Re: SatPulse: server-oriented alternative to gpsd for chrony

On Tue, Apr 14, 2026 at 04:25:07AM +0200, James Clark wrote:
> Yes, it is.  It is not hugely noticeable with an F9T (because the sawtooth
> amplitude is small), but it does make a significant difference with an M8T.
> 
> Embarassingly, I had the sign wrong for a while. When I fixed that, it made
> quite a noticeable difference to the M8T:
> 
> https://github.com/jclark/satpulse/discussions/163#discussioncomment-15656148

That looks great. I'm curious to see how it compares to higher-rate PPS +
filtering. IIRC the u-blox sawtooth correction works only with 1Hz PPS.

> I have sometimes wondered whether it would be possible to extend the
> refclock SOCK interface so that something like satpulse could provide
> sawtooth corrections when chrony is reading the PPS, especially with PHC
> extpps. Concretely, it would be an addiional kind of message giving the
> amount of the correction as a float and the true time of the pulse (e.g.
> UTC in ms) to which it applied.

From the chrony point of view it would be simpler if satpulse could
provide a PPS-based SOCK with the corrections already applied. The
chrony SOCK refclock would just need a new option to specify the PHC
as the base clock. When the multi-clock support is finished (a draft
MR is on gitlab), that will be easy.

-- 
Miroslav Lichvar


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