AP_Mission: do not use float functions on integers

[peterbarker]

pitch is int8_t, yaw is int16_t

Completely untested. Well, CI will make sure it compiles.

[IamPete1]

This must be correct. But I do wonder if this means were missing the NaN check on the command write. The incomming MAVLink could be NaN here:

ardupilot/libraries/AP_Mission/AP_Mission.cpp

Lines 1360 to 1367 in 748fe53

	case MAV_CMD_DO_GIMBAL_MANAGER_PITCHYAW:
	cmd.content.gimbal_manager_pitchyaw.pitch_angle_deg = packet.param1;
	cmd.content.gimbal_manager_pitchyaw.yaw_angle_deg = packet.param2;
	cmd.content.gimbal_manager_pitchyaw.pitch_rate_degs = packet.param3;
	cmd.content.gimbal_manager_pitchyaw.yaw_rate_degs = packet.param4;
	cmd.content.gimbal_manager_pitchyaw.flags = packet.x;
	cmd.content.gimbal_manager_pitchyaw.gimbal_id = packet.z;
	break;

Presumably if NaN the intended behavior would be that it is not used. So we could set to a out of range value so it is ignored via the abs. I guess we would also have to return a NaN in the MAVLink read....

edit: It looks like NaNs are not in the spec, so we might be OK. https://mavlink.io/en/messages/common.html#MAV_CMD_DO_GIMBAL_MANAGER_PITCHYAW

[peterbarker]

This is probably the wrong way to fix this. We should probably add a uint8_t field_invalid field to struct PACKED gimbal_manager_pitchyaw_Command.

We have the same problem with the handle-rate-commands block below the one I've modified here.

[rmackay9]

I'm pretty sure that the caller is meant to set the unused fields to NaN

[tridge]

a simple change would be to use -128 as a magic value meaning invalid for int8 rates, and set to -128 for NaN in the mavlink msg. If someone asks for -128 then instead set -127

[nexton-winjeel]

@IamPete1:

edit: It looks like NaNs are not in the spec, so we might be OK.

It's in the message description, not the field descriptions.

MAV_CMD_DO_GIMBAL_MANAGER_PITCHYAW (1000)

Set gimbal manager pitch/yaw setpoints (low rate command). It is possible to set combinations of the values below. E.g. an angle as well as a desired angular rate can be used to get to this angle at a certain angular rate, or an angular rate only will result in continuous turning. NaN is to be used to signal unset. Note: only the gimbal manager will react to this command - it will be ignored by a gimbal device. Use GIMBAL_MANAGER_SET_PITCHYAW if you need to stream pitch/yaw setpoints at higher rate.

[peterbarker]

We currently bounce NaN values in mission upload. The Mount backend doesn't cope if either value is NaN.

I've created a branch which preserves NaN values in storage using INT8_MIN and INT16_MIN, but I reckon that's probably just a waste of flash space at this point.