[ntp:questions] SIRF time output wobble, GPS or NTP fault?
David J Taylor
david-taylor at blueyonder.co.uk.invalid
Thu Mar 8 15:50:16 UTC 2012
"Ron Frazier (NTP)" <timekeepingntplist at c3energy.com> wrote in message
news:4F58B4FC.4060500 at c3energy.com...
> On the Status tab, that's where it displays all the offsets, similar to
> the ntpq -p command. I don't know how it gets this data. On the
> Statistics screen, if you select the directory where your statistics
> files are, you can graph either loopstats or peerstats files. I think
> clockstats is the third type. I don't know if there is anything to
> graph in that or not.
No, I've not played with those fields in that program. I wrote my own
>> The Fix Quality field. 0 = Invalid, 1 = GPS fix, 2 = DGPS fix. I
>> would hope that NTP rejects any data with 0 in this field, but I don't
>> read the sources at all well.
> OK. I see your point. They call that FIX_MODE on this page which you
> mentioned before.
> I didn't see that field before.
There are lots of things I can't even find, let alone "see" them! <G>
> Based on the aforementioned web page, it looks like the possible
> validity fields are as follows:
> GPRMC sentence - POS_STAT
> GPGLL sentence - POS_STAT
> GPGGA sentence - FIX_MODE
> GPZDA sentence - none, as you observed
> GPZDG sentence - V or maybe signal strength
> I don't know if my GPS will do GPZDG. Otherwise I might try it. It may
> be proprietary to some GPS's.
> We still don't know if NTPD recognizes any of these fields, or if the
> behavior is different in Windows and Linux. If it does, I might switch
> back to another sentence. However, I already know it will increase my
> NMEA jitter. If I can get PPS working, that won't matter as much.
> That's not an option with the BU-353 though.
Take a look at the source, refclock_nmea.c, around line 868 in the copy I
have. It does checks on $GPZDG, $GPMRC, $GPGGA and $GPGLL, but what it
does with the checks I can't easily follow.
> Peerstats is now on. Not totally sure what to do with it, but it's
David Lord answered this, I wrote a small Windows program for my own
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