Hacker News Reader

Comment by metaphor | Hacker News Reader

> That's the reason computers have a clock, to make sure all transistors in a given stage of a CPU reach a steady state before moving on to the next instruction.

Here I was thinking[1][2] the reason computers had clocks was merely a consequence of the synchronous architectures that characterize them.

[1] https://en.wikipedia.org/wiki/Metastability_(electronics)

[2] https://en.wikipedia.org/wiki/Quasi-delay-insensitive_circui...

View on HN

What point are you trying to make?

You are correct that clock free designs exist. But calling it a mere consequence of sync design seems to be a misunderstanding of why sync design has a clock in the first place.

In the case of synchronous design patterns that handle metastability, it was to point out that the clock clearly isn't there "to make sure all transistors in a given stage of a CPU reach a steady state". The clock is there to invoke state transition, whereas achieving steady state is a function of satisfying setup/hold times; the former is fundamentally constrained by the latter.

In the case of QDI circuits, it was to point out that there exists CPUs which do not contain clocks, again challenging the assertion that the reason computers have clocks is "to make sure all transistors in a given stage of a CPU reach a steady state".

The purpose of synchronous designs is to minimize the overhead of the handshaking that asynchronous designs bring with them. There is no other meaningful difference between them, really.

Reply on news.ycombinator.com