Good evening,

This is my first post in this forum and as you will see I’m not really experience working with Linux.

My problem is about setting up a NTP server with my own GPS receiver with RH Linux 2.6.9-55EL. I've used ntp package: ntp-4.2.0.a.20040617-6.e14

I’ve set up my receiver for outputting GGA strings at 4800 (tried as well 9600 bps), modified ntp.conf (127.127.0.2) and created link /dev/gps2 (pointing to ttyS0).

I can see that I have a sync problem with my server. I check var/log/messages, ntpdate –u 127.127.0.2 and can see message “no server suitable for sync found”.

What surprise me is that typing ntpq –p I can see my NMEA (2) but with jitter value of 4000 (meaning the sync problem). I can see data coming trough my serial port and when typing ntpq –p I can see GGA data coming in and peer 127.0.0.1--->127.127.20.2 created.

Running ntptrace –n gets 127.0.0.1 reply

I have tried different gps receivers, set them to output RMC and GLL strings @ 4800 and 9600 bps (modifying ntp.cong and dev links) and still same problem.

It could be something simple but I can’t see it. Maybe something related with permissions?

Any suggestion?

Thanks

Seb

Make sure that your NMEA messages i.e. GPRMC are set to transmit once per second or if your receiver can not time sync the message output then this could be your problem. Also make sure if your not using PPS that it is disabled in the configuration file.

I am assuming that your just using NMEA messages which by themselves do not provide accurate time. If you want millisecond accuracy you will need a receiver that has a 1 Pulse Per Second (PPS) output. Consult your GPS manual but I would generalize that most average priced consumer receivers do not have this capability.

Obviously your actual accuracy is limited by the precision of the timecode, the latencies of the serial interface and the operating system.

BTW what is the make/model of your GPS receivers. And welcome to LinuxQuestions.

Michael,

My GPS receiver supports PPS output but I would like to make it work first with NMEA GGA.

What do you mean about disable pps in the configuration file? Which of the configuration files? Sorry because for sure it is an obvious answer...

Thanks

Maybe not. Ok it appears that the PPS is disabled by default. I think the key is knowing the update rate of the messages.
http://www.cis.udel.edu/~mills/ntp/h.../driver20.html

I've been working at 4800 & 9600 bps with that kind of NMEA strings (GLL, GGA, RMC) and still same problem.

I am thinking about something basic I forgot during installation of RH.

What is the make/model of your receiver?
What I mean by update rate is the message string must at transmitted from the receiver at a fixed interval of once per second which is independent of baud rate. I could be on the wrong track and not a ntp guru by any means.

I am using a Trimble.

The update rate is set to 1 second for NMEA and TSIP. I can see that data it's been recieved on my ntp server every second.