Re: [chrony-users] Multi-PPS+RTC Setup Questions

[Matt Corallo <ntp-lists@xxxxxxxxxxxxxxx>]

On 9/29/20 10:44 AM, Miroslav Lichvar wrote:
> On Tue, Sep 29, 2020 at 10:27:51AM -0400, Matt Corallo wrote:
> > Relevant selectdata on 4.0 (which seems to be working great) is:
>
> Ok, if you are using the trust option, then there should be an
> improvement in 4.0 over 3.5 in that it will allow non-trusted sources
> to be selected in more cases.

Indeed, I am now. 4.0 fixed the most important issue by far (namely that I wasn't able to use trust because chrony would 
ignore the PPS inputs), so thanks for the work on that one and +1 to the new code :).

> > Indeed, RTC1 is an external daemon that reads in from an RTC, checks that
> > chrony isn't using it as its timesource and then roughly disciplines it
> > according to chrony's time, all before feeding samples back into chrony over
> > sock. Indeed, the two GPS refclocks are of different model, and do adjust
> > slightly differently as their internal RTCs drift, but all within noise, or
> > only slightly outside of it (at least once I compensate for them being
> > persistently off by 30us, which, uhhh...wtf u-blox?).
>
> Try adding something like "mindelay 0.0001" to both sources.

Would this also force combination of the two ala combinelimit, or only allow them to be selected in 3.5 when the RTC is 
not "trust"?

> > With 3.4, I had to add "combinelimit 100" to get chrony to look at both
> > refclocks instead of picking one and deciding that the other one was
> > persistently off (from the first?) by just enough that it wasn't worth
> > looking at (which does seem like a bug?), and its still in my chrony.conf,
> > though I haven't tested whether I can remove it with 4.0.
>
> combinelimit should have no impact on the selection of the '*' source,
> or which sources are considered to be selectable. It only decides
> later after that point in the selection, whether each selectable
> should be combined (+) with the '*' source, or not (-).

Right, sorry, indeed. My goal was to force chrony to combine the two GPS PPS inputs (cause why not, and it seems strange 
that chrony would, by default, pick one and stick with it, ignoring the other...plus results show much more stability 
when they're combined =D).

Thanks,
Matt

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