Clockless Computing 342
ender81b writes "Scientific American is carrying a nice article on asynchronous chips. In general, the article advocates that eventually all computer systems will have to move to an asynchronous design. The article focuses on Sun's efforts but gives a nice overview of the general concept of asynchronous chip design." We had another story about this last year.
One problem with asynchronous logic (Score:2, Interesting)
The Amiga Zorro Bus was Asyncronous (Score:4, Interesting)
Explanation, sorta (Score:3, Interesting)
This is really cool. I was learning a little about asynchronous systems in my Logic Design and Computer Organization class last fall...they seemed pretty cool on a small scale, however they could get really difficult to work with when you're dealing with something as complex as a processor.
Return of the 68000? (Score:2, Interesting)
Small scale, and then larger (Score:3, Interesting)
I foresee lots of bugs, but if they can pull this off, more power to them.
Re:Return of the 68000? (Score:3, Interesting)
Re:Explanation, sorta [--OT?] (Score:2, Interesting)
But I think an asynchronous computer would still use a RTC to keep track of calendar time. It has to keep time even when it's turned off.
Low-Power Async Procs (Score:2, Interesting)
I think this was from Seiko-Epson. I might have the states screwed up but that's the idea.
Re:Intel, AMD, etc and marketing (Score:2, Interesting)
This of course has problems because a lot factors into the speed of a computer. For instance motherboard chipsets will become increasingly important.
Re:Return of the 68000? (Score:4, Interesting)
Those who forget the past (Score:2, Interesting)
The famous PDP-6 was asynch logic. It made a very fast machine out of very few transistors, but was a nightmare to maintain. The follow-on PDP-10 was syncronous logic.
There must be some history out there somewhere of the problems DEC had with the asynchronous logic. Any old MIT research notes?
Clockless issues (Score:2, Interesting)
The problem with overcooling async logic (Score:2, Interesting)
Here's why:
There are two main aspects to consider in an asynchronous chip, gate delay (the time for a gate to open/close) and propagation delay (the time it takes for a signal to go from one gate to the next).
Asynchronous logic works by carefully arranging the length and geometry of the wiretraces between gates, so that the signals coming from those traces all hit their target gate (nearly) simultaneously.
The problem is that gate delays are affected by temperature differently than propagation delays. They both get faster with cooling, and slower with heating, but they do so nonlinearly, and at *different rates*. And asynchronous logic requires those rates to be carefully matched. Change the rates too much, and the chip breaks.
Synchronous logic doesn't have this problem (as much), because the whole point of latching everything between clock cycles is to give the slower signals time to catch up to the faster ones, and to force them all to wait up until everybody is ready (at which point the clock releases the latch, and the next cycle starts). But this has the downside of the extra wiring, circuitry, and power required to run all the clock lines and latches.
Real-Time (Score:3, Interesting)
No mention of Theseus Logic? (Score:4, Interesting)
Unless I missed it, there was no mention of Theseus Logic's [theseus.com] Null Convention Logic [theseus.com] at all which is a real disappointment. Theseus has one of the few approaches that doesn't require a PhD-level of education to understand and design in.