Confidential

Software Driven Low Power Optimization for ARM Based Mobile Architectures

Frank Schirrmeister, Synopsys

1

Confidential

AgendaA Mobile Device

Where did all the energy go?Components of Energy Consumption

Software Rules PowerChallengesVirtual PlatformsSystemC TLM-2.0Enabling Virtual Platforms for Low Power

ResultsDemonstration: Freescale i.MX31Demonstration: Texas Instruments OMAP2420

Conclusions

2

Confidential

WHERE DID ALL THE ENERGY GO?

A Mobile Multimedia Device Example

3

Confidential

A Mobile Device

4

Confidential

What’s in a Mobile Device?

5

A/V andTransport

LCDDriver

Base band to

RF

Dual LNA

RF to Base band

Mobile Station Modem

Processing

LCDControl

AudioMemory

Memory

Video

PowerAnalogASIC

Confidential

And where did all the energy go?

6

Confidential

Six CPUs and Various Accelerators!

7

3 CPUs

MemoryMemory

AMSAMS

Audio Processor

2 standard CPUs4-6 accelerators

AMS

AMS

AMS

Control

Analog

A/V andTransport

Mobile Station Modem

Processing

Audio

Confidential

Software Rules!

8

Software

Control Hardware

Memory

Analog / Mixed Signal

Data Flow Hardware

Confidential

Power Optimization Techniques

SWDF HWCTRL HW MemoryAnalog/MS

Layout

Gate Level

RT Level

ES Level

Des

ign

Tim

e

Impact on O

ptimization

Highest Impact Optimizations

Confidential

COMPONENTS OF ENERGY CONSUMPTION

A three minute excursion to the basics!

10

Confidential

Sources of Power Consumption

Paverage = Pshort

Energy consumption during the switching of CMOS gates when the complementary parts are

open simultaneously

Energy consumption caused by currents during the non-conducting

state of gates

Dynamic energy consumption happens during the data dependent switching of capacities in transistors and the connections between them

+ Pleakage + Pdynamic

Confidential

Short Circuit Energy Consumption

Pshort

Energy consumption during the switching of CMOS gates when the complementary parts are open simultaneouslyShorter transition times can help optimize this type of energy consumptionMain influencing parameters

VoltageOperating Speed

Confidential

Leakage Energy Consumption

Pleakage

Energy consumption caused by currents during the non-conducting state of gatesMain influencing parameters:

Supply Voltage Vdd

Threshold Voltage Vt

Transistor Size W/LTransitor StateTemperature

Confidential

Dynamic Energy Consumption

Pdynamic

Dynamic energy consumption during data dependent switching of capacities (transistors & connections)Often largest contributorMain influencing parameters:

Vdd (Squared)CapacityActivity

Source: ChipVision

Confidential

Energy Consumption Trends

<20

~50

~75

>60

~35

~15>20 ~15 ~10

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

>=70nm 45nm 22nm

Leakage Dynamic Short Circuit

Observations:Smaller geometries require improved handling of leakageDynamic energy due to capacity switching remains significant in mainstream design well into the 65nm technology node

ConclusionOptimize data efficiencyOptimize activity, resourcesOptimize SoftwareReduce voltage

Lower clock speed for slower cells at lower voltage

Confidential

Mobile Multimedia Drives EnergyMultimedia is performance hungry

Dominates power consumptionDrives processing speed

Software!Impacts memory (caches)drives processor speeds

Memory accesses!

ConclusionMultimedia/Consumer

Drives higher clock speedDrives lots of data transfers

16

Source: Linux World 06’06

Confidential

SOFTWARE RULESImpact of Software on Power Consumption

17

Confidential

It’s the Software, Stupid …

“Phone differentiation used to be about radios and antennas and things like that. We think, going forward, the phone of the future will be differentiated by software.”

Steve JobsCEO, Apple

August 11, 2008http://online.wsj.com/article/SB121842341491928977.html

Confidential

Software starts late Bugs are expensive

19

There really are only two issues …

Software has to wait for prototype => Semi cannot

sell silicon …

Confidential

ChipArchitecture

Si ProtoRTL Netlist GDSII

Firmware OS & Driver

ProductArchitecture

Device Proto

OS & Driver Middleware Application SW

SI Prototype

Device Prototype

Trad

ition

al

Des

ign

Flow

SemiconductorHouse

System House

Start Software as Early as Possible

ChipArchitecture

Si ProtoRTL Netlist GDSII

Firmware OS & Driver

ProductArchitecture

Device Proto

OS & Driver Middleware Application SW

Device Proto

End

to E

nd P

roto

typi

ngD

esig

n Fl

ow

SemiconductorHouse

System House

SI Prototype

Virtual PrototypeFPGA Prototype

SI Prototype

Virtual PrototypeFPGA Prototype

Schedule Improvement

SDK usage

SDK usage

Previous Chip (for derivative)

