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

Jonathan jonathanNOFISH at sprintmail.com
Thu Jan 1 19:10:04 UTC 2004


Yep, I have no doubt that the Radio Shack unit is mostly for reporting
position.  I think it will work fine for home use though.  If I can just get
millisecond accuracy, which I think I can, that will be sufficient.  The
timing receivers you're talking about sound like different animals entirely.

Thanks for the info.

"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in message
news:JICdnddMztf6wW6i4p2dnA at comcast.com...
> I'm planning to try something very similar.  I'm running NTP 4.2 on an
> Ultra Sparc 5 with Solaris 8 (10/02 release), unpatched.  I've ordered a
> Motorola Oncore M12 Timing evaluation kit from Synergy Systems (for
> considerably more than Radio Shack charges).
>
> I'm speaking from no experience whatever but I believe that there is a
> generic NMEA driver in V3.59e.   Don't expect too much, however!  The
> GPS receivers designed for navigation; e.g. Delorme Tripmate or
> Earthmate, the DigiTraveler and others, are programmed to devote their
> efforts to reporting position.  While they have (they must) the exact
> time internally, they don't try too hard to report it in a timely
> fashion.  The timing receivers, OTOH, do a site survey to figure out
> exactly where they are and then go into "position hold" and concentrate
> on the time.  They also generate a PPS tick that is accurate to better
> than 100ns.  So then the timing message becomes "at the next tick the
> time will be...." or "at the last tick the time was...."; I'm not sure
> which.  By connecting the PPS signal to the serial port and enabling the
> PPS driver, you enable the software to set the clock to approximately
> the accuracy of the PPS tick.
>
> Shall we form Chimeheads Anonymous and develop a "Twelve Tick Program"?
:-)
>
> Jonathan wrote:
>
> >Hi,
> >I've got a teensy little bit of experience with the ancient xntpd that
Sun
> >ships with Solaris 8, but am totally new to GPS.  I am setting up a cheap
> >GPS receiver and building a Stratum 1 time source for home use.
> >
> >This weekend, I purchased an "el cheapo" GPS unit:  the Radio Shack
> >DigiTraveler GPS.  This unit is on clearance for US$30.  It looks like a
> >4"-dia. flying saucer, uses a Sony 16-channel GPS chipset, and outputs
NMEA
> >strings on its serial port at 4800bps.  There's a hobbyist web page with
> >some info at:  http://www.grundlgasse.at/thomas/digitraveler/
> >
> >I have the DigiTraveler hooked up to a Sun SPARCstation LX serial port,
and
> >can 'tip gps' and watch the GPS spew NMEA strings.
> >
> >I downloaded the ntp-4.1.1a package from Sunfreeware.com and ntpd seems
to
> >sync up with the DigiTraveler no problem!!  I was really happy to see
this
> >work so easily.
> >
> >I have a few questions though:
> >
> >1)  Can the xntpd from Solaris 8+patch 109667-05 (v3-5.93e) support NMEA
GPS
> >receivers?  It did not seem to work at all when I tried it; only 4.1.1a
> >worked.
> >2)  What NMEA strings are required/supported in (x)ntpd?  The Sony
chipset
> >supports $GPRMC, $GPGGA, $GPGLL, and $GPZDA, which I think some or all
are
> >supported by (x)ntpd?
> >3)  Does (x)ntpd rely purely on NMEA data for accurate timekeeping?  I
saw
> >some posts related to people using PPS with GPS units but I'm not sure I
> >understand the connection yet.
> >
> >So far I think I'm in good shape, ntp is happy and is syncing with the
GPS.
> >But any answers to the above would help fill in some gaps in my
knowledge.
> >
> >thanks,
> >Jonathan
> >
> >
> >
> >
> >
>





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