On Tue, 24 Feb 2004 18:52:33 +1300, you wrote: >> >> I note that Dick Smith are offering a GPS receiver that is M$ >> >> compliant, and is around the NZD250 mark. Is there any support for it >> >> under linux > >These things always have a serial port -> trivial. The protocol they speak >is NMEA-0183, http://www.nmea.org/pub/0183/ unfortunately an expensive >standard. It's based on the exchange of ASCII lines of 15 - 80 characters >(usually). If you get a manual which describes which control messages and >info messages are supported by this receiver (should be possible), you're >home and hosed. > >The serial port will give you a time accuracy of around 1 second and a >resolution of 1 second. > >> >I've been looking at these as well. I'd be curious to see what the >> >clock accuracy is like on one of these devices. >> >> Allegedly 0.1sec according to the label. I might nip in next time the >> boss isn't around (: > >Ooouuuuuuch, man that's bad. That's 100ms. Not a good NTP source. NTP can >synchronise the time over the internet between Europe and America to within >5-20ms, and this box is hanging straight off the back of your computer. >Cheap though, and you never have to set your watch. (I had this in 1985 in >Germany for less money than you mentioned - nahnahnahnahnah... ;))) ) > >Note the accuracy below 1s comes from a pulse signal which the receiver >should also supply. You can expect 1ms accuracy here. Good receivers should >manage <1us. > >Some other trivia: GPS runs on neither TAI (international atomic time) nor >UTC (which one could call civil time) (no comment). You'll have to >compensate yourself. NTP is probably supposed to use UTC, but leap seconds >are not implemented. Whenever there is a leap second in UTC, (in the words >of David Mills, inventor of NTP) "the behaviour of NTP can be described in >terms of a pinball machine". No comment either. > >Volker
Thanks for the info Volker. According to the blurb on the outside of the box ( contents removed! ) it was purely an USB interface, and I've not programmed that. Come to think of it, it's the best part of 20 years since I used ioctl on a serial device (: Off to google nmea and usb! Steve
