* feat(pps_capture): allow selecting GPS receiver by device ID
Add PPS_CAP_GPS_ID parameter to select which GPS receiver's data
is used for PPS timestamp correlation. Matches by device ID rather
than uORB instance index, which avoids dependence on instance ordering.
When set to 0 (default), uses the first available instance for
backward compatibility.
* docs(pps_capture): document PPS_CAP_GPS_ID for multi-GPS setups
* fix(pps_capture): use GPS_MAX_RECEIVERS constant and mark PPS_CAP_GPS_ID reboot-required
If the PPS GPIO is exposed to a signal with high frequency changes, a lot of
interrupts are scheduled and the handling of these calls can worst-case
starve flight critical processes leading to a loss of
control. Since PPS is not flight critical, we now give up the PPS
functionality and stop the interrupts to prevent the starvation of other processes.
The existing implementation has about 100ms difference to a reference clock. With the changes this error less than 25us.
- Use sensor_gps messages with hrt timestamps as RTC reference and not the system realtime clock. The PPS interrupt can then be aligned with the GPS clock system.
- Keep fallback based on system RTC when no PPS pulse was captured
