Update Feb 2002

The NMEA signal wasn't working all that great. There wasn't a lot of jitter, but that was because the NMEA signal was output using the internal clock. While I could adjust the fudge factor, there wasn't any way to tell what the difference between the internal clock and the GPS clock. I had to keep changing the fudge factor. I found a solution on the newsgroup. Jeff sent me a driver for the Tripmate that accesses the Rockwell GPS chipset. The Delorme Tripmate uses the Rockwell twelve channel GPS chipset code named Jupiter. Thanks Jeff.

Actually the refclock_jupiter.c driver file that Jeff sent was for the Delorme Earthmate which was an updated model of the Tripmate I had. Christian Vogel wrote the driver as a replacement for the original refclock_jupiter.c driver and based it on the refclock_nmea.c driver. Christian Vogel's driver doesn't require the PPS clock signal that the original driver did. I modified it so that it could be used for the Tripmate as well as the Earthmate. I also added logging features so that it could create the statistics files. 

Instructions for building the JUPITER driver.

The basic function is as follows. When NTP requests the time, the driver signals the receiver to get the time from GPS. It reads the time, location and some flags about the condition of the signal. While accurate enough for many purposes, it lacks information about the delay and other things that the big guys consider important. For my installation, I just use a fudge factor for the delay. Here is a sample query:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 LOCAL(0)        LOCAL(0)        10 l   41   64  377    0.000    0.000   0.008
*GPS_JUPITER(0)  .GPS.            0 l   41   64  377    0.000   -0.135   3.798
+sue.cc.uregina. clock.uregina.c  2 u   60   64  377   16.378    0.200   6.566
+wxo-svr1.cmc.ec gps-ntp-clock.c  2 u   53   64  357  117.543   -0.457   1.426
 hssx-sktn-167-1 wysenburg.River  2 u  405 1024  377   30.712    0.750   0.240

The last server shown is a peer ntp server at a remote location. It is a stratum 2 as it gets the time from my system. I  dropped the third NTP server, mostly because I eliminated the computer it was running on. I had a second source for a GPS signal, but they were having trouble with the GPS receiver so I lost that connection also. The network is now just between the two computers. It uses four outside stratum 2 sources plus the GPS signal.

Correction:

A short time after I published this page I received a message from Peter who manages the NTP server "wxo-svr1.cmc.ec.gc.ca". He pointed out that the canonical name for that server was "dns1.cmc.ec.gc.ca" in February of 2002 and not "wxo-svr1.cmc.ec.gc.ca" as shown in the printout above. He caught me. While the text here reflects the updates I did in 2002, the sample query shown above is from sometime in February, 2003 when I authored this page. Who else would notice that but the time keeper. (mm oct.04.2004)

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