L29:Lower Power Embedded Architecture Design

성균관대학교 조 준 동 교수 , 1999. 8

http://vada.skku.ac.kr

Low Power MPU

Levels for Low Power Design

System

Algorithm

Architecture

Circuit/Logic

Technology

Hardware-software partitioning,

Complexity, Concurrency, Locality,

Parallelism, Pipelining, Signal correlations

Sizing, Logic Style, Logic Design

Threshold Reduction, Scaling, Advanced packaging

Possible Power Savings at Different Design LevelsLevel of

Abstraction Expected Saving

Algorithm

Architecture

Logic Level

Layout Level

Device Level

10 - 100 times

10 - 90%

20 - 40%

10 - 30%

10 - 30%

Regularity, Data representation

Instruction set selection, Data rep.

SOI

Power down

Present- Day Digital Systems

• Current systems are complex and heterogenous Contain many different types of components– Programmable and Re-configurable processors– Application- specific integrated circuits (ASICs)– Application-specific Instruction processor (ASIP)– Read- Only Memory (ROM) and RAM– I/ O devices and circuitry

• Typically designed from a (large) software specification

• These heterogenous systems are called embedded systems

Embedded System Characteristics

• Limited user programmability– Completely transparent to user, e. g.

automotive engine control– Limited user interface e. g., intelligent

telephones– Programmable through application

specific language e.g., postscript printer

• Real- time response No batch processing

Embedded Systems: Products - 1

Computer Relatedpersonal digital

assistantprinterdisc drivemultimedia

subsystemgraphics

subsystemgraphics terminal

Communicationscellular phonevideo phonefaxmodemsPBX

Consumer ElectronicsHDTVCD playervideo gamevideo tape recorderprogrammable TVcameramusic system

Embedded Systems: Products - 2

• Control Systems– Automotive:engine, ignition, brake system– Manufacturing process control: robotics– Remote control: satellite control, spacecraft control– Other mechanical control: elevator control

• Office Equipment– smart copier, printer, smart typewriter, calculator– point- of- sale equipment, credit- card validator,UPC code rea

der, cash register

• Medical Applications: instruments( EKG, EEG), scanning, imaging

Problem Domain Shift

Embedded System Trends - I

• Microcomponents grow in importance in IC industry due to their reusability: DSP, P, C

• More embedded systems will require ASICs– From 20- 70% in 1992 to 60- 70% in 1996

Moral of the story: u-P are joining with high- speed highly-complex ASIC in embedded systems

Embedded System Trends - II

• Embedded systems will require more application software– Average moves from 16- 64k lines in 1992 to

64k-512k in 1996– Requires migration from assembler to C/ C++,

implying requirement for automatic compilation– From 40- 70% of programmers versus ASIC

designers in 1992 to 60- 90% in 1996

Moral of the story: Increase in code- size / code- complexityis causing a migration to C/ C++ from assembly coding

Embedded Software Optimization

• Code size becomes an important objective Software will eventually become a part of the chip:– Need to generate the best possible code– Can afford longer compilation time

• Need not only traditional optimization techniques, but also new application- domain-specific optimizations (e. g., DSP and microcontroller architectures)

Implementing Digital Systems

What is an ASIP?

• Application- Specific Instruction Processor

• Processor architecture tailored not just for application domain (e. g., DSP, microcontrollers), but for specific sets of applications (e. g., audio, engine control)

• ASIP characteristics– Greater design cost (processor + compiler)– + Higher performance, lower power than commercial cores, m

ore flexibility than ASIC

ASIP Design

• Given a set of applications, determine architecture of ASIP (i. e., configuration of functional units in datapaths, instruction set)

• To accurately evaluate performance of processor on a given application need to compile the application program onto the processor datapath and simulate object code

• However, the architecture of the processor is a design parameter!

Processor Design Flow

Required Compiler Optimizations

• Machine independent optimizations– Parallelizing transformations (lots of them!) Common subexpression

elimination, Strength reduction, Code motion

• Machine dependent optimizations– Loop unrolling and software pipelining– Static allocation (non- recursive procedure calls)– Storage layout (arrays, scalars)– Optimization of mode setting instructions Instruction selection, scheduling, and register allocation

Common Subexpression Elimination

Constant Propagation and Folding

Dead Code Elimination

Loop Invariant Code Motion

Array Access Strength Reduction