Clock Less

CLOCKLESS CHIPS

Clockless CPU PresentationTue April 1 2014NIJIL NSpeakerThe History of Clockless CPU1989 -Alain Martin1998 -Commercial clockless chip2001-Pentium 4 microprocessorAsynchronous microprocessors

World-first Asynchronous Microprocessor (1988)MiniMIPS (1998)Lutonium 8051 Microcontroller (2005)Lattice-Structure Filter (1994)What does clockless mean ?The system doesnt have a clock.It uses a handshake instead.Asynchronous System(Distributed Control)handshakinginterfaceSynchronous System(Centralized Control)clockSolution 1Alice uses 2 lamps:1 to indicate that she is ready with the message, and1 for the message itselfBob uses 1 lamp:to indicate that he has received the messagegot itAliceBob

readyyes/no

Solution 2Alice uses 2 lamps:Green lamp to indicate yesRed lamp to indicate noBob uses 1 lamp:to indicate that he has received the message8got itAliceBobnoyes

Solution 3What if Alice and Bob could keep time?

Alice uses 1 lamp for the message:At 12 midnight: turns on lamp if message = yesAt 12:01: turns lamp offBob needs no lamps!Takes down the message between 12 and 12:01

Pros: Fewer signals, lesser processing neededCons: Alice and Bob must keep their clocks closely synchronizedIf Bobs watch is off by a minute, incorrect communication possibleDifferent Handshake protocols4-phase ,dual-rail protocol2-phase,dual-rail protocol

Muller C-element circuitWhat is it and how it is related to clockless CPUs?ABY00001No change

10No change111Muller Pipeline

Speed IndependenceClocks make your slowest task into weakest linkWithout a clock , we can compensate and adjust to fit faster tasksSpeed Comparison

Why Asynchronous Design? (1)Higher PerformanceMay obtain average-case operation (not worst-case)not limited by slowest componentAvoids overheads of multi-GHz clock distributionLower PowerNo clock power expendedInactive components consume negligible power15Why Asynchronous Design? (2)Better Electromagnetic CompatibilitySmooth radiation spectra: no clock spikesMuch less interference with sensitive receivers [e.g., Philips pagers, smartcards]The ability to provide superior encryption.Replacing any part with a faster version improves the speed again and againNo clock distribution/skew problems

Challenges of Asynchronous Designcommunication must be hazard-free!special design challenge = hazard-free synthesisTestability Issues:absence of clock means no single-steppingHandshaking takes up chip spaceData validation for completenessControl logic takes more time

17Hazards: potential glitches on wireclean signalshazardous signalsclock tickno problemfor clockedsystemsSYNCHRONOUS CHIPSAdvantageChip Design Very Simple Because Of Clock

DisadvantagesWastage Of Computational Time Affects The Speed Of ChipHigher Power ConsumptionDesign Of Complex Circuits Cannot Be Done Because Of High Power Consumption18ApplicationsPersonal computersEncryption devicesMobile electronics19In recent yearsSeveral commercial asynchronous chips:Philips: asynchronous 80c51 microcontrollersused in commercial pagers [1998] and smartcards [2001]Univ. of Manchester: async ARM processor [2000]Motorola: async divider in PowerPC chip [2000]HAL: async floating-point dividerin HAL-I and II processors [early 1990s]Recent experimental chips:IBM, Sun and Intel:fast pipelines, arbiters, instruction-length decoderIBM/Columbia/UNC: asynchronous digital FIR filterSeveral recent startups:Theseus Logic, Fulcrum, Self-Timed SolutionsCOMPANYACHIEVEMENTSGOALSSUN MICROSYSTEMSPalo Alto, CAPrototypes have demonstrated two to three times the speed ofStandard chips.Gradually integrate islands of clockless logic into futureGenerations of microprocessors.INTELSanta Clara, CAClockless prototype in 1997 ran three times faster than the conventional chip equivalent, on half the power.Stay current with clockless R&D.ASYNCHRONOUS DIGITAL DESIGNPasadena, CAFounded by students of Caltechs Alain Martin, who developed the First asynchronous microprocessor.Produce chips for cell phones and other low-power communications devices.Clockless companies21THESEUS LOGICMaitland, FLPatented null convention logic, a way of letting clockless chips know when an operation isComplete.License designs to manufacturers of smart cards and mobile devices; Motorola is a current customer.PHILIPS ELECTRONICSEindhoven, NetherlandsMarkets a clockless chip that gives its pagers up to twice the battery life of competitors.Clockless chips for mobile devices and smart cards.SELF-TIMED SOLUTIONS Manchester, EnglandFounded by Steve Furber who has developed clockless chips for communications devices.Clockless chips for smart cards.Continued 22Overview of clockless CPUsThe HandshakesNot in use todayClocks make life easier ReferencesPrinciples of Asynchronous Circuit Design - A Systems Perspective -JENS SPARS and STEVE FURBERhttp://stackoverflow.com/questions/530180/what-happened-to-clockless-computer-chipshttp://www.cs.columbia.edu/async/misc/technologyreview_oct_01_2001.html

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