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EECS 150 - Components and DesignTechniques for Digital Systems
Lec 24 ±Power, Power, Power
11/27/2007
David Culler Electrical Engineering and Computer SciencesUniversity of California, Berkeley
http://www.eecs.berkeley.edu/~culler http://inst.eecs.berkeley.edu/~cs150
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Broad Technology Trends
Today: 1 million transistors per $
Moore¶s Law: # transistors on
cost-effective chip doubles every
18 months
Mote! years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
Workstation
PC
Cell
1:1
1:103
Bell¶s Law: a new computer
class emerges every 10 years
Same fabrication technology provides CMOS radios
for communication and micro-sensors
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Sustaining Moore¶s Law
³If unchecked, the increasing power requirements of computer chips couldboost heat generation to absurdly highlevels,´ said Patrick Gelsinger, Intel¶s
CTO is reported to have said.
³By mid-decade, that Pentium PC may
need the power of a nuclear reactor. Bythe end of the decade, you might aswell be feeling a rocket nozzle than
touching a chip. And soon after 2010,PC chips could feel like the bubbly hot
surface of the sun itself,´
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Power, Power, Power
IT devices represent 2% of globalCO2 emissions worldwide
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
Workstation
PC
Cell
1:1
1:103
Mote!
Mobil
t l com, 9%
LAN offic
t l com,
7%
Fix -li
T l com, 15%
Pri t rs, 6%
S r rs, 23%
P s
Monitors, 39%
Source Gartner
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What is EECS150 about?
ra sf r Fu tio
ra sistor Physi s
D vi s
Gat s
Cir uits
FlipFlops
EE 40
HDL
a hi r a i atio
I stru tio S t Ar h
Pgm La guage
Asm / a hi e La g
CS 61C
Deep Digital Design Experience
Fundamentals of Boolean Logic
Synchronous Cir cuits
Finite State achines
iming & Clocking
Device echnology & Implications
Controller Design
Arithmetic Units
Bus Design
Encoding, Framing
Testing, Debugging
Hardwar e Ar chitectur e
HDL, Design Flow (CAD)
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Data Centers
1.5% of total US energyconsumption in 2006
60 Billion kWh
Doubled in past 5 years
and expected to double innext 5 to 100 Billion kWh ± 7.4 B$ annually
EPA report aug 4 2007 delivered tocongress in response to public law109-431
Client
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
MiniWorkstation
PC
Cell
1:1
1:103
Mote!
48% of IT budget spent on energy
50% of data center power goes intocooling
1 MW DC => 177 M kwH + 60 Mgals water + 145 K lbs copper +
21 k lbs lead
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Servers: Total Cost of Ownership (TCO)
Machine roomsare expensive «removing heatdictates howmany servers can
fit
Electric bill addsup! Powering theservers +powering the airconditioners is abig part of TCO
Reliability: running computers hotmakes them fail more often
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M. K. Patterson, A. Pratt, P. Kumar,
³ rom UPS to Silicon: an end-to-end evaluation of datacenter efficiency´, Intel Corporation
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+1V -
1 Ohm
Resistor
1A0.24 Calories per Second
Heats 1 gram of water0.24 degree C
This is how electric tea pots work ...
1 Joule of Heat
Energy per Second
20 W rating: Maximum powerthe package is able totransfer to the air. Exceed
rating and resistor burns.
P watts = I amps * V volts
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Data Center Power Usage Today
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PC
HPxw4200 ± 180 w active with two LCDs
± 130 w w/o monitor, 110 w idle,
± 6 w suspend
60% are left on around the clock
15% of all office power
US: ± 1.72 B$ & 15 M tons CO2 annually
Mid size company: ± 165 K$ & 1400 tons of CO2
Existing power mgmt (hibernation)can reduce by 80%
=> Do nothing well
PC Energy Report 2007, 1E
Client
EnterpriseServer
J2EE
SO
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
MiniWorkstation
PC
Cell
1:1
1:103
Mote!
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Do Nothing Well
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Notebooks ... now most of the PC market
Performance: Must be ´close enoughµ to desktopperformance ... many people no longer own a desktop
Heat: No longer ´laptopsµ -- top may get ´warmµ,bottom ´hotµ. Quiet fans OK
Size and Weight: Ideal: paper notebook
1 in
8.9 in
12.8 in
Apple MacBook -- Weighs 5.2 lbs
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Battery: Set by size and weight limits ...
Almost full 1 inch depth.Width and height set byavailable space, weight.
Battery rating:55 W-hour
At 2.3 GHz, IntelCore Duo CPU
consumes 31 Wrunning a heavy load- under 2 hoursbattery life! And,
just for CPU!
At 1 GHz, CPU consumes13 Watts. ´Energy saverµ
option uses this mode ...
