毕业设计 外文翻译 CAN总线系统的实时对象调用Word格式.docx
- 文档编号:18693187
- 上传时间:2022-12-31
- 格式:DOCX
- 页数:8
- 大小:26.76KB
毕业设计 外文翻译 CAN总线系统的实时对象调用Word格式.docx
《毕业设计 外文翻译 CAN总线系统的实时对象调用Word格式.docx》由会员分享,可在线阅读,更多相关《毕业设计 外文翻译 CAN总线系统的实时对象调用Word格式.docx(8页珍藏版)》请在冰豆网上搜索。
毕业设计外文翻译CAN总线系统的实时对象调用@#@InvocationofReal-TimeObjectsinaCANBus-System@#@Abstract@#@Thepaperfocusesonmethodinvocationofreal-timeobjectsinaCAN-baseddistributedreal-timesystem.Asimpleobjectmodelisintroduced,whichallowstheconvenientmodellingofhardwareandsoftwarecomponents.Relatedtotheobjectmodel,twoissuesarediscussed.Firstly,amodelisintroducedwhichallowstoformandaddressobjectgroups.Thisreflectsabasicneedinareal-timesystemtodistributeinformationtomultipleclientsefficiently.Secondly,wediscussanapproachtoexpresstimingrequirementsforobjectinvocations.Toachievedistributedconsensusoncommunicationresourceaccess,anEDF-likeapproachisintroduced,whichtakesadvantageofknowledgeaboutdeadlines,thenumberofremainingcommunicationactivities,andtheremainingworst-caseexecutiontimefortheinvokedmethodateachpointoftime.@#@1.Introduction@#@Futurecomputersystemswill,toalargeextent,monitorandcontrolreal-worldprocesses.Thisresultsinaninevitabledemandfortimelinessandreliability.Distributedsystemswhichinherentlyprovideimmunityagainstsinglefailuresareanadequatearchitecturetomeetthegoalofreliability.Additionally,becauserealworldapplicationsoftenrequirethespatiallydistributedcontrolofelectromechanicalcomponents,adistributedsystemarchitecturebringscomputingpowertothepointswhereitisneeded.Theavailabilityofinexpensiveyetpowerfulmicrocontrollerssupportsadistributedsolution.Thisresultsinasystemmodelwhichiscomposedfromsmartcomponentsimplementingtheinstrumentationinterfacetotherealworldcomprisingsensorsandactuators.Aconvenientwaytomodelsuchanenvironmentistouseanobject-basedapproachwhereobjectsencapsulateallkindsofentitiesnecessarytocontrolaphysicalprocess.@#@Wecanidentifyatleasttwolayersinsystemsinteractingwiththerealworld.Alowerresponsivesystemleveltightlycontrollingthesensor/actuatorinterfacetotheworldandahighersystemlevelresponsibleforinterpretationandevaluationoftheperceptionoftheworldascommunicatedbytheinstrumentationinterface.Inthislayer,higherleveldecisionsareperformed.Althoughthesedifferentlevelshavedifferentrequirementsconcerningresponsiveness,theyaresometimesnotseparatedclearlysimplybecauseofthehardwarearchitecture.Weconcentrateonthelowersystemlevelanddescribeanobjectmodelwhichismotivatedbyasystemstructurewhichreliesonamodulardesignandindependentcomputingresourcesforthecomponentsoftheinstrumentationinterface.Ratherthanhavingacentralpowerfulprocessorinwhichelectromechanicalcomponentsareonlymodelledasobjectsfromwhichcontrolsignalsaregenerated,theelectromechanicalcomponentsareobjectsthemselvespoweredbyinexpensivemicrocontrollers.Theobjectsofthislayerhaveawelldefinedinterfacetobeeasilycontrolledbyahigherlevelinstancewhichcanexploitthisabstractionratherthandealingwithlowlevelcontrolsignals.@#@Thehardwaremodulesareconnectedbyafield-bus.WechoosetheCAN-bus(CAN:
@#@ControllerAreaNetwork),developedbyBOSCH[[28]]becauseitprovidesadvancedtechnicalfeaturesandrepresentsanemergingstandardwithawideapplicability.Moreover,popularmicrocontrollersareavailablewithanon-chipCANcontroller.CANisasharedbusdesignedtoconnectcontrolsystemsinaspatiallyrestrictedarealikecars,robots,toolmachines,andotherautomotiveorindustrialautomationapplications.Itistargetedtooperateinanoisyenvironmentwithspeedsofupto1Mbit/sec,exchangingsmallreal-timecontrolmessages.WeusetheCANmessageformattouniformlyinvokemethodsonourobjects.Thisallowsatransparentobjectinvocationinthesensethataninvokingobjectmustnotknowwheretheinvokedobjectresidesinthesystem.Additionally,wecanaddressgroupsofobjectswithasingleCANmessage.@#@Asacommonresource,thecommunicationmediumhastobesharedbyallcomputingnodes.Accesstothemediumhastobescheduledinawaythatdistributedcomputationsmeettheirdeadlinesinspiteofcompetitionforthecommunicationline.Sincetheschedulingofthebuscannotbebasedonlocaldecisions,adistributedconsensusaboutthebusreservationhastobeachieved.Clearly,thisisonlyaspecialcaseofthemoregeneralproblemtoscheduleacooperativedistributedcomputation.@#@Thereexistseveralalternativeapproachestosolvethisproblembasedontheassumptionsaboutthebehaviourofthesystemandtheenvironment.Thefirstapproach,knownastime-triggeredapproach[[18]],[[21]],[[19]]assumesacompleteknowledgeofallfutureactionsofthesystem.Hence,duringoperationthesesystemsexhibitminimaloverheadpairedwithamaximumofpredictabilityandarehighlyappropriateforsafety-criticalapplicationswhichcanbemodelledbyaperiodicbehaviour.