Implementing a Voltage Scaling Reference Flow Based on ARM’s IEM

Giorgio ParapiniCadence ICD Product Engineer

AbstractRelative to ARM's IEM technology, this session describes a reference flow to implement voltage scaling along with dormant mode to shutdown the standard cell circuitry on an ARM1176JZF-S processor core. We focus on the low power features leveraged from Cadence Encounter Platform, including multiple supply voltage, DVFS implementation with multi-corner libraries, and variable VDD and ECSM-based sign-off. The entire flow is based on a single specification of the design power intent, including power domains, power modes, level shifting and isolation rules. This session also helps attendees understand RTL and library support required for IEM implementation.

AgendaARM and Cadence Collaboration

iRM

ARM1176JZF-S™ IEM™

ARM® Artisan® Library Support

ARM1176JZF-S™ IEM™ implementation flow using Cadence Encounter Platform

Conclusion

ARM and Cadence Collaboration

ARM Alliance ARM and Cadence Alliance History

Multi-year partnership to: • Address design challenges • Optimize ARM offerings for design and implementation• Increase productivity and IP use predictability

Verification

AHB, eVC, and AMBA complianceSystem C

Encounter and RTL Compiler

ReferenceMethodology

Improved QoS

SI & X Architecture

Support

27% Wire reduction

June 00 June 03 Sept 03 Sept 06Mar 05/May 06

Low Power

40% PWR & PSO savings

June 06

Functional Verification

Kit

ReducedRisks

Cortex-A8 Express

SynthesizableQoS

And TAT

May 07

Low PowerMethodology

Kit

Faster deployment of low power

flows

Nov 07

PFI SiliconProof Point

Silicon Validated low power

flow

iRM

ARM-Cadence Reference Methodology

Scripted RTL to GDSII flow delivers

Optimised PPAReduced Turnaround TimeRisk/Cost reduction

Key elementsCore hardeningGeneration of abstract models

Available from ARMJointly developed flowsQualified/released with coresDesign kit gives complete out-of-box experience

Perf

orm

ance Max Attainable Performance

ARM-Cadence Solution

Proprietary Solutions

Faster Time To Market Time

Cadence iRMs Available For All ARM Processors

SageX 130G4.23ARM966E-S

4.24.24.2

4.24.24.24.26.16.16.16.16.26.26.2

6.2-CPFEncounterEncounter

SageX 130G3ARM7EJ-SSageX 130G3ARM7TDMI-SSageX 130G3ARM946E-S

SageX 130G3ARM1026EJ-SSageX 130G2ARM968E-SSageX 130G2ARM1136J[F]-SSageX 130G2ARM1156J[F]-S

Advantage 90G1ARM926EJ-SAdvantage 90G1ARM1176JZ[F]-SAdvantage 90G1CORTEX-M3Advantage 90G1CORTEX-R4

Advantage 90G, 65LP1CORTEX-A8Advantage 90G1ARM11 MPCOREAdvantage 90G1CORTEX-R4[F]

Metro 130LP1ARM1176JZF-S IEMARM Library (TSMC)ARM Library (TSMC)TierTierProcessorProcessor

ARM1176JZF-S IEM

What Consumers Care About

Users want more features in their mobile devicesMP3, Camera, Video, GPS...

But also need long battery lifeConvenient form factor, affordable price

Battery technology is not evolving fast enough!Need to manage power consumption

Heart of all these devices - Microprocessor

Power Dissipation

Minimise Ileak by:Reducing operating voltageFewer leaking transistors

Minimise Iswitch by:Reducing operating voltageLess switching capLess switching activity

dtIVfCVE lkgDD

t

cDD )(0

2 += ∫

∫t

leakDD dtIV0

Total PowerDissipation

Total PowerDissipation

Dynamic PowerDissipation

Dynamic PowerDissipationStatic Power

DissipationStatic PowerDissipation ∫

t

cDD dtfCV0

2

IleakIswitch

Improving Dynamic Energy Efficiency

Dynamic Frequency Scaling (DFS)Reduce operating frequency if possibleReduces average power (but not task energy)Eliminates idle cycle

