Hi
> On Jul 14, 2020, at 6:13 PM, Trent Piepho <[email protected]> wrote: > > On Mon, Jul 13, 2020 at 4:52 PM Hal Murray <[email protected]> wrote: >>> Is there any way for a USB device to synchronise with the CPU clock (perhaps >>> via the USB framing) so that a special-purpose device could timestamp the >>> PPS >>> occurrence with respect to CPU time ? > > It seems maybe this was thought about in USB 1.1. From the UHCI spec: > > Minor adjustments can be made to this value [ 1-ms frame time] > ... This feature permits minor changes to be made to the frame time > period, if necessary, to maintain real-time synchronization throughout > a USB system. > > It seems like it would not be that hard to get the USB frame sequence > phase locked to the system clock. One would need a way to measure the > phase offset of the USB S-o-F vs the system clock, and then it's a > standard process to phase lock, with the necessary control to do this > described above. To make this work, both ends of the USB link would need to “understand” what is going on. With part of the link buried in a USB <-> serial chip, that might not be very easy to do. Bob > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
