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基于IEEEP1687的可变扫描链设计
Introduction
Asthecomplexityofdigitalcircuitscontinuestoincrease,thetestingprocessbecomesmorechallenging.TheriseofSystem-on-Chip(SoC)designshasledtoanincreaseinthenumberoftestpointsandtheneedforamoreefficientandeffectivetestingstrategy.Asaresult,theIEEE1687standard,alsoknownastheInternalJTAG(IJTAG),hasemergedasapromisingsolutionforfacilitatingtestingofcomplexdesigns.OneofthekeyfeaturesofIEEE1687istheuseofVariableScanChains(VSCs),whichallowsforflexibleandefficienttestingofcircuits.ThispaperexplorestheconceptofVSCsinmoredetailanddiscussestheirpotentialbenefits.
VariableScanChains
Traditionalscanchainsrequirethatallinputsandoutputsofthescanchainbeconnectedtothetestaccessmechanism(TAM)fortesting.Thisapproachcanbecomeimpracticalforcomplexdesignsasthenumberoftestpointsincreases.VSCsprovideamoreflexiblesolutionbyallowingcertainscanchainelementstobeexcludedfromthetest.Thisapproachreducesthenumberoftestpointsandcanleadtosignificantsavingsintestingtimeandcost.
TheuseofVSCsalsoprovidesflexibilityindesign-for-testability(DFT)andtestscheduling.Theabilitytoprogramthescanchainelementsthatparticipateintestingcanbeleveragedtoreducethenumberoftestpatternsneededtovalidatethedesign.Thisreductionintestpatternstranslatestoadecreaseintestingtimeandcost.
Inaddition,VSCsenablethetestingofspecificregionsofthecircuit.Thiscapabilityallowsfortargetedtestingofcriticalcomponentsofthedesign,suchasthememoryorthecommunicationbus,whichcanincreaseconfidenceintheoverallfunctionalityofthedesign.
IEEE1687andVSCs
TheIEEE1687standarddefinesaflexibleandcustomizableinfrastructureforaccessingembeddedinstrumentswithinadesign.Thestandarddefinesahierarchicalstructureforinstruments,whereeachlayerofthehierarchyrepresentsadifferentlevelofabstraction.Theinfrastructureisdesignedtobescalableandcanaccommodatedifferentlevelsofcomplexityinthedesign.
VSCsareanessentialfeatureofIEEE1687.ThestandarddefinestheuseofVSCstoprovideflexibilityintestingandtoreducethenumberoftestpointsrequired.Thestandarddefines