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Power, Power, Power: Understanding Energy Consumption in Digital Systems

This lecture discusses the increasing power requirements of computer chips and the impact on energy consumption in digital systems. Topics include deep digital design, synchronous circuits, hardware architecture, and battery technology.

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Power, Power, Power: Understanding Energy Consumption in Digital Systems

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  1. 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

  2. Computers Per Person 1:106 Mainframe Mini 1:103 Workstation PC Laptop 1:1 PDA Cell 103:1 Mote! years Broad Technology Trends Today: 1 million transistors per $ Moore’s Law:# transistors on cost-effective chip doubles every 18 months 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. Computers Per Person 1:106 Mainframe Mini 1:103 Workstation PC Laptop 1:1 PDA Cell Source Gartner 103:1 Mote! years Power, Power, Power • IT devices represent 2% of global CO2 emissions worldwide

  5. 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) Pgm Language Asm / Machine Lang CS 61C Instruction Set Arch Machine Organization HDL FlipFlops Gates Circuits Devices EE 40 Transistor Physics Transfer Function What is EECS150 about? Power!

  6. Computers Per Person 1:106 Mainframe Mini 1:103 Workstation PC Laptop 1:1 PDA Cell 103:1 Mote! years 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 => 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. 1A 1 Joule of Heat Energy per Second 20 W rating: Maximum power the package is able to transfer to the air. Exceed rating and resistor burns. 1 Watt 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

  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

  11. Data Center Power Usage Today

  12. Computers Per Person 1:106 Mainframe Mini 1:103 Workstation PC Laptop 1:1 PDA Cell 103:1 Mote! years 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% => Do nothing well J2EE SOAP Enterprise Server PC Energy Report 2007, 1E

  13. Do Nothing Well

  14. 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

  15. Almost full 1 inch depth. Width and height set by available space, weight. 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 ...

  16. Toshiba Portege 3110 laptop - 20% Handspring PDA - 10% Nokia 61xx - 33% 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

  17. 55 W-hour battery stores the energy of 1/2 a stick of dynamite. If battery short-circuits, catastrophe is possible ...

  18. “other” GPU CPU LCD Backlight LCD 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!

  19. 500 Million Internet Computers Today’s Internet Internet Users 1.5 Billion Automobiles 700 Million Telephones 4 Billion X-Internet Electronic Chips 60 Billion “X-Internet” Beyond the PC Forrester Research, May 2001 Revised 2007

  20. Millions PC Internet X Internet Year “X-Internet” Beyond the PC Forrester Research, May 2001

  21. Cooling an iPod nano ... Like a resistor, iPod relies on passive transfer of heat from case to the air Why? 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. Real specs for iPod nano : 14 hours for music, 4 hours for slide shows Battery has 1.2 W-hour rating:Can supply 1.2 W of power for 1 hour 85 mW for music 300 mW for slides 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 wouldn’t be “nano” anymore!

  23. 0.55 ounces 12 hour battery life $79.00 1 GB

  24. 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 24 hour battery life for audio 5 hour battery life for photos Thinner than 2005 iPod nano 12 hour battery life

  25. Battery WiFI antenna GSM antenna What’s in the iPhone? Motherboard USB & GSM http://www.anandtech.com/printarticle.aspx?i=3026

  26. 3 ARM processors What’s in your iPhone? Main Processor ARM1176 + 1GB mem LCD i/f WiFi & Most of Cell Phone 4 GB NAND Flash

  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. Computers Per Person 1:106 Mainframe Mini 1:103 Workstation PC Laptop 1:1 PDA Cell 103:1 Mote! years UCB Mote Platforms * * * Crossbow variation

  29. Sensor Interface analog sensors ADC digital sensors Data SRAM pgm EPROM 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 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

  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. * System design * Leakage (~RAM) * Nobody fools mother nature 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 active WiFi: 300 - 500 mW => several hours GPS: 50 – 100 mW => couple days WSN: 50 mW active, 20 uW passive 450 uW => one year 45 uW => ~10 years Ave Power = fact * Pact + fsleep * Psleep + fwaking * Pwaking

  33. WakeUP WakeUP Work Work Sleep Sleep Mote Power States at Node Level 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

  35. Power to Communicate

  36. Multihop Routing • Upon each transmission, one of the recipients retransmits • determined by source, by receiver, by … • on the ‘edge of the cell’

  37. Datasheet Analysis 20mA 10mA 10 ms 5 ms 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

  38. Example: TX maximum packet

  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 Time I 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. total energy 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 Watts = Joules/seconds Units: A very practical formulation! If we would like to know total energy

  43. 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

  44. Older Logic Families have Pullup R nMOS Inverter R

  45. Power in CMOS Switching Energy: energy used to switch a node Calculate energy dissipated in pullup: Energy supplied Energy stored Energy dissipated An equal amount of energy is dissipated on pulldown

  46. activity factor number of nodes (or gates) clock rate 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:

  47. “Short Circuit” Current: Other Sources of Energy Consumption • Junction Diode Leakage : Transistor drain regions “leak” charge to substrate. 10-20% of total chip power ~1nWatt/gate few mWatts/chip

  48. 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 Other Sources of Energy Consumption Transistor s/d conductance never turns off all the way Low voltage processes much worse

  49. 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? Controlling Energy Consumption: What Control Do You Have as a Designer?

  50. Example • What is the cost of optimistic compute and select? • How might we reduce it? Operand Registers A B add/sub and/or cmp MUX R Result Register

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