[ntp:questions] HELP PLEASE::: NTP Garmin GPS 18lvc with PPS and gpsd

sleek daelite sleekstar at gmail.com
Mon Jul 31 01:18:16 UTC 2006

 <questions at lists.ntp.isc.org>Hey guys,

Could anyone help me with Garmin GPS 18lvc device that comes with PPS
output. I've been trying to configure the device to achieve about 1ms
accuracy. The specification of this device states it could achieve about 1ns
accuracy. Im quite puzzled as to why i can't achieve such accuracy. My
software include:

Debian  Kernel 2.6.16-2-486
gpsd 2.33

My content of ntp.conf is:
server minpoll 4 maxpoll 4
fudge time1 0.320 refid GPS

server minpoll 4 maxpoll 4 prefer
fudge refid GPS1

My command line arguments for gpsd is:
gpsd /dev/ttyS0 -n -D 5 -N 2

When i run ntpq the output i get is:
ntpq> peers
remote       refid       st t when poll reach   delay   offset  jitter
*SHM(0)       .GPS.         0 l    4   16  377    0.000   -6.006   6.758
 SHM(1)        .GPS1.       0 l    -   16    0    0.000    0.000   0.004

ntpq> assoc

ind assID status  conf reach auth condition  last_event cnt
  1  1576  9624   yes   yes  none  sys.peer   reachable  2
  2  1577  8015   yes   yes  none    reject  clock expt  1

ntpq> rl
assID=0 status=0964 leap_none, sync_telephone, 6 events,
version="ntpd 4.2.2p3-RC at 1.1581 Tue Jul 25 02:07:02 UTC 2006 (1)",
processor="i686", system="Linux/2.6.16-2-486", leap=00, stratum=1,
precision=-18, rootdelay=0.000, rootdispersion=15.597, peer=1576,
refid=GPS, reftime=c877d40c.174f6c36  Mon, Jul 31 2006 10:57:48.091,
poll=4, clock=c877d418.085b5148  Mon, Jul 31 2006 10:58:00.032, state=4,
offset=-6.472, frequency=1.799, jitter=8.704, noise=4.119,

So im unable to achieve accuracy anywhere around 1ns, Some times i get
offset about 8ms. There seesm to be something weird about:
remote       refid       st t when poll reach   delay   offset  jitter
SHM(1)        .GPS1.       0 l    -   16    0    0.000    0.000   0.004

and when i envoke the ntpq > assoc with the information about SHM(1).

If anyone can offer me some assistants and help it would be greatly
appreciated. Thanks in advance.


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