DARPADARPA

GTX: The GSRC Technology Extra-GTX: The GSRC Technology Extra-polation System, “A Living Roadmap”polation System, “A Living Roadmap”

A. Caldwell, A. B. Kahng, F. Koushanfar,A. Caldwell, A. B. Kahng, F. Koushanfar,

H. Lu, I. Markov, M. Oliver andH. Lu, I. Markov, M. Oliver and

D. StroobandtD. Stroobandt

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OverviewOverview

IntroductionIntroduction

Previous roadmapping effortsPrevious roadmapping efforts

Overview of GTX: goal and structureOverview of GTX: goal and structure

Fundamental featuresFundamental features

DemonstrationDemonstration

Example use scenarios:Example use scenarios:Roadmap emulation, development, and maintenanceRoadmap emulation, development, and maintenance

Roadmap evaluation and comparisonRoadmap evaluation and comparison

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Introduction: Technology ExtrapolationIntroduction: Technology Extrapolation

Evaluates impactEvaluates impact of ofdesign technologydesign technologyprocess technologyprocess technology

Evaluates impact onEvaluates impact onachievable designachievable designassociated design problemsassociated design problems

Questions to be addressedQuestions to be addressed

Sets Sets new requirementsnew requirements for CAD tools and methodologies for CAD tools and methodologies

RoadmapsRoadmaps: familiar and influential example: familiar and influential example

How and when do L, How and when do L, SOI, SER, etc. matter?SOI, SER, etc. matter?

What is the most power-efficient noise What is the most power-efficient noise management strategy?management strategy?

Will layout tools need to perform Will layout tools need to perform process simulation to efficiently process simulation to efficiently model cross-die and cross-wafer model cross-die and cross-wafer

manufacturing variation?manufacturing variation?

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Introduction: RoadmappingIntroduction: Roadmapping

Roadmapping efforts drive development of design technology:Roadmapping efforts drive development of design technology: System architects, designers, CAD managers use roadmaps to determineSystem architects, designers, CAD managers use roadmaps to determine

tough problemstough problems risks, …risks, …

EDA suppliers use roadmaps to determineEDA suppliers use roadmaps to determine R&D investmentR&D investment product pipelineproduct pipeline

Government and consortia use roadmaps to determine levels of investmentGovernment and consortia use roadmaps to determine levels of investment

Roadmaps serve as a guide to the most promising directions, the Roadmaps serve as a guide to the most promising directions, the

most critical problemsmost critical problems

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Roadmap Process and Its ImplicationsRoadmap Process and Its Implications

Basic TechnologicalAssumptions

Basic MethodologicalAssumptions

Implications tothe Community

Models andDiscussion

Translation to SpecificResearch Agendas

“Timing closure is a hard problem and will only get harder”

“We will fund research ontiming-aware partitioning”

Research Proposedto Implement Agenda R. Newton, ICCAD99 panel

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Roadmap ProcessRoadmap Process

Basic TechnologicalAssumptions

Basic MethodologicalAssumptions

Implications tothe Community

Models andDiscussion

Couched in Terms ofRoadmap Implications

“Timing closure is a hard problem and will only get harder”

Research Proposed to Solve Hard Problem

“I can make a breakthrough in technology or methodology”

“Here’s how my work is critical for addressing your problem”

Newmodels

R. Newton, ICCAD99 panel

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Introduction: RoadmappingIntroduction: Roadmapping

Difficulties of roadmappingDifficulties of roadmappingNo crystal ballNo crystal ballNew technologies, new circuitNew technologies, new circuit

techniques, new designtechniques, new design

methodologies and toolsmethodologies and toolsAlways difficult to predict achievable design, especially in the Always difficult to predict achievable design, especially in the

futurefuture

Roadmaps rely onRoadmaps rely onModels: technology projections, design attributes, design toolsModels: technology projections, design attributes, design toolsCalibrations: measurements of technology and design parametersCalibrations: measurements of technology and design parameters

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Roadmapping in the pastRoadmapping in the past

Previous and ongoing effortsPrevious and ongoing efforts ITRS RoadmapsITRS Roadmaps Tools: SUSPENS, GENESYS, RIPE, BACPAC, …Tools: SUSPENS, GENESYS, RIPE, BACPAC, … Numerous tools in industryNumerous tools in industry

ObservationsObservations Predict “same” parameters but with different assumptions, inputsPredict “same” parameters but with different assumptions, inputs Lack of documentation and visibility into internal calculationsLack of documentation and visibility into internal calculations Single inference chain for a given output (hard-coded modeling)Single inference chain for a given output (hard-coded modeling) Inflexible: user cannot define studies of other, related parametersInflexible: user cannot define studies of other, related parameters Near-total duplication of effortNear-total duplication of effort Missing: models of CAD tools and optimizations (what is really “achievable”?)Missing: models of CAD tools and optimizations (what is really “achievable”?) Missing: scope, comprehensive coverageMissing: scope, comprehensive coverage

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Questions To Ask About RoadmapsQuestions To Ask About Roadmaps

How do different roadmap predictions How do different roadmap predictions comparecompare??