Middleware

Previous Chip

Middleware

Software has to wait for prototype => Semi cannot sell silicon …

Confidential

End-To-End Prototyping

FPGA Prototype: Pre-SiliconFully functional hardware

representation of SoC, board, I/O

Implements unmodified ASIC RTL code

Runs at almost real-time with all external interfaces and stimulus

connected

High system visibility and control

Virtual Platform: Pre-RTLFully functional software model of

SoC, board, I/O, user interface

Executes unmodified production code

Runs close to real-time with external interfaces as Virtual I/O

High system visibility and controlincl. multi-core debug

Silicon Prototype: Post-Silicon

Using the real chip

Running at real time

Little visibility and control

Confidential

Synopsys’ Virtual Platform PortfolioDesignWare®

System-Level Library Innovator Services

High-performance models to build virtual

platforms

SystemC™ TransactionLevel Models

Processors

DesignWare®

System-Level Library

Pre-Assembled Platforms

DesignWare Cores

DesignWareAMBA

Components

Environment for developing, running &

debugging virtual platforms

Expert services for model creation, virtual platform

assembly & customization

Virtual Platforms

Start SW development early and shrink time-to-market using high-

performance Virtual PlatformsEnhance design quality through

SystemC executable specificationIncrease design confidence through complete HW/SW system verification

Confidential

Functional Specification – Defining the overall hardware / software system

RTL to GDSII Implementation Flow (Discovery VCS to Galaxy & Synplicity)

Virtual Platforms in the Design Flow

Platform Creation & Analysis

SynopsysInnovator

Platform Deployment

SynopsysInnovator-RT

3rd Party Software

Debuggers

Model Creation

System Studio

SynopsysCreator (XML)

SystemC

DesignWare® System-Level

Library

Your-lib-1Your-lib-1Your-lib-1

Confidential

The Impact of SystemC TLM-2.0Previously proprietary (backdoor) APIs & new additions have now been standardized:

(DMI) Direct Memory InterfaceDirect backdoor access into memoryAllows un-inhibited ISS execution

LT (Loosely Timed) modelingTiming declarationAllows speed/accuracy trade-offs

Temporal DecouplingOnly synchronize when necessaryAllows multicore speedup

1G

100M

10M

1M

100K

10K

1K

100

00 100908070605040302010

% Accuracy

Perf

orm

ance

(IPS

)

ESL

Implementation

Speed & Visibility

Accuracy Hardware development

Application software development

(Platform Level !)

AV: Application ViewLT: SystemC Loosely Timed

AT: SystemC Approximately TimedCA: Cycle Accurate

AV

LT

AT

CAFirmware

development

Confidential

The Impact of SystemC TLM-2.0Innovator

PV (LT) modeling PV+T (AT) “timing annotation”

DesignWare® IPImplementation, Verification and System-Level IP

Modeling Services

VCSFor hard CA requirements running in software

Synplicity HAPS

1G

100M

10M

1M

100K

10K

1K

100

00 100908070605040302010

% Accuracy

Perf

orm

ance

(IPS

)

ESL

Implementation

Speed & Visibility

Accuracy Hardware development

Application software development

(Platform Level !)

AV: Application ViewLT: SystemC Loosely Timed

AT: SystemC Approximately TimedCA: Cycle Accurate

AV

LT

AT

CA

Innovator Virtual

Platforms

Firmware development

Confidential

LOW POWER ENABLED VIRTUAL PLATFORMS

26

Confidential

Power Instrumentation ObjectivesIncrease visibility

Global system stateIndividual power/clock domains

Power trade-offsPerformance vs. powerPower schemes with “system software” load

Power-related SW developmentRelative power consumption used for optimizationPower management softwareSystem power consumption while running actual software

Confidential

Power Modeling SupportThe following power support is added to a TLM platform:

Power management modeling Clock modeling – gating, scaling freq(t), …Voltage distribution - power domains, scaling V(t) , …Power state control – power state sequencing (power down, retention, …)

Power estimation equations – evaluated at run-timeDashboards – clocks, state, voltage, power

