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Re: gpsd losing connection to ublox

From: Niall Parker
Subject: Re: gpsd losing connection to ublox
Date: Thu, 11 Nov 2021 15:11:59 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

On 2021-11-11 1:47 p.m., Gary E. Miller wrote:
[ .. ]

# GPS PPS reference (NTP1)
server prefer
fudge refid PPS
Best to put this first, before the pool servers, so it starts first.

Once the system is stable, position does not mattter, but people complain
when it does not start fast.
Got it, reordered ntp.conf, thanks.
[ .. ]
No "shift".  Your command line explicitly asked to put pps0 on NTP2.

The first source on the command line uses NTP0 and 1, the second (pps0)
uss NTP2 and NTP3.  The third uses NTP4 and 5.  Ditto for the 4th one.

MAGIC_HAT is only on a raspberry pi. Not a factor for you.

OK, I think I may be understanding it now. If PPS is linked to gps device (either via line discipline, MAGIC_HAT for specific rpi hardware) then the PPS will be on +1 from base device (ie odd SHM). When independent and specified as separate device to gpsd then it will be on an even SHM. ntpshmmon is tool to see what is active.

It is not clear why gpsmon acted differently in reporting PPS between 3.23.1 and 3.23.2-dev but not really important either, red herring ...

Goal probably minimum jitter, system providing time to local cluster
sharing video tasks so synch within a frame time would be nice.
Those are competing goals.  Minimum jitter is in conflict with
minimum dispersion between clients.
Not understanding that yet but maybe not important, likely to be good enough. The GPS connected node serves time to the other clients via NTP over ethernet so I figured minimum jitter on server would make it easier clients to stay close, no ? The rack is small enough that I could probably share the PPS signal directly if it becomes an issue.
Remote and headless so will grab the data from /var/log/ntpstats and
use ntpviz locally,
Common configuration.
Initially I tried pulling in the Ubuntu package with ntpviz but it takes in a ton of dependencies and breaks my existing setup on my workstation. For anyone in a similar situation just build ntpsec from source, it doesn't make such a mess ...

            ... Niall

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