[ntp:questions] use NMEA 0183 as time source has 180ms difference

flyfatpig at gmail.com flyfatpig at gmail.com
Tue Apr 4 09:32:11 UTC 2006


dear all,
I use garmin gps 15 as ntp time source ,the CPU is 486.
I find it has about 180ms difference with M12+Pentium.
so I setup the ntp.conf as below :

server 127.127.20.0 mode 2
fudge 127.127.20.0 refid GPS time1 0.18


but the server is unstable. the rootdispersion is very big.

ntpq> rv
status=0084 leap_none, sync_unspec, 8 events, event_peer/strat_chg,
version="ntpd 4.2.0 at 1.1161-r Fri Jun 11 17:23:32 CST 2004 (8)",
processor="486", system="Linux/2.4.20", leap=00, stratum=16,
precision=-19, rootdelay=0.000, rootdispersion=160.812, peer=0,
refid=STEP, reftime=c7dcb890.aa5aff2a  Tue, Apr  4 2006 17:19:12.665,
poll=4, clock=c7dcb920.0952d234  Tue, Apr  4 2006 17:21:36.036,
state=2,
offset=0.000, frequency=-500.000, jitter=155.387, stability=252.087
ntpq> pe
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
 GPS_NMEA(0)     .GPS.            0 l   16   64    1    0.000   29.170
 0.002
ntpq> cv
status=0000 clk_okay, last_clk_okay,
device="NMEA GPS Clock",
timecode="$GPGGA,092143,3118.1825,N,12128.8331,E,1,10,0.9,84.2,M,9.7,M,,*43",
poll=20, noreply=0, badformat=0, baddata=0, fudgetime1=180.000,
stratum=0, refid=GPS, flags=0

ntpq> pe
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
*GPS_NMEA(0)     .GPS.            0 l    1   64  377    0.000  368.904
173.386
ntpq> rv
status=04a4 leap_none, sync_uhf_clock, 10 events, event_peer/strat_chg,
version="ntpd 4.2.0 at 1.1161-r Fri Jun 11 17:23:32 CST 2004 (8)",
processor="486", system="Linux/2.4.20", leap=00, stratum=1,
precision=-19, rootdelay=0.000, rootdispersion=589.944, peer=47892,
refid=GPS, reftime=c7dcbb57.cd260f5e  Tue, Apr  4 2006 17:31:03.801,
poll=6, clock=c7dcbb5b.9b877ab3  Tue, Apr  4 2006 17:31:07.607,
state=3,
offset=0.000, frequency=-500.000, jitter=160.174, stability=218.324
ntpq> cv
status=0000 clk_okay, last_clk_okay,
device="NMEA GPS Clock",
timecode="$GPGGA,093109,3118.1827,N,12128.8332,E,1,10,0.9,83.6,M,9.7,M,,*4E",
poll=29, noreply=0, badformat=0, baddata=0, fudgetime1=180.000,
stratum=0, refid=GPS, flags=0




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