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Re: gpsd losing connection to ublox

From: Gary E. Miller
Subject: Re: gpsd losing connection to ublox
Date: Thu, 11 Nov 2021 13:47:12 -0800

Yo Niall!

On Thu, 11 Nov 2021 13:34:12 -0800
Niall Parker <> wrote:

> On 2021-11-11 12:44 p.m., Gary E. Miller wrote:
> > And it shows gpsd is sending on NTP0 and NTP2, which is odd
> > considering what I though was you configuration.
> >
> > How exactly are you running gpsd?  Put another way, what is
> > the output of this, run as root:
> >
> > # pstree -paul | fgrep gpsd  
>    |-gpsd,18077,nobody -n -s 115200 /dev/ttyTHS1 /dev/pps0
>    |   |-{gpsd},18305
>    |   `-{gpsd},18308
>    |               |-grep,17309 -F --color=auto gpsd

Different from what you said before.  Now pps0 on NTP2 makes sens.
No MAGIC_HAT invovled.

> mostly been starting gpsd via systemd, which pulls in config info
> from /etc/default/gpsd

Nether part of gpsd, I'll not comment on systemd(umb) and gpsd.

> >> ... this gave me the clue it wasn't NTP1 I needed but rather NTP2,
> >> adjusting that in ntp.conf and finally it was able to reach the PPS
> >> signal.  
> > Good, but fishy.  What is you full ntp.conf now?  
> # /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help


> # GPS Serial data reference (NTP0)
> server noselect
> fudge time1 0.134 refid GPS

OK, but best to put last.  No point starting SHM0 first, then not use it.

> # 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.

> This setup is running to refine the time1 fudge factor, will adjust
> when good enough and stick with just GPS time (system will have
> intermittent network access).

time1 is only on a noselect SHM(0), so it will never be used.

> I wasn't expecting the shift to NTP2 as hw is a Nvidia Jetson, not
> rpi but I guess it has more to do with pps-gpio driver ?

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.

> >> Now that PPS is getting through I can follow the tuning procedure
> >> in the howto, give it some time get some stats.  
> > Patience, and ntpviz, are required to tune it.  Ad tuning depends on
> > what you want to optimize.
> >  
> 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.

> Remote and headless so will grab the data from /var/log/ntpstats and
> use ntpviz locally,

Common configuration.

> probably enough data now to get started.

Yes, you are well started now.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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