AW: PPS stopped once => stopped forever?

[Wielant, Ulrich]

Hi Gary!

>
> Yo Ulrich!
>
> On Mon, 4 Nov 2024 12:38:11 +0000
> "Wielant, Ulrich" <U.Wielant@leonardogermany.com> wrote:
>
> > > > Ok, understood. Is there any way to change that?
> > >
> > > No.  But you can use SHM(2) and SHM(3).  That is not a good idea.
> >
> > Sorry, I don't understand what you recommend.
>
> I recommended nothing.  That is why I said: "not a good idea".
>
> > > > I am using chrony. Does this problem disappear by using sockets
> > > > instead of SHM?
> > >
> > > Nope.  It is a design decision.
> > >
> >
> > This means gpsd will never forward the PPS signal to chrony/ntp if the
> > GPS receiver is started after gpsd.
>
> Correct.  Don't do that!

That would be good. But reality is sometimes very different.
How does gpsd handle USB devices? I haven't tried them but they are started and 
connected with hotplug capability. Is gpsd not capable to use them as a time 
source?

>
> > Do you see any chance to handle such a case
>
> No.  And trying to do so would be a bad idea.  If you are doing timekeeping 
> you should start gpsd with the time source on the command line.  And that 
> source had better be very reliable.

chrony and ntpd are fine and designed for alternating time sources. So gpsd 
should also be fit for it: you never have a 100% reliable source.

>
> > would it be possible to implement a new variant so that gpsd does not
> > exit pps_monitor on error so that it can continue providing PPS
> > information after reconnect?
>
> As a general solution no.  Hard enough to get PPS right without trying to 
> handle error conditions that should never happen.

"Should" - but it happens - you cannot ignore that fact.

Best regards
Ulrich
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