Px4-autopilot: Remove Mixer from PX4IO; Use Only Direct PWM Passthrough

[JacobCrabill]

(Placeholder for discussion on this topic)

Describe problem solved by the proposed feature
The PX4IO processor is running out of memory (particularly for large mixer files)

Describe your preferred solution
A possible solution is to remove the mixer from px4iofirmware, and instead use direct pwm control from the FMU, rather than sending actuator controls.

An example of this direct pwm control can be seen in the 'test' portion of the 'pwm' systemcmd.

Additional context
Other benefits of this change include simpler debugging of PWM outputs, as all mixing input/output would be available for viewing on the FMU.

Also worth noting is that this method is used by ArduPilot, which further leverages this by allowing the mixer mapping to be defined via run-time parameters, rather than baked-in mixer files.

[mrpollo]

📌Subscribed

[dlwalter]

This would be fantastic. Currently using 8 simple mixers as a passthrough from an FMU mixer but there's all sorts of weirdness with NANs indicating disarmed that need to be handled and passed correctly.

[jlecoeur]

Related PR: https://github.com/PX4/Firmware/pull/13581
This adds a pass-through mixer, with the short term goal to make it possible to do mixing on either FMU or IO, and longer term goal to move features from IO to FMU.

[stale[bot]]

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