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EECS 150 - Components and Design Techniques for Digital Systems
Lec 24 –Power, Power, Power11/27/2007
David CullerElectrical Engineering and Computer Sciences
University of California, Berkeley
http://www.eecs.berkeley.edu/~cullerhttp://inst.eecs.berkeley.edu/~cs150
2
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
WorkstationPC
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
3
Sustaining Moore’s Law
“If unchecked, the increasing power requirements of computer chips could boost heat generation to absurdly high levels,” said Patrick Gelsinger, Intel’s
CTO is reported to have said.
“By mid-decade, that Pentium PC may need the power of a nuclear reactor. By
the end of the decade, you might as well 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,”
4
Power, Power, Power
• IT devices represent 2% of global CO2 emissions worldwide
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
WorkstationPC
Cell
1:1
1:103
Mote!
Mobile telecom, 9%
LAN and office telecom, 7%
Fixed-line Telecom, 15%
Printers, 6%
Servers, 23%
PCs and Monitors, 39%
Source Gartner
5
What is EECS150 about?
Transfer Function
Transistor Physics
Devices
Gates
Circuits
FlipFlops
EE 40
HDL
Machine Organization
Instruction Set Arch
Pgm Language
Asm / Machine Lang
CS 61C
Deep Digital Design Experience
Fundamentals of Boolean Logic
Synchronous Circuits
Finite State Machines
Timing & Clocking
Device Technology & Implications
Controller Design
Arithmetic Units
Bus Design
Encoding, Framing
Testing, Debugging
Hardware Architecture
HDL, Design Flow (CAD)
6
Data Centers
• 1.5% of total US energy consumption in 2006
• 60 Billion kWh• Doubled in past 5 years
and expected to double in next 5 to 100 Billion kWh
– 7.4 B$ annually
EPA report aug 4 2007 delivered to congress in response to public law 109-431
Client
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
WorkstationPC
Cell
1:1
1:103
Mote!
48% of IT budget spent on energy
50% of data center power goes into cooling
1 MW DC => 177 M kwH + 60 M gals water + 145 K lbs copper + 21 k lbs lead
7
Servers: Total Cost of Ownership (TCO)
Machine rooms are expensive … removing heat dictates how many servers can fit
Electric bill adds up! Powering the servers + powering the air conditioners is a big part of TCO
Reliability: running computers hot makes them fail more often
8
M. K. Patterson, A. Pratt, P. Kumar, “From UPS to Silicon: an end-to-end evaluation of datacenter efficiency”, Intel Corporation
9
+1V -
1 Ohm Resistor
1A0.24 Calories per Second
Heats 1 gram of water 0.24 degree C
This is how electric tea pots work ...
1 Joule of Heat Energy per Second
1 Watt
20 W rating: Maximum power the package is able to transfer to the air. Exceed rating and resistor burns.
P watts = I amps * V volts
10
Basics
• Warning! In everyday language, the term “power” is used incorrectly in place of “energy”
• Power is not energy– E = P * T
• Power is not something you can run out of
• Power can not be lost or used up
• It is not a thing, it is merely a rate
• It can not be put into a battery any more than velocity can be put in the gas tank of a car
12
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
J2EESOAP
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
WorkstationPC
Cell
1:1
1:103
Mote!
14
Notebooks ... now most of the PC market
Performance: Must be “close enough” to desktop performance ... many people no longer own a desktop
Heat: No longer “laptops” -- top may get “warm”, bottom “hot”. Quiet fans OK
Size and Weight: Ideal: paper notebook
1 in
8.9 in
12.8 in
Apple MacBook -- Weighs 5.2 lbs
15
Battery: Set by size and weight limits ...
Almost full 1 inch depth. Width and height set by available space, weight.
Battery rating: 55 W-hour
At 2.3 GHz, Intel Core Duo CPU consumes 31 W running a heavy load - under 2 hours battery life! And, just for CPU!
At 1 GHz, CPU consumes 13 Watts. “Energy saver” option uses this mode ...
46x energy than iPod nano. iPod lets you listen to music for 14 hours!
16
Battery Technology
• Battery technology has developed slowly• Li-Ion and NiMh still the dominate technologies• Batteries still contribute significantly to the
weight of mobile devices
Toshiba Portege 3110 laptop - 20%
Handspring PDA - 10%
Nokia 61xx - 33%
17
55 W-hour battery stores the energy of
1/2 a stick of dynamite.
If battery short-circuits, catastrophe is possible ...
18
CPU Only Part of Power Budget
2004-era notebook running a full workload.
If our CPU took no power at all to run, that would only double battery life!CPULCD
Backlight
“other”
LCD
GPU
19
Automobiles700 Million
Telephones4 Billion
Electronic Chips60 Billion
X-Internet
“X-Internet” Beyond the PC
Forrester Research, May 2001Revised 2007
500Million
1.5 Billion
Internet Computers
Internet UsersToday’s Internet
20
“X-Internet” Beyond the PC
Forrester Research, May 2001
0
5000
10000
15000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Millions
Year
XInternet
PCInternet
21
Cooling an iPod nano ...
