fix: Internal PXX exclusive S.PORT

[raphaelcoeffic]

This PR is meant to solve the issue caused by the shared S.PORT line between internal and external module on FrSky radios. The internal module on these radios take the S.PORT line in ownership when turned ON, and there is no way to turn it OFF.

Summary of Changes:

• Force release S.PORT owned by the external module when a PXX1 internal is turned ON.
• Re-Init external module (if powered ON) when a PXX1 internal module is turned OFF.
• MPM: automatically send "disable telemetry" if S.PORT is not owned by the MPM.
• PXX1 external module: automatically send "disable telemetry" if S.PORT is not owned by this module.
• Fixes to improve conflict detection between different drivers using the same pins (USART / timers).

Please note: In case an external module uses S.PORT both for TX and RX (CRSF, GHOST), the initialisation of the internal module will fail. The UI should prevent this with the existing code.

PXX2 internal modules:

• It seems that latest ISRM firmwares (tested with 2.1.9 EU on X10 Express) do not clog S.PORT anymore,
• Express LRS / MPM seem to work normally in parallel with ISRM switched ON (both receivers connected).

[3djc]

Tested on X7 with internal XJT and external multi, each having a receiver connected to it:
what works:

• individual (only one module on) module bind and use
• both module at the same time (telemetry from receiver is logicaly received from XJT connected receivers)

what doesnt:
turn radio with both module on, turn off XJT, multi doesn't get back telemetry
turn radio with only MULTI on, turn on XJT, multi telem doesn't get cut and is corrupted
turn raido with both modules on, turn both module off, turn multi on, displays: no telemetry

[raphaelcoeffic]

Ok, so I'll to check it out with real hardware. Maybe I can add some unit tests for MPM and see how that goes.

[pfeerick]

I'm having trouble with the MPM here. Before this PR, with X9D+2019 (ISRM) + external MPM, I could use both MPM and ISRM simultaneously... just the MPM telemetry would get cut. As soon as I load this PR, I can not get the MPM telemetry up, regardless of whether the ISRM is on or off.

[raphaelcoeffic]

As soon as I load this PR, I can not get the MPM telemetry up, regardless of whether the ISRM is on or off.

I'm having issues understanding this. This PR does not change PXX2 handling, nor should it change anything in the MPM behaviour in your specific case. There must be something big I missed here.

[pfeerick]

I'll try this again today, and also double-check against main to make sure the issue isn't actually there.

[pfeerick]

Both nightly and the latest rebase are fine on X9D+2019 (ISRM) now. 🤷 I've also tried on the X9D+ now with this PR, and gone through all three of JCs failure cases and they are working for me. It's nice to see the prompt about disabling internal RF rather than just "no telemetry".

[pfeerick]

A