Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Computers without clocks (2002) [pdf]

cs.virginia.edu

Post reply on HN
Print view View original

11–20 of 29 posts

Re: Computers without clocks (2002) [pdf]

#11

Post by kurthr »

nbingham wrote: post #4

Heyo, I'm a PhD student in the field. I figured I can talk about its current status. First, here are various search terms: clockless, self-timed, delay-insensitive, latency-insensitive, quasi delay-insensitive (QDI), speed independent, asynchronous, bundled-data There are a wide variety of clockless circuits that each make their own timing assumptions. QDI is the most paranoid, making the fewest timing assumptions. B…

Yours matches the commentary of a friend in the field from about 2000. I do hope that the end of Moore sees improvement in this sort of design, and the tools required.

I do see some high speed low power networking hardware moving this way: Router Using Quasi-Delay-Insensitive Asynchronous Design

https://dl.acm.org/citation.cfm?id=2634996&preflayout=flat

Re: Computers without clocks (2002) [pdf]

#12

Post by nbingham »

kurthr wrote: post #11
nbingham wrote: post #4

Heyo, I'm a PhD student in the field. I figured I can talk about its current status. First, here are various search terms: clockless, self-timed, delay-insensitive, latency-insensitive, quasi delay-insensitive (QDI), speed independent, asynchronous, bundled-data There are a wide variety of clockless circuits that each make their own timing assumptions. QDI is the most paranoid, making the fewest timing assumptions. B…

Yours matches the commentary of a friend in the field from about 2000. I do hope that the end of Moore sees improvement in this sort of design, and the tools required. I do see some high speed low power networking hardware moving this way: Router Using Quasi-Delay-Insensitive Asynchronous Design https://dl.acm.org/citation.cfm?id=2634996&preflayout=flat

Yep, I saw that go by, and a lot of my work is heavily influenced by Andrew Lines. But what I've been seeing is that QDI is really bad at arithmetic because the acknowledgement requirements turn XORs into a nightmare hairball of signal dependencies. But QDI is really good at complex control.

Re: Computers without clocks (2002) [pdf]

#13

Post by tachyonbeam »

jacquesm wrote: post #8
nbingham wrote: post #4

Heyo, I'm a PhD student in the field. I figured I can talk about its current status. First, here are various search terms: clockless, self-timed, delay-insensitive, latency-insensitive, quasi delay-insensitive (QDI), speed independent, asynchronous, bundled-data There are a wide variety of clockless circuits that each make their own timing assumptions. QDI is the most paranoid, making the fewest timing assumptions. B…

> What they seem to be doing right now is buying asynchronous start-ups and shutting them down. There's a plan!

Investment Program for Embracing Innovation (IPEI) is best-spent capex.

Re: Computers without clocks (2002) [pdf]

#14

Post by tachyonbeam »

snazz wrote: post #2

The GA144, a 144-processor stack machine that’s insanely energy efficient, is clockless: http://www.greenarraychips.com/home/documents/index.html#arc... I haven’t seen any legitimate uses for it yet, but it’s very cool.

I watched a presentation on this chip at Strange Loop 2013. Unfortunately, the whole presentation was a sequence of "look at this cool cryptic programming trick I can do on this chip" by Chuck Moore, without a single legitimate use case outlined. It made the design look needlessly complicated to use and really didn't answer the question of why the chip is actually useful or in any way better than existing low-power microcontrollers. That says more about Chuck Moore's lack of marketing abilities than about clockless designs, however.

Strange Loop 2013 presentation: https://www.infoq.com/presentations/power-144-chip

Re: Computers without clocks (2002) [pdf]

#15

Post by avmich »

nbingham wrote: post #4

Heyo, I'm a PhD student in the field. I figured I can talk about its current status. First, here are various search terms: clockless, self-timed, delay-insensitive, latency-insensitive, quasi delay-insensitive (QDI), speed independent, asynchronous, bundled-data There are a wide variety of clockless circuits that each make their own timing assumptions. QDI is the most paranoid, making the fewest timing assumptions. B…

> A clockless pipeline is always going to be slower than a clocked one

How come? In a clocked design, you have to have clocks slow enough so all possible logic paths would finish. In a clockless one the propagation only takes as much as needed, and in a case of shorter path can take less time, doesn't it?

