Low Power Processors Josh Nanni Matt Rosonke Matt Tannenbaum

Power is dissipation of energy over time A device consuming lots of power over a long period of time will dissipate lots of heat A device using lots of energy decreases the battery life Power vs. Energy 2 [Brehob]

About Power: High power draws for extended periods of time can produce a lot of heat Lots of heat can o melt components o cause faulty behavior o harm the user About Energy High energy consumption will decrease battery life Good battery life will increase portability Why Do We Care? 3

What Can I Power? Device/ReferenceAverage Power Consumption Light Bulb20-75 Watts [1] Smartphone (CPU) mW (12-60 mW) [2] Hearing Aid, CalculatorMicrowatts [3] 2 AA batteries can power a cheap calculator for several years [1] My House [2] "An Analysis of Power Consumption in a Smartphone". Aaron Carroll, Gernot Heiser. NICTA, University of New South Wales, Open Kernel Labs [3]

Increase functionality, decrease power consumption o Performance increases -> increase power o Nvidia Tegra (Kal-El) o University of Michigan's Phoenix processor Challenge in Industry 5

Nvidia Kal-El, also known as the Tegra processor is a quad core system on a chip developed for mobile applications Multicores excel in achieving better power to performance than single cores Nvidia Kal-El 6 [C]

Kal El runs a companion core that runs background processes at low frequency and power Extends battery life! Background Processes 7 [E]

Main cores (fast ARM Coretex A9s) are enabled one by one for high performance applications Core switching invisible to apps Disabling cores when not needed saves energy Nvidia Kal-El 8 [E]

Designated cores for media processing can also be disabled when not needed to save power Each media core is designed to do only one task as efficiently as possible Nvidia Kal-El 9 [E]

How does a slower core save power? Narrower Gates = o Less gate capacitance o Lower saturation current Architects make a trade off between the two to achieve the clock speed and power consumption desired from the device EECS 312 Mumble Mumble [Sylvester]

Stage Skip Pipeline Used during loops to skip instruction fetched and decodes by using a Decoded Instruction Buffer (DIB) EECS 370 Mumble Mumble [B]

Collapsable Pipelines High performance = shorter stages, faster clock Lower power = longer stages, slower clock EECS 370 Mumble Mumble [A]

Companion Core - Low Leakage Current Main Cores - Higher Leakage Current, Power Gated Cores switch at optimal time Nvidia Kal-El Power / Performance 13 [E]

Developed by PhD students at University of Michigan as an embedded systems processor specializing in extremely low standby power o Mingoo Seok, Scott Hanson, Yu-Shiang Lin, Zhiyoong Lee, Nurrachman Liu, with Dennis Sylvester and David Blaauw Goal was to build a very small processor with a very long battery life Relies on aggressive power gating to minimize sleep power Phoenix: a 30 pW Processor [h] 14

Phoenix uses ~300nW in active mode and 29.6 pW in sleep mode Meant for embedded systems that spend most of their time in sleep mode ~20ms of active time vs. 10 minutes of sleep time Phoenix: a 30 pW Processor [h][MS Paint] 15

Essentially, you use a transistor as a switch, cutting off sections you aren't using Sizing is very important to consider.... Power Gating [j] 16

Can power gate: o ROM o Arithmetic units o Logic units o Non-volatile RAM Cannot power gate: o Volatile RAM o Timers o Anything that needs to preserve state So what can you power gate? [h] 17

Certain processors are better for some systems than for others o You would never put this in a phone! Note that as you deal with very low power, weird things become important o In Phoenix, instruction ROM is used to supplement now dominant instruction memory Situational Awareness [h] 18

Questions? 19

[A]"Stage-Skip pipeline: A Low Power Processor Architecture Using a Decoded Instruction Buffer" Mitsuri Hiraki, Raminder S. Bajwa, Hirotsuga Kojima, Douglas J. Gorny, Ken-ichi Nitta, Avadhani Shridhar, Katsuro Sasaki, Koichi Seki. [B]"A Low-Power Processor Architecture Optimized for Wireless Devices" Aristides Efthymiou, Jim D. Garside, Ioannis Papaefstathiou. [C]“The New Era of Tera-Scale Computing” 2009, Shu-ling Garver, Bob Crepps. [D] “The Benefits of Quad Core CPUs in Mobile Devices” Nvidia a.pdf a.pdf [E]“Variable SMP –A Multi-Core CPU Architecture for Low Power and High Performance” Nvidia b.pdf b.pdf References (1) 21

Phoenix Processor: [h] "The Phoenix Processor: A 30pW Platform for Sensor Applications" Mingoo Seok, Scott Hanson, Yu-Shiang Lin, Zhiyoong Lee, Nurrachman Liu, Dennis Sylvester, David Blaauw [j] "A Low-Voltage Processor for Sensing Applications With Picowatt Standby Mode" Scott Hanson, Mingoo Seok, Yu-Shiang Lin, Zhiyoong Lee, Nurrachman Liu, Dennis Sylvester, David Blaauw Power Gating: [k] "Power Gating Implementation in SoCs". Charwak Apte. References (2) 22