Dynamic Voltage & Frequency Scaling (DVFS)Requires DFSReduces voltage if frequency is reducedReduces task energyBased on characterized frequency – voltage pairs (lookup table)

How IEM Works?Batteries have finite amounts of energy stored in themRunning fast and then idling wastes energy

Time

Voltage Reduce VoltageReduce Voltage

ReduceVoltageReduceVoltage

Reduce VoltageReduce Voltage

Task 1 Task 2 Task 3Idle

Only need to run just fast enough to meet the application deadlinesOnly need to run just fast enough to meet the application deadlines

Energy

EnergySaved

Energy

Run Task Slow as Possible

Run Task Slow as Possible

Run Task in Available TimeRun Task in

Available Time

IEM System Implementation

ARM1176JZ-S Power Management

Two Complementary Techniques:

ARM1176 Dormant Mode, allowsComplete Power-off of Core (no leakage in core)Retain system state in Cache/TCM at low voltage

Minimize energy loss due to leakage in standby modes.

Note : Requirement of isolation cells to clamp the RAM inputs

IEM–compatible core and design flowEnables dynamic voltage and frequency scalingTune Performance dynamically to current demand

Substantial reduction of energy consumption, extended Battery Life.

ARM Artisan Library Support

VDD2

VDD1

VDD1

VDD1

VDD2

VDD2

Power gates (MT-CMOS)Power control of voltage islands via switchable voltage rails using header (shown) or footer cells

Level shifter and isolation cells Up and down shifting with optional enable signal

Retention flip-flopsMaintain FF state after power down for leakage reduction

Back-bias support Reduce leakage current via well-biasing with special fill_tie cells

Always on bufferBuffering of signals in powered-down areas Global VDD

Global VSS

ARM Power-Management Kit

Note: Picture shows a conceptual implementation

AgendaARM and Cadence Collaboration

iRM

ARM1176JZF-S™ IEM™

ARM® Artisan® Library Support

ARM1176JZF-S™ IEM™ implementation flow using Cadence Encounter Platform

Conclusion

ARM and Cadence iRMARM-Cadence

Reference Methodology

RTL Compiler

SOC Encounter

Fire & Ice QX

Celtic NDC

VoltageStorm

ConformalLow Power

ARM Artisan Power Management Kit

Compiled Views for Fire&ICE,

VoltageStorm and Celtic NDCTiming ECSM

extensions

ARM Artisan Metro™Standard Cell

ARM1176-IEM iRM FeaturesCPF based flow

CPF file is used to describe the low power intent and to drive implementation and verification flow

Automated RTL to GDS Multi Supply Voltage Implementation flowMulti Mode Multi Corner (MMMC) analysis and optimization

Ensures design is optimized across complete voltage and frequency range

Tri-lib based flowProvides accurate interpolation for DVFS and IR drop analysisECSM extensions to .lib

Cadence Low-Power Solution

Define power architecture early-on in the design flowCapture once using CPF; no re-entry or translation later on

Entire design flow understands CPF and helps preserve the power-intent Verification: Comprehensive low-power simulation and formal verification

Design: Power-aware synthesis, equivalence checking, and DFT

Implementation: Automated power-aware RTL-to-GDS layout

Management: Power plan and metrics

What is the Common Power Format?

Design intentPower domain

Logical: hierarchical modules as domain membersPhysical: power/ground nets and connectivityAnalysis view: timing library sets for power domains

Power LogicLevel Shifter LogicIsolation LogicState-Retention logicSwitch Logic & Control Signals

Power modes DefinitionsTransition Expressions

Technology information

Level shifter cellsIsolation cellsState-retention cellsSwitch cellsAlways-on cells

Single specification of power intent used throughout design, verification, and implementationASCII File that captures:

