[LinuxPPS] Occasionally ntpd stops receiving NMEA data

[Udo van den Heuvel]

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?


> 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.

> And here's a log of ntpd:
> 
> nmea: gpsread 72 $GPRMC,051330,A,3300.6600,N,09643.3346,W,000.0,016.2,050606,004.8,E,A*0B

[...]

You have quite a lot of sentences 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?)

> 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?

> Once I restart ntpd, for a little while everything's fine again -- it
> can see NMEA data.
> 
> Any ideas?

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.
(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?

Udo