Modelling patterns for analysis and design of real

ModellingPatternsforAnalysisandDesignofReal-TimeSystemsOanaFlorescu,JeroenVoeten,HenkCorporaalESReportsISSN1574-9517ESR-2006-0515July2006EindhovenUniversityofTechnologyDepartmentofElectricalEngineeringElectronicSystems©2006TechnischeUniversiteitEindhoven,[e-mail]echnologyDepartmentofElectricalEngineeringElectronicSystemsPOBox513NL-5600MBEindhovenTheNetherlandsModellingPatternsforAnalysisandDesignofReal-TimeSystems∗OanaFlorescu,JeroenVoetenandHenkCorporaalEindhovenUniversityofTechnologyElectricalEngineeringDepartmentP.O.Box513,5600MBEindhoven,[e-mail]tnessandperformanceofreal-timeembeddedsystems,earlyevaluationofpropertiesisneeded.Basedondesignexperienceforreal-timesystemsandusingtheconceptsofthePOOSLlanguage,weintroducemodellingpatternsthatalloweasycompositionofmodelsfordesignspaceexploration.Thesepatternscoverdifferenttypesofreal-timetasks,resourcesandmappings,andincludealsoaspectsthatareusuallyignoredinclassicalanalysisapproaches,liketaskactivationlatencyorexecutioncontextswitches.Theconstructionofsystemmodelscanbedonebyintegratingthenecessarypatterns,asillustratedintwocasestudies.1.IntroductionComplexreal-timeembeddedsystemsareusuallycomprisedofacombinationofhardwareandsoftwarecom-ponentsthataresupposedtosynchroniseandcoordinatedifferentprocessesandactivities.Fromearlystagesofthedesign,manydecisionsmustbemadetoguaranteethattherealisationofsuchacomplexmachinemeetsallthefunctionalandnon-functional(timing)requirements.Oneofthemainproblemstoaddressconcernsthemostsuitablearchitectureofthesystemsuchthatalltherequirementsaremet.Toproperlydealwiththisquestion,thecommonapproachesaredesignspaceexplorationandsystemlevelperformanceanalysis.Anextensiveoverviewofsuchmethodologiesisgivenin[3]and[12].Theyrangefromanalyticalcomputation(ModularPerformanceAnalysis[25])tosimulation-basedestimation(Spade[16],Artemis[21]).Theseareoftenspecialisedtechniqueswhichclaimthatgeneralpurposelanguagesareill-suitedforsystem-levelanalysis.However,duetotheheterogeneityandcomplexityofsystems,fortheanalysisofdifferentaspectsdifferentmodelsneedtobebuiltandtheircouplingisdifficult.Therefore,aunifiedmodel,coveringalltheinterestingaspects,isactuallyneededtospeedupthedesignprocess.ThisishowtheUnifiedModellingLanguage(UML)[20]cametobeconceived.Thelanguagewasdesignedmainlyforobject-orientedsoftwarespecification,butrecentlyitwasextended(UML2.0)toinclude(real-time)systemsaswell.Duringthedevelopmentofnewsystems,specificproblemsareencounteredagainandagain,andexperienceddesignersapplythesolutionsthatworkedfortheminthepast[9].Thesepairsofproblem-solutionarecalleddesignpatternsandtheirapplicationhelpsingettingadesign“right”faster.Withtheincreaseinthedevelopmentofreal-timesystems,designpatternswereneededfordealingwithissueslikeconcurrency,resourcesharing,distribution[8].AsUMLhasbecomethestandardlanguageformodelling,thesepatternsaredescribedinUML.However,thesemanticsofthelanguageisnotstrongenoughtoproperlydealwiththeanalysisofreal-timesystem∗ThisworkhasbeencarriedoutaspartoftheBodercprojectundertheresponsibilityoftheEmbeddedSystemsInstitute.ThisprojectispartiallysupportedbytheNetherlandsMinistryofEconomicAffairsundertheSenterTSprogram.behaviour.Therefore,anexpressiveandformalmodellinglanguageisrequiredinsteadinordertocaptureinacompactmodeltiming,concurrency,probabilitiesandcomplexbehaviour.Designpatternsrefertoproblemsencounteredinthedesignprocessitself,butproblemsappearalsointhespecificationofcomponentsthatarecommonlyencounteredincomplexsystems[11].Althoughcomponentsoftheanalysedsystemsexhibitsomecommonaspectsforallreal-timesystems(e.g.characteristicsoftaskslikeperiodicityoraperiodicity,processors,schedulersandtheiroverheads),theyarebuilteverytimefromscratchandsimilarissuesareencounteredoverandover.Contributionsofthepaper.Toreducetheamountoftimeneededtoconstructmodelsfordesignspaceex-ploration,weproposemodellingpatternstoeasilycomposemodelsforthedesignspaceexplorationofreal-timeembeddedsystems.Thesemodellingpatterns,providedasalibrary,actliketemplatesthatcanbeappliedinmanydifferentsituationsbysettingtheappropriateparameters.Theyarebasedontheconceptsofamathematicallydefinedgeneral-purposemodellinglanguage,POOSL[24],andtheyarepresentedasUMLdiagrams.Theseboil-erplatesolutionsareacriticalsuccessfactorforthepracticalapplicationinanindustrialsettingandareasteptowardsthe(semi-)automateddesignspaceexplorationintheearlyphasesofthesystemlife-cycle.Thispaperisorganisedasfollows.RelatedresearchworkispresentedinSection2.Section3brieflypresentsthePOOSLlanguage,whereasSection4providesthemodellingpatterns.ThecompositionofthesepatternsintoamodelisdiscussedinSection5andtheiranalysisapproachinSection6.TheresultsofapplyingthisapproachontwocasestudiesarepresentedinSection7.ConclusionsaredrawninSection8.2.RelatedResearchAnextensiveoverviewofperformancemodellingandanalysismethodologiesisgivenin[3]and[12].Theyrangefromanalyticalcomputat