Clockless CPU design

Clockless CPUs are so called asynchronous CPUs where are not clock generator needed which clocks every synchronous operation. Asynchronous processors gives results not after defined number of clocks, but after it finishes operations. This is a key of effective usage of energy and asynchronous processors generates less noise than synchronous.

Asynchronous processors have couple advantages against synchronous:

Components can run in different speeds inside clockless CPU while clocked CPU components are tied to clock generator.

Clockless CPU operation stages doesn’t depend on clocks and can be finished faster than normal and there is no time gap between stages as there is no need to wait for next clock cycle. For instance in it can show results of operation rather than waiting for next clock cycle like it is in sychronous CPU.

So why asynchronous processors aren so popular? There are many factors but I think the biggest is historical, because instead asynchronous technology engineers of middle of nineteenth century decided to develop synchronous technology as they looked potentially more productive, reliable and there were easier to project them.

So now there is a lack of professionals in this area. In other hand it is problematically to match synchronous and asynchronous technologies together. There can be commercial reason too because it is almost impossible to determine comparable productivity of asynchronous processors so it can be hard to sell.

There is no any pure asynchronous processors in the market as practically they have some synchronous parts built in. Synchronisation is used to turn circuitry on event. Usual synchronisation in clockless CPU is replaced with handshaking algorithms.

Asynchronous CPU manufacturers are „Sun Microsystems“, „Intel“, „Theseus Logic“, „Philips Electronics“, „Self-timed solutions“, „Fulcrum Microsystems Inc.“. „Fulcrum Microsystems Inc.“.