Embedded Computing

From Theory to Practice

November 2008USTC Suzhou

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FAQs

How useful is theory in practice?

How hard is reality ?

Some example to illustrate

what way of thinking is expected in practice.

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Embedded Systems

Specific applications– Communications: mobile phone, DSL home gateway– Automotive: engine & brake control, …– Consumer, Aerospace, Medical …

Embedded computing hardware– EDA tools– Performance, cost, power, size

Embedded software– Correct functions and realtime-ness– Performance, cost, power

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Example 1: Automotive Trend

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Example 2: Mobile Phone Trend

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Very Large Integration Trend

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Computing Architecture Trend

Intel Tera-Scale architecture with 80 Cores*Intel Technology Journal Issue 3, 2007

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Theory & Practice

A Hardware Case

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Hardware fundamentals

Processor architecture– RISC: 16bit, 32bit, 64bit – Pipeline: for high clock frequency– Cache: L1, L2, etc

Memory Bus & IO Accelerator

Embedded Computing Platform

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Processor performance

MIPS = Million Instructions Per Second– Important measure of CPU performance

Theory– RISC processor– IPC: One instruction per cycleIPC = 1.0– Clock frequency F = 100 MHzMIPS = F * IPC = 100

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Design practice ( I )

Application– Run code and measure instructions executed– Assume 1000 M I P S

Taking 2 x 500 MHz ARM core ? – 10 % branches: 3 x 100 Mio cycles – 20 % load/store: 10 x 200 Mio cycles

Additional MHz needed– 2 x 100 MHz for branches– 9 x 200 MHz for loads/stores

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Design practice ( II )

Add 4 x 500 MHz cores. IPC = ? How can I get in all the instructions ?

– 1000 M I P S– Bus / DRAM clock: 266 MHz– Instruction words 266 per second– Solution 4 x width = 128 bit

To consider inst. reuse and cache miss– more than 1000 Mio. instructions per second

All these need to be considered in your design.

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Theory & Practice

A Software Case

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Programming fundamentals

Data structure– Array e.g.

int a[100], b[100];

– Pointer e.g.int *p = malloc( 100*sizeof(int) );

– Linked liststruct list {list *pre; list *suc; int member;} *mylist;

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Software design practice ( I )

What does malloc( ) do ?– System dependent– Library function of OS– May differ 1000% in performance

malloc( ) Optimization

0

5000

10000

15000

normal optimized

Cyc

le Reihe1

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Software design practice ( II )

Data assignment

for (i=0; i<100; i++) a[i] = b[i] ;

How many memory accesses?– 0?– 100 ?– 200 ?

Impact on– speed and power consumption

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Software design practice ( III )

Data assignment

for (i=0; i<100; i++) { a[i] = mylist ->member; mylist = mylist -> suc; }

How many memory accesses?– 100 ?– 200 ?– 300 ? ….

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Conclusions

Examples from real project

Way of thinking– I have a solution.– I have a working solution.– I have a optimally working solution.

The latter is paid more