> Now I am confused. I thought it used the internal crystal clock for > the timing, and selected which pulse to output for the 1PPS, and > this is what causes the sawtooth. If so, the timing is determined by > the crystal.
Correct. For example, if the xtal were 20.00 MHz then the hardware timing pulse could be off by up to +/- 25.00 ns from the nominal value. But the firmware knows approximately how far off, and so it outputs this value as a correction message. The correction is not perfect, but if used, is always better than hardware alone. > I don't use software to correct the sawtooth. It is a whole new way > of locking to the 1PPS. You might want to check out James Miller's excellent GPSDO. His simple design also does not use sawtooth correction and the results are very good. See: http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm http://www.leapsecond.com/pages/gpsdo/ http://www.febo.com/pages/oscillators/g3ruh_gpsdo/ /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.