Hi JW --
--- In "jywmpg" <> wrote:
>
> Has anyone got GPSD running using the PPS (Pulse Per Second)
signal to
> synchronize NTP?
>
> I have a Garmin 18LVC connected to COM1 on a 7260, with the PPS
line
> connected to the DCD pin of COM1. Using a scope, I can tell that
the
> Garmin is supplying a 100 ms pulse to DCD once a second.
>
> GPSD is supposed to detect the transitions on DCD and use that
> information to provide a clock to NTP, via shared memory.
>
> Unfortunately, running GPSD at a high debug level shows no
indication
> that GPSD sees the PPS transitions on DCD. If the transitions are
> detected, debug messages should be generated
>
> I have removed /dev/ttyAM0 from /etc/inittab, and redirected the
> console output to COM2 via JP4 and JP2.
>
> I have downloaded the GPSD 2.34 and built from scratch, making
sure
> that both SHM and PPS are enabled, and that PPS is input on DCD.
>
> GPSD is capable of producing both a low resolution clock (derived
fro
> m characters arriving on the serial line) and a high resolution
clock
> (derived from the PPS signal). The low precision clock works, but
the
> high precision one does not.
>
> This is demonstrated in the following:
>
> # ntpq -p
Before bringing ntpd into the picture, I'd verify that gpsd is
getting the pps OK. I think there is a level 5 or 6 debug log for
gpsd that will tell you more details about gpsd finding (or not .. )
the pps signal.
> remote refid st t when poll reach delay
offset
> jitter
>
==============================================================================
> *SHM(0) .GPSa. 0 l 7 16 377
0.000 -198.66
> 37.583
> SHM(1) .PPSa. 0 l - 16 0 0.000
0.000
> 0.061
> tss1 .STEP. 16 u - 64 0 0.000
0.000
> 0.000
> tss6 .STEP. 16 u - 64 0 0.000
0.000
> 0.000
> LOCAL(0) .LOCL. 10 l 8 64 377 0.000
0.000
> 0.061
>
>
> Questions:
>
> 1. Does anyone have this setup working?
No (haven't tried), but I'd like to someday ....
> 2. Is there some other way to monitor the DCD line to see if it is
> actually getting into the 7260?
Try the oldie-but-goody statserial to monitor it; there is a debian
package for it.
>
> Any suggestions would be appreciated.
A few things to try:
* There is a patch for "setserial" program that adds a 'hardpps'
command option and does the needed ioctl on the port. See:
http://wiki.enneenne.com/index.php/LinuxPPS_support#setserial
* Reading through the gpsd sources, I see that it needs or at least
wants TIOCMIWAIT to be defined, so it can 'wait for a change on
serial input lines'. Can you check to be sure this define is
picked up when compiling gpsd? Maybe it is missed in a
cross-compile; gpsd skips pps entirely if TIOCMIWAIT is not
available.
* There was a pps patch for linux 2.4 kerenls maintained for a long
time. Google for 'ppskit' (assuming here you use a 2.4 kernel; if
not, see the 2.6 pps stuff at
http://wiki.enneenne.com/index.php/LinuxPPS_support).
* There's a gpsd build option to use CTS instead of DCD, maybe give
that a shot. Unlikely though.
HTH, ......... Charlie
>
>
> jw
>
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