Date: Fri, 19 Sep 2008 18:39:57 -0400 From: "Bob Johnson" <fbsdlists@gmail.com> To: "Tom Storey" <tom@snnap.net> Cc: freebsd-questions@freebsd.org Subject: Re: ntpd and GPS Message-ID: <54db43990809191539l558faaa3qc6b4f42d8090569e@mail.gmail.com> In-Reply-To: <57037.172.25.144.4.1221827796.squirrel@imap.snnap.net> References: <57037.172.25.144.4.1221827796.squirrel@imap.snnap.net>
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On 9/19/08, Tom Storey <tom@snnap.net> wrote: > Hi all, > > Ive been toying with setting up my old Garmin GPS12 as a reference for a > server (FreeBSD 6.2) running ntpd, but Ive run into an issue. > Is it possible the issue isn't what you think it is? > Ive searched around a bit and cant find an answer, perhaps because there > isnt one. I once (years ago) had a Garmin GPS working with ntpd, so it's reasonable to believe it can be done again, unless support for that capability was dropped (which I doubt). Unfortunately, it was long enough ago that I don't remember what I did. It's possible I used the 1 PPS output without NMEA sentences, but that's not my recollection. > > Is there any way I can set ntpd to expect a $GPRMC string every 2 seconds, > which is the frequency at which the GPS12 transmits them? > > Alternatively, does anyone know how to make the GPS12 transmit a $GPRMC > string every second? I'm almost certain you can't. The complete set of all NMEA sentences takes more than one second at the default 4800 baud, so IIRC it outputs sentences only on odd seconds, and perhaps the older units are too slow to compute a fix once per second. Two things that may work around this are to turn off everything except the GPRMC sentence: $PGRMO,,2 $PGRMO,GPRMC,1 and perhaps free up some CPU time (for faster position calculation) by (oddly enough) reducing the output data rate to 1200 bps: $PGRMC,,,,,,,,,,1, but I don't think that will actually work. To go back to 4800 bps, use 3 instead of 1. I think there are 11 commas after the "C" in that command, but my eyes aren't so sharp any more. There is a Linux driver for the Garmin proprietary protocol. Don't know if it is distributed in a FreeBSD version. Try http://jensar.us/~bob/garmin/ > > If there is a better place I can post this, please let me know. This is probably a good place for this question, but if you don't get a better answer, try the archives of the "time nuts" mailing list https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts which unfortunately appears to be down right now. General info about that group is at http://www.leapsecond.com/time-nuts.htm If that yields nothing, you might post your question to the Time Nuts list, time-nuts @ febo.com. It is probably a FAQ for them, but they will be polite about it. And I had hoped to once again stick an old Garmin on an NTP server, so I'll be curious to know if this turns out to be insurmountable. Good luck, -- Bob Johnson fbsdlists@gmail.com
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