[ntp:questions] timing issue with a HP 58534A

Dave Hart hart at ntp.org
Mon Feb 6 07:59:09 UTC 2012


On Mon, Feb 6, 2012 at 05:52, Mark C. Stephens <marks at non-stop.com.au> wrote:
> Good, GPS working with ntpd in survey mode:
>
> ntpq> cv 23560
> associd=23560 status=0000 , no events, clk_unspec, device="NMEA GPS Clock",
> timecode="$GPGGA,052557,3345.8224,S,15105.5288,E,1,08,02.22,000089.0,M,0020.5,M,,",
> poll=21, noreply=0, badformat=0, baddata=0, fudgetime1=0.000, stratum=0, refid=GPS, flags=1
>
> Bad, GPS not working with NTPD when set to timing mode:
>
> ntpq> cv 43305
> associd=43305 status=0000 , no events, clk_unspec, device="NMEA GPS Clock",
> timecode="$GPGGA,054142,3345.8218,S,15105.5278,E,0,08,00.35,000090.0,M,0020.5,M,,",
> poll=42, noreply=0, badformat=0, baddata=0, fudgetime1=0.000, stratum=0, refid=GPS, flags=1
>
> Is the only difference the nmea gga fix word?

It's the only one that matters here.  refclock_nmea.c treats both as
valid timecodes, but the timing mode GGA output tells it the GPS
Quality Indicator is 0, meaning "Fix not available or invalid."  That
makes some sense in that it's not attempting to provide position fixes
in timing mode, but the NMEA driver can't distinguish that from "I've
just started and have no clue if my time code is synchronized to UTC."

Perhaps instructing the driver to use a different NMEA sentence will cure it?

> Footnote:
> To further complicate matters, I wired up a tee cable and sent the NMEA to another NTP server here running windows NTPD 4.2.7p238-o.
> NMEA works fine on that server in either mode.

Which NMEA sentence is the Windows ntpd showing in ntpq clockvar (cv) output?

Cheers,
Dave Hart


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