Re: Re: [chrony-users] chrony with gps + pps not stable

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finally, i solved this problem.because chronyd metioned, the refcock's offset between PPS and SHM or other refclock must little than 200ms.i found the offset comes from read GPS modules nmea data, when GPS modules work a few hours later, or it's signal changed, The amount of data in the module increases, processing serial data will take more time.so i set mask of GPS module's output to reduce it's output, more highly serial baudrate also be work.

tangmc@xxxxxxxxxxx
 
From: Alexei R
Date: 2021-12-24 01:09
To: chrony-users
Subject: Re: [chrony-users] chrony with gps + pps not stable
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On Thu, Dec 23, 2021 at 5:25 AM tangmc@xxxxxxxxxxx <tangmc@xxxxxxxxxxx> wrote:
>
> Hello,
>         My imxu6l board have RTC and GPS device, sometime,  it maybe should work without network. it use GPIO PPS。
> I wan to get a high-precision (10 ms) time between different board 。chrony.conf like below:
> --------------------------------------------------------------------
> logchange 0.5
> noclientlog
> rtcsync
> lock_all
> makestep 0.1 -1
>
> refclock SHM 0  offset 0.9 refid GPSD noselect
> refclock PPS /dev/pps2 lock GPSD prefer refid PPS trust
> --------------------------------------------------------------------
>
> And gpsd run with parameters:
> --------------------------------------------------------------------
> /usr/sbin/gpsd -n -P /var/run/gpsd.pid -S 2947 /dev/ttymxc2
> -------------------------------------------------------------------
>
> When chronyd work with this, the log will record some information:
>
> Thu Dec 23 09:34:03 2021 daemon.info chronyd[1253]: chronyd version 2.4.1 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP -SCFILTER -SECHASH +ASYNCDNS +IPV6 +DEBUG)
> Thu Dec 23 09:34:03 2021 daemon.info chronyd[1253]: Initial frequency -50.497 ppm
> Thu Dec 23 09:35:18 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 09:35:18 2021 daemon.warn chronyd[1253]: System clock wrong by -4.158916 seconds, adjustment started
> Thu Dec 23 09:35:18 2021 daemon.warn chronyd[1253]: System clock was stepped by -4.158916 seconds
> Thu Dec 23 09:41:43 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 09:45:11 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 09:47:19 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 09:48:23 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 09:50:31 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 09:55:03 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 09:59:20 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:04:56 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:07:04 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:10:32 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:12:40 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:13:44 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:15:52 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:17:12 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:19:21 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:24:57 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:29:13 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:34:01 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:38:02 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:41:46 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:43:54 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:50:34 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 10:52:42 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 10:57:15 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 11:01:31 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 11:06:03 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 11:08:11 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
> Thu Dec 23 11:13:47 2021 daemon.info chronyd[1253]: Selected source PPS
> Thu Dec 23 11:15:56 2021 daemon.info chronyd[1253]: Can't synchronise: no selectable sources
>
>
> Why it work unstable ? some board work fine at begining, but after few hours, it  lost lock foever !
>
> Then chrony config directive "offset" set to 0.9,  I think this is not suitable, it will case 1 second  deviation。I try to set to 0.2~0.5, it can not lock with SHM0.
>
>
> tangmc@xxxxxxxxxxx
 
 
 
--
Alexei Rozenvaser
 
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