ARM1176-IEM CPF: MSV setup

create_power_domain -name VCORE \-instances $VCORE_moduleInst_list \-boundary_ports "$VCORE_pins" \-shutoff_condition {SWITCH_VCORE}

update_power_domain -name VCORE \-internal_power_net VDDCORE

create_global_connection -net VDDCORE -domain VCORE -pins VDDcreate_global_connection -net VSS -domain VCORE -pins VSS

create_power_domain -name VRAM …create_power_domain -name VSOC –default …create_isolation_rule -name rule_VCORE2VRAM \

-from VCORE -to VRAM \-isolation_output low \-isolation_condition {!RAMCLAMP}

update_isolation_rules -names rule_VCORE2VRAM \-location to -combine_level_shifting \-cells {LVLLHEHX8M}

create_level_shifter_rule -name rule_VRAM2VCORE \-from VRAM -to VCORE

update_level_shifter_rules -names rule_VRAM2VCORE \-cells {LVLHLX8M} -location

create_level_shifter_rule -name rule_VSOC2VCORE …create_isolation_rule -name rule_VCORE2VSOC_low …create_isolation_rule -name rule_VCORE2VSOC_high …

create_power_nets -nets VDDRAM create_power_nets -nets VDDCORE \

-external_shutoff_condition {SWITCH_VCORE}create_power_nets -nets VDD

Multi Mode Multi Corner (MMMC)

Voltagebbb

bbw

www

wwb

Process

TempMulti PVT Corners

Analysis View

Corner definition Power mode

Library Set Operating Conditions

(PVT).lib

(.ecsm* ext).cdb (SI)

.sdcRC Corner -SPEF -QX tech -Cap Table

Dynamic Voltage Frequency Scaling

250MHz

90MHz

166MHz

250MHz

Frequency

0.72V0.72V1.08VPM_lowV

0.72VOff1.08VVCORE_Dormant

0.90V

1.08V

VCORE

0.90V

1.08V

VRAM

1.08VPM_medV

1.08VPM_highV

VSOCMode

Multiple Modes with multiple constraints (.sdc)

ARM1176-IEM CPF: Power modes

Dynamic Voltage and Frequency Scaling

250MHz

90MHz

166MHz

250MHz

Target frequency

0.72V0.72V1.08VPM_lowV

0.72VOff1.08VVCORE_Dormant

0.90V

1.08V

VCORE

0.90V

1.08V

VRAM

1.08VPM_medV

1.08VPM_highV

VSOCMode

create_nominal_condition -name highV -voltage 1.08update_nominal_condition -name highV -library_set libs-worst-1.08v…create_nominal_condition -name OFF -voltage 0

create_power_mode -name PM_highV -default \-domain_conditions {VCORE@highV VRAM@highV VSOC@highV} \

update_power_mode -name PM_highV -sdc_files ARM1176JZFS.constraints_PM_highV.sdc

create_power_mode -name VCORE_dormant \-domain_conditions {VCORE@OFF VRAM@highV VSOC@highV}

…

Same power modes are used by both Logic Synthesis (RTLCompiler) and by Place & Route (SOCEncounter)

ARM1176-IEM CPF: Corners & Analysis viewsOperating corners and analysis views are only used for physical implementationAnalysis and physical optimization are working concurrently on active analysis views

create_operating_corner -name WCORNER_1.08 \-voltage 1.08 -temperature 125 -process 1 -library_set libs-worst-1.08v

create_operating_corner -name WCORNER_0.72 \-voltage 0.72 -temperature 125 -process 1 -library_set libs-worst-0.72v

…create_operating_corner -name BCORNER \

-voltage 1.32 -temperature "-40" -process 1 -library_set libs-best-1.32

create_analysis_view -name WCVIEW_1.08 \-mode PM_highV \-domain_corners {VCORE@WCORNER_1.08 VRAM@WCORNER_1.08 VSOC@WCORNER_1.08}

create_analysis_view -name WCVIEW_0.72 \-mode PM_lowV \-domain_corners {VCORE@WCORNER_0.72 VRAM@WCORNER_0.72 VSOC@WCORNER_1.08}

