Re: Report GPS/sync time difference

[Roger Oberholtzer]

Follow-up to my quastion.

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.

Our GPS receivers don't do a PPS until they are properly initialized. As they are high-end (OxTS) designed to be used in a moving vehicle, this means you have to drive a bit. This is also because of the IMU and how it is integrated in positions and orientation.

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

There is the time difference I was after. If it is the most accurate time difference one can get reported is not clear to me. But it serves my purpose. I guess this is that first time step that chrony does at the start, before doing the small incremental steps to keep the time in sync.

Roger Oberholtzer

 

RST Systems

 

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roger.oberholtzer@ramboll.se

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From: gpsd-users on behalf of Gary E. Miller
Sent: Friday, October 14, 2022 19:47
To: gpsd-users@nongnu.org
Subject: Re: Report GPS/sync time difference

Yo Roger!

On Fri, 14 Oct 2022 10:52:50 +0000
Roger Oberholtzer <Roger.Oberholtzer@ramboll.se> wrote:

> Is it possible to have gpsd report the difference in time on the
> system clock compared to the current GPS time as it sees that time?

Sure, just look at ntpshmmon while gpsd is running.

> If I run gpsd -D 5 -N /dev/gps, I see lots of things. But I don't
> think I see this time difference.

Its there, be hard to dig out.  Just use ntpshmmon.

> I use chrony to sync time. When chrony is running to do a time sync,
> I can get status info that I think reports this difference: chronyc
> -m "timeout 500" "retries 1" sources

Yup, that's best.

> But then chrony is running. I want to know the difference when no
> time sync is happening.

Why would you not always time sync?

> Classification: Confidential

Seriously???

RGDS
GARY
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        gem@rellim.com  Tel:+1 541 382 8588

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Classification: Confidential