Re: NMEA but no PPS in ntp, Ubuntu 18.04.5

[Gary E. Miller]

Yo Steve!

On Tue, 1 Dec 2020 15:24:18 -0600
Steve Bourland <sbourland@swri.org> wrote:

>    Super happy to learn about new places to look for information :)

So much internet, so little time.

> > But no PPS.  You also do not have enough other chimers.  Hard to
> > vote with only 2 voters.  
> 
> I have 4 other voters but figured their info wasn't relevant, and
> knew I was already going to have a long message, just trying to keep
> it as short as possible.

When removing data, this tells us you did: [...]

> > That is good.  What is your gpsd command line?  See it this way:
> >        # pstree -paul | fgrep gpsd  
> 
> # pstree -paul | fgrep gpsd
>    |-gpsd,25099,nobody -b -n /dev/ttyS0
>    |   `-{gpsd},25100
>    |                       |-grep,25730 -F --color=auto gpsd

Why are you using -b?  That is to fix Bluetooth problems.  Otherwise looks
good.


> > Uh, you have if backwards.  The kernel feeds PPS to gpsd.  Then gpsd
> > uses a SHM to eed it to ntpd.  
> 
> Is the lack of /dev/pps0 on the gpsd command line causing the issue?

Normally not.  But cant hurt to try it.  Then your PPS would be
on SHM(2) if you did: gpsd -n /dev/ttyS0 /dev/pps0

What does this show:
        gpsd -n -D 6 /dev/ttyS0 |& fgrep PPS

It should show PPS being configured properly.  As long as you start as root.


> ntpshmmon
> ntpshmmon: version 3.21
> 
> # Name Seen@ Clock Real L Prc
> 
> sample NTP0 1606854237.160599667 1606854236.723461751
> 1606854236.000000000 0 -20
> sample NTP2 1606854237.160618091 1605548548.531056191
> 1605548548.000000000 0 -20

For some reason your PPS is on SHM(2), not SHM(1).  Odd, that usually
happens when you ut /dev/pps0 on the gpsd command line.

Adjust your nto.conf to fit and it should all work fine.

> Using this super cool new tool on a functioning system,
> I see NTP2, NTP3, and then NTP0, NTP1 every second.

That would mean you have two serial and two PPS sources nn that system.

> > You need to be running gpsd and ntpd as root, of course.  
> 
> They both start as root but then drop privleges so gpsd runs as
> nobody, and ntpd runs as "ntp."  I believe this is expected behavior?

Yes.  Good.

> So hopefully I'm following along here, but it looks to me like gpsd
> isn't putting the PPS timing in the shared memory for ntpd,

No.  We confirmed gpsd is putting PPS on SHM(2), not SHM(1) as you,
and I, expected.

> Restarted gpsd on the command line with -D 5 to see if there was
> useful information:

Once again, the interesting parts you deleted.  Do this:

        # gpsd -n -D 6 /dev/ttyS0 |& fgrep PPS

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  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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