How to How to evaluateevaluate underlying models? (sanity checks) underlying models? (sanity checks)

How do we How do we reusereuse and and extendextend models to encompass new models to encompass new

aspects of technology, new axes of achievable design?aspects of technology, new axes of achievable design?

What is the impact of modeling What is the impact of modeling choiceschoices on predictions? on predictions?

Need a new infrastructure, new concept!Need a new infrastructure, new concept!

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Previous Systems versus Ideal SystemPrevious Systems versus Ideal System

Same parameters but Same parameters but

different assumptionsdifferent assumptions

Inflexible, not easy toInflexible, not easy to

add other studies add other studies

Hard-coded, no easy Hard-coded, no easy

changeschanges

No internal visibilityNo internal visibility

Duplication of effortDuplication of effort

FlexibilityFlexibility

QualityQuality

TransparencyTransparency

Prevention of Prevention of

redundant effortredundant effort

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Goals of A New Technology Extrapolation SystemGoals of A New Technology Extrapolation System

FlexibilityFlexibility Interactively edit chains of relations between parametersInteractively edit chains of relations between parameters

Define new parameters and relations between themDefine new parameters and relations between them

Perform specific studies (but different studies at different times)Perform specific studies (but different studies at different times)

QualityQualityContinuous improvementsContinuous improvements

World-wide participation of expertsWorld-wide participation of experts

TransparencyTransparency

Prevention of redundant effortPrevention of redundant effort

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Goals of New Technology Extrapolation (cont.)Goals of New Technology Extrapolation (cont.)

FlexibilityFlexibility

QualityQuality

TransparencyTransparencyOpen-source mechanismOpen-source mechanism

Models are visible to the userModels are visible to the user

Prevention of redundant effortPrevention of redundant effortPermanent repository of first choicePermanent repository of first choice

Adoptability and maintainabilityAdoptability and maintainability

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GTX: GSRC Technology Extrapolation SystemGTX: GSRC Technology Extrapolation System

GTX is set up as a GTX is set up as a frameworkframework for technology extrapolation for technology extrapolation

Flexibility, quality, visibility allow a “living roadmap”:Flexibility, quality, visibility allow a “living roadmap”:emulateemulate existing roadmap (modeling) efforts existing roadmap (modeling) effortsdevelopdevelop new roadmaps (models) new roadmaps (models)evaluateevaluate roadmaps (models) roadmaps (models)comparecompare roadmaps (models) to each other roadmaps (models) to each other

KnowledgeData

ModelsImplementation

Derivation

Presentation

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GTX StructureGTX Structure

Knowledge representation:Knowledge representation: ParametersParameters (description of technology, circuit and design attributes) (description of technology, circuit and design attributes)

RulesRules (methods to derive unknown parameters from known ones): (methods to derive unknown parameters from known ones): closed-form modelsclosed-form models executable algorithm implementationsexecutable algorithm implementations table-lookupstable-lookups

Rule chainsRule chains (serialized user-defined rules) (serialized user-defined rules) interactive specification and comparison of alternative modeling choicesinteractive specification and comparison of alternative modeling choices

ImplementationImplementation Execution by a Execution by a derivation enginederivation engine to perform studies to perform studies

Embedding into Embedding into GUIGUI for ease of use, interactivity, display of results for ease of use, interactivity, display of results

See poster for details of GTX frameworkSee poster for details of GTX framework

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Knowledge RepresentationKnowledge Representation

Rules and parameters are specified separately from the Rules and parameters are specified separately from the

derivation enginederivation engine

Human-readable ASCII grammarHuman-readable ASCII grammar

#rule #rule BACPAC_dl_chipBACPAC_dl_chip#description#description#output#outputdouble {m} dl_chipdouble {m} dl_chip;;

#inputs#inputsdouble {m^2} dA_chipdouble {m^2} dA_chip;;

#body #body sqrt(dA_chip)sqrt(dA_chip)#reference#reference#endrule#endrule

#parameter #parameter dl_chipdl_chip#type #type doubledouble#units {#units {mm}}#default#default1e-21e-2

#description#descriptionchip side lengthchip side length

#reference#reference#endparameter#endparameter

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Knowledge Representation (cont.)Knowledge Representation (cont.)

