集成电路设计-版图设计

1集成电路设计第九章

版图设计

2outlineFloor-PlanningBlockPlacement.GlobalRouting.SwitchboxRouting.3布图规划Floorplanning输入层次化网表描述模块间的互联，模块内逻辑单元及互联逻辑网表—物理描述的转换。布置模块、焊盘、电源、时钟。4datapathRAMstdcellfloorplanblocks5FloorplanningstrategiesFloorplanningmusttakeintoaccountblocksofvaryingfunction,size,shape.Mustdesign:spaceallocation;signalrouting;powersupplyrouting;clockdistribution.6PurposesoffloorplanningEarlyindesign:Prepareafloorplantobudgetarea,wirearea/delay.Tradeoffsbetweenblockscanbenegotiated.Lateindesign:Makesurethepiecesfittogetherasplanned.Implementthegloballayout.7PlaceandRoute8LayoutsynthesisTwocriticalphasesoflayoutdesign:placementofcomponentsonthechip;routingofwiresbetweencomponents.Placementandroutinginteract,butseparatinglayoutdesignintophaseshelpsusunderstandtheproblemandfindgoodsolutions.9布局Placement根据布图规划，布置模块内逻辑单元。目标：可布线最小延迟最小尺寸最小电压衰减10PlacementmetricsQualitymetricsforlayout:area;delay.Areaanddelaydeterminedinpartbywiring.Howdowejudgeaplacementwithoutwiring?Estimatewirelengthwithoutactuallyperformingrouting.11Wirelengthasaqualitymetricbadplacementgoodplacement12WirelengthmeasuresEstimatewirelengthbydistancebetweencomponents.Possibledistancemeasures:Euclideandistance(sqrt(x2+y2));Manhattandistance(x+y).Multi-pointnetsmustbebrokenupintotreesforgoodestimates.13PlacementtechniquesCanconstructaninitialsolution,improveanexistingsolution.Pairwiseinterchangeisasimpleimprovementmetric:Interchangeapair,keeptheswapifithelpswirelength.Heuristicdetermineswhichtwocomponentstoswap.14PlacementbypartitioningWorkswellforcomponentsoffairlyuniformsize.Partitionnetlisttominimizetotalwirelengthusingmin-cutcriterion.Partitioningmaybeinterpretedas1-Dor2-Dlayout.15Min-cutbisectingpartitioningpartition1partition2ABCD3nets1net16Min-cutbisectingpartitioningSwappingAandB:Bdrags1net;Adrags3nets;totalcutincrease:4nets.Conclusion:probablynotagoodswap,butmustbecomparedwithotherpairs.17BlockplacementBlockshave:area;aspectratio.Blocksmaybeplacedatdifferentrotationsandreflections.Uniformsizeblocksareeasiertointerchange.18BlocksandwiringCannotignorewiringduringblockplacement—largewiringareasmayforcerearrangementofblocks.Wiringplanmustconsiderareaanddelayofcriticalsignals.Blocksdividewiringareaintoroutingchannels.19ChanneldefinitionChannelsendatblockboundaries.Severalalternatechanneldefinitionsarepossible:ABCchannel1ch2ch1ch2ch320ChanneldefinitionchangeswithblockspacingChangingspacingchangesrelationshipbetweenblockedges:ABCC21ChannelgraphABCDE22ChannelgraphusageNodesarechannels,edgesplacedbetweentwochannelsthattouch.Channelgraphshowspathsbetweenchannels.Channelgraphcanbeusedtoguideglobalrouting.23ChannelsmustberoutedinorderWireoutofendofonechannelcreatespinonsideofnextchannel:channelAchannelBconstraint24WindmillsCancreateanunroutablecombinationofchannelswithcircularconstraints:ABCD25Slicable

floorplan26SlicabilitypropertyAslicable

floorplancanberecursivelycutintwowithoutcuttinganyblocks.Aslicable

floorplanisguaranteedtohavenowindmills,thereforeguaranteedtohaveafeasibleorderofroutingforthechannels.Slicabilityisadesirablepropertyforfloorplans.27Routing目标：Completepower/ground/clockroutingCompleteroutingconformingtospecifiedwiringrulesandorders28RoutingMajorphasesinrouting:globalroutingassignsnetstoroutingareas;detailedroutingdesignstheroutingareas.Netorderingisamajorproblem.Orderinwhichnetsarerouteddeterminesqualityofresult.Netorderingisaheuristic.29GlobalroutingGoal:assignwirestopathsthroughchannels.Don’tworryaboutexactroutingofwireswithinchannel.Canestimatechannelheightfromglobalroutingusingcongestion.30DetailedroutingDoglegrouterbreaksnetintomultiplesegmentsasneeded.Trytominimizenumberofdoglegsegmentspernettominimizecongestionforfuturenets.Onegoodheuristic—useleft-edgecriteriononeachdoglegsegmenttofillupthechannel.31MazeroutingWillfindshortestpathforasinglewire,ifsuchapathexists.Twophases:Labelnodeswithdistance,radiatingfromsource.Usedistancestotracefromsinktosource,choosingapaththatalwaysdecreasesdistancetosource.32Mazeroutingexample33LineproberoutingHeuristicmethodforfindingashortroute.Workswitharbitrarycombinationofobstacles.Doesnotexploreallpossiblepaths—notoptimal.34LineprobeexampleAAline1line235ChannelutilizationWanttokeepallchannelsaboutequallyfulltominimizewastedarea.Importanttoroutetime-criticalsignalsfirst.Shortestpathmaynotbebestforglobalwiring.Ingeneral,mayneedtorip-upwiresandreroutetoimprovetheglobalrouting.36TypesofroutingChannelrouting:channelmaygrowinonedimensiontoaccommodatewires;pinsgenerallyononlytwosides.Switchboxrouting:cannotgrowinanydimension;pinsareonallfoursides,fixingdimensionsofthebox.37ChannelsandswitchboxeschannelswitchboxchannelswitchboxpinsCan’texpandaswitchboxtomakeroomformorewiring.Switchboxmaybedefinedbyintersectionofchannels.38RoutingorderandswitchboxesSwitchboxesfrequentlyneedmoreexperimentationwithwiringorderbecausenetsmayblockothernets:BABABblocksA39LayoutDesign:P&RvsFullCustomFullCustomLayoutManualdesign,MostPlacementandRouteisspecifiedbyengineerP&RAutomatic40静态时间分析（Statictiminganalyzer）calculatespoint-to-pointtimingforsynchronouscircuits:建起与保持时间（setupandholdtime）错误关键路径（criticalpath）分析