[ntp:questions] How to debug GPS PPS?

xyz-2041 xyz2041 at gmail.com
Fri Jan 1 19:37:24 UTC 2010


On Dec 31 2009, 9:14 am, Thomas Laus <lau... at acm.org> wrote:
> On 2009-12-30, xyz-2041 <xyz2... at gmail.com> wrote:
>
> > On Dec 28, 7:59?am, Thomas Laus <lau... at acm.org> wrote:
> >> On 2009-12-28, xyz-2041 <xyz2... at gmail.com> wrote:
>
> >> > Plugged in the GPS unit's serial cable into a Windows
> >> > computer running WinOncore12 v1.0 (Build 37):
>
> >> > ?http://www.google.com/#q=WinOncore12Installation.exe
>
> >> > Seemed to work without any problems. ?Generated
> >> > all sort of graphs and charts. ?Let it run and it
> >> > told me exact latitude, longitude and height above
> >> > sea level.
>
> >> > Used an analog volt meter and from pin 5 (supposed
> >> > to be ground), I only noticed voltage on pins 2 and 3.
> >> > Pin 2 was going erratically negative once a second.
> >> > I believe that this must be received data as per
> >> > standards. ?Pin 3 was +5 volts, but dropping to
> >> > -5 volts once per second.
>
> >> You did not mention how your Oncore receiver was being interfaced to
> >> your computer or it's model number. ?
>
> > GT+.  Serial port.
>
> >>I use one of the TAPR boards and
> >> Oncore UT+ combination. ?The NTP refclock driver for the Oncore includes
> >> the code for receiving the PPS signal on the computer DCD pin.
>
> > It doesn't need pulse stretching?
>
> >> > I've changed my configs a bit, /var/log/ntp.log and
> >> > /var/log/ntpd.log don't show any errors.
>
> >> > However, "ntpq -c pe" still doesn't show any response:
>
> >> > ?GPS_NMEA(0) ? ? .GPS. ? ? ? ? ? ?0 l ? ?- ? 16 ? ?0 ? ?0.000
> >> > 0.000 ? 0.001
> >> > ?PPS(0) ? ? ? ? ?.GPS. ? ? ? ? ? ?0 l ? ?- ? 16 ? ?0 ? ?0.000
> >> > 0.000 ? 0.001
> >> > ?GPS_ONCORE(0) ? .GPS-. ? ? ? ? ? 0 l ? ?- ? 16 ? ?0 ? ?0.000
> >> > 0.000 ? 0.001
>
> >> You should not be using GPS_NMEA or PPS. ?
>
> > OK.  Turned both of those off.
>
> >>The type 30 refclock
> > OK.  Used WinOncore to default.  Made sure that it was
> > set to Motorola/binary.  Power cycled.  Hooked back
> > up to FreeBSD server.  This is what was produced--for
> > a while:
>
> >      remote           refid      st t when poll reach   delay
> > offset  jitter
> >======================================================
> >  GPS_ONCORE(0)   .GPS.            0 l   99   16   40    0.000
> > 192.362   0.002
>
> >  GPS_ONCORE(0)   .GPS.            0 l  200   16    0    0.000
> > 192.362   0.002
>
> >  GPS_ONCORE(0)   .GPS.            0 l  418   16    0    0.000
> > 192.362   0.002
>
> This does not look like anything is happening when NTP is trying to
> comunicate with your Oncore.  You might get some insight by enabling
> some of the statistics.  You add them to /etc/ntp.conf
>
> # NTP Statistics
> statsdir /var/log/ntp/
> statistics clockstats loopstats peerstats
> filegen clockstats file clockstats type day enable
> filegen loopstats file loopstats type day enable
> filegen peerstats file peerstats type day enable

OK, done:


  cd /var/log
  mkdir ntp

  cd /etc
  nano /etc/ntp.conf

Seems to be talking to the unit:
  http://www.A7H.com/~stuph/clockstats-Edited-2010-Jan-1-1300.txt

Nothing in peerstats or loopstats showing anything Oncore-GPS related.

> NTP will write events to these files when it runs.  The satellites that
> are in view will be listed by PRN number.  It also will show any RS-232
> handshaking issues.  I had to change the flag for reading the PPS pin
> because it was triggering on the trailing edge instead of the leading
> edge.  My TAPR board pulsewidth was OK and did not require 'stretching'


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