46x energy than iPod nano.iPod lets you listen to musicfor 14 hours!
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Battery Technology
Battery technology has developed slowly Li-Ion and NiMh still the dominate technologies
Batteries still contribute significantly to theweight of mobile devices
Toshiba ortege
110 laptop - 20%
Handspring
D - 10%Nokia 1xx -
%
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55 W-hour battery stores
the energy of
1/2 a stick of dynamite.
If battery short-circuits,
catastrophe is possible ...
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CPU Only Part of Power Budget
2004-era notebook running afull workload.
If our CPU took no powerat all to run, that wouldonly double battery life!CPULCD
Backlight
´otherµ
LCD
GPU
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Automobiles700 Million
Telephones4 Billion
Electronic Chips60 Billion
X-Internet
³X-Internet´ Beyond the PC
Forrester Research, May 2001Revised 2007
500Million
1.5 Billion
Internet Computers
Internet Users
Today·s Internet
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³X-Internet´ Beyond the PC
Forrester Research, May 2001
0
000
10000
1 000
2 0 0
1
2 0 0
2
2 0 0
2 0 0
2 0 0
2 0 0
2 0 0
2 0 0
2 0 0 2
0 1 0
Millions
Year
XInternet
PCInternet
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Cooling an iPod nano ...
L
ike a resistor, iPod relieson passive transfer of heatfrom case to the air
Why? Users don·t wantfans in their pocket ...
To stay ´cool to the touchµ via passive cooling,
power budget of 5 W
If iPod nano used 5W all the time, its battery would last15 minutes ...
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Powering an iPod nano (2005 edition)
Battery has 1.2 W-hourrating: Can supply1.2 W of power for 1 hour
1.2 W / 5 W = 15 minutes
Real specs for iPod nano :
14 hours for music,4 hours for slide shows
85 mW for music
300 mW for slides
More W-hours require bigger batteryand thus bigger ´form factorµ --it wouldn·t be ´nanoµ anymore!
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0.55 ounces
12 hourbattery life
$79.00
1 GB
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12 hourbattery life
24 hourbattery life foraudio
5 hour batterylife for photos
20 hour battery life for audio,6.5 hours for movies (80GB version)
Up from 14 hoursfor 2005 iPod nano
Up from 4hours for 2005
iPod nano
Thinner than 2005 iPod nano
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What¶s in the iPhone?
http://www.anandtech.com/printarticle.aspx?i=3026
Battery
Wi I antenna
GSM antenna
MotherboardUSB & GSM
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What¶s in your iPhone?
3 ARM processors
Wi i & Most of Cell Phone
Main Processor
ARM1176 + 1GB mem
4 GB NAND lash
LCD i/f
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iPhone Parts (?)
Baseband processor: Infineon ± S-Gold3/ARM926? Applications/video processor:
Samsung/ARM10 or 11 802.11 chip: Marvell/ARM9? Touchscreen controller: Broadcom Touchscreen: Balda/TPK Bluetooth: CSR USB IC: Alcor, Phison Audio: Wolfson Memory module: A-Data, Transcend lash memory: Samsung, Toshiba,
Hynix Position sensor (MEMS?):
STMicroelectronics, Analog
devices? Light sensor: ??? Proximity sensor: ???
Camera sensor: Micron? Camera module: Altus or Lite-On
Technology, Primax Electronics Camera lens: Largan Precision Microphone: ??? Power management: NXP? Passives: Cyntec
Quartz: TXC Assembly: oxconn, IH Casing & mechanical parts:
oxconn & Catcher Push button: Sunrex Connectors & cable: Entery,
Cheng Uei, oxlink, AdvancedConnectek
PCB: Unimicron & Tripod
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UCB Mote Platforms
*
* Crossbow variation
*
years
omputerser Person
103:1
1:106
Laptop
PDA
Mainframe
MiniWorkstation
PC
Cell
1:1
1:103
Mote!
