[ntp:questions] fudge time1 for gps-18x-LVC?

David Lord snews at lordynet.org
Sun Feb 7 02:54:02 UTC 2010

David Lord wrote:


> Next experiment is to try type 22 atom driver without type 20
> nmea driver and have the three ntp servers for giving the
> correct second. I'll try with parallel pps first since I was
> unable to get this to work on desktop downstairs and it is
> already wired up for that.

This just does not appear to work on NetBSD and a refclock
is needed otherwise I get exact same as when tried on desktop.
ie. I'd need both serial and parallel cables so might as well
just use the serial. First indications are that parallel
might be giving slightly lower offset and jitter but for my
needs the extra cable is probably not worthwhile.

I've now tried with atom driver with pps connected to both lpt
and serial dcd at same time, with /dev/pps0 via ppbus then
symlink /dev/pps0 -> /dev/tty00.

With atom driver alone, PPS(0) remains unreachable.
With addition of NMEA driver PPS(0) takes over a few minutes
after NMEA has been selected.

Below seems best option as it avoids use of fudge time1
and PPS(0) is selected here after only 7 minutes albeit still with
a long way to converge.

Now NMEA(0) 92u/6u and PPS(0) 75u/2u, 60 minutes after ntpd restarted.


  pps to lpt0
  pps to serial dcd
  lpt0 at ppbus
  pps0 at ppbus
  crw-r--r--  1 root    wheel     164,       0 Feb  7 01:47 pps0
  server mode 1 prefer minpoll 6   maxpoll 8
  server minpoll 4 maxpoll 6

  7 Feb 01:46:18 ntpd exiting on signal 15
  7 Feb 01:47:38 clock PPS(0) event 'clk_noreply' (0x01)
  7 Feb 01:51:58 synchronized to, stratum 2
  7 Feb 01:51:58 kernel time sync status change
  7 Feb 01:51:59 synchronized to GPS_NMEA(0), stratum 0
  7 Feb 01:53:09 synchronized to PPS(0), stratum 0

       remote       refid      st t when poll reach delay offset  jitter
  +GPS_NMEA(0) .GPS.            0 l   19   64  377  0.000 -1.680 253.141
  oPPS(0)      .PPS.            0 l   10   16  377  0.000 -1.652   0.150
  -k6x400      xxx.xxx.xxx.xxx  2 u   26   64  377  0.740  0.822   0.778
  +me6000g     .PPS.            1 u   21   64  377  1.767 -0.439   0.309
  -p4x2400c    xxx.xxx.xxx.xxx  2 u   22   64  377  1.893  0.611   0.520

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