MAV_PROTOCOL_CAPABILITY_FLIGHT_TERMINATION - improve linking to command

[hamishwillee]

MAV_PROTOCOL_CAPABILITY_FLIGHT_TERMINATION this explicitly names the supported command. That both removes any ambiguity about the command (were there to be one in future) and also creates a link in the documentation.

Note that we probably shouldn't have wasted a protocol bit on this. It isn't needed - you could just sent the command with param1=0 and the vehicle should not terminate, but should ACK to indicate that it understand the command.

[hamishwillee]

We should define what flight termination means:

• ArduPlane https://ardupilot.org/plane/docs/advanced-failsafe-configuration.html#afs-termination
• PX4: https://docs.px4.io/master/en/advanced_config/flight_termination.html#flight-termination-configuration
• ArduCopter?

On PX4 the FC sets failsafe values, which for FW attempt a glide land, and for MC just turn off all motors. You can also trigger things like a chute off unused ports. On ArduPlane Plane it looks like this does similar, but not clear what Copter does

I think the common story here is that the vehicle will immediately land and that this operation cannot be reset until the vehicle has landed? Anything much else that can be said? I'd like to mention turning off motors if both platforms do that.

@auturgy @julianoes Otherwise OK?

[julianoes]

I think the common story here is that the vehicle will immediately land

I would not call it land although it will eventually "land" on the ground. In my mind termination is something like parachute, fixed bank angle, or drop like a stone. Otherwise you could just tell it to "land" which would be more graceful.

[hamishwillee]

Agreed by @auturgy too (offline). Merging.

@julianoes I think I assigned you a bug in PX4 to match to this behaviour (last week).