Embedded Software in Real-Time Signal Processing Systems: Application and Architecture Trends

Presented by Cedric Ma

for EE249

09/04/2001

Gert Goossens, Johan Van Praet, Dirk Lanneer, Werner Geurts, Augusli Kifli Clifford Liem, and Pierre G. PaulinProceedings of the IEEE, Vol 85, No. 3, March 1997

Outline

I. Introduction II. Market & Processor Trends III. Embedded Processors in Multimedia,

Wireless, & Telecom IV. Embedded Systems Application Trends V. Embedded Software Development Needs

Some Terms

ASIP - application specific instruction-set processor cores

MPU - Microprocessor Unit MCU - Microcontroller Unit DSP - Digital Signal Processor

I. Introduction

Telecom, Multimedia, Consumer Electronics – Rapid evolution toward single chip integration

– Range of solutions: general purpose cores to ASIP

– Future role of embedded processors?• Convergence of computing, communication, and consumer

electronics: short time-to-market, very low costs

• Stabilization of PC market growth

• Increasing growth of wireless and multimedia

– Consumer oriented applications most influential to technology evolution in early 21st century

• especially wireless communications, multimedia

II. Market & Processor Trends

A. Overall Semiconductor B. Embedded Processor

A. Overall Semiconductor

Two key trends:– Continued growth of: Processors & Memories

– Growth leaders are: Multimedia & Wireless

New Technology Drivers– General purpose computing chips and memories in the

past were main contributor to evolution of VLSI technology and design methods

– New role assumed by:• Wireless: GSM, DECT cordless phone

• Multimedia: MPEG2 decoders, DVD, HDTV

B. Embedded Processor Trends

Main application classes for programmable processors– Computing Applications

• Desktop, notebooks, workstations, server– characterized by user programmability

– Embedded Applications• More specific• Dedicated function: ABS, autopilot• Real-time behavior (strict requirements)• Correctness of design (impact to environment)

B: Embedded Processor Classes

Embedded Processors– Instruction-set programmable processors used in

embedded systems– Include MCU, DSP, MPU (CISC & RISC)

ASIP– Programmable processor for specific, well-defined class

of applications– Small, well-defined instruction set– Specialized/stripped down versions of MCU/DSP/MPU– Applications: real-time signal/image processing

B: Processor Volume Distributions

Parts volume dominated by 4 & 8-bit MCU– MPU: 60% total processor sales revenue

• but lower volume than MCU & DSP• reason: higher price of MPU

32-bit Processors:– Uses: 43% computing / 57% embedded– x86-based:

• 90% (revenue) of computing applications market• 30% of embedded market: diversity of architectures

III. Embedded Processors in Multimedia, Wireless, & Telecom Multimedia

– set-top boxes, HDTV, DVB, videophones

Wireless communication– GSM, DECT, IS-54B digital cellular

Telecommunications– broad range of high volume products

A1. Multimedia Processors

Widespread use of custom ASIP cores– Low cost

• Most revenue comes from 2nd generation cost-reduced versions

– 32-bit MPU not well suited• Specialized video compression algorithms

• No need for processor cache

– Software compatibility not an issue• Carefully optimized set of specific tasks

A2. 3-D Video Acceleration

Most vendors use dedicated ASIP– Lack of standard RISC/CISC MPU– Reason: high performance requires dedicated

architectures

MMX for x86 (introduced ~1997)– Allows 3-D processing in software– 10x speedup needed to handle high-quality

game programs

B. Wireless Communications

ASIP the preferred choice– France Telecom: ASIP achieved 50% power

reduction over commercial DSP– Italtel: 2 in-house ASIP replaced 8 commercial

DSP in GSM base station– AT&T: ASIP design is a key advantage– Northern Telecom: ASIP used in many strategic

high-volume products

C. General Telecom

Northern Telecom survey– Number of design teams using

• 2/3 of teams use commercial DSP/MCU chips

– Number of processors shipped• 2/3 in-house ASIP, 1/3 commercial

– What this means:• ASIP: large volume, low cost applications

• Commercial: minimize time-to-market

D. Embedded Processor Conclusions

Diversity of processor architectures– Driven by low-cost consumer markets

Diversity of building blocks– RISC/ASIP/hard-wired co-processors

Dominance of ASIP– High-volume, low cost segments

D: ASIP vs. General Purpose Processors

“Today’s General-Purpose Processors Solve Yesterday’s Problems”– Applications themselves do not stand still– Dedicated multimedia processor more cost

effective– API for x86 can be mapped to low cost ASIP

D: Outlook for Embedded Systems Market Emerging (consumer) embedded

applications expected to be available at competitive prices– Justify development of dedicated ASIP– General purpose processors continue to

dominate low volume applications– Not clear cut: ASIP often coupled with RISC or

MCU

IV. Embedded Systems Application Trends Growth of Complexity

– New wireless handsets features, cell phone/PDA merge, videophone standard, new video & audio coding standards

– Many functions moved from hardware to software

• ASIP required for performance & cost reasons

V. Embedded S/W Development Needs

Design teams developing embedded software require sophisticated tools– Commercial tool support trends– Northern Telecom survey– Ideal hardware-software codesign tool

environment

A. Processor Tool Support Trends

Commercial C compilers: low quality– MCU:low code size; DSP:execution speed– 4-10x slower than hand coded assembly– Embedded design: no speed degradation!

• Designers continue to program in assembly code

• Long term problem: assembly code locks designers to old architectures

B. Northern Telecom Survey

Dominance of assembly– ANSI C is the only high-level language used– Assembly preferred for algorithm capture

• MCU: 75% of code; DSP: 90%

– Poor quality of generated assembly code– Unwilling to sacrifice performance

• DSP code has greater portion written in assembly

B. Northern Telecom Survey

Development effort rapidly increasing– embedded software development effort exceeds

hardware-oriented development

Future tool needs– Improved compiler technology

• allows high-level language for expressing algorithm

– High-performance instruction-set simulator– Source-level debugger– Cross assembler: remap legacy code

C. Embedded S/W Needs

High-performance compilers for low-cost irregular architectures

Environment that supports rapid development of compilers Associated tools: performance profilers, source-level

debuggers, in-circuit emulators; retargetable ASIP based designs: quick feedback on instruction set

decisions Rapid deployment of cycle-accurate instruction set models Synthesis of lightweight RTOS

C: Ideal hardware-software co-design environment

Key characteristic of “ideal” environment:– Functional co-simulation allows validation of global

behavior of software and hardware– Retargetable compiler (to new platforms)

• source-level debugging & complete assembler/linker back-end

– Instruction set definition used to generate model of target processor’s instruction set

• permits execution of object code on virtual model of processor

– Allows for exploring ASIP architectures– Profile tool measures performance guides instruction set

selection