Post #2958990
2026-03-26 15:54 UTC
You need a GPS that can also deliver PPS on a GPIO pin, or separate serial port. PPS uses a voltage rise (that causes a kernel interrupt, providing accuracy) once per second to get a measure of accurate time, in nanoseconds range, which is zero point seconds (compared to milliseconds accuracy for GPS).
That gets the time into GPSd. Getting the time into Chrony (or NTPd) was also quite painful (for me, at least).
3/x
Replies (1)
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@rune@social.intothecloud.net 2026-03-26 15:54
Chrony and GPSd use shared memory to communicate, which requires the daemons to start in a specific order, otherwise they don't talk to eachother. GPSd is supposed to send GPS on SHM0 (shared memory slot 0) and PPS on SHM1... which didn't work for me. I got GPS fine, but no PPS data. No idea why. GPSd definitely has PPS info, but wasn't sending it. 4/x