Rules and parameters are specified separately from the derivation Rules and parameters are specified separately from the derivation

engineengine

Human-readable ASCII grammarHuman-readable ASCII grammar

Benefits:Benefits: Easy creation and sharing of parameters / rules by multiple usersEasy creation and sharing of parameters / rules by multiple users

D. Sylvester and K. Cao: device and power modules that “drop in” to GTXD. Sylvester and K. Cao: device and power modules that “drop in” to GTX

Extensible to models of arbitrary complexity (specialized prediction methods, Extensible to models of arbitrary complexity (specialized prediction methods, technology data sets, optimization engines)technology data sets, optimization engines) Avant! Apollo or Cadence SE P&R tool: just another wirelength estimatorAvant! Apollo or Cadence SE P&R tool: just another wirelength estimator

Applies to any domain of work in semiconductors, VLSI CADApplies to any domain of work in semiconductors, VLSI CAD Transistor sizing, single wire optimizations, system-level wiring predictions,…Transistor sizing, single wire optimizations, system-level wiring predictions,…

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Parameter and Rule NamingParameter and Rule Naming

Importance of consistent naming cannot be overstatedImportance of consistent naming cannot be overstated

Naming conventions for parametersNaming conventions for parameters[<preposition>] _ <principal> _ {[qualifier] _ <place>} _ {<qualifier>} _ [<adverbial>] _ [<index>] _ [<unit>][<preposition>] _ <principal> _ {[qualifier] _ <place>} _ {<qualifier>} _ [<adverbial>] _ [<index>] _ [<unit>]

Example: Example: r_int_tot_lyr_pu_dlr_int_tot_lyr_pu_dl

Benefits:Benefits:Relatively easy to understand parameter from its nameRelatively easy to understand parameter from its nameDistinguishable (no two parameters should have the same name)Distinguishable (no two parameters should have the same name)

r_int (interconnect resistance) = r_int (interconnect resistivity) ?r_int (interconnect resistance) = r_int (interconnect resistivity) ?

Unique (no two names for the same parameter)Unique (no two names for the same parameter) R_int = R_wire ?R_int = R_wire ?

Sortable (important literals come first)Sortable (important literals come first)

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Additional FeaturesAdditional Features

Optimization over a collection of rules (with constraints)Optimization over a collection of rules (with constraints)Example: buffer insertion for minimal delay with area constraintsExample: buffer insertion for minimal delay with area constraints

Executables can be calledExecutables can be calledExample: various optimizations of global delay through IPEM Example: various optimizations of global delay through IPEM

(Interconnect Performance Estimation Models, J. Cong, UCLA)(Interconnect Performance Estimation Models, J. Cong, UCLA)

Internal code rules for optimizationsInternal code rules for optimizationsExample: optimization of number and size of repeaters for global Example: optimization of number and size of repeaters for global

wireswires

Storing of calibration data (e.g., “technology files”) for Storing of calibration data (e.g., “technology files”) for known process, design pointsknown process, design points

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Additional Features (cont.)Additional Features (cont.)

Visualization (plotting, printing, saving to file) Visualization (plotting, printing, saving to file)

Sweeping over sets of input valuesSweeping over sets of input valuesExample: clock frequency for different Rent exponents and Example: clock frequency for different Rent exponents and

varying logic depthvarying logic depth

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GTX: Open and User-friendlyGTX: Open and User-friendly

Openness in grammar, parameters and rulesOpenness in grammar, parameters and rulesEasy sharing of data in research environmentEasy sharing of data in research environment

Contributions from other groupsContributions from other groups

Allows developing of proprietary modelsAllows developing of proprietary modelsSeparation between supplied (shared) and user-defined Separation between supplied (shared) and user-defined

parameters / rulesparameters / rules

GTX offers usability behind firewallsGTX offers usability behind firewalls

Framework for sharing results instead of data is plannedFramework for sharing results instead of data is planned

Multi-platform (SUN Solaris, Windows, Linux)Multi-platform (SUN Solaris, Windows, Linux)

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Demonstration Demonstration

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GTX Current StatusGTX Current Status

EmulationEmulation of ofCycle-time models of SUSPENS (with extension by Takahashi), Cycle-time models of SUSPENS (with extension by Takahashi),

