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Re: No PPS from gpsd

From: Gary E. Miller
Subject: Re: No PPS from gpsd
Date: Thu, 29 Jul 2021 10:50:54 -0700

Yo Jim!

On Thu, 29 Jul 2021 14:01:07 +0000 (UTC)
Jim Pennino <> wrote:

> Using Ubuntu 20.04.2 and gpsd 3.20.

3,20 is a tad old, and has a fatal bug appearing on October 23, 2021
> I replaced the long running USB GPS with a RS-232 device,
> reconfigured and rebooted.

Would be nice to know how you reconfigured.  The devil is in the details.

> NMEA data is just fine and ppscheck works but gpsd is not processing
> the PPS signal on CTS.

Did you use "-D 4" with gpsd?  That is the best way to debug PPS.

> ppstest and ppswatch fail

Fail how?

> xgps does not show PPS,

I assume you mean in the JSON window?

> and ntpshmmon
> shows only NTP0, i.e. not NTP1 and NTP2 as one would expect.

And what exactly does NT0 show?

> I ran gpsd as a regular user

gpsd can not do KPPS as a regular user.  The man page states to run gpsd
as root or lose functionality.

> with -D3 -N to look for errors but it
> looked OK and was accepting PPS.

PPS, but not KPPS.  You lost functionality running as a plain user.

> ntpshmmon showed NTP2 and NTP3 and

Which is not what you want, but normal when running as a normal user.

> xgps did show PPS. So the problem is not the hardware.


> Guessing it was some sort of permissions issue I had introduced over
> the years,

The one thing you did not share was how you start gpsd as root.  I'm
guessing that is your problem.

> I did an apt purge gpsd, apt install gpsd and started
> fresh with a reboot.
> No change.

Oh.  So you are running under systemd(umb) and forgot to change your
config after re-install.

Verify by runnng gpsdebuginfo from here:

> Thinking maybe apparmor was doing something, I stopped it and did a
> teardown.

Always a good idea to shoot AppArmor in the head.

> No change.
> /etc/default/gpsd contains:
> USBAUTO="false"
> DEVICES="/dev/ttyS4 /dev/pps0"

Wrong.  Just specify /dev/ttyS4.  If you have /dev/pps0 before starting
gpsd then gpsd can not create /dev/pps0 and things go bad.

> # Other options you want to pass to gpsd
> GPSD_OPTIONS="-n -b -s9600 "

Why -b?  You are not running on bluetooth.

> Now I have no clue where to go next...

Shoot systemd(umber) in the head.

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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