…create_analysis_view -name BCVIEW_1.32 \

-mode PM_highV \-domain_corners {VCORE@BCORNER VRAM@BCORNER VSOC@BCORNER}

Automated CPF-driven MSV flow

Use the CPF to drive synthesis and physical implementation

MSV/power domain partition (power domains with assigned instances, toplevel IO pins and power ground connections)Setup MMMC environment (power modes, delay corners and analysis views )Isolation rules and level_shifterrules to automatize the usage of shifter / isolation cells: definition, identification from RTL, insertion, placement and optimizationSynthesize, place, optimize, and route based on power domainsDomain-aware Clock Tree Synthesis

GDSII

Constraints CPF Netlist

Floorplanning / Silicon Virtual Prototype

Power Routing

Low Power Clock Tree Synthesis

Domain-aware Post-CTS Optimization

IRDrop-Aware Timing/SI Opt.

Sign-off

Isolation/level shifter cells check and insertion

Placement includingSRPG/Level shifters/Iso cells

Top-down MSV/MultiModeSingle-pass Synthesis

Power Grid Synthesis

Domain Aware NanoRoute

Low P

ower Functional V

erificationS

I & S

tatic Timing A

nalysisS

tatic/Dynam

ic Pow

er Analysis

MSV/MMMC Infrastructure

Timing/P

ower O

ptimization

Top VSOC

Logic synthesis

Top-down single-pass synthesis with power domain definitionIdentification of level shifters and isolation cells already instantiated in RTLMulti-mode synthesis to consider frequency and voltage scaling Implementation of separated scan chains, for VSOC and VCORE domainsLeakage power optimization using High-Vt cells

CRead/constrain top

Apply power constraints

Synthesize “Top”

Analyze timing/power

Lib10.72V

Lib20.90V

B

Chip SDCRTL

Lib10.72V

VCORE

Power DomainsShiftersIsolationPower modesLeakageDynamicClock Gating

Chip CPF

Adjust / incremental update

VRAM

Isolation

PSO

Lib20.90V

Lib31.08V

Lib31.08V

Isolation

Floorplan: Power Domains• Each power domain has

its own dedicated row structure automatically created depending on the associated cell libraries

• Hard block placement is scripted and easily customizable through relative floorplan commands

• Power structure is automatically built via tcl script.

create_power_domain -name VCORE \-instances $VCORE_moduleInst_list -boundary_ports "$VCORE_pins" \-shutoff_condition {SWITCH_VCORE}

create_power_domain -name VRAM \-instances "$env(VRAM_moduleInst_list)" -boundary_ports "$VRAM_pins“

create_power_domain -name VSOC -default \-boundary_ports "$VSOC_pins"

Floorplan: Power StructureVRAM

Rings and stripes for:

VDDRAM, VSS

VCORERings and Stripes for:

VDDCORE, VSS

VSOCRings and stripes for:

VDD,VSS

create_ground_nets -nets VSScreate_power_nets -nets VDDRAM create_power_nets -nets VDDCORE -external_shutoff_condition {SWITCH_VCORE}create_power_nets -nets VDD

PlacementStandard cells, level shifters (single and multi-height) and isolation cells automatically placed in a single pass

verifyPowerDomaincommand checks:

nets crossing the boundaries (both level shifter cells and isolation cells)

library binding

placement of instances in a power domain

IO pins assigned to the correct power domain

Level Shifters / Clamps: VCORE-VRAM

VCOREcreate_isolation_rule -name rule_VCORE2VRAM \

-from VCORE -to VRAM -isolation_output low \-isolation_condition {!RAMCLAMP}

update_isolation_rules -names rule_VCORE2VRAM \-location to -cells {LVLLHEHX8M} \-combine_level_shifting

create_level_shifter_rule -name rule_VRAM2VCORE \-from VRAM -to VCORE

update_level_shifter_rules -names {rule_VRAM2VCORE} \-cells {LVLHLX8M} -location to

