[time-nuts] OpenBSD / ntpd / gpsd / PPS problems

[Rich Wales]

I'm trying to construct a stratum-1 NTP server, using a Garmin 18x LVC
GPS unit (with the PPS line wired to the serial port's carrier pin),
running on an OpenBSD system (current release, 4.6).  It's not working
for me (yet), and I could use some advice from anyone who has actually
managed to get this running.

I've read that the PPS signal can be handled in a stock OpenBSD 4.6
system, using gpsd to process and merge the NMEA and PPS data, and
interfacing the gpsd output to ntpd (the official implementation from
ntp.org -- *not* the OpenBSD project's own OpenNTPD) via shared memory.
(See http://linux.die.net/man/8/gpsd for an example of this claim.)

First, I installed and configured the latest ntpd (version 4.2.5p236
release candidate).  I then installed gpsd 2.38 (the OpenBSD package).
The GPS was detected (based on output from cgps), but ntpd didn't see
any data from either of the two shared-memory segments.

I removed OpenBSD's gpsd package and built/installed gpsd 2.39 from
sources.  The GPS was detected, and this time, the raw NMEA time stamps
was seen by ntpd (in the first of the two shared-memory segments).  But
the PPS-corrected data (second shared-memory segment) was still nowhere
to be seen.

Despite the claim (see above) that gpsd uses OpenBSD's NMEA line discipline
to export PPS time stamps, I can't find any substantiation for this in
the gpsd source code.  I tried enabling the NMEA line discipline manually
on the GPS's serial port (via the ldattach command), but this made gpsd
totally unable to read anything from the GPS at all.

I know the PPS signal itself is working because I've successfully tested
this setup using FreeBSD 7.2 (custom kernel with PPS_SYNC compiled in).
The main reason why I want to get an OpenBSD-based system to work is
that OpenBSD is allegedly able to handle the PPS signal without needing
to build a custom kernel (as would be required for FreeBSD or Linux).

Any suggestions welcome.

Rich Wales  /  richw at richw.org