Re: [chrony-users] Help with GPS timesync/config

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Ok, I think I understand, now, the noselect suggestion earlier and to focus in on the offsets.  I found a link that discusses comparing to NTP sources and then calculating the offsets and making adjustments (

I've started doing that and I'm getting better results with measured and corrected offsets.  I'll continue to do that. I'm down to only 3-5 losses of majority in any given hour which is much better than every 2 minutes.

I still have the outstanding question of:
If I'm on GPS, social distincing myself in the woods, is there an option for a 3rd reference clock for "majority?"  I could do two GPS units though that's just a bit overkill I think as I am ok with a bit of wobble. I could do an RTC but I know that'll drift and just be tied to the GPS anyway.

Thanks for the guidance from everyone so far. I've already learned more about chrony and ntp stuff in a week than for the last 20 years of just throwing up an ntp server to make sure all the clocks in my work networks are accurate(ish).

On Mon, Mar 30, 2020 at 1:46 AM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
On Thu, Mar 26, 2020 at 12:41:07PM -0600, Dave Hajoglou wrote:
> =>If I remove the lock NEMA then the pps source is seen and processed and
> that's when I get the flapping where it selects first NEMA, the GPS refid
> then falls into the majority sync error. This is a weird one as it won't
> process the PPS if I lock it.  Does that have to do with the fact that the
> PPS is from GPIO rather than serial?

That shouldn't matter, but what is important is the offset between the
two refclocks. If it's too large (close or over 0.4s) the locking
wouldn't work. Try adding "offset 0.25" to the SHM refclock line and
see if that helps. You can measure the offset of the SHM refclock
against an NTP server.

Miroslav Lichvar

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