Testing and Debugging DSP Systems.docx

Testing and Debugging DSP Systems.docx

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TestingandDebuggingDSPSystems

TestingandDebuggingDSPSystems,Part1

RobOshana,TexasInstruments

2/22/20073:

00AMEST

Parttwo explainstheworkingsoftheJTAG（IEEE1149.1）boundary-scantechnology.

Insoftwaredevelopment,perhapsthemostcritical,yetleastpredictablestageintheprocessisdebugging.Manyfactorscomeintoplaywhendebuggingsoftwareapplications.Amongthesefactors,timeisoftheutmostimportance.Thetimerequiredtosetupanddebuga software applicationcanhavesignificantimpactsontime-to-market,meetingcustomerexpectations,andthefinancialimpactofawelldevelopedproductthatsucceedsinthemarket.Theintegrationofanapplicationfollowsamodelofmultiplespiralsthroughthestagesofbuild,load,debug/tune,andchange,asshowninFigure1.

Figure1Theintegrationanddebugcycle.Thegoalistominimizethenumberoftimesaroundthisloopaswellasminimizingthetimespentineachsegment.

Debuggingembeddedreal-timesystemsispartartandpartscience.Thetoolsandtechniquesusedindebuggingandintegratingthesesystemshaveasignificantimpactontheamountoftimespentinthedebug,integration,andtestphase.Themorevisibilitywegainintotherunningsystem,thefasterweareabletodetectandfixbugs.

Oneofthemoretraditionalandsimplestwaysofgainingvisibilityintothesystemistoaddmessagesatcertainpointsinthesoftwaretooutputinformationaboutthestateofthesystem.Thesemessagescanbeintheformof"printf"statementsoutputtoa monitor ortheblinkingofaLEDorsetofLEDstoindicatesystemstatusandhealth.Each function ortaskcanbeginbyoutputtingastatusmessagetoindicatethatthesystemhasmadeittoacertainpointintheprogram.Ifthesystemfailsatsomepoint,diagnosisofthe outputmessagescanhelptheengineerisolatetheproblembyknowingwherethesystemwaslast"good."Ofcourse,instrumentingthesysteminthiswayintroducesoverhead,whichchangesthebehaviorofthesystem.Theengineermusteitherremovetheinstrumentationafterthesystemhasbeentestedandre-validatethesystembeforeshipping,orshipthesystemwiththeinstrumentedcodeinthesystem.Theengineermustusuallyshipwhatisbeingtested（includingthisinstrumentation）andtestwhatisgoingtobeshipped.

Engineerscanusemoresophisticateddebugapproachestoreducethetimespentintheintegrationandtestphase.Oneapproachistheuseofadevicecalleda"debugmonitor."AdebugmonitorisarelativelysmallpieceofcodeembeddedinthetargetapplicationorintegratedintothemicrocontrollerorDSPcorethatcommunicatesovera serial interface toahostcomputer[1].Thesemonitorsprovidetheabilitytodownloadcode,readandwriteDSPmemoryandregisters,setsimpleandcomplex breakpoints, singlestep theprogram,andprofile sourcecodeatsomelevel.

ForsystemswithROMbasedsoftwareprograms,anotherformofdebugmonitor,calledaROMemulator,isused.AROMemulatorisaplug-inreplacementforthetargetsystemROMdevices.Theplug-indeviceconnectstothehostcomputeroveralink（serial,parallel,Ethernet,andsoon）.AROMemulatorprovidestheengineerwithfasterturnaroundtimeduringthedebuggingprocess.Insteadofre-programmingtheROMdeviceusingaROMprogrammerforeachsoftwareiteration,thecodecaninsteadbedownloadedintofastRAMontheROMemulator.ThesystemisthenrunasifcodewasrunningoutoftheROMdevice.

DebugmonitorsandROMmonitorscertainlyprovidealargebenefittotheembeddedsystem debugphase.But,asembeddedprocessorsbecomefasterandfaster,andassystemsmigratetosystemonachipsolutions,visibilityintotheinternalprocessorpresentschallengesthatrequireevenmoresophisticateddebugsolutions.

Integratinganddebuggingcomplexdigitalsystemsalsorequirestheuseofsophisticatedandcomplexdebugtoolssuchas logicanalyzers.Alogicanalyzerisatoolthatallowsthesystemintegratortocaptureanddisplaydigitalsignalsinvariousformatssuchasbit,byte,andwordformats.Usingalogicanalyzer,thesystemintegratorcananalyzedigitalbehaviorsuchas:

∙Digitalcounters

∙Complexstatemachines

∙BuffersandFIFOs

∙Systembuses

∙Othersystemonachip（SoC）functionssuchasFPGA,ASICandstandardcellimplementations

Logicanalyzersarepowerfultoolsthatarealsoportableandveryversatile.Thesetoolsrequireasmalllearningcurveaswellashighinitialinvestment（dependingonhowmuchcapabilityisneededbythetoolandwhatclockratesneedtobesupported）.Byusingtriggeringmechanismsinthetool,thesystemintegratorcancapturedataintolargebufferswithinthelogicanalyzer.Thisdatacanbepre-triggerdata,post-triggerdata,oracombination.Tracescanbesavedandprintedandthedatacanbefilteredinanumberofdifferentways.

