On Wed, Jan 20, 2010 at 04:36:17PM +0100, Hattink, Tjalling (FINT) wrote:
I agree with you that chrony will be able to keep time between the pps
pulses. But in my situation I cannot blindly trust the incoming PPS
signal
being the correct time. When the GPS card has no lock it keeps
generating
PPS pulses from its own oscillator, but it will be free running and
drifting
fast as no GPS corrections come in. So somehow I have to tell chrony not
to
trust the PPS source anymore when GPS lock is gone. I used to do this
for
ntpd by making the SHM clock unreachable, but it works differenty in
chrony.
I agree that sometimes it may be dangerous to keep using PPS signal
without any reference, but sometimes it's useful. When local stratum
is enabled, you can even use PPS signal without any reference and
correct the seconds by wristwatch if needed.
Ideally, this would be configurable. Perhaps a refclock option to bind
it with another one. This would also allowed to use PPS signal
immediately without waiting for first sync.
If you would like to always trust any incoming PPS signals, even if no
absolute reference source is available, maybe I can solve it by
implementing a chronyc command to disable specific reference clocks.
Suspend/resume refclock commands would be certainly useful also in
other cases.