[ntp:questions] ppspeer and prefer

rtxo gnu at wraith.sf.ca.us
Wed Dec 22 21:26:04 UTC 2004

Hi Folks--

Currently, when using a PPS capable device, ntpd must configure a "prefer" peer so that
the daemon will recognise and utilise the PPS timing.

Now, I have a couple sources of PPS (IRIG-B and a WWVB clock) but would rather have
the GPS be "preferred" as it is the highest quality of time at this facility.

This makes for a minor problem, in that it seems risky to "prefer" the GPS when
it may well be that the WWVB, say, is bonkers, thus causing its PPS signal to
chatter. However, I must "prefer" *something* or else lose access to the
generated PPS timing signals. Currently my (bogus) scheme is to have two
"prefer" statements. This (cough) "works" but I doubt ntpd was really intended
to be operated in this fashion.

So, I'm wondering if it is worth having a "ppspeer" configuration command, that will
act to light up a reference clocks associated PPS signal, while keeping the
existing "prefer" in place.

It might be in the form of an identifier command, perhaps of the reference clock
ID, so that, say, WWVB unit 0, has its associated PPS configured as 4-0,
WWVB unit 1 PPS as 4-1, etc. No identifier falls back to existing behavior,
thus preserving compatability.

Background: I have a "fanout box" that provides GPS to all my servers. I plan
to have additional clocks, such as the WWVB and IRIG units, as backups. The
WWVB will possibly get its own fanout box as well since this scheme works
so well with the GPS (NMEA) driver and ntpd.


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