Introduction

Lin ZhongELEC518, Spring 2011

Please connect to power

3

Battery density

10% vs. 50% Annual Growth Rate

One watt steady power13°C surface temperature increase

Burning pain: 41-43°CTissue damage: 45°C

Electricity bill

• Data center– Electricity bill is more than equipment bill

• Home appliances

8

There is no silver bullet for an energy-efficient mobile device

9

DEEP SLE

EP

SLEEP

Compu

ting

LCD

Ligh

ting-

1

Ligh

ting-

2

Ligh

ting-

3

Ligh

ting-

4

Keybo

ard

light

ing

Speak

er

Speak

er-M

ax

WiF

i-Con

necte

d (B

atte

ry)

WiF

i-Con

necte

d (P

erf.)

WiF

i dat

a tra

nsfe

r (1M

bps)

Bluet

ooth

(Disc

over

able

)

Bluet

ooth

(Pag

ing)

Bluet

ooth

(Con

necte

d)

Bluet

ooth

dat

a tra

nsfe

r (11

5kbp

s)

GSM (s

tay c

onne

cted)

GSM vo

ice

GPRS0

200

400

600

800

1000

1200

1400

1600

1800

5 3

221142

88 92 80 93142

2

180

315

704

1615

990

3297

25

900

725

Pow

er

(mW

)

Power profile: T-Mobile MDA

Power profile !=Energy profile

Rule No. 1• Focus on the big one!

– Amdahl’s Law• Reduction of the power of α % of the system by p% leads to

α∙p % reduction of the total power

10

α

Rule No. 2

• Minimize static energy consumption– IC consumes static power when it is merely

powered

11

Rule No. 3

• Minimize activity– When not doing things useful

• Turn it off• Stop the clock• Check the manual for power-saving modes• Be aware of state transition overhead

– Interrupt-driven instead of polling

12

Rule No. 4

• Don’t forget parasites – More integrated solution leads to lower energy

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