To answer about how they get good timing. Many times you run a loop that runs off a timer at say exact 1000 times per second. Having something like a 1KHz loop gives very deterministic timing. Lots of ways to do it. One is to run some RTOS. I had to make all the axis of a machine tool move at exact timing to cut a curve. Not hard just have decide to do it. I'm sure most engineers looked at the NMEA spec and read "with the second" and stopped at that.
> On Jul 20, 2016, at 5:40 PM, Bob Camp <[email protected]> wrote: > > HI > >> On Jul 20, 2016, at 7:51 PM, Mark Sims <[email protected]> wrote: >> >> I added the ability of Lady Heather to calculate the time offset of the >> timing message from "wall clock" time. It calculates the difference between >> the system clock time to the time that the (end of) the timing message >> arrived. The result is only as good as your system clock, so the system >> clock really needs to be synced to something like NTP (otherwise it does a >> decent job of showing how much your system clock is drifting). Heather can >> plot the results and calculate xDEVs on both the message jitter and the >> message offset time in real time. >> >> On another note, I did some jitter measurements on Jupiter-T and Jupiter-T >> Pico receivers. I can't imagine how they do it, but those things are >> insanely good. Running at 9600 baud, their message jitter into a hardware >> serial port is less than a millisecond peak-peak! Somebody paid a LOT of >> attention to getting the message timing consistent… > > Just pre-load it all into a big shift register and let the PPS output gate > the clock to the beast. There’s not a lot of doubt about what the label on > the next second going out will be :) > > Bob > >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
