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

Jonathan jonathanNOFISH at sprintmail.com
Wed Dec 31 20:30:00 UTC 2003


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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