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Platform-Based Design: Part 3, Applications

Wayne Wolf Princeton University

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Outline

Challenges in platform design.Example systems/platforms:

generic; set-top box; printers; wireless; network processors.

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Mapping an application to a platform

System topology.Processing element types.Communication channel types.Software services.

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How many processing elements?

Why not one big CPU? Depends on real-time requirements.

Tight deadlines are incompatible with multitasking. May be CPU or hardwired unit.

Similarly, tight communication deadlines discourage shared communication links.

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Reasons for a dedicated unit

No shared unit is fast enough.Limits on reliable scheduling:

RMS utilization asymptotically approaches 69%.

Overhead effects: RTOS context switching; cache thrashing.

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What types of processing elements?

Hardwired vs. programmable: look for algorithms that can be mapped

very efficiently.What type of programmable CPU:

chip vendor selection usually limits choice;

maximum parallelism.

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CPUs vs. accelerators

CPU speedups should obey n% rule on entire application.

Accelerator speedups must consider n% rule, communication overhead.

CPU accel

new instruction?

accelerated operation?

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Multithreading is important

High performance from accelerators requires multithreading: stalling units throws away a great deal

of performance.

CPU

accel

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What type of memory system?

Cache: size, # sets, block size.

On-chip main memory: amount, type, banking, network to PEs.

Off-chip main memory: type, organization.

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RTOS

Software and platforms

Many vendors supply APIs and libraries.

Long-term goal: custom optimization tools. hardware

BIOS

libraries

applications

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PC-based platform

Basic hardware components: CPU; memory; timers; DMA; minimal I/O devices.

Basic software: BIOS.

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PC-style hardware architecture

CPU

system bus

memory

DMAcontroller

timers

businterface

brid

ge

high-speed bus

low-speed bus

I/O

I/O

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Strong ARM

StrongARM system includes: CPU chip (3.686 MHz clock) system control module (32.768 kHz

clock).• Real-time clock;• operating system timer• general-purpose I/O;• interrupt controller;• power manager controller;• reset controller.

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Pros and cons

Plentiful hardware options.Simple programming semantics.Good software development

environments.Performance-limited.

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Apple Newton hardware architecture

ARM 610 ROM RAM

RuntASIC

LCD

speaker

serial I/F

A/D

tablet

PCMCIA

infrared

Design Automation for Embedded Systems

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Motorola Envoy hardware architecture

PCMCIA 1 MB DRAM 4 MB flash

AstrosystemASIC

68439CPU

audio

modem

infrared

power supply

A/Dtouchscreen

Magicbus

Design Automation for Embedded Systems

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InfoPad hardware architecture

Wireless networkinterface

Speechcodec

Videodecompressor

ARM 60

display

Keyboard/pointer

other I/O

IEEE Trans. Computers

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Hardware vs. software

Special-purpose hardware often consumes much less power.

Need to think about communication between units, multiprocessing.

Accelerators often require limits on parameters. May be OK if standards limit

parameters.

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Philips set-top box hardware architecture

Networkinterface

MPEGdemux

MPEGaudio

MPEGvideo

NTSCCD-I

graphicsPCMCIA

DRAM

I/O

NVRAM

DRAM

DRAM

Philips journal

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Customized processors

Tensilica synthesizes custom processor, associated software.

http://www.tensilica.com/technology.html

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Printers

High-speed vs. low-cost: uniprocessor vs. multiprocessor

hardware? multiprocessor requires more complex

software.

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The printing process

page descriptionlanguage

rasterizer

raster memory

printercontroller

printer

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HP PPA printer controller

Controller ASIC68EC000 ROM

P IF

data path

motor ctrl

carriage pos

SRAM

DRAM

I/Oconnector

motorsASIC

encoder

printcartridgeASIC

mask ROM

flash

HP JournalJune 1997

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HP DesignJet hardware architecture

i960KAi960

components

proc.supportASIC

penctrl

ASIC

swathRAM

servoproc.

(8052)

EEPROM

DRAMctrlfront panel stepper

motor

carriagePC board

swath generation

drawing

parsing and rasterization

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TI Open Multimedia Applications Platform

Dual-processor shared memory system:

GPPOS

DSPmanager

General-purposeprocessor

DSP

DSPOS

DSPtask

& I/Octrl

bridge

Memctrl

external memory

http://www.ti.com/sc/docs/apps/wireless/omap/overview.htm

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Wireless handset

Generic handset (TI):http://www.ti.com/sc/docs/psheets/diagrams/gdgradio.htm

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ADI ADSL engine

Bus-based multiprocessor (ADI):

http://www.analog.com/industry/signal_chains/auto/communications/comms_1.html

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Agere StarPro platform

http://www.lucent.com/micro/starpro/arch.html

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C-Port C5 network processor

HDLCengine

HDLCengine

Memoryctrl

… (16 total)

to mem

toframer

600 Mbps

RISCexecutivecontroller

fabricprocessor

to ATM

otherchannel processors

http://www.cportcorp.com/products/digital.htm

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Summary

Consider system requirements to select system architectures.

Multiprocessors rule high-performance applications. Co-processors can be important for low-

power applications.