Hi Very nice data !!
Hmmm….. software averaging against the MCU (or FPGA) clock source … NTP seems to get some pretty good results down into the single digit ms (or lower) doing that based on some equally jittery inputs. Looking at the data by eyeball (maybe not the best way): A 10 to 30 sample finite impulse average (boxcar) would do a lot for the result. Yes, you could get much fancier. Bob > On Jul 18, 2016, at 3:50 PM, Mark Sims <[email protected]> wrote: > > That plot was from a 12 hour run. I've done 48+ hour runs and did not see > anything strange. I'm not currently measuring the offset of the message > from the 1PPS, just the stability/jitter in the timings of the last byte of > the timing message. If the timing message offset time from 1PPS jumped, it > would show up as a spike in the message jitter (and if the offset jump was > not particularly large, would be hidden in the normal noise of the > end-of-timing-message time stamps. > > Adding the message jitter measurements to Lady Heather was a quick and dirty > 5 line code hack to investigate whether one needed a 1PPS signal to usefully > drive a clock display. So far it looks like you could easily get +/- 30 msec > stability from a cheap GPS without the 1PPS (and much better with some > software averaging)... and that is on a non-real-time, multi-tasking > operating system going through who knows how many layers of serial port > message buffering, etc. Using a dedicated micro to do the deed should be > quite a bit better. You should, of course, measure and compensate for your > chosen receiver's message offset time to the 1PPS to get an accurate time > display. > > -------------------------- > > How long did you run your tests? > _______________________________________________ > 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.