BACPAC, Fisher (ITRS)BACPAC, Fisher (ITRS) Interconnect tuning studiesInterconnect tuning studiesMain modulesMain modules

Clock / powerClock / power SOISOI Domino logicDomino logic Device and PowerDevice and Power Global interconnectGlobal interconnect System-level powerSystem-level power PackagingPackaging Reliability and YieldReliability and Yield ……

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GTX Current StatusGTX Current Status

EvaluationEvaluation of cycle-time models of cycle-time modelsParameter sensitivityParameter sensitivity

ComparisonComparison between cycle-time models between cycle-time modelsModel sensitivityModel sensitivity

DevelopmentDevelopment of new models of new modelsModel of via impact on required routing resources (number of Model of via impact on required routing resources (number of

layers, pitch, etc.)layers, pitch, etc.)

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Change parameter values and observe resulting difference Change parameter values and observe resulting difference

in outputsin outputs

See poster on Sensitivity Analysis for further detailsSee poster on Sensitivity Analysis for further details

Evaluation: Parameter SensitivityEvaluation: Parameter Sensitivity

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Comparison: Model SensitivityComparison: Model Sensitivity

Replace rule in a model’s rule chain by another model’s Replace rule in a model’s rule chain by another model’s

rule and observe the difference in outputsrule and observe the difference in outputs

See poster on Sensitivity Analysis for further detailsSee poster on Sensitivity Analysis for further details

BACPAC BACPAC with rule from Fisher

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Development: Via Impact ModelDevelopment: Via Impact Model

Goal: model impact of vias on layer track utilizationGoal: model impact of vias on layer track utilization

Only taking into account area taken by via is not enoughOnly taking into account area taken by via is not enough

Stochastic model of the number of wires blocked by vias Stochastic model of the number of wires blocked by vias

used to estimate the via impactused to estimate the via impact

Via impact model improves prediction of number of layers Via impact model improves prediction of number of layers

needed for the routingneeded for the routingVerified with recent 4LM block, Cadence Silicon Ensemble P&RVerified with recent 4LM block, Cadence Silicon Ensemble P&R

See poster on Via Impact Model for further detailsSee poster on Via Impact Model for further details

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ConclusionConclusion

GTX: a new framework for roadmapping models and technology GTX: a new framework for roadmapping models and technology

extrapolation effortsextrapolation efforts Flexible and extensibleFlexible and extensible

Enables easy reuse of modelsEnables easy reuse of models

Provides a common parameter base between all modelsProvides a common parameter base between all models

Provides user interactionProvides user interaction

Relies on open-source and contributions by expert usersRelies on open-source and contributions by expert users

““Living Roadmap”Living Roadmap”

Technology extrapolation becomes easierTechnology extrapolation becomes easier

More principled understanding of requirements for CAD toolsMore principled understanding of requirements for CAD tools

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GTX Project InformationGTX Project Information

Design: A. Caldwell, A. B. Kahng, I. Markov, M. OliverDesign: A. Caldwell, A. B. Kahng, I. Markov, M. Oliver

Implementation: M. OliverImplementation: M. Oliver

Knowledge gathering and implementation: A. B. Kahng,Knowledge gathering and implementation: A. B. Kahng,

F. Koushanfar, H. Lu, D. StroobandtF. Koushanfar, H. Lu, D. Stroobandt

Detailed information and downloading of prototype version Detailed information and downloading of prototype version of GTX: of GTX: http://www.gigascale.org/GTX/http://www.gigascale.org/GTX/

To contact the developers, ask questions, send comments, To contact the developers, ask questions, send comments, or to contribute with models to be included in GTX, please or to contribute with models to be included in GTX, please send E-mail to send E-mail to GTX@cs.ucla.eduGTX@cs.ucla.edu

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AcknowledgementsAcknowledgements

MARCO GSRCMARCO GSRC

F.W.O. (Belgium) for D. Stroobandt’s grant to visit UCLAF.W.O. (Belgium) for D. Stroobandt’s grant to visit UCLA

Dr. Phil Fisher, Dr. Dennis Sylvester and Kevin Cao for Dr. Phil Fisher, Dr. Dennis Sylvester and Kevin Cao for

providing access to their models and helpful inputsproviding access to their models and helpful inputs

Professors Ken Rose, James Meindl, Scott Wills and Kurt Professors Ken Rose, James Meindl, Scott Wills and Kurt

Keutzer for fruitful discussionsKeutzer for fruitful discussions