Re: Report GPS/sync time difference

[Gary E. Miller]

Yo Roger!

On Tue, 25 Oct 2022 06:51:40 +0000
Roger Oberholtzer <Roger.Oberholtzer@ramboll.se> wrote:

> I was trying to find out what the time difference between the
> GPS/gpsd and system time/chrony was. This when the system time had
> not yet been syncd.

Yes, I understood that.  Note that I use NTPSec, not chrony, but the
basics still apply.

> Our GPS receivers don't do a PPS until they are properly initialized.

Does not matter, gpsd ignores PPS until the receiver has locked in the
time.

> As they are high-end (OxTS) designed to be used in a moving vehicle,

One mans "high-end" is anothers trash.  Care to be more specific?

> this means you have to drive a bit. This is also because of the IMU
> and how it is integrated in positions and orientation.

Which makes no sense.  Time is from the GPS, not the IMU.

> If we power on the system as usual with gpsd and chrony running, but
> have not yet syncd, when the GPS is eventually initialized and gpsd
> is happy, chrony will report this in the system log:
> 
> Oct 18 13:17:32 rstraptor1 chronyd[2772]: System clock wrong by
> -67.652005 seconds Oct 18 13:16:24 rstraptor1 chronyd[2772]: System
> clock was stepped by -67.652005 seconds

So?  Looks normal.

> There is the time difference I was after.

Sadly, by the time you know, it is gone.  So not really a useful answer
to your question.

> If it is the most accurate
> time difference one can get reported is not clear to me.

Unless you have a more accurate clock available, that is as good as it
gets.

> But it
> serves my purpose.

Which is?

> I guess this is that first time step that chrony
> does at the start,

Yes.

> before doing the small incremental steps to keep
> the time in sync.

Yes, and more.

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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