[ntp:questions] How do I know my GPS-based NTP server is actually working properly?
David J Taylor
david-taylor at blueyonder.not-this-bit.nor-this-bit.co.uk
Sat Nov 3 10:43:22 UTC 2007
John Ioannidis wrote:
> Thanks for the reply, but this is not answering my question. I wasn't
> asking how to *configure* the beast (I've already done this
> successfully), I was asking how to verify that it actually works as
> What measurements do I have to take that will show the difference
> between a setup that's actually using the PPS signal from the GPS
> receiver and one that's not (because, for example, the DCD line on the
> motherboard is cracked, to give a stupid example).
There is information on how I monitor here:
The GPS-locked accuracy is some three orders or magnitude better than
Internet only. Compare the top graph (+/- 20 microseconds) and the lower
graphs (+/- 100 milliseconds). In my particular case, with a limited view
of the sky from quite far north (56 degrees), The drift which starts when
there are too few satellites to allow the GPS-18 to declare "lock" is very
obvious. You could simulate that by disconnecting the GPS, of course. My
simple notes are here:
Search for the word "pixie" to see the effect of PPS_SYNC, with extra
lines in the "ntpdc -c kern" output.
More information about the questions