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Key Design Elements
Efficient wireless protocol primitives
Flexible sensor interface
Ultra-low power standby
Very Fast wakeup
Watchdog and Monitoring
Data SRAM is critical limiting resource
proc
DataSRAM pgm
EPROM
timersSensor Interface digital sensors
analog sensors ADC
Wireless NetInterface
Wired NetInterface
RF
transceiver antenna
serial link USB,EN,«
Low-power Standby & Wakeup
Flash Storage
pgm images
data logs
WD
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TinyOS-driven architecture
3K RAM = 1.5 mm2
CPU Core = 1mm2
± multithreaded
RF COMM stack = .5mm2
± HW assists for SW stack
Page mapping
SmartDust RADIO = .25 mm2
SmartDust ADC 1/64 mm2
I/O PADS
Expected sleep: 1 uW ± 400+ years on AA
150 uW per MHz
Radio: ± .5mm2, -90dBm receive sensitivity
± 1 mW power at 100Kbps
ADC: ± 20 pJ/sample
± 10 Ksamps/second = .2 uW. jhill mar 6, 2003
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Microcontrollers
Memory starved ± Far from Amdahl-Case 3M rule
Fairly uniform active inst per nJ ± Faster MCUs generally a bit better
± Improving with feature size
Min operating voltage ± 1.8 volts => most of battery energy
± 2.7 volts => lose half of battery energy
Standby power ± substantial improvement in 2003
± Probably due to design focus
± Fundamentally SRAM leakage ± Wake-up time is key
Trade sleep power for wake-uptime ± Memory restore
DMA Support: permits ADCsampling while processor issleeping
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What we mean by ³Low Power´
2 AA => 1.5 amp hours (~4 watt hours)
Cell => 1 amp hour (3.5 watt hours)
Cell: 500 -1000 mW => few hours active
WiF
i: 300 - 500 mW => several hoursGPS: 50 ± 100 mW => couple days
WSN: 50 mW active, 20 uW passive
450 uW => one year
45 uW => ~10 years
Ave Power = f act * Pact + f sleep * Psleep + f waking * Pwaking
* System design
* eakage (~R M)
* Nobody fools
mother nature
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Mote Power States at Node Level
Sleep WakeUP Work Sleep WakeUP Work
Active Active
Telos: Enabling Ultra-Low Power Wireless Research, Polastre, Szewczyk, Culler, IP SN/S POT S 2005
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Radios
Trade-offs: ± resilience / performance => slow wake up
± Wakeup vs interface level
± Ability to optimize vs dedicated support
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Power to Communicate
0
20
40
60
80
100
120
140
0 1 2 3 4
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Multihop Routing
Upon each transmission, one of the recipientsretransmits ± determined by source, by receiver, by «
± on the µedge of the cell¶
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Energy Profile of a Transmission
Power up oscillator &
radio (CC2420) Configure radio
Clear Channel
Assessment, Encrypt
and Load TX buffer
Transmit packet
Switch to rcv mode,
listen, receive ACK
10m
20m
5 ms 10 ms
Datasheet
nalysis
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Example: TX maximum packet
0
5
10
15
20
25
-15 -10 -5 0 5 10 15
ms
m A
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The ³Idle Listening´ Problem
The power consumption of ³short range´ (i.e., low-power) wireless communications devices is roughlythe same whether the radio is transmitting, receiving,or simply ON, ³listening´ for potential reception ± includes IEEE 802.15.4, Zwave, Bluetooth, and the many variants
± WiFi too!
± Circuit power dominated by core, rather than large amplifiers
Radio must be ON (listening) in order receive anything. ± Transmission is infrequent. Reception Transmit x Density
± Listening (potentially) happens all the time
Total energy consumption dominated by idle listening
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Communication Power Consumption
Sleep~10 uA
Transmit
~20 m x 1-5 ms
[20 - 100 u s]
I
I
Time
Time
isten
~20 m
Receive
~20 m x 2- ms
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Announcements
Project Check-offs this week ± TAs posting extra ³office hours´ for use of slip days
Dr. Robert Iannucci, Nokia on Thurs ± Bring questions, show off projects
Short HW 10 out tonight ± Due next wed.
Wrap-up and Course Survey 12/4
Project Demos Friday 12/7 ± Signup sheet is posted
± 5 min demo + 5 min Q&A ± Set up 20 mins in advance
Final Exam Group: 15: TUESDAY, DECEMBER 18,2007 5-8P
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Power supply provides energy for charging and discharging wiresand transistor gates. The energy supplied is stored & thendissipated as heat.
If a differential amount of charge dq is given a differential increasein energy dw, the potential of the charge is increased by:
By definition of current:dqdwV /!
dt dq I /!
dt dw P /|Power: Rate of work being done wrt time
Rate of energy being used
I dt
dq
dq
d dt d vv/
´g
!t
Pdt w total energy
Units: t E P (!Wa
tts = J oules/seconds
A ve ry pra ct ic a l fo rmul a t ion !
If we would l ike
to kno w tot a
l ene rgy
Basics ± Power and Digital Design
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Recall: Transistor-level Logic Circuits
Inverter (NOT gate): Vdd
Gnd
Vdd
Gnd0 volts
in out
3 volts
what is therelationship
between in and out?
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Older Logic Families have Pullup R
nMOS Inverter
R
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Switching Power
Gate power consumption: ± Assume a gate output is switching its output at a rate of:
1/f
P
clock f
f E
savg E rate s itching t E !(!
