On 2019-08-11, Per Hedeland <p...@hedeland.org> wrote: > https://lists.freebsd.org/pipermail/freebsd-usb/2019-August/016078.html > > TL;DR^2 The author carried out a pretty sophisticated (IMHO) test with > two different USB-to-serial adapters feeding PPS to ntpd, and found an > offset of some 200 usec with 20-30 usec jitter. You can of course tell > ntpd to correct for the offset (once you know how large it is...), and > the jitter doesn't seem too bad to me, although it is of course higher > than for more "direct" connections.
An offset of 200 microsecond is much larger than a typical error of NTP in a local network, so maybe that's why people don't like refclocks over USB. However, with a custom driver and firmware it's possible to reduce the offset and jitter to few microseconds. See this great post from Dan Drown: https://blog.dan.drown.org/pps-over-usb/ -- Miroslav Lichvar _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
