Clockless Computing

Montek Singh

Thu, Sep 20, 2007

More on Asynchronous Pipelines(one classic and two latest approaches)

1. Sutherland’s “micropipelines”– 1989 Turing Award lecture

2. Sutherland et al.’s “GasP” pipelines– 2001 ASYNC Best Paper Award

3. IBM’s “IPCMOS” pipelines– 2000; very highly publicized; holds current “record” for speed

Sutherland’s Micropipelines (1989)• Basic FIFO (no logic)

Sutherland’s Micropipelines (1989)• Pipeline with logic• Also: more robust construction

Sutherland’s Micropipelines (1989)• Details of the storage elements:

– “capture-pass” latches

GasP PipelinesSutherland & Fairbanks [2001]

• A “minimal” control circuit for pipelines

• Very highly regarded; “cool”

• But… fairly low-level design

– Transistor level

– Stringent (2-sided) timing requirements

reqin

ackin

En (latchenable)

latch

stagecontrol reqout

ackout

datainputs

dataoutputs

GasP: A Pipeline Stage

GasP: Controller Details

IPCMOS (IBM 2000)

• “Interlocked Pipelined CMOS”• Really fast: 3.3GHz in 0.18

– Even faster (4.5GHz) for extreme corner cases– Bragging rights!

• But … very low-level design– Transistor-level design– Stringent (2-sided) timing constraints– Not clear if it really should be that fast…!

• Technology-independent comparison: unsure if faster than GasP

reqin1

reqinn

ackin ackout

reqout

En (latchenable)

stagecontrol

latch

datainputs

dataoutputs

IPCMOS: A Pipeline Stage

reqinnreqin1

ackin

(latchenable)

reqout

ackout

R1 Rn

X

A

En

switch

switch

IPCMOS: Controller Details

“pulse catcher”

En

reqini

Y

reqout

Ri

(conditionedrequest)

(inputrequest)

switch(“pulse catcher”)

IPCMOS: Pulse Catcher