[LinuxPPS] Struggling w/ PPS

[Dave Hart]

On Thu, Mar 1, 2012 at 18:55, Nathan Mapes <nm4p3s at gmail.com> wrote:
> I've been working on this for a number of days and haven't gotten my jitter
> down to < 1 ms.  I have a Garmin GPS 18 LVC attached to my Ubuntu 11.10 mini
> PC (w/ Atom processor).  From the logs I appear to be getting PPS assert and
> clears.  The clock is syncing with the GPS, just not using the PPS.  I
> compiled the 3.2.8 kernel checking off the PPS modules under drivers.  I
> didn't compile ntp because the docs say my version is new enough to have
> LinuxPPS support.  I've tried several variations for the ntp.conf file.
> They all do about the same.  Any help would be appreciated.

Most likely you do need to recompile ntpd, ensuring you have an
up-to-date timepps.h which ntpd's configure script finds to enable
PPSAPI.  You can verify this by attempting to configure the PPS-only
ATOM driver:

server 127.127.22.0

If that results in a syslog message about an unrecognized refclock
type 22 and you see no assocation for PPS(0)/127.127.22.0 in the ntpq
-p output, that is confirmation your ntpd binary doesn't have the ATOM
driver, which usually means it doesn't have PPSAPI but could also be
because that driver was not enabled in configure options.

You don't mention the version of ntpd in use, but recent ones will
whinge to syslog if NMEA flag1 1 is set and PPSAPI fails:

			msyslog(LOG_WARNING,
				"%s flag1 1 but PPSAPI fails",
				refnumtoa(&peer->srcadr));

Good luck,
Dave Hart