221 dd avg c f P ! E
221 dd avg avg avg c f n P ! E
Chip/circuit power consumption:
a ctivity f a ctor clock r a te
Therefore :
number of nodes (or g a tes)
(prob a bility of switc hing on a ny p a rticul a r clock period)
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Other Sources of Energy Consumption
³Short Circuit´ Current:
Vout
Vin
Vin
I
I
VoutVin
I
V
DiodeCharacter istic10-20% of total chip power
~1nWatt/gatefew mWatts/chip
Transistor drain regions´leakµ charge to substrate.
Junction Diode Leakage :
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Other Sources of Energy Consumption
Consumption caused by ³DC leakage current´ (Ids leakage):
This source of power consumption is becoming increasingsignificant as process technology scales down
For 90nm chips around 10-20% of total power consumptionEstimates put it at up to 50% for 65nm
Ioff
Vout=VddVin=0
Ids
VgsVthTransistor s/d conductance
never turns off all the way
Low volta g e processes much worse
Controlling Energy Consumption:
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Controlling Energy Consumption:What Contr ol Do Y ou Have as aDesigner?
Largest contributing component to CMOS power consumption is switching power:
Factors influencing power consumption: ± n: total number of nodes in circuit
E: activity factor (probability of each node switching)
± f: clock frequency (does this effect energyconsumption?)
± Vdd: power supply voltage What control do you have over each factor?
How does each effect the total Energy?
221 dd avg avg avg V c f n P ! E
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Example
What is the cost of optimistic compute andselect?
How might we reduce it?
A B Operand Registers
add/sub and/or cmp
R
MUX
Result Register
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Discussion: Digital Design and Power
Think about« ± n
E
± f
± c
± Vdd
In
±F
unction units ± Registers, FSMs, Counters
± Busses
± Clock distribution
221 dd avg avg avg c f n P ! E
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Technology Scaling and Design Learning
S li S it hi E G t
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Scaling Switching Energy per Gate
Moore·s Lawat work «
From: ´Facing the Hot Chips Challenge Againµ, Bill Holt, Intel, presented at Hot Chips 17, 2005.
Due toreduced V andC (length andwidth of Csdecrease, butplate distancegets smaller)
Recent slopereducedbecause V isscaled lessaggressively
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Device Engineers Trade Speed and Power
From: Silicon Device Scaling to the Sub-10-nm Regime
Meikei Ieong,1* Bruce Doris,2 Jakub Kedzierski,1 Ken Rim,1 Min Yang1
We can reduce leakage
(Pstandby) by raising Vt
We can increase speed
by raising Vdd
andlowering Vt
We can reduce CV2 (Pactive)by lowering Vdd
Customize processes for product types
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Customize processes for product types ...
From: ´Facing the Hot Chips Challenge Againµ, Bill Holt, Intel, presented at Hot Chips 17, 2005.
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Intel: Comparing 2 CPU Generations ...
Clock speedunchanged ... Lower Vdd, lower C,
but more leakage
Design tricks:architecture & circuits
Find enoughtricks, and
you canafford toraise Vdd a
little so that you can raisethe clockspeed!
Switching Energy: Fundamental Physics
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Switching Energy: Fundamental Physics
Vdd
C
1
2C
Vdd
E1-
>0=
21
2C
Vdd
E0-
>1=
2
Vdd
Every logic transition dissipates energy
Strong result: Independent of technology
How canwe limit
switching
energy?
(1) Slow down clock (fewer transitions). But we like speed ...
(2) Reduce Vdd. But lowering Vdd lowers the clock speed ...
(3) Fewer circuits. But more transistors can do more work.
(4) Reduce C per node. One reason why we scale processes.
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0V =
Second Factor: Leakage CurrentsEven when a logic gate isn·t switching, it burns power «
Igate: Ideal capacitors havezero DC current. But moderntransistor gates are a few atomsthick, and are not ideal.
Isub: Even when this nFetis off, it passes an Ioffleakage current.
We can engineer any Ioffwe like, but a lower Ioff alsoresults in a lower Ion, and thusthe lower the clock speed.
Intel·s current processor designs,
leakage vs switching power
A lot of work wasdone to get a ratiothis good ... 50/50is common.
Bill Holt, Intel, Hot Chips 17.
Engineering ´Onµ Current at 25 nm
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Engineering On Current at 25 nm ...
Ids
Vs
Vd
Vg
0.7 = Vdd
0.25 § Vt
Ids
1.2 mA = Ion
Ioff
= 0 ???
We can increase Ion byraising Vdd and/or lowering Vt.
Plot on a ³Log´ Scale to See ³Off´ Current
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Plot on a Log Scale to See Off Current
IdsV
s
V
dV
g Ids
Ioff
§ 10 nA
We can decrease Ioff byraising Vt - but that lowers Ion
0.25 §V
t
1.2 mA = Ion
0.7 = V
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