Switch into last mode after landing and disarming after RTL/Land

[AmeliaEScott]

Describe problem solved by the proposed pull request
Closes #12354 .

Test data / coverage
Ran several missions in SITL, starting from every non-auto mode. After landing (Either via RTL or just landing in place), I verified that the mode returned to the most recent non-auto mode.

Describe your preferred solution
After an RTL or Auto Landing, and after disarming, the Commander will now automatically switch to the last mode that was used before the auto mission. For example, if the sequence of modes is:

Position -> Auto Mission -> Auto RTL

After the landing and disarming, it will switch back to Position.

[julianoes]

I think that's all correct except that one comment.

[Antiheavy]

How will this effect battery swaps in Qgroundcontrol? When flying a large survey mission, it is common for low battery failsafe to trigger and the vehicle executes RTL (Return Mode).

[AmeliaEScott]

@dakejahl I didn't realize rebasing would dismiss your review. I haven't made any more changes, so this should still be ready to go!

[dakejahl]

I have such mixed feelings about rebasing lol

[bkueng]

If a user switches to mission again within MISSION_FINISH_DISARM_TIMEOUT, it will be true again, so the comment is not quite right.
Since the timeout is 500ms, the logic should be fine, but I'd be more comfortable if multiple triggering of this is prevented (for example we might have to increase MISSION_FINISH_DISARM_TIMEOUT for some reason).

How does COM_DISARM_LAND matter for this?

[julianoes]

How does COM_DISARM_LAND matter for this?

I think it won't work if COM_DISARM_LAND is bigger, right? Because too much time has lapsed by the time it disarms.

[AmeliaEScott]

I changed this to not rely on timing. Now, it just makes sure all of the following conditions are met:

• The vehicle just now disarmed
• The vehicle is currently landed
• The current mode is an auto mode
• The current mission is finished

Here's the code:

bool just_disarmed = !armed.armed && was_armed;
bool just_finished_auto_mission = is_auto_state(internal_state.main_state) && _mission_result_sub.get().finished;
bool last_state_valid = last_non_auto_state != commander_state_s::MAIN_STATE_MAX;

if(just_disarmed && land_detector.landed && just_finished_auto_mission && last_state_valid){
	PX4_INFO("Just finished auto mission, transitioning back to last manual mode.");
	main_state_transition(status, last_non_auto_state, status_flags, &internal_state);
}

Is this sufficient? Or did I miss some edge case?

[hamishwillee]

When this goes in, can you ping me. Probably should be documented in the land/return mode docs.

[LorenzMeier]

If you do two consecutive RTLs this stays in the first non-auto state and will switch back to the manual mode in the first RTL, even if the second RTL was triggered out of an auto state. You need to reset the state in an else statement to not have history in your state machine.

[AmeliaEScott]

Let me make sure I understand correctly: If you have the sequence, for example, Manual -> Mission -> RTL -> Mission -> RTL, then it will switch back to Manual after the final RTL completes. Should it not do this? Under what circumstances exactly should it not switch back to a manual mode after an RTL?

[julianoes]

I guess what @LorenzMeier means is that in this case it should switch back to Mission for this case.

This would mean the check should be for any mode that is not RTL, instead of non-auto mode.

@LorenzMeier can you confirm please?

[LorenzMeier]

My expectation would be here that it switches back to the mode it had before RTL, not the last manual mode before RTL - otherwise I could have been through a number of mission - RTL - mission - RTL sequences and be left with the manual mode from an hour ago

[stale]

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

[julianoes]

This is pending a comment by @LorenzMeier.

[LorenzMeier]

What Problem is this PR trying to solve?

[MischaZihler]

What Problem is this PR trying to solve?

when landed after an RTL, PX4 requires to be switched back to a flight mode manually, before being able to take off. IMO this is confusing. I would expect it to be ready for take off, after the RTL command is finished.

[stale]

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

[LorenzMeier]

Closing as stale.