r3 - 2007-05-05 - 16:48:58 - SteveKosteckeYou are here: NTP >  Support Web > ConfiguringNTP > ConfiguringRefclocks > ConfiguringUBloxAntarisRefclocks
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REFACTOR See ConfiguringUBloxAntarisRefclocksDev for discussion of this topic.

6.1.18. Configuring u-blox Antaris Refclock

The GPS receiver from u-blox is very nice for the use as a time source, as the 1 PPS time pulse is routed to the DCD line of its serial ports, just where the PPSAPI will look for it. I use their GPS Evaluation Kit, as it has got all the level shifting issues already solved for me.

By default the GPS module toggles its timepulse on the clear edge, and its duration is 100 ms, so if you see the time of your reference clock being wrong by that amount, then the PPS signal on-time edge configuration flag in your ntp.conf is configured in a wrong manner.

I use the NMEA driver of the NTP server, which is hardcoded to run at 4800 baud, 8-bits, no parity. So the GPS receiver may simply be configured to output just the NMEA RMC message on the serial port connected to the PC. The receiver's default baudrate is different, so this has to be reconfigured as well. The configuration of the receiver is done using the u-center software accompanying the evaluation kit.

# NMEA GPS driver for u-blox receiver
server 127.127.20.0 prefer
fudge 127.127.20.0 time1 0.0 flag2 1 flag3 0

I got it running smoothly on a Debian/GNU Linux system (sarge) and NTP server version 4.2.0a. Both the kernel and the NTP server needed the nanokernel patches and recompiling in order to make use of the PPS pulse.

The result I get looks like this:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*GPS_NMEA(0)     .GPS.            0 l   17   64  377    0.000    0.009   0.001

-- EtienneFavey - 19 Jan 2006

Related Topics: UBloxAntarisRefclockUsers

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