[ntp:questions] Maximum time2 fudge value for NMEA refclock?

jimmyterrence jimmyterrence at gmail.com
Fri Jul 16 13:14:31 UTC 2010


On Jul 16, 1:56 am, "David J Taylor" <david-
tay... at blueyonder.co.uk.invalid> wrote:
> > Is there a maximum fudge value above which the NMEA refclock throws
> > away input? Both my 18xLVC GPS receivers output serial data about 550
> > ms after the PPS signal. That works fine with gpsd, but I've been
> > trying to set up the NMEA driver with pps compiled in the 2.6.34
> > kernel and it doesn't seem to work.I thought I read somewhere that it
> > accepts a max of 400 ms but I can't seem to find that anywhere. Could
> > anybody tell me what the value is, and maybe point me to the line in
> > refclock_nmea.c (if that's where it is) that governs that?
>
> > Thank you,
>
> > Court
>
> Court,
>
> This site suggests nearer 350ms than 550ms:
>
>  http://www.dangl.at/ausruest/gps18lvc_e.htm
>
> Are you using the minimum sentences, and the right edge of the PPS signal?
> I have no such problems with a GPS18x LVC on Windows with ntpd
> 4.2.6p2-RC5-o, but I haven't tried it on FreeBSD which still runs my GPS18
> LVC.
>
> Cheers,
> David

If it was triggering on the wrong edge of the pps signal, wouldn't it
be off of the rest of the servers by the length of the pulse? I think
that it's triggering properly.

remote           refid      st t when poll reach   delay   offset
jitter
=================================================
*SHM(1)          .PPS.            0 l    2   16  377    0.000
-0.005   0.005
+SHM(0)          .NMEA.           0 l    4   16  377    0.000
12.034  15.490
-dense.utcc.utor 128.100.103.253  2 u  490  512  377   16.047
-0.029   5.304
-ntp-2.gw.illino 128.174.38.133   2 u  844 1024  377   33.467
3.084   1.829
-rs1.tor1.rogers 192.43.244.18    2 u  875 1024  377   19.683
17.259   1.058
+ntp-4.cns.vt.ed 198.82.247.164   2 u    3   64  377   47.869
3.035   3.673

My 555 ms fudge, from the config file.

#gpsd PPS
server 127.127.28.1 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.1 refid PPS
#gpsd
server 127.127.28.0 minpoll 4 maxpoll 4
fudge 127.127.28.0 refid NMEA flag4 1 time1 0.555

I stopped gpsd to check and make sure I had set the outputs properly,
but it shows just one sentence, GPRMC.

$GPRMC,130803,A,4416.2422,N,07823.4033,W,000.0,143.4,160710,011.6,W*71
$GPRMC,130804,A,4416.2422,N,07823.4033,W,000.0,143.4,160710,011.6,W*76
$GPRMC,130805,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*74
$GPRMC,130806,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*77
$GPRMC,130807,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*76
$GPRMC,130808,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*79
$GPRMC,130809,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*78
$GPRMC,130810,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*70
$GPRMC,130811,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*71
$GPRMC,130812,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*72
$GPRMC,130813,A,4416.2421,N,07823.4033,W,000.0,143.4,160710,011.6,W*73




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