>> I have noticed skipped 1PPS on the Adafruit GPS also. > > I've always assumed this could happen but as a result of RF signal loss not > a glitch in the gps. So I've started recording event timestamp deltas
To be clear, we are not talking about a system-wide GPS problem here; the satellites are fine. All my other GPS receivers are fine. It's just one particular GPS receiver board that Bob, and now Bob and I, are questioning. > using the Linux kernel PPS interface. I read assert events (e.g. > 1398449188.001000242#1741672) and compute timestamp and event deltas. If > the t delta is < .9 something horrible must have happened and if it's > 1 > some didn't happen assuming the event count delta is always 1. > > I wonder if this is a reasonable approach or if I'm being lazily > optimistic. I just started (and I haven't added a join with the valid fix > indicator yet) but I've had two missing pulses in the last 24 hours. Sure, that's reasonable. I'm using a 53132 TIC to compare my house atomic 1PPS (start) against the Adafruit GPS 1PPS (stop) and so no timestamping is even necessary: the readings themselves tell you if there is a missed pulse. For example, you get TI readings like 0.0000000nn for hours or days and then once in a while you get a 1.0000000nn or 2.0000000nn, indicating a missed pulse. After Bob Stewart's first mention of the Adafruit Ultimate GPS board, I dug out mine and collected 30 days of data to see if I could duplicate or understand his measurements. As usual, a simple and quick test has turned into something more complicated and perplexing. I'll share some results maybe next week. The test is now multiple GPS boards, antennas, and counters. /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.
