(hmm, it took over 3 months for this message to reach the list) On Tue, May 27, 2014 at 03:03:47PM +0400, Vladislav Ross wrote: > I have NTP server with Ublox LEA-6T GPS receiver. I want to determine my > server's oscillator accuracy and stability. I've read about Allan deviation > and learnt how to make ADEV plot, but I don't fully understand how to > use this method. > > My question is: what method should I use to determine server clock > accuracy and stability using PPS as reference? Can I use ntpd to collect > data about clock error? As far as I understand ntpd will adjust the > clock, but I need freely running clock.
You could use the "disable ntp" directive in ntp.conf to disable the clock discipline, but I'm not sure if ntpd will keep logging PPS offsets as the clock will be slowly drifting away. If you are on Linux, you might find the following tool useful: https://github.com/mlichvar/ppsallan It can be used like this: ppsallan -p adev.plot /sys/class/pps/pps0/assert This will collect raw PPS timestamps from the file in /sys and while it's running, a rough graph of Allan deviation will be shown in the console. On exit it will save the x, y coordinates of the plot to the file specified by -p and the plotallan script can be used to create a nice graph with gnuplot. -- Miroslav Lichvar _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