Like a resistor, iPod relies on passive transfer of heat from case to the airWhy? Users don’t want fans in their pocket ...
To stay “cool to the touch” via passive cooling, power budget of 5 W
If iPod nano used 5W all the time, its battery would last 15 minutes ...
22
Powering an iPod nano (2005 edition)
Battery has 1.2 W-hour rating: Can supply 1.2 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 music300 mW for slides
More W-hours require bigger battery and thus bigger “form factor” -- it wouldn’t be “nano” anymore!
24
12 hour battery life
24 hour battery life for audio
5 hour battery life for photos
20 hour battery life for audio, 6.5 hours for movies (80GB version)
Up from 14 hours for 2005 iPod nano
Up from 4 hours for 2005
iPod nano
Thinner than 2005 iPod nano
25
What’s in the iPhone?
http://www.anandtech.com/printarticle.aspx?i=3026
Battery
WiFI antenna
GSM antenna
Motherboard
USB & GSM
26
What’s in your iPhone?
• 3 ARM processors
WiFi & Most of Cell Phone
Main Processor
ARM1176 + 1GB mem
4 GB NAND Flash
LCD i/f
27
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 • Flash 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: Foxconn, FIH • Casing & mechanical parts:
Foxconn & Catcher • Push button: Sunrex • Connectors & cable: Entery, Cheng
Uei, Foxlink, Advanced Connectek • PCB: Unimicron & Tripod
28
UCB Mote Platforms
*
* Crossbow variation
*
years
ComputersPer Person
103:1
1:106
Laptop
PDA
Mainframe
Mini
WorkstationPC
Cell
1:1
1:103
Mote!
29
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 sensorsADC
Wireless NetInterface
Wired NetInterface
RFtransceiver
antenna
serial linkUSB,EN,…
Low-powerStandby & Wakeup
Flash Storage
pgm images
data logs
WD
30
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
31
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-up time
– Memory restore
DMA Support: permits ADC sampling while processor is sleeping
32
What we mean by “Low Power”
• 2 AA => 1.5 amp hours (~4 watt hours)• Cell => 1 amp hour (3.5 watt hours)
Cell: 500 -1000 mW => few hours activeWiFi: 300 - 500 mW => several hoursGPS: 50 – 100 mW => couple days
WSN: 50 mW active, 20 uW passive450 uW => one year45 uW => ~10 years
Ave Power = fact * Pact + fsleep * Psleep + fwaking * Pwaking
* System design
* Leakage (~RAM)
* Nobody fools mother nature
33
Mote Power States at Node Level
Sleep WakeUP Work Sleep WakeUP Work
Active Active
Telos: Enabling Ultra-Low Power Wireless Research, Polastre, Szewczyk, Culler, IPSN/SPOTS 2005
34
Radios
• Trade-offs: – resilience / performance => slow wake up– Wakeup vs interface level– Ability to optimize vs dedicated support
36
Multihop Routing
• Upon each transmission, one of the recipients retransmits
– determined by source, by receiver, by …– on the ‘edge of the cell’
37
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
10mA
20mA
5 ms 10 ms
DatasheetAnalysis
39
The “Idle Listening” Problem
• The power consumption of “short range” (i.e., low-power) wireless communications devices is roughly the same whether the radio is transmitting, receiving, or simply ON, “listening” 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 α Transmit x Density– Listening (potentially) happens all the time
⇒Total energy consumption dominated by idle listening
40
Communication Power Consumption
Sleep~10 uA
Transmit~20 mA x 1-5 ms[20 - 100 uAs]
I
I
Time
Time
Listen~20 mA
Receive~20 mA x 2-6 ms
41
Announcements
• Project Check-offs this week– TAs posting extra “office 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
42
• Power supply provides energy for charging and discharging wires and transistor gates. The energy supplied is stored & then dissipated as heat.
• If a differential amount of charge dq is given a differential increase in energy dw, the potential of the charge is increased by:
• By definition of current:dqdwV /=
dtdqI /=
dtdwP /≡Power: Rate of work being done wrt time
Rate of energy being used
IVPdt
dq
dq
dwdtdw ×==×=/
∫∞−
=t
Pdtw total energy
Units: tEP ∆= Watts = Joules/seconds
A very practical formulation!
If we would liketo know total energy
Basics – Power and Digital Design
43
Recall: Transistor-level Logic Circuits
• Inverter (NOT gate):Vdd
Gnd
Vdd
Gnd0 volts
in out
3 volts
what is the relationship
between in and out?
