On: Myths about USB NKRO and how USB HID works

[mschuster91]

The only thing "high end" in there are the switches, and even that not necessarily.

[DiabloD3 → mschuster91]

Believe it or not, there is a very small number of keyboards that use custom USB 3.0 controllers purely for isosynchronous mode, to get "PS/2 port interrupt"-like behavior.

However, if you have a modern USB 2.0 "gaming keyboard controller" polling at 1000ms, who cares. Job done, go home.

[rasz → DiabloD3]

Do you mean Endpoint Ready (ERDY)? That is only available for non-isochronous endpoints.

[monocasa → rasz]

No, I think they're just constantly streaming out updates over a custom isochronous endpoint so the driver doesn't have to go out and request it at all like you do even with ERDY.

[rasz → monocasa]

Wouldnt that swamp CPU with interrupts?

[monocasa → rasz]

I mean, as much as a USB microphone does. That'd be isochronous too, and about the same bitrate and latency.

[amluto → monocasa]

That would be awful for a keyboard. With sound, either the CPU wakes up to process sound very frequently or it processed sound in big chunks with high latency. Neither choice is reasonable for a keyboard.

[monocasa → amluto]

If you're the kind of person that gets that keyboard, you don't really care about power consumption on your CPU. Handling it as it's streamed in really isn't that big of a deal.

It's not even like sound where you'd be doing a bunch of DSP on it right after.