On Mon, July 28, 2008 1:26 pm, Marc Balmer wrote: > * Chris Babcock wrote: >> Can those LVC units be used for as a GPS reference time source for NTP? > > Yes. They output NMEA sentences, are fully (and easily) configurable > and provide a PPS signal (which has to be turned on by sending the > unit some commands).
The ntpd NMEA driver is "atomized", meaning it will use the PPS signal if applied to the DTR pin (by default, you can specify CTS if needed). I observed on my setup that this will typically keep it synced to within 10-15 microseconds. If you don't mind voiding your warranty on the Net4501 you can solder a wire connecting the R62/R62 junction to a GPIO pin and driving that with the PPS you can get down to within about 1.5 microseconds, the limiting factor being temperature-dependent clock drift. If you really want to go nuts, you can remove the oscillator and replace it with a precision frequency source. Take a look at <http://www.febo.com/pages/soekris/>. I made my connections slightly differently, but haven't written it up yet. The oscillator hack is probably overkill when using a GPS 18 LVC, which is only specified to be accurate to 1 microsecond on the PPS. Truly impressive when for the cost of a Net4501 plus $60 US or so for the GPS 18 LVC you can get this level of accuracy. Ralph _______________________________________________ Soekris-tech mailing list Soekris-tech@lists.soekris.com http://lists.soekris.com/mailman/listinfo/soekris-tech
