Hi, Since the idea of using a USB-to-serial adapter for PPS is often dismissed here as more or less pointless/useless, (due to the inherent delays in the USB communication AFAIU), I found this recent post to a couple of FreeBSD mailing lists quite interesting:
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. In subsequent discussion he pointed out that it is significant that the test was done on FreeBSD - while he would expect similar results on Linux, performance on Windows would be "all bets off" due to varying driver quality. --Per Hedeland _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
