In message <2370.202.27.185.71.1083729519.squirrel(a)www.crypt.gen.nz>, "Kerry Tho mpson" writes:

Simon Blake said:

...

Setting up a GPS NTP source has been on the list of things I've wanted to get done for a while now - I've got several rooftop mounted PC's that have stunning views of the heavens. [....]

Dick Smiths have a usb GPS receiver ( http://www.dse.co.nz & search for XH6831 ) which uses the standard NMEA protocol over what seems to be an emulated serial port.

IIRC that GPS receiver doesn't do PPS (pulse-per-second). Without pulse per second you can't get NTP-accurate time out of a GPS -- there's just too much jitter in the timing reports. (NMEA output is fairly slow (9600bps?) and in many GPSes they don't even treat the NMEA output as a high priority, so it's only "near the second" not on starting on the second.)

From what I remember most GPSes under about $400-$500 won't do PPS, and some of the more expensive ones don't either. I think there are some models around the $500-$600 range which will do PPS, but I don't recall which ones off hand.

Ewen