Preliminary results of using GPS to look for clock skew

Jan Ceuleers jan.ceuleers at
Fri Sep 23 05:24:40 EDT 2011


Can I suggest another method for your comparisons of GPS time to ntp (or 
rather network) time?

The whole purpose of ntpd is to compare multiple sources of time, 
whether local refclocks such as a GPS receiver or remote-ones. In fact, 
when acquiring a new refclock and before pressing it into service it is 
necessary to calibrate the offset between its PPS signal (as seen by the 
ntpd process, and therefore incorporating the propagation delay in the 
cable, in the receiver circuit and the processing delay in the OS) and 
the true UTC second.

This is done by adding the new refclock to the ntpd config file, but by 
also telling ntpd to distrust it (using the noselect keyword). You can 
then leverage all of ntpd's stats for comparing the refclock to all 
other available time sources.

More info at

HTH, Jan

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