Re: 3.22 not sending PPS to SHM

[Gary E. Miller]

Yo David!

On Sun, 10 Jan 2021 10:55:43 +0000
David Taylor <gm8arv@yahoo.co.uk> wrote:

> Yes, I know this sounds unlikely, so perhaps I#m doing something
> wrong here!

Perhaps.

> Raspberry Pi, current OS: Linux RasPi-18 4.19.66-v7+ #1253 SMP Thu
> Aug 15 11:49:46 BST 2019 armv7l GNU/Linux

A somewhat old kernel, but should be OK.

> PPS check:
> 
> pi@RasPi-18:~ $ sudo ppstest /dev/pps0

Good.  What receiver?  Serial?  USB?

> Never had gpsd installed before.  Compiled 3.22 from scratch.  Build
> log: ~~~~~~~~~~~~~~~~~~~~~~~~~~~

Your build log should be a lot longer than that!

Compiled from tar ball or git?  What were the exact commands you
used to configure, build and install?  What was the complete build output?

> Could install asciidoctor
> Couldn't find matplotlib - python3-matplotlib
> Could install python3 python3-matplotlib python3-serial version 3.5.3

None affect PPS at all.

> "cgps -s" works as expected.

Uh, skipped one very big step.  How are you starting gpsd?  What is
the exact command line you used.

And skipped another big step.  Did you check that gpsd is filling
SHM?  Easy, do this:

# ntpshmmon
ntpshmmon: version 3.22
#      Name  Seen@               Clock                Real                 L Prc
sample NTP0 1610312676.185569137 1610312676.138862976 1610312676.000398741 0 -20
sample NTP2 1610312676.185580566 1610312675.670412876 1610312675.670381223 0 -30
sample NTP2 1610312676.670607960 1610312676.670520866 1610312676.670489507 0 -30
sample NTP0 1610312677.109004918 1610312677.108473011 1610312677.000399004 0 -20
sample NTP2 1610312677.670675567 1610312677.670633768 1610312677.670602759 0 -30


> server 127.127.28.0 minpoll 4 maxpoll 4 prefer

Absolutely not.  Do not use prefer on serial time!  

> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> NTP result:
> 
> pi@RasPi-18:~ $ ntpq -pn
>       remote           refid      st t when poll reach   delay
> offset jitter
> ==============================================================================
> *127.127.28.0    .GPS.          0 l    8   16  377    0.000 1.401 2.349

The "prefer" worked.  So NOT GOOD.

>   127.127.28.1    .PPS.         0 l    -   16    0    0.000 0.000 0.000

But no PPS.

> So the "127.127.28.1" is either not being seen by NTP or NTP isn't 
> seeing the data, or?

Yup.

> I tried with and without the "prefer" on the  127.127.28.1  server
> line. Many Web sites show the prefer present, but my understanding is
> that the prefer should be on the source of time-of-day data, and not
> on the PPS line.

You should have prefer on SHM(1), and nothing else.

> Is there a simple way to test whether the SHM 1 segment is being
> filled?

See ntpshmmon above.

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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