| Re: [chrony-users] GPS + PPS |
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On Sun, Oct 26, 2014 at 01:28:32AM +0200, Dominik Auras wrote:
> I am trying to setup chrony for my new GPS. Unfortunately, chrony won't
> select any source if I enable both the NMEA and PPS source. I bet that my
> configuration is wrong ... but it is unclear to me how to configure the PPS.
>
> Could you maybe explain me what I do wrong, or point me to something that
> explains it? Thank you in advance!
>
> Part of my chrony.conf
>
> server ptbtime1.ptb.de iburst noselect maxpoll 6 minpoll 6
> refclock SHM 0 refid GPS offset 0.546 poll 6 delay 0.9999
> refclock SHM 1 delay 0.2 refid PPS lock GPS
The SHM refclock doesn't support PPS samples, so it can't be locked to
another refclock with the lock option, that works only with the PPS
and SOCK refclocks.
Looking at the rpi_gpio_ntp program source code, it seems to align the
pulses blindly to the nearest second, so it shouldn't be started
before the clock is already close to zero offset, otherwise it will
send incorrect time and the source will fail in the source selection.
If internet was available, you could add NTP sources, which would
outvote the bad PPS source on start. You will probably need to delay
starting of rpi_gpio_ntp, the chronyc waitsync command could be used
for that.
Another option would be to modify rpi_gpio_ntp to use the SOCK
protocol instead of SHM and send the samples as pulses, so chronyd
can align them properly.
--
Miroslav Lichvar
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