[ntp:questions] New to NTP on Linux

David J Taylor david-taylor at invalid.com
Wed Nov 3 10:44:08 UTC 2004

dusty bin wrote:
> I had a similar set up to Dave (actually 3 machines running w2k all
> peering with each other and all sync'ed to the internet), and in that
> configuration I obtain quite good results, typically within a couple
> of mS unless there are other applications interferring with things -
> exactly what Dave's link shows.
> In this situation, I assume that the principal error is mainly the
> computers ability to maintain a stable knowledge of time... so, if I
> go from internet sync'ed to a reference clock (be it 1 microsecond for
> Garmin or 100 nS accuracy for Oncore) the performance would be the
> same, or marginally better (ref clock interrogated at 64 sec instead
> of 1024 sec for internet servers).

Yes, I would agree.  There would be less drift and more frequent 
corrections with a 64s poll, but in principle "about the same".

> The machine where I installed the NMEA ref clock isn't doing anything
> else, that is why I am rather suspicious of the instability I have
> seen.  In fact I needed to delete all the other peers/servers (except
> .lcl.) from the configuration in order to force ntpd to use the NMEA
> clock and so get a decent record of this clock's stability.

One minor point - and it probably doesn't apply - my Garmin hand-held GPS 
(GPS 12 XL) can't output serial data at the 1 per second required - you 
can't make the sentences short enough.  This seems to preclude using it as 
a serial port reference source.  It doesn't have PPS at all.


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