On Mon, Jul 13, 2020 at 8:54 AM Petr Titěra <p...@titera.eu> wrote: > > All Prolific chips I saw claimed to be USB 2.0 Full-speed. That means > they are polled only once in 1ms and there is no way how to change it > (poll rate is selected at hardware level).
Looking at the UHCI specification, for USB 1.1 HCIs, while there poll rate is fixed at about 1 ms, it is possible to tweak it slightly via the start of frame modify register. If one is measuring a PPS, then the pulses are not random. It's possible to try to align the USB frames with the PPS and do quite a bit better than just a 1 msec poll rate would do at random. Certainly would be hard to fit this into the software stack. And I don't see this ability in the EHCI spec, though I'm certainly no expert with USB HCI drivers, so perhaps it's gone now because no one could figure out how to use it. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
