[LinuxPPS] Occasionally ntpd stops receiving NMEA data

[Philip M. White]

On Mon, Jun 05, 2006 at 07:47:18AM +0200, Udo van den Heuvel wrote:
> Philip M. White wrote:
> > I do not claim correlation, but once I upgraded my LinuxPPS to version
> > 2.1.0, ntpd began behaving poorly: after several minutes of running
> > correctly, it stops receiving the GPS data.
> 
> 'the GPS data'?
> what exatly do you mean?
> PPS stops?
> NMEA stops?
> Both?
> Or?

Looks like both, because NMEA stops scrolling in ntpd debug mode, and
ntpd marks the GPS device as being completely unusable.  If PPS was
still available, I'd expect that ntpd would treat it in the same manner
it treats the SHM driver: we can still synchronize with it, just not
read the wall clock time.

> > Here's a log of `dmesg':
> [...]
> > [it stops here]
> 
> dmesg looks normal, stopping is not normal.
> The fetching should continue, whether it gets a timestamp is depending
> on the PPS signal.

Exactly, but it stops.

> You have quite a lot of sentences enabled.

Yes. :)  I know I don't need all of them, but can't hurt.  I've always
had them enabled.
> 
> > It's clear from the log that the GPS saw six satellites at the time of
> > the incident, so the PPS signal did not stop.
> 
> ntpd thinks it did.
> Please verify using the /proc interface.
> # cat /proc/pps/00/assert
> 1149486295.999996675 #478873
> 
> (repeat, do you the numbers change?)

Indeed, the numbers do NOT change.  The 'assert' node's data is:
1149484412.1091000 #135
where #135 is one greater than the last visible number in `dmesg'.

> > When I Ctrl-C the ntpd process (which is running in the foreground with
> > the -d switch), it takes a while for the process to die, like it's stuck
> > waiting for something.
> 
> That is abnormal?

When everything is working fine, pressing Ctrl-C ends ntpd instantly.
So yes, this appears to be abnormal.

> Dunno. I am still running the (patched now) versio I made for 2.6.16.x.
> Please reduce the number of NMEA sentences. Just one should be enough.

Which one is required?  GPRMC?
Like I said earlier, I've *always* had these enabled without any
problems.  The problems started after upgrading my LinuxPPS version, and
the problem is pretty severe -- the GPS device in ntpd dies just minutes
after starting it.  So, I couldn't have not noticed it before. :)

> (it is for me, I use the default sentence that the NMEA driver uses).
> Please verify PPS using the /proc interface.
> What kernel/npt are you using?

Right now I am using kernel 2.6.16.19 with LinuxPPS 2.1.0 that's
available in Rodolfo's patches/ directory.  It patched, compiled, and
loaded cleanly.

-- 
Philip
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