Re: AW: [chrony-users] How to set GPS and PPS source offline

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Thu, 24 Nov 2016, Wielant, Ulrich wrote:

> > On Thu, Nov 24, 2016 at 10:25:26AM +0100, Wielant, Ulrich wrote:
> > > After chrony synchronized once to the PPS it never selects another time source although the PPS/GPS signal might disappear. This might be the case if gpsd is not running, the GPS is off or the GPS has no fix.
> > >
> > > MS Name/IP address         Stratum Poll Reach LastRx Last sample
> > > ===============================================================================
> > > #- GPS                           0   4     0   21m    +44ms[  +44ms] +/-  200ms
> > > #* PPS                           0   4     0   21m  -1211ns[-2913ns] +/- 1634ns
> > > ^- ntp03.cc-netzwerk.de          3   8   377    47  -1809us[-1809us] +/-   42ms
> > > ^- ts1.sct.de                    2   8   377    55   -403us[ -403us] +/-   60ms
> > > ^- news01.nierle.com             2   8   377   246  -1518us[-1518us] +/-   38ms
> > > ^- xserv-01.tenretni.org         2   8   377    53  -4528us[-4528us] +/-   58ms
> > >
> > > What do I have to do so that chrony no longer synchronizes to the non available PPS/GPS source?
> >
> > Just wait a bit longer :). The PPS source was much better than the NTP servers, so it may take couple hours before chronyd assumes the clock has drifted so much that it should switch to the significantly worse NTP sources. It's a feature, not a bug. If chronyd switched immediately to another source, that would be bad for accuracy of the clock, e.g. when the GPS has a weak signal and PPS stops for couple of minutes at a time.
>
> Thanks!
> Is there a parameter so that chrony switches faster although it is bad for accuracy?
>
> > > I would also modify the stratum of the PPS/GPS source but this doesn't seem to be possible with refclock sources. Correct?
>
> > Right, there is currently no option to set stratum for refclocks. It wouldn't make much of a difference in the source selection anyway.
>
> Is there an option so that common NTP servers are preferred and PPS/GPS is taken only if there is no other server? This might sound strange (it is ;-)) but this is a requirement for my current project. GPS/PPS should be used as fallback only.

Not strange-- bizarre. Why would you want to use a source which is far less
accuarate in general?


> Ulrich
>
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