45
Power in CMOS
C
p u l l u pn e t w o r k
p u l l d o w nn e t w o r k
V d d
G N D
10
i ( t )
v ( t )t 0 t 1
v ( t )
V d d
Switching Energy: energy used to switch a node
Energy supplied Energy dissipatedEnergy stored
Calculate energy dissipated in pullup:
222 2121
)()()()()(
1
0
1
0
1
0
1
0
1
0
dd
t
t
t
t dddddd
t
t dd
t
t dd
t
tsw
cVcVcVdvvcdvcV
dtdtdvcvVdttivVdttPE
=−=⋅−=
=⋅−=⋅−==
∫ ∫∫∫∫
An equal amount of energy is dissipated on pulldown
46
Switching Power
• Gate power consumption:– Assume a gate output is switching its output at a rate of:
1 / f
P a v g
c l o c k f
f⋅α
swavg ErateswitchingtEP ⋅=∆=
221 ddavg cVfP ⋅⋅= α
221 ddavgavgavg VcfnP ⋅⋅⋅= α
• Chip/circuit power consumption:
activity factor clock rate
Therefore:
number of nodes (or gates)
(probability of switching on any particular clock period)
47
Other Sources of Energy Consumption
• “Short Circuit” Current:
V o u t
V i n
V i n
I
I
V o u tV i n
I
V
D i o d eC h a r a c t e r i s t i c10-20% of total chip power
~1nWatt/gatefew mWatts/chip
Transistor drain regions“leak” charge to substrate.
• Junction Diode Leakage :
48
Other Sources of Energy Consumption
• Consumption caused by “DC leakage current” (Ids leakage):
• This source of power consumption is becoming increasing significant as process technology scales down
• For 90nm chips around 10-20% of total power consumption Estimates put it at up to 50% for 65nm
I o f f
V o u t = V d dV i n = 0
I d s
V g sV t hTransistor s/d conductance
never turns off all the way
Low voltage processes much worse
49
Controlling Energy Consumption: What Control Do You Have as a Designer?
• Largest contributing component to CMOS power consumption is switching power:
• Factors influencing power consumption:– n: total number of nodes in circuit�α: activity factor (probability of each node switching)– f: clock frequency (does this effect energy consumption?)– Vdd: power supply voltage
• What control do you have over each factor? • How does each effect the total Energy?
221 ddavgavgavg VcfnP ⋅⋅⋅= α
50
Example
• What is the cost of optimistic compute and select?
• How might we reduce it?
A B Operand Registers
add/sub and/or cmp
R
MUX
Result Register
51
Discussion: Digital Design and Power
• Think about…– n�α– f– c– Vdd
• In – Function units– Registers, FSMs, Counters– Busses– Clock distribution
221 ddavgavgavg VcfnP ⋅⋅⋅= α
53
Scaling Switching Energy per GateMoore’s Lawat work …
From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005.
Due to reduced V and C (length and width of Cs decrease, but plate distance gets smaller)
Recent slope reduced because V is scaled less aggressively
54
Device Engineers Trade Speed and Power
:F r o m -1 0 - S ilic o n D e v ic e S c a lin g t o t h e S u b n m R e g im e ,M e ik e i Ie o n g 1 * ,B r u c e D o r is 2 ,J a k u b K e d z ie r s k i 1 ,K e n R im 1 M in Ya n g 1
We can reduce leakage (Pstandby) by raising Vt
We can increase speed by raising Vdd and lowering Vt
We can reduce CV2 (Pactive) by lowering Vdd
55
Customize processes for product types ...
From: “Facing the Hot Chips Challenge Again”, Bill Holt, Intel, presented at Hot Chips 17, 2005.
56
Intel: Comparing 2 CPU Generations ...
Clock speed unchanged ... Lower Vdd, lower C,
but more leakage
Design tricks: architecture & circuits
Find enough tricks, and you can afford to raise Vdd a little so that you can raise the clock speed!
57
Switching Energy: Fundamental Physics
Vdd
C
1
2 C Vdd
E1->0
= 21
2 C Vdd
E0->1
= 2
Vdd
Every logic transition dissipates energy
Strong result: Independent of technology
How can we 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.
58
0V =
Second Factor: Leakage CurrentsEven when a logic gate isn’t switching, it burns power …
Igate: Ideal capacitors have zero DC current. But modern transistor gates are a few atoms thick, and are not ideal.
Isub: Even when this nFet is off, it passes an Ioff leakage current.
We can engineer any Ioffwe like, but a lower Ioff also results in a lower Ion, and thus the lower the clock speed.
Intel’s current processor designs, leakage vs switching power
A lot of work was done to get a ratio this good ... 50/50 is common.
Bill Holt, Intel, Hot Chips 17.
59
Engineering “On” Current at 25 nm ...
I ds
Vs
Vd
V g
0.7 = Vdd
0.25 ≈ Vt
I ds
1.2 mA = Ion
Ioff
= 0 ???
We can increase Ion by raising Vdd and/or lowering Vt.
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