Current behaviour

Flight controllers can currently only have a serial connection to the Raspberry Pi via a USB port. This unnecessarily prevents connecting an autopilot via a UART using the GPIO pins, which can be useful for space-saving, as well as general accessibility (more available interfaces -> higher chance of at least one of them being appropriate for a given application).

Issue first realised in this forum post.

Expected or desired behaviour

• Ideally: all serial ports should be considered as potential autopilot candidates - not just the ones identified as USB
  • Initial attempt in core: ardupilotmanager: fix support for autopilots on non-usb serial ports #1580, although as per discussion there, that approach may only partially resolve the issue
• Minimally: support manual overrides, for users who know the path/name for the serial port their device is connected to

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.