Transcript Embedded Software in Real-Time Signal Processing Systems:

Gert Goossens, Johan Van Praet, Dirk Lanneer, Werner Geurts, Augusli
Kifli Clifford Liem, and Pierre G. Paulin
Proceedings of the IEEE, Vol 85, No. 3, March 1997
Embedded Software in RealTime Signal Processing Systems:
Application and Architecture Trends
Presented by Cedric Ma
for EE249
09/04/2001
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 costreduced 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