AfundamentaldisadvantagetousingalogicanalyzerforembeddedDSPsoftwaredebugisthattheyarecomplexhardwaredebugtoolsbeingusedforsoftwaredebug.Thedegreeofsuccessusingalogicanalyzerisrelatedtohowhardwaresavvythesystemintegratorissincethetoolishardware-debugbasedandmayrequirecomplexsetupandconfigurationtogettherightinformationtoanalyze.

Anotherdisadvantagetousingalogicanalyzerforsystemdebugisvisibilityofthesignals.AlogicanalyzerneedstobeconnectedtothepinsoftheDSPdeviceinordertogetvisibilityintothesystem.ThevisibilityislimitedbythetypesofpinsontheDSP.AsDSPdevicesbecomemoreintegratedintosystemonachipcapability,thevisibilitytoseewhatisgoingoninsidethedevicediminishes.

Footnote

1.ArnoldBergerprovidesaveryintuitiveoverviewofdebuggersin EmbeddedSystemsDesign,Chapter6,CMPBooks,copyright2002.

TestingandDebuggingDSPSystems,Part1

RobOshana,TexasInstruments

2/22/20073:

00AMEST

DebugChallengesforDSP

Vanishingvisibility

In1988,theembeddedsystemindustrywentthroughachangefromconventional InCircuitEmulation[2]toscanbasedemulation.Thiswasmotivatedbydesigncycletimepressuresandnewlyavailablespaceontheembeddeddeviceforon-chipemulation.Scan-based,or JTAG,emulationisnowwidelypreferredovertheolderandmoreexpensive"in-circuitemulation,"or"ICE"technology.

DebugChallengesforDSP

ThehavebeenanumberofindustryforcesthathavebeenchangingtheDSPsystemdevelopmentlandscape:

Systemlevelintegration;Asapplicationcomplexityhasincreasedandsystemonachipcomplexityhasledtosmallerfootprints,thevisibilityintothesystemcomponentshasdiminished（Figure2）.Embeddedsystembusesleadtoaninstrumentationchallenge.Widersystembusesalsoleadtosystem bandwidthissues.Programcontrolintheseenvironmentsisdifficult.

Figure2Systemlevelintegrationleadstodiminishingvisibility（courtesyofTexasInstruments）

Inordertorestorevisibility,DSPvendorshaveaddressedtheissueonseveralfronts:

On-chipinstrumentation –Assystemsbecomemoreintegrated,on-chipvisibilityintothedeviceoperationisbecomingblocked（Figure3）. Bus snoopinglogicanalyzerfunctionshavebeenimplementedinon-chiplogic.Examplesofthisincludetriggeringlogictofindtheeventsofinterest,tracecollectionandexportlogictoallowingtheviewingofevents,andmaximizingexportbandwidthperavailablepinontheDSPcore.Debugcontrolisthroughanemulatorwhichextractstheinformationofinterest.

Figure3Vanishingvisibilityrequiresadvanceddebuglogicon-chip（courtesyofTexasInstruments）

Offchipcollectionfoundation –OncethedataisexportedfromtheDSPcore,thedatamustbestored,processed,filtered,andformattedinsuchawayastobeusefultothosetestengineerstointerpretthedatameaningfully.

Datavisualizationcapability –DSPintegrationcapabilitiesincludetheabilitytoeasilyviewthedataindifferentconfigurations.TheentirechainisshowninFigure4.Thelogicanalyzerfunctionsarenowon-chip,thecontrolandinstrumentationcollectionisprimarilythroughtheemulationcontroller,andthedataisdisplayedonthehostinavisualizationcontainer.Thekeychallenge,then,istoproperlyconfigurethesystemtocollecttherightdataattherighttimetocatchtherightproblem.

（Clicktoenlarge）

Figure4DSPtoolsareusedtovisualizedebugdataextractedfromtheDSP（courtesyofTexasInstruments）

Applicationspacediversity –DSPapplicationsarebecomingmorediverseandthispresentschallengestoDSPtestandintegrationengineers.Thisdiverseapplicationspacespectrumrequiresdifferentcostmodelsfordebugsupport:

∙DSPbasestationapplicationsrequirehighbandwidth,highfrequencydebugcapabilities.

∙Voiceover IP applicationsrequireMIPSdensityandmanyhomogeneousprocessorsperboard.

∙Cellphoneandother wireless applicationsrequireheterogeneousmultiprocessorsandveryhighsystemlevelintegration.

∙AutomotiveDSPapplicationsrequirelowcostdebugsolutionswhereDSPchippinsareatapremium.

Userdevelopmentenvironment;thedevelopmentenvironmentforDSPdevelopersischangingandDSPdebugtechnologiesarechangingtoaccommodatethesenewenvironments.DSPengineersaretransitioningdebugplatformsfromdesktopPCsystemstolaptopsthatareportabletothefieldfordebuginthecustomer'senvironment.PortableremoteapplicationsrequireportableDSPdebugenvironments.

Continuedclockrateincreases;asDSPcoreclockspeedsincreasemoredataisrequiredtoperformdebugging.Infact,theamountofdatarequiredtoperformdebugandtuningisdirectlyproportionaltotheDSPcore clock speed.MoreDSPpinsandmoredataperpinarerequiredtomaintaintherequiredvisibilityi