Unruh <unruh-s...@physics.ubc.ca> writes: >leitu...@gmail.com (Diego Ramos) writes:
>>All right. I'll show those options to my manager, but I think he will prefer >>the USB Option as we don't need to be extremely accurate. >Some consider 1ms extremely accurate. Some consider it extremely >inaccurate.( Mine runs about 500 times better than this). > Both would consider 1s pretty crude. >But then again, some consider running a mile in 12 min the height of >accomplishment. >>Once more, I'm really glad for all the help I'm getting here. I'm stuck with >>this problem for a long time and the help I got here saved me a lot of days. >Actually I withdraw my reccomendation of the USB unit. It seems that Garmin >uses a proprietary protocol on this interface, and I am not sure that there >exists a driver for this. It is not NMEA. I think one needs to do a more >thorough research than I have done. >Thus, either get a 18PC and supply the 12V it needs from some other source >(It comes with a cigarette lighter type input which you can plug into a car >lighter output. However your manager might get upset if you told him you >have to buy a car as well and park it in your office). or think that the >18LVC is probably the best bet still depite the need to wire it up. There >are a number of places on teh web that will teach you how to do that. There is a set of programs on sourceforge: garmin_gps and garminusb2nmea which are claimed to be able to use the usb version. Now one post found on google re the use of garmin_gps with the gpsd program which can link up with ntpd. How well it works I have no idea. The garmin_gps driver is supposed to be a part of the kernels after 2.6.8 already (try modprobe garmin_gps and see if it finds it or says no such module) I have also seen one post that claims taht the garminusb2nmea is not well programmed and can get confused. I have used neither and have no idea how well they work. >For anyone with a modicum of soldering experience, hooking up an LVC is >fast and simple. >>Thanks a lot. >>Diego >>On Fri, Jan 9, 2009 at 10:22 PM, Unruh <unruh-s...@physics.ubc.ca> wrote: >>> leitu...@gmail.com (Diego Ramos) writes: >>> >>> >> To sync to a second any gps receiver will do. The Garmin 18PC or USB >>> will >>> >> do and will get you down to about 5ms accuracy with some tuning. The >>> PPS >>> >> on the 18LVC will do 1000 times better ( again $50-100 range) >>> >> >>> >> On the 18PC you have to supply the, I think it is 12 V from somewhere >>> else. >>> >> On the USB it will supply its own voltage if I read correctly. >>> >> >>> >> >>> >But I'll be able to use the Garmin 18 USB and xntpd? Which refclock I'll >>> >use? >>> >>> nmea >>> >>> The gps nmea signal message includes the time. It takes about 200ms for >>> that nmea sentence to be sent, but that can be roughly zeroed out by an >>> appropriate >>> fudge to the nmea driver in the ntp.conf file. The usb port is a bit >>> flakey in its timing etc, but that will onely be a few millisec. Thus if >>> you are happy with 5ms or so, the nmea driver and the GPS usb should be >>> fine. (someone may have done it so could refine that 5 ms figure to be an >>> accurate estimate of the time error you could get.) It is certainly much >>> better than 100ms (1/10) >>> >>> Why use xntpd? That is ancient. Use the latest ntpd 4.2.4p6 >>> >>> >>> _______________________________________________ >>> questions mailing list >>> questions@lists.ntp.org >>> https://lists.ntp.org/mailman/listinfo/questions >>> _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions