[ntp:questions] Re: beginner needs help with gps nmea setup and pps

ramb at sonic.net ramb at sonic.net
Sat Feb 12 05:30:56 UTC 2005

Ronan Flood <ronan at noc.ulcc.ac.uk> writes:

> ramb at sonic.net wrote:
>> I'm getting started with NTP and am having some trouble setting it up.
> First question: what version of ntpd are you running?
> It should log this at startup.  It's important to know
> this as the behaviour of different versions can vary.

ntpd 4.2.0a

>> Is there a difference between these two pps things? I have a gps receiver
>> that has a pps output. I want to set up an NTP server that is talking to
>> the gps receiver and uses the pps output as well.
>> I think I've enabled the PPS output of my GPS receiver.
>> Is this enough for /etc/ntp.conf?
>> enable stats monitor pps
>> server
>> server
>> logconfig +clockall
> When using driver 20 (refclock_nmea), I don't think you
> need driver 22 (refclock_atom) -- the NMEA driver can
> deal with PPS directly itself if you have the PPASPI.
> Try removing "server".

Removing that line, plus removing the files in /etc/ntp/* did the
trick. Now I get this:

[root at scrub include]# ntpq -p scrub
     remote           refid      st t when poll reach   delay   offset  jitter
*GPS_NMEA(0)     .GPS.            0 l   58   64  377    0.000  -45.567  19.244

[root at scrub include]# ntptime
ntp_gettime() returns code 0 (OK)
  time c5b812b9.b5234000  Fri, Feb 11 2005 21:29:29.707, (.707569),
  maximum error 69025 us, estimated error 10369 us
ntp_adjtime() returns code 0 (OK)
  modes 0x0 (),
  offset -44904.000 us, frequency -392.452 ppm, interval 4 s,
  maximum error 69025 us, estimated error 10369 us,
  status 0x1 (PLL),
  time constant 6, precision 1.000 us, tolerance 512 ppm,
  pps frequency 0.000 ppm, stability 512.000 ppm, jitter 200.000 us,
  intervals 0, jitter exceeded 0, stability exceeded 0, errors 0.

I was surprised to learn that the most recent linux kernels don't
support PPS. Next task is to down grade the kernel!! :-(

Thanks for the help!


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