooadvancedorboth.Thisbookisourattempttoprovideanintroductorytextthatfollowsthespiritoffocusingonmodelsandtheirrelationshiptorealizationsofsystems.
Thevarietyoftextbooksonembeddedsystemsthathaveappearedinrecentyearsissurprising,oftenreflectingtheperspectiveofamoreestablisheddisciplinethathasmi-gratedintoembeddedsystems,suchasVLSIdesign,controlsystems,signalprocessing,robotics,real-timesystems,orsoftwareengineering.Someofthesebookscomplementtheonewepresentnicely.Westronglyrecommendthemtothereaderwhowishestobroadenhisorherunderstandingofthesubject.
Specifically,PattersonandHennessey[17],althoughnotfocusedonembeddedprocessors,isthecanonicalreferenceforcomputerarchitecture,andamust-readforanyoneinter-estedembeddedprocessorarchitectures.SriramandBhat-tacharyya[20]focusonsignalprocessingapplications,suchaswirelesscommunicationsanddigitalmedia,andgivepar-ticularlygoodcoveragetodataflowprogrammingmethod-ologies.Wolf[23]givesanexcellentoverviewofhardwarede-signtechniquesandmicroprocessorarchitecturesandtheirimplicationsforembeddedsoftwaredesign.MishraandDutt[13]giveaviewofembeddedarchitecturesbasedonarchi-tecturedescriptionlanguages(ADLs).Oshana[15]special-izesinDSPprocessorsfromTexasInstruments,givinganoverviewofarchitecturalapproachesandasenseofassembly-levelprogramming.
Focusedmoreonsoftware,Buttazzo[5]isanexcellentoverviewofschedulingtechniquesforreal-timesoftware.Liu[11]givesoneofthebesttreatmentsyetoftechniquesforhandlingsporadicreal-timeeventsinsoftware.E
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