Re: [chrony-users] PPS time

[scs@xxxxxxxxxx (Steve Summit)]

Several days ago, I wrote:
> ...If I want to use "raw" PPS, I need to (a) configure chronyd with
> something like "refclock PPS /dev/pps0" and (b) configure the Linux
> kernel so that /dev/pps0 reflects my actual PPS input.

With thanks to previous assistance from this list, I've got
chrony listening to /dev/pps0 directly, and it's working great.
But -- there's always a "but", isn't there? -- something else
has come up.

I'm getting the impression that /dev/pps0 is a particularly
virtual form of device.  It seems to be created on the fly, when
the PPS line discipline is attached to an actual serial port, by
a program such as gpsd or ldattach.  But if that process is ever
performed again -- if gpsd or ldattach should ever exit and be
restarted -- next time, the virtual device that's created might
be /dev/pps1.

(Oddly, at least on my system, further restarts seem to
recreate pps1 over and over again; I don't get a sequence pps2,
pps3, pps4 as I might otherwise expect.)

But of course this means that my shiny new chrony configuration
with its "refclock PPS /dev/pps0" line already has a blemish on
it, in that it's theoretically vulnerable to a restart of an
unrelated process which might yank /dev/pps0 out from under it.

So I'm wondering if there's a good way around this.  Is there
a way to configure chrony to look for, in effect, /dev/pps*?

(I suspect the answer is "no"; it would be kind of crazy to have
chronyd not only do that sort of sh-style globbing, but also to
detect that, say, pps0 had disappeared out from under it and
that it therefore had to perform the expansion again and open
a different fd.)

Barring that -- although I guess this is more of a question for
the LinuxPPS folks -- is there a way to get pps0 "nailed down",
so that it doesn't change to pps1 if it's recreated?  (Perhaps,
as I've seen some discussion of on the net, I should be using a
udev rule to explicitly create pps0.)

Thanks for any additional suggestions.

-- 
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx 
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx 
with "help" in the subject.
Trouble?  Email listmaster@xxxxxxxxxxxxxxxxxxxx.