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0 pointsWithinReason4y ago0 comments

Isn't PS/2 interrupt based, while USB is based on periodic polling?

0 comments

Polling is often lower latency than interrupts on modern hardware, since it can run at much finer grains and has so much less overhead to startup over an ISR.

wtallis4y ago

That's often true on a scale of microseconds, but USB input devices are polled at intervals on millisecond scale.

cma4y ago

Only in the slowest modes. It is possible to go faster than the 1ms poll rate, though it is back to interrupts:

> Transaction latency

> For low speed (1.5 Mbit/s) and full speed (12 Mbit/s) devices the shortest time for a transaction in one direction is 1 ms.[6] High speed (480 Mbit/s) uses transactions within each micro frame (125 µs)[7] where using 1-byte interrupt packet results in a minimal response time of 940 ns. 4-byte interrupt packet results in 984 ns.

https://www.wikipedia.org/wiki/USB_(Communications)

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