[ntp:questions] Re: Garmin gps18: The best DIY gps refclock?

Terje Mathisen terje.mathisen at hda.hydro.com
Mon Nov 28 18:08:48 UTC 2005


John Pettitt wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: RIPEMD160
> 
> Roman Mäder wrote:
>>server 127.127.20.0 mode 2 prefer
>>server 127.127.22.0
>>fudge 127.127.22.1 flag3 1
>>
> The NMEA driver (20) has PPS code built in so you don't need the stand
> alone PPS driver (22) - that's why you don't see any difference.  If
> you remove the link to pps0 from /dev and restart ntpd you'll see the
> non PPS results (not even close to the PPS numbers).

I don't think you need even the /dev/pps0 link/device:

The NMEA driver assumes that a PPS signal will be on the DCD pin (if
available), and uses it automatically:

ntp1# ls -la /dev/pps*
ls: No match.
ntp1# ls -la /dev/gps*
lrwxr-xr-x  1 root  wheel  10 Nov 23 14:07 /dev/gps0 -> /dev/cuad0
ntp1# ntpq -p
     remote     refid    st t when poll reach   delay   offset  jitter
==============================================================================
+ntp9.hda.hydro. .GPS.   1 u    7   16  377    0.673    0.018   0.013
-nontp1.hydroisp 136.15  2 u   22   64  377    1.398    0.537   0.202
-nontp2.hydroisp .GPS.   1 u   53   64  377    1.513    0.353   0.053
+nontp8.hydroisp .GPS.   1 u   46   64  377    8.108    0.230   5.128
*GPS_NMEA(0)     .GPS.   0 l    3   16  377    0.000   -0.004   0.002

ntp9 is located on the same LAN segment, while the other servers are
behind firewalls, and (as seen from the delay values) even on the other
side of the country.

Terje

-- 
- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"




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