[ntp:questions] How to debug GPS PPS?
xyz2041 at gmail.com
Wed Dec 30 20:03:24 UTC 2009
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
> communicates with the receiver using Motorola Binary protocol. You may
> need to use WinOncore to set your receiver communications to use the
> binary protocol or even better, reset the receiver to factory defaults.
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
remote refid st t when poll reach delay
GPS_ONCORE(0) .GPS. 0 l 99 16 40 0.000
GPS_ONCORE(0) .GPS. 0 l 200 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 418 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 636 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 938 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 1167 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 1226 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 1352 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 2028 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 61m 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 67m 16 0 0.000
GPS_ONCORE(0) .GPS. 0 l 176m 16 0 0.000
Re-defaulted. Now back to this:
GPS_ONCORE(0) .GPS. 0 l - 16 0 0.000
> Your config files already have your position defined, so there is no
> need to have anything in your receiver at startup. The almanac will be
> received while NTP is settling down after startup. You will need to
> configure at least 4 other NTP servers to speed up the initial startup.
> The refclock code wants to have a synchronized NTP server before adding
> itself to the peer selection. I find about 30 minutes after a cold
> start my PPS LED will start to flash and I observe that my Oncore gets
PPS LED was flashing, but NTP never synchronized.
> > - Create symbolic links:
> > ln -s /dev/cuad0 /dev/oncore.pps.0
> > ln -s /dev/cuad0 /dev/oncore.serial.0
> > ln -s /dev/cuad0 /dev/gps0
> > ln -s /dev/cuad0 /dev/pps0d
> > - Create /etc/devfs.conf links:
> > link cuad0 pps0
> > link cuad0 gps0
> > link cuad0 oncore.pps.0
> > link cuad0 oncore.serial.0
> I think that you will find that the symbolic links in /dev are not required and
> only the /etc/devfs.conf entries are all you will need. You won't need
> either pps0 or gps0 entries for anything. Only the oncore* stuff is
> needed for the refclock type 30.
Well, this just doesn't seem to be working. Does anyone have other
suggestions on how to get this GT+ working?
If not, does anyone have some other suggestions? Would I be able
to use this Motorola antenna with another GPS unit? Other low-cost
ways of getting GPS accuracy on this FreeBSD/NTP box?
> Public Keys:
> PGP KeyID = 0x5F22FDC1
> GnuPG KeyID = 0x620836CF
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