ublox refclock

Gary E. Miller gem at rellim.com
Sun Nov 24 22:07:47 UTC 2019

Yo Udo!

On Sun, 24 Nov 2019 09:23:19 +0100
Udo van den Heuvel via devel <devel at ntpsec.org> wrote:

> I cam across this ublox ntpsec refclock:
> https://gitlab.com/trv-n/ntpsec-ublox
> Would it be usable for incorporation in the ntpsec tree?
> (AFAIK this is a 'straight' refclock; no extra lines needed besides
> rx/tx and pps)

I just took a quick look at refclock_ubx.c

An interesting start, but followup messsages today on the list are
assuming this driver does things that it does not do.

1) It does not, ever, config the u-blox.  It does not, ever, write to
the u-blox to query it.

Configuration is up to the user.

2) It decodes UBX-TIM-TM2 (Current time) and UBX-TIM-TIMELS (for the
leap second).  Then does some limited sanity checking.

It will fail to catch known u-blox time failure modes.

3) It does some interesting things with TIO that the comments claim
improves the time stability.  But it does not use KPPS which would
just work better and simpler.

Anything that uses KPPS will work much better.

4) It does not look at qErr, which combined with KPPS, might eventually,
theoretically, lead to better time.  When CPU time quantization gets better.

In summary, not an improvement on current u-blox best practice.  Maybe,
eventually, an improvement, with some work (configuration, KPPS, etc.).

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at 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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