Re: Computers without clocks (2002) [pdf]

#16

Post by nbingham »

avmich wrote: post #15
nbingham wrote: post #4

Heyo, I'm a PhD student in the field. I figured I can talk about its current status. First, here are various search terms: clockless, self-timed, delay-insensitive, latency-insensitive, quasi delay-insensitive (QDI), speed independent, asynchronous, bundled-data There are a wide variety of clockless circuits that each make their own timing assumptions. QDI is the most paranoid, making the fewest timing assumptions. B…

> A clockless pipeline is always going to be slower than a clocked one How come? In a clocked design, you have to have clocks slow enough so all possible logic paths would finish. In a clockless one the propagation only takes as much as needed, and in a case of shorter path can take less time, doesn't it?

Synchronous design tools are very good at making all of the pipeline stages have about the same logic depth, which is generally 6-8 transitions/cycle but can be much less. The fastest possible QDI circuit is a very simple, very small WCHB buffer which has 6 transitions/cycle. Most QDI logic will have 10-14 transitions/cycle.

Also, the speed of a linear pipeline is limited to the slowest stage in the pipeline whether or not you use clockless. Clockless only helps pipeline speed when you have a complex network.

Re: Computers without clocks (2002) [pdf]

#17

Post by kurthr »

nbingham wrote: post #12
kurthr wrote: post #11

Earlier quoted context omitted.

Yours matches the commentary of a friend in the field from about 2000. I do hope that the end of Moore sees improvement in this sort of design, and the tools required. I do see some high speed low power networking hardware moving this way: Router Using Quasi-Delay-Insensitive Asynchronous Design https://dl.acm.org/citation.cfm?id=2634996&preflayout=flat

Yep, I saw that go by, and a lot of my work is heavily influenced by Andrew Lines. But what I've been seeing is that QDI is really bad at arithmetic because the acknowledgement requirements turn XORs into a nightmare hairball of signal dependencies. But QDI is really good at complex control.

Interesting analysis... I wonder if "locally clocked" ALUs could help with that sort of thing. Clockless shouldn't have to be a purity test :^)

Re: Computers without clocks (2002) [pdf]

#18

Post by nbingham »

kurthr wrote: post #17
nbingham wrote: post #12

Earlier quoted context omitted.

Yep, I saw that go by, and a lot of my work is heavily influenced by Andrew Lines. But what I've been seeing is that QDI is really bad at arithmetic because the acknowledgement requirements turn XORs into a nightmare hairball of signal dependencies. But QDI is really good at complex control.

Interesting analysis... I wonder if "locally clocked" ALUs could help with that sort of thing. Clockless shouldn't have to be a purity test :^)

Hence my thesis :)

Re: Computers without clocks (2002) [pdf]

#19

Post by deepnotderp »

kurthr wrote: post #17
nbingham wrote: post #12

Earlier quoted context omitted.

Yep, I saw that go by, and a lot of my work is heavily influenced by Andrew Lines. But what I've been seeing is that QDI is really bad at arithmetic because the acknowledgement requirements turn XORs into a nightmare hairball of signal dependencies. But QDI is really good at complex control.

Interesting analysis... I wonder if "locally clocked" ALUs could help with that sort of thing. Clockless shouldn't have to be a purity test :^)

That's more or less GALS ("globally asynchronous locally synchronous ")

Re: Computers without clocks (2002) [pdf]

#20

Post by deepnotderp »

nbingham wrote: post #12
kurthr wrote: post #11

Earlier quoted context omitted.

Yours matches the commentary of a friend in the field from about 2000. I do hope that the end of Moore sees improvement in this sort of design, and the tools required. I do see some high speed low power networking hardware moving this way: Router Using Quasi-Delay-Insensitive Asynchronous Design https://dl.acm.org/citation.cfm?id=2634996&preflayout=flat

Yep, I saw that go by, and a lot of my work is heavily influenced by Andrew Lines. But what I've been seeing is that QDI is really bad at arithmetic because the acknowledgement requirements turn XORs into a nightmare hairball of signal dependencies. But QDI is really good at complex control.

That's not true for all ways of doing things, for example, with bundled data, dual rail domino QDI and various commercial groups like wave computing and ETA computing which have their own asynchronous flavors, often optimized for arithmetic operations.
Post reply on HN