[ntp:questions] Re: ntpd/GPS on Sun: newbie questions

Jonathan jonathanNOFISH at sprintmail.com
Thu Jan 1 23:04:43 UTC 2004

"Allen McIntosh" <mcintosh at nospam.com> wrote in message
news:bsvkr1$t37$1 at mc-pc.research.telcordia.com...
> In article <_bednQmjsfyZr26iXTWc-g at speakeasy.net>,
> Jonathan <jonathanNOFISH at sprintmail.com> wrote:
> >2)  What NMEA strings are required/supported in (x)ntpd?  The Sony
> >supports $GPRMC, $GPGGA, $GPGLL, and $GPZDA, which I think some or all
> >supported by (x)ntpd?
> It's in the comment at the start of refclock_nmea.c.

So RMC, GGA, and GLL are supported in ntpd 4.x.

Is there an advantage in using any one of these over the other?
Or is there a real advantage to selecting more than one?

I could see selecting one sentence over the others, if it offered greater
time precision or something.  However according to the datasheet for the
Sony chipset in my cheapy receiver, there is no difference in precision for
any of those sentences.  (In fact, the Sony doesn't even output fractions of
a second, which "real" GPSes do, I think.)

The only advantage I could think of in selecting multiple sentences is to
reduce the amount of time between time updates.  ntpd will "see" many more
messages per second if it's looking for all 3 sentences.  Since the Sony
chipset supports all 3, this is probably good.  True?


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