Re: Help needed to configure and compile gpsd to run on a Raspberry Pi 4 and NOT use systemd

[Gary E. Miller]

Yo Mick!

On Wed, 20 Nov 2024 19:41:11 +0000
Mick Durkin <mickdurkinuk@gmail.com> wrote:

> We implemented Mike's suggestion about adding the "nohz=off" parameter
> to the end of the single line in "cmdline.txt"and rebooted the Pi.

People do suggest that, but I don't recall anyone testing that it
actually helps on a modern system.

> This was after a few minutes run, so maybe the offset and jitter
> values for PPS will settle down. At least, ntpd is locking on to the
> PPS signal and has a couple of externals with a '+' as well.

ntpd can take many days to settle.  Keeping the system in a thermaly
stabilized environment helps.  Keep the system load stable and don't run
big cron jobs.

> Maybe we can say that we have a good installation now?

Yes.  Pretty good.

> If it is considered that our setup is "valid", maybe some of the
> pitfalls could be added to the gpsd site documents?

Doc suggestions always welcome.

> We can easily
> summarise what we did, both initially (h/w setup) and relevant changes
> to the "config.txt" and "cmdline.txt" if it would help.

You pretty much ended up where the gpsd docs should have pointed you.
I expect most changes would be for better clarity, and to assure the
reader that it also applies to "pihole" and Pi4.

> Can anyone (I reckon Mike is a likely candidate) running a similarly
> configured Pi 4 (gpsd not under systemd with an NTPsec derived ntpd)
> let us know what kind of offset and jitter  numbers they get from PPS?

I have a lot of those.  With careful attention a jitter of 0.0001 is
possible.  But you start to trade jitter for offset.  Run ntpviz as any
changes you make now will have subtle effecs on the results.  May take
hours to see a change, and be masked by thermal effects.


RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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