@#@Amoreadaptableandeconomicwaytomanagesystemresourceshastobebasedonrun-timeinformation.Thesereal-timesystemshavetoplantheiroperationatrun-time,atleasttoacertainextent.Althoughthetrade-offgenerallyisbetweenadaptabilityandpredictability,thesesystemsarescalableinthesensethattheyallowacoexistenceofactivitieswithdifferentreal-timerequirements.Thesesystemsrelyonrun-timeguarantees[[30]],[[11]]ratherthanonapreplannedfeasibilityguaranteeonly.Aformofcalendar-basedscheduling[[22]],[[30]]isanapproachtorun-timeguaranteeswherehardreal-timeactivitieshavethepossibilitytoreserveresourcesinadvance.Thefreeresourcescanbeusedbylessimportanttasks.Itshouldbenotedthatschedulingpolicieslikee.g.earliestdeadlinefirst(EDF),leastlaxityfirst(LLF)orratemonotonicschedulingonlyguaranteeoptimality,i.e.ifascheduleexists,itwillbefound.Butinthedynamicsystem,theremaybeconflictingrequestsforwhichtheseschedulingpolicieswillnotfindasolution.Inthiscasetheyfailtoguaranteeanything.Acalendar,ontheotherhand,isamechanismtoguaranteeresourceavailabilityforreservationswhichhavealreadybeenmade.@#@@#@2.TheSystemModel@#@Oursystemmodelisinfluencedbyouranticipatedhardwarebasis.Weassumeanumberofdifferentmicrocontrollerswithdifferentperformanceattributesrangingfrom8Bitto32Bitarchitectures.AllmicrocontrollersareequippedwithaCAN-Businterface.Weexploitthedifferentperformanceandpricecharacteristicsofthemicrocontrollerstostructuretheoveralltaskofthesystemintosmallpackages.Sincethesimplemicrocontrollersareintherangeofafew$s,itmustnolongerbearareresource.Inourapplicationexample,asimpleactivesuspensionsystem(Fig.2-1),weuseasimplemicrocontrollerforeachservoorcomplexsensor.Aservoiscomposedfromamotorandaninternalsensorwhichprovidesfeedbackonthecurrentposition.Thissensor/actuatorsystemisconnectedtotheCAN-bustocooperatewithothersimilarobjectsandreceivecontrolcommandsthroughCANmessages.Nodirect,lowlevelcontrolsignalsarevisibleoutsidethemodule.Thus,encapsulationandawelldefinedinterfacearesupported.Onthelogicallevel,thesensor/actuatorblockisseenasanobjectonwhichcertainmethodscanbeinvoked,e.g.topositionitselftoaspecificangel,tocommunicatetheangel,etc.Asensor/actuatorconstitutesthelowestlevelinthecontrolhierarchy,comparablewithasimplereflexloopinabiologicalsystem.Highercontrolinstancesareavailabletocontrolgroupsofobjectsoreventuallytheentiresystemusingmorepowerfulmicroprocessors.Thus,thehighercontrolinstanceshaveawelldefinedinstrumentationinterfacewhichiscomposedfromobjects,eachencapsulatingacertainfunctionality.@#@Anobjecthasauniquenameandasetofassociatedoperations.Theuniquenameoftheobjectistranslatedtoashortformsystemnameduringrun-timeandmaintainedbyaconfigurationservice.Objectsinsuchanenvironmentmusthavesomeextensionstothesequential,passivemodelknownfromthefieldofprogramminglanguages.Particularlyourmodelincludes:
@#@@#@1).Active,autonomousobjects.@#@Sinceobjectsmayhaveadedicatedprocessor,itisstraightforwardtoassumeamodelofautonomous,activeobjects.Anobjectischaracterizedbyanameandalistofmethodswhichcanbeinvokedontheobject.Becausetheobjectisactive,itcanalsoexportinformation.Thisisequivalenttosendinganinvocationtoanotherobjectortoagroupofobjectswithoutapreviousrequest.Asdescribedinchapter3,weprovideatransparentgroupcommunicationmechanism,i.e.anobjectitselfusuallydoesnotknowwhetheritcommunicateswithanobjectonaremoteoronthelocalnode.Thisgroupcommunicationmechanismisabasisforremotemethodinvocationofobjectgroups.Infact,communicationrelationscandynamicallybedefinedduringruntime.So,objectsmayjoinorleaveagroup,andareautonomousindecidingwhentoprocessarequest.@#@TheconceptofTMO(time-triggeredmessagetriggeredobject)[[16]]derivedfromtheRTO.K(Real-TimeObject)[[17]]conceptenhancestheconventionalobjectmodelbymechanismstospecifythetemporalbehaviourofanobject.Itprovidesaframeworktospecifyacomplexreal-timesystemtogetherwithitsenvironmentinthesameuniformrepresentation.Theaimisanintegrateddesignofadistributedreal-timesystemandsimulatorsgeneratingreal-timeinputmodellingthetargetapplications.ATMOexhibitsactive,spontaneousbehaviouraswellasprovidingservicesrequestedbyamethodcall.ThreeexecutionmodelsarederivedforexecutingTMOS[[17]].Amongthem,theexecutionmodelwhichprovidesadedicatedprocessorforeachobject(TypeII)isverys
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 毕业设计 外文翻译 CAN总线系统的实时对象调用 外文 翻译 CAN 总线 系统 实时 对象 调用
![提示](https://static.bdocx.com/images/bang_tan.gif)