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

Richard B. Gilbert rgilbert88 at comcast.net
Wed Dec 31 23:31:50 UTC 2003


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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