EECS 150 - Components and Design Techniques for Digital Systems Lec 24

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EECS 150 - Components and Design Techniques for
Digital Systems Lec 24 Power, Power,
Power11/27/2007

• David Culler
• Electrical Engineering and Computer Sciences
• University of California, Berkeley
• http//www.eecs.berkeley.edu/culler
• http//inst.eecs.berkeley.edu/cs150

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Broad Technology Trends
Moores Law transistors on cost-effective chip
doubles every 18 months
Bells Law a new computer class emerges every 10
years

• Today 1 million transistors per

Same fabrication technology provides CMOS radios
for communication and micro-sensors
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Sustaining Moores Law
If unchecked, the increasing power requirements
of computer chips could boost heat generation to
absurdly high levels, said Patrick Gelsinger,
Intels 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,
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Power, Power, Power

• IT devices represent 2 of global CO2 emissions
  worldwide

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What is EECS150 about?
Power!
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Data Centers
Client

• 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
48 of IT budget spent on energy 50 of data
center power goes into cooling 1 MW DC gt 177 M
kwH 60 M gals water 145 K lbs copper 21 k
lbs lead
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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
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M. K. Patterson, A. Pratt, P. Kumar, From UPS
to Silicon an end-to-end evaluation of
datacenter efficiency, Intel Corporation
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P watts I amps V volts
This is how electric tea pots work ...
Heats 1 gram of water 0.24 degree C
0.24 Calories per Second

1V
-
1 Ohm Resistor
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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

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Data Center Power Usage Today
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PC
Client

• 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
• gt Do nothing well

J2EE SOAP
Enterprise Server
PC Energy Report 2007, 1E
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Do Nothing Well
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Notebooks ... now most of the PC market
Apple MacBook -- Weighs 5.2 lbs
8.9 in
1 in
12.8 in
Performance Must be close enough to desktop
performance ... many people no longer own a
desktop
Size and Weight Ideal paper notebook
Heat No longer laptops -- top may get warm,
bottom hot. Quiet fans OK
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Battery Set by size and weight limits ...
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!
46x energy than iPod nano. iPod lets you listen
to music for 14 hours!
At 1 GHz, CPU consumes 13 Watts. Energy saver
option uses this mode ...
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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

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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 a full workload.
If our CPU took no power at all to run, that
would only double battery life!
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X-Internet Beyond the PC
Forrester Research, May 2001 Revised 2007
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X-Internet Beyond the PC
Forrester Research, May 2001
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Cooling an iPod nano ...
Like a resistor, iPod relies on passive transfer
of heat from case to the air
Why? Users dont 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 ...
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Powering an iPod nano (2005 edition)
1.2 W / 5 W 15 minutes
More W-hours require bigger battery and thus
bigger form factor -- it wouldnt be nano
anymore!
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0.55 ounces
12 hour battery life
79.00
1 GB
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20 hour battery life for audio, 6.5 hours for
movies (80GB version)
24 hour battery life for audio 5 hour battery
life for photos
Thinner than 2005 iPod nano
12 hour battery life
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Whats in the iPhone?
Motherboard USB GSM
http//www.anandtech.com/printarticle.aspx?i3026
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Whats in your iPhone?
Main Processor ARM1176 1GB mem
LCD i/f
WiFi Most of Cell Phone
4 GB NAND Flash

• 3 ARM processors

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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
• 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

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UCB Mote Platforms


Crossbow variation
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Key Design Elements
Flash Storage
timers
proc
data logs
Wireless Net Interface
antenna
RF transceiver
pgm images
WD
Wired Net Interface
serial link USB,EN,
Low-power Standby Wakeup

• Efficient wireless protocol primitives
• Flexible sensor interface
• Ultra-low power standby
• Very Fast wakeup
• Watchdog and Monitoring
• Data SRAM is critical limiting resource

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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 gt most of battery energy
• 2.7 volts gt 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
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What we mean by Low Power

• 2 AA gt 1.5 amp hours (4 watt hours)
• Cell gt 1 amp hour (3.5 watt hours)
• Cell 500 -1000 mW gt few hours active
• WiFi 300 - 500 mW gt several hours
• GPS 50 100 mW gt couple days
• WSN 50 mW active, 20 uW passive
• 450 uW gt one year
• 45 uW gt 10 years
• Ave Power fact Pact fsleep Psleep
  fwaking Pwaking

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Mote Power States at Node Level
Active
Active
Telos Enabling Ultra-Low Power Wireless
Research, Polastre, Szewczyk, Culler, IPSN/SPOTS
2005
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Radios

• Trade-offs
• resilience / performance gt slow wake up
• Wakeup vs interface level
• Ability to optimize vs dedicated support

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Power to Communicate
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Multihop Routing

• Upon each transmission, one of the recipients
  retransmits
• determined by source, by receiver, by
• on the edge 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

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Example TX maximum packet
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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 a 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 mA x 1-5 ms 20 - 100 uAs
I
Time
I
Time
Listen 20 mA
Receive 20 mA x 2-6 ms
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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 QA
• Set up 20 mins in advance
• Final Exam Group 15 TUESDAY, DECEMBER 18,
  2007   5-8P

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Basics Power and Digital Design

• 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

Power Rate of work being done wrt time Rate of
energy being used
Units
Watts Joules/seconds
A very practical formulation!
If we would like to know total energy
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Recall Transistor-level Logic Circuits

• Inverter (NOT gate)

Vdd
Gnd
what is the relationship between in and out?
Vdd
in
out
0 volts
Gnd
3 volts
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Older Logic Families have Pullup R
nMOS Inverter
R
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Power in CMOS
Switching Energy energy used to switch a
node
Calculate energy dissipated in pullup
Energy supplied
Energy dissipated
Energy stored
An equal amount of energy is dissipated on
pulldown
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Switching Power

• Gate power consumption
• Assume a gate output is switching its output at a
  rate of

(probability of switching on any particular
clock period)
Therefore

• Chip/circuit power consumption

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Other Sources of Energy Consumption

• Junction Diode Leakage

• Short Circuit Current

Transistor drain regions leak charge to
substrate.
10-20 of total chip power
1nWatt/gate few mWatts/chip
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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

Transistor s/d conductance never turns off all
the way Low voltage processes much worse
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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
• ? 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?

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Example
Operand Registers
A
B
add/sub
and/or
cmp
MUX
R
Result Register

• What is the cost of optimistic compute and
  select?
• How might we reduce it?

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Discussion Digital Design and Power

• Think about
• n
• a
• f
• c
• Vdd
• In
• Function units
• Registers, FSMs, Counters
• Busses
• Clock distribution

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Technology Scaling and Design Learning
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Scaling Switching Energy per Gate
Moores Lawat work
From Facing the Hot Chips Challenge Again,
Bill Holt, Intel, presented at Hot Chips 17, 2005.
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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
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Customize processes for product types ...
From Facing the Hot Chips Challenge Again,
Bill Holt, Intel, presented at Hot Chips 17, 2005.
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Intel Comparing 2 CPU Generations ...
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Switching Energy Fundamental Physics
Every logic transition dissipates 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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Second Factor Leakage Currents
Even when a logic gate isnt switching, it burns
power
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Engineering On Current at 25 nm ...
We can increase Ion by raising Vdd and/or
lowering Vt.
Vd
I ds
V g
I ds
Vs
0.7 Vdd
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Plot on a Log Scale to See Off Current
We can decrease Ioff by raising Vt - but that
lowers Ion
Vd
Ids
Vg
I ds
Vs
0.7 Vdd