mission: write next mission item into pos_sp_triplet->current if current mission item did not have position

[ndepal]

Fixes #13668

I was only able to reproduce the issue described when the drone is already flying.

The problem is that, if a new mission begins and it's first item is a command, Mission::set_mission_items() will not write to pos_sp_triplet->current, but that was marked invalid by reset_triplets().

FlightTaskAuto then goes into failsafe.

https://github.com/PX4/Firmware/blob/master/src/modules/mc_pos_control/mc_pos_control_main.cpp#L564-L567

Additionally, depending on timing, the takeoff state machine uses NAN constraints to update its state, causing the state machine to fail to progress, which then makes it impossible to detect landing (we will make have a separate PR to guard against that: #13973).

https://github.com/PX4/Firmware/blob/master/src/modules/mc_pos_control/mc_pos_control_main.cpp#L598

[dagar]

Thanks for fixing this and the daily reminder that navigator complexity is really becoming untenable.

I understand the specific fix you described, it's just not clear to me how we ensure navigator isn't filled with more of these cases.

[dagar]

Trivial style failure in CI. http://ci.px4.io:8080/blue/organizations/jenkins/PX4%2FFirmware/detail/PR-13971/1/pipeline

[ndepal]

I understand the specific fix you described, it's just not clear to me how we ensure navigator isn't filled with more of these cases.

Yes, seems almost impossible.

Trivial style failure in CI.

I'll fix it on Monday.

[ndepal]

Fixed the style issue and rebased on master.

[julianoes]

I understand the specific fix you described, it's just not clear to me how we ensure navigator isn't filled with more of these cases.

I agree :(

[ndepal]

With #14020 merged, I believe the problem of the flight task going into failsafe no longer happens. So this fix is less critical. However, I still think the mission should not publish a current.valid == false triplet.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.