Clockless CPU design

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

Asynchronous processors have couple advantages against synchronous:

  • Components can run at different speeds inside a clockless CPU, while clocked CPU components are tied to a clock generator.
  • Clockless CPU operation stages don’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 the next clock cycle. For instance, it can show the operation results rather than waiting for the next clock cycle like it is in a synchronous CPU.

So why asynchronous processors aren’t so popular? There are many factors, but I think the biggest is historical. Instead, asynchronous technology engineers of the middle of the nineteenth-century decided to develop synchronous technology as they looked potentially more productive, reliable, and easier to project.

So now there is a lack of professionals in this area. On the other hand, it is problematic to match synchronous and asynchronous technologies together. There can be a commercial reason, too, because it is almost impossible to determine the comparative productivity of asynchronous processors, making it hard to sell.

There are no pure asynchronous processors in the market as practically they have some synchronous parts built-in. Synchronization is used to turn circuitry on the event. Usual synchronization in a 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..”

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