Single-row height LVLHL shifters

Triple-row height LVLLHEH shifters

Vertical connections of VDDI pins to

VDDCORE power net – automatically

routed

VRAM

VDDCORE

VDDRAM

VSS

VSS

Clock Tree Synthesis & RoutingCTS in SOC Encounter is power domain awareFor all clocks crossing power domains, CTS assumes that level shifters are present (according to CPF rules)A single pass top-down clock tree is created by CTSCTS does the following:

Establishes a single entry/exit point for each domainSelects buffers from appropriate libraries and places them within domain boundariesBalance skew through domains and for all active corners/views

Both trialRoute and nanoRoute honour power domains in SOC Encounter

Cross-Domain Timing Optimization

Optimization transparently considers level shifter / clamp placement and signal direction

Parts of net should be “don’t touch”Buffer needs to be inserted from the correct library and into the correct moduleBuffer location is timing driven

Optimizes timing and design rules concurrently for all active corners/views

Power Domain ALibraries A

Power Domain BLibraries B

Power Domain ALibraries A

Power Domain BLibraries B

Don’t touch nets

Power Domain B (1.0V)Libraries B

0.8V I/O

Power Domain A (0.8V)Libraries A

0.8V I/O

Variable VDD Flow Assign non-pre-characterized VDD value as the operating voltage and run through timing optimization closureUsing ECSM and tri-lib technology for better accuracyRequires a minimum of two library characterized for different voltages for good a accuracy in full rangeSupported by analysis and optimization

1.08V

0.72V

0.90VProcessTemp

Delay Calculator

SS, 125oC

Dynamic Voltage and Frequency Scaling

250MHz

200MHz

166MHz

250MHz

Target frequency

1.00V1.00V1.08VPM_triV

0.72VOff1.08VVCORE_Dormant

0.90V

1.08V

VCORE

0.90V

1.08V

VRAM

1.08VPM_medV

1.08VPM_highV

VSOCMode

Library support for MMMC

Library /ProcessARM Metro libraries for TSMC CL013G process

Available voltage cornersWC: 0.72V, 0.9V, 1.08V BC: 0.88V, 1.1V, 1.32V

Required viewsTiming models (.lib) characterized at available voltage corners,optionally with ECSM extensions for better accuracyNoise models (.cdB) characterized at available voltage corners

ECSM advanced timing modelsDelay sensitivity to Vdd increases nonlinearly at smaller geometries.lib and K-factors not accurate at low Vdd and between characterization points need for more accurate cell models for IR-drop and MSVECSM accurately models delay variations with Vdd:

Captures the waveform-dependent non-linear behavior of the receiver-pin capacitanceDriver modeled as a current source: I/V curve for each slope, load combination

ARM-Cadence RM deploys ECSM models for signoff STA within Encounter, leveraging detailed instance voltages output by power analysis.

0

50

100

150

200

250

300

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

Voltage (Vdd)D

elay

(ps)

SPICE

ECSM-based

K Factor

30%

Non-linear increase in Delay due to Vdd scaling

Linear Approximation

90nm Buffer, 1V nominal supply

Formal VerificationFunctional equivalence checkStructural checks (Conformal Low Power Solution)

Missing level shifters and power connectivityMissing isolation and power connectivityBad isolation cell and level shifterCorrect cell placement in physical domainIsolation cell enable

VCORE VRAMA Y

VoVi

Enable

Power and Rail analysis

VDDCORE IR drop analysis

Placed & Routed DesignDatabase

Static & DynamicIR-drop Analysis

PowerLibraries

Derive Power-PinLocation

CPF ModeSpecification

Power-SwitchECO

DecapECO

Report Power(Common Power Engine)

Plots

Waveforms & IR drop Files

Timing &Critical Path

Analysis

ConclusionComprehensive Low Power support across RTL2GDSLeverages state of the art features, including DVFS and variable VDD flowOptimized and tested for use with latest Cadence tool releasesComplete offering

Processor IPReference librariesPortable Reference Methodology Scripts for Cadence tools

ARM and Cadence collaborationStreamlining rapid deployment of ARM processor products

Accelerate time to market for the ARM PartnerAvailable to ARM partners and Cadence customers

Thank You…