[ntp:questions] NTP server with Garmin GPS 18 LVC

Adrian P ntp at pascalau.ro
Mon Dec 16 22:15:57 UTC 2013


On 16 December 2013 13:16, Adrian P <ntp at pascalau.ro> wrote:
> Hi,
>
> In an old IBM thinkpad T22 laptop that runs FreeBSD 9.2, I have
> configured a NTP server that gets the PPS signal from a Garmin GPS 18
> LVC, as described here:
> http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
>
> The /etc/ntp.conf contains the following generic NMEA GPS receiver
> driver configuration:
>
> server 127.127.20.0 mode 1 minpoll 4 maxpoll 4 prefer
> fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 refid PPS
>
> I let it run for a few days, however I still have every now and then
> huge peaks (between -50 and +30 us) of the clock offset as seen in the
> following graph: http://goo.gl/JpSyeO
>
> So I am wondering:  why those repeating huge clock offsets? They
> allays starts with a negative peak, followed immediately by a positive
> one. Is this because of the faulty laptop internal clock, that drifts
> away with 30-40 us every now and then? Any thoughts?
>
> Many thanks,
> Adrian

Thanks for all your help. Unfortunately the hard drive in my old T22
laptop failed this evening, after couple of days running without
interruption. So I will come back to this when I have it back up and
running, hopefully by the end of this week.

Many thanks again,
Adrian


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