[WIP]: GPS clock set time updates

[dagar]

WORK IN PROGRESS - opening early for discussion and testing

• remove drivers/gps set clock callback
• drivers/gps try to set sensor_gps timestamp_sample as closely as possible
• move mavlink timesync to new lib/timesync library
• sensors/vehicle_gps_position consume all sensor_gps sources and determine time GPS utc time offset using lib/timesync
• once time offset is stable update system clock if sufficiently different
• updated hrt ts_to_abstime and abstime_to_ts to work relative to CLOCK_REALTIME
• increase drivers/gps priority to reduce timing jitter

Requires PX4/PX4-GPSDrivers#90

TODO

• review mavlink timesync and test (thresholds may need to be configurable for different usage)
• improve hrt and time update helpers (critical sections, minimize error)
• review EKF2 GPS delay? ublox timestamp_sample has shifted by more than 10 milliseconds (closer to truth)

[ShiauweiZhao]

maybe we can support gps 1pps signal to Correct time?This allows for more accurate timing

[dagar]

maybe we can support gps 1pps signal to Correct time?This allows for more accurate timing

That's also coming, although it's handled much lower level.

[ShiauweiZhao]

I have the hardware to support 1pps and can do 1pps development, but I'm not quite sure how to combine it with timesync at the moment.

[kaklik]

I have the hardware to support 1pps and can do 1pps development, but I'm not quite sure how to combine it with timesync at the moment.

Hi! I am interested in your hardware solution to handle the 1PPS signal from the GNSS receiver. We currently solved that at a payload level. By allowing the payload to read out the PPS signal from GPS and GPS time data. We are using that to connect, the measurements done by payloads to precise absolute time. An improvement could be done, in the case of uLog file has precise GNSS time data also.

[dagar]

@kaklik as a start did you see #18849?