SFY variant with external UBLOX GPS

gauteh commented 1 month ago

Implements #170 .

gauteh commented 1 month ago

gauteh commented 1 month ago

@edwinrainville (and also @jerabaul29 if you are interested? :)), I'm trying to think of a sub-millisecond sync algorithm:

Ublox PVT updated ( 20 Hz)
Ublox PPS -> ext-gps-mod
pps_time = ext-gps-mod.micros()
ext-gps-mod PPS -> SFY
SFY: stores sfy_pps_time: for incoming PVT telegram
read_time = ext-gps-mod.micros()
ext-gps-mod reads PVT related to PPS. Is the T updated or is it fixed to the PPS? maybe all of this is fast enough to ignore.
ext-gps-mod push PVT to SFY + (read_time - pps_time)
sfy_read_time = sfy.micros()/RTC
SFY reads PVT related to PPS
SFY sets local time to T + (sfy_read_time - sfy_pps_time)

Does that make sense? I have PPS working on the arduino-code, not yet on SFY. We need the synchronization to match IMU and GPS timeseries.

gauteh commented 1 month ago

According to 12.1.8 the maximum jitter of the RTC is 1 ms for XR crystal, or 8 ms for LFRC, which is good enough.

gauteh / sfy