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Re: [gpsd-users] Shared Memory: PPS timestamps not set?


From: Gary E. Miller
Subject: Re: [gpsd-users] Shared Memory: PPS timestamps not set?
Date: Thu, 4 Jul 2019 08:55:42 -0700

Yo Guido!

On Thu, 4 Jul 2019 17:31:03 +0200
Guido Gavilanes <address@hidden> wrote:

> Thank you Gary for taking time to answer.
> My ntpshm works on, I see the timestamps and ntp synch is working
> linke a charm (after a bunch of calibration runs).

Good. so gpsd works.

> the problem in fact is that in my program, when I read the pps
> timestamps I get:
> with socket:
> PPS clk: 1562247898.884325242  -> a realistic pps timestamp (UTC
> epoch in seconds, with subsecond information).
> and with shared memory:
> PPS clk: 0.1077805056              -> not comparable with the actual
> timestamp.

So the problem is in your program.  Can't say much without seeing
your code.

> in fact with socket export i can know how much time has passed since
> the PPS hit, but with shared memory export i cannot compare my local
> UTC time with pps timestamp, since seconds part is missing.

A) Nothing missing.

b) You don't need it.

> So it
> makes me conclude that the same information decoded under two
> different export methods is in fact different. The only explanation I
> have is that PPS is not exported in shared memory export. Is it
> really that?

gpsd sends PPS time to ntpd over SHM.  So we know that workx.

Look at the ntpshmmon code, and your code.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  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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