Applies both to LT & AT modelingLT

Instantaneous power consumption, at each point in timeAT*

Supports trade-off of performance vs. powerGraphs: Power(t) & Energy(t)Improved accuracy for accounting for (memory) transactions power contribution * Under development

Confidential

Clock Modeling

Functional clock modelingModels functional operation of the clock controller, including:

Clock distributionIncludes its control over peripheral clock gatingRegisters, to model software control over clock frequencies

Periph

CPU(s)Instruction

Set Simulator

TLM Bus

Master2Master1

Periph

Clock Controller

Signal is used to transmit value of clock frequency from controller to peripheral; does not model actual clock waveform

Confidential

Voltage & Power State Control ModelingFunctional models of:

On-chip Power Manager (SoC)

Control of (internal) voltage distribution & domainsState control & sequencing

Power management chip (PMIC)

Voltage scaling of SoCSoC I2C control interface, power sequencing, LDO regulators control, DC/DC convertors, …

Confidential

Power Estimation - ConceptsParametrizable power model, consisting of:

Component power characteristicsComponent power calc. equationsPower accumulator

Confidential

Power Analysis Concepts

PV / PVT Model

Power EstimationEquation

PowerAccumulator

VoltageFrequency

Power State

Power request / response APIs

Power eventLogging (file)

Power DashboardExample – PRCM (OMAP2420)

Parametrizable model:• Power characteristics• Power equations• Power accumulator

Confidential

Component Characterization for PowerPower parameters

Components are characterized by a set of representative power parameters (‘kernels’)Used in power equations to calculate powerFlexible to support specific component characteristics Interactively changeable by user

SourcePower consumption numbers are delivered by semiconductor companyBased on (1) budget planning, (2) estimations, (3) measurements

ExampleCPU

Power active (mA / MHz)Power dormant (mA)Power inactive (mA)Power shutdown (mA)

Peripherals:Power clock off (mA)Power idle (mA / MHz)Power typical (mA / MHz)Power maximum (mA / MHz)

On-chip Memories (RAM / ROM)Power clock off (mA)Power idle (mA / MHz)Power read (mA / MHz)Power write (mA / MHz)

Confidential

Power EstimationSystem power estimations expressions, contain:

Component power characteristicsPower state of APLLs & DPLLs { off, on }Power state of domain { off, ret, on }Voltage applied (to domain)

At run-time power estimation expressions are evaluated on the fly, as triggered by user requests

Complements functional component modelLeverage power state & frequency modeling of func. component modelExpressed in C code (Magic-C or C++)

Expressions can be linear, or more complex, depending on:Component typeData / charatistics which can be measured / estimated

Fixed modeling APIs for voltage, frequency & power state updates, and reporting to accumulator

Confidential

Power Estimation - Example

ARM1136 (OMAP2420)

PRCM

Powerupdate request

Power updateresponse

MPU Power State (on, off, …)

MPU Clock(frequency (MHz))

MPU Voltage (Volt)

ARM MPU Power Estimation Component

Power Parameters

Graphical C Power Model

Confidential

Platform Analyzer *

Power(t)

Energy(t)

Power EventsVoltage

Clocks

States

time

time

Power Estimation – AT Platform

PMIC

System-on-Chip

CPU(s)Instruction

Set Simulator

TLM Bus

SlavePeriph

SystemI/O

TLM B

us

Camera

MemCtrl

FlashMemory

SystemI/O

System/Device

SlavePeriph

USB

Mem

Fixed power f(V,f,st)

Penalty whenCache miss

(Δcache iss) I$ D$

Penalty for each bus transaction

(Δ transaction (length))Fixed power f(V,f,st) Penalty for each bus

transaction (Δ transaction (length))

Penalty for each bus transaction

(Δ sys memory (length))

APLL

DPLL

Fixed power f(freq,St)

* Under development

Confidential

On-chip Power Reset Controller

Power Dashboard

Dashboards Examples

Clock Dashboard

SoC Voltage DashboardVoltage Monitor

Confidential

RESULTSDemonstrations

38

Confidential

Demo 1: Linux on OMAP2420

39

Confidential

Demo 2: WinCE on i.MX31

40

Confidential

CONCLUSIONS

41

Confidential

Software Rules Power ConsumptionMultimedia drives power consumption in mobile applications

SoftwareMemory Accesses

Virtual Platforms allow pre-silicon embedded software development

TLM-2.0 enables interoperabilityPower instrumentation allows trade offs and development of power related software

42