Philips, ARM Collaborate On Asynchronous CPU

Sean D. Solle writes "While not an actual off-the-shelf chip, Philips and ARM have announced a clockless ARM core using what they call "Handshake Technology." Read on for more about just what that means; according to this article, the asynchronous ARM chip has yet to be developed, but the same Philips subsidiary has applied similar technology to other microprocessors.

Sean D. Solle continues "Back in the early 1990's there was a lot of excitement (well, Acorn users got excited) about Prof. Steve Furber's asynchronous ARM research project, "Amulet". The idea is to let the CPU's component blocks run at their own rate, synchronising with each other only when needed. Like a normal RISC processor, one instruction typically takes one clock cycle; but in a clockless ARM, a cycle can take less time for different classes of instructions.

For example, a MOV instruction could finish before (and hence consume less power than) an ADD, even though they both execute in a single cycle. As well as energy-efficiency, running at effectively random frequencies reduces a chip's RFI emissions - handy if it's living in a cellphone or other wireless device."

Comments

Way Back When

[opos]

A long long time ago (1970s) Charlie Molnar, designer of the Linc tape (the Linc computer was an NIH funded (late 1960s) minicomputer that evolved into the PDP 8 and pushed DEC into the minicompuer business) explored asynchronous computing. Along the way they discovered synchronizer failure - i.e. the inability to reliably synchronize asyncronous subsystems - see Chaney, T.J. and Molnar, C.E. 1973. Anomalous behavior of synchronizer and arbiter circuits. IEEE Trans. Comp. pages 421-422. The bottom line is that it is physically impossible to guarantee that the data setup requirements (the minimum time the data must be asserted before it can be reliably clocked into the flip flop) of a flip flop can be met when the clock is asserted by one async component and the data are asserted by another async component. To my knowledge, this fundamental limitation has never been overcome.