[ntp:questions] How to debug GPS PPS?

xyz-2041 xyz2041 at gmail.com
Wed Feb 17 16:53:52 UTC 2010


On Feb 16, 4:01 pm, Thomas Laus <lau... at acm.org> wrote:
> On 2010-02-16, xyz-2041 <xyz2... at gmail.com> wrote:
>
> > Thanks, Tom and guys.  I really appreciate your help!
>
> > Looks like something is going on with the Oncore:
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > # ntpq -c pe
> >      remote           refid      st t when poll reach   delay
> > offset  jitter
> >==============================================================================
> >  GPS_ONCORE(0)   .GPS.            0 l    -   16    0    0.000
> > 0.000   0.000
> > xPPS(0)          .PPS.            0 l   11   64  377    0.000
> > -3.085   0.017
> >  192.168.2.255   .BCST.          16 u    -   64    0    0.000
> > 0.000   0.001
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > # ntpq -c rv
> > assID=0 status=0615 leap_none, sync_ntp, 1 event, event_clock_reset,
> > version="ntpd 4.2.7... at 1.2108-o Mon Feb 15 20:10:40 UTC 2010 (1)",
> > processor="i386", system="FreeBSD/7.2-RELEASE", leap=00, stratum=2,
> > precision=-20, rootdelay=44.827, rootdisp=44.339, refid=192.43.244.18,
> > reftime=cf25709c.1130eea8  Tue, Feb 16 2010 13:29:32.067,
> > clock=cf257657.3d54896e  Tue, Feb 16 2010 13:53:59.239, peer=54924,
> > tc=10, mintc=3, offset=-4.877, frequency=-49.876, sys_jitter=1.658,
> > clk_jitter=2.179, clk_wander=0.056
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> > "precision=-20" how does one interpret this?
>
> > Why wouldn't the PPS be taken as preferred?
>
> > /var/log/ntp/clockstats:
> >http://www.a7h.com/~stuph/var--log--ntp--clockstats-2010-Feb-16.txt
>
> > Contained in /etc/ntp.conf:
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > # GPS Oncore driver
> > # server 127.127.30.0  prefer
>
> One note about your configuration, I don't think that you can
> have two 'prefer' statements.  It was discussed recently in this
> newsgroup and my memory of recent events is not as good as it used to
> be.

Right.  Commented one of them out--shown in previous post.

> Try restarting your Oncore without the pps driver.  Mine seems to
> see the receiver pps without having that statement in my /etc/ntp.conf
> file.  

OK.  Edited:

# GPS Oncore driver
# server 127.127.30.0  prefer
server 127.127.30.0   prefer
fudge  127.127.30.0   refid GPSo

# PPS driver:
# server 127.127.22.0   prefer
# fudge  127.127.22.0   refid PPS

# Generic NMEA GPS Receiver:
# server 127.127.20.0
# fudge  127.127.20.0   time1 0.752 refid NMEA


and restarted:
  /etc/rc.d/ntpd restart


# ntpq -c pe
     remote           refid      st t when poll reach   delay
offset  jitter
==============================================================================
 GPS_ONCORE(0)   .GPS.            0 l    -   16    0    0.000
0.000   0.000
 192.168.2.255   .BCST.          16 u    -   64    0    0.000
0.000   0.001


# ntpq -c rv
assID=0 status=0615 leap_none, sync_ntp, 1 event, event_clock_reset,
version="ntpd 4.2.7p19 at 1.2108-o Mon Feb 15 20:10:40 UTC 2010 (1)",
processor="i386", system="FreeBSD/7.2-RELEASE", leap=00, stratum=2,
precision=-20, rootdelay=48.985, rootdisp=7.101, refid=68.248.203.43,
reftime=cf269d00.775aa0dc  Wed, Feb 17 2010 10:51:12.466,
clock=cf269d18.be4e82f0  Wed, Feb 17 2010 10:51:36.743, peer=1901,
tc=7,
mintc=3, offset=-2.549, frequency=-50.209, sys_jitter=1.232,
clk_jitter=2.539, clk_wander=0.020


> It still looks like your Oncore receiver is not seeing the data
> being requested by the ntp refclock driver.  Can you post the Oncore
> related lines of your syslog?  

OK.  Did yesterday:
http://www.a7h.com/~stuph/var--log--ntp--clockstats-2010-Feb-16.txt

This is today's output:
http://www.a7h.com/~stuph/var--log--ntp--clockstats-2010-Feb-17--1025.txt


> The driver does a lot of setup work after
> a restart and the results are sent to the log.  It may provide some
> insight into what is happening.  Your Oncore pps on the DCD pin is doing
> something, but the rest of the data is still not getting seen by the
> daemon.

I wonder why that is.  Is there some kind of tool to look at
the raw output in FreeBSD command line mode?   No X-windows
on this box.


>Precision of -20 is what I see on my setup.

What does this mean exactly?


Thanks again for your help, Tom.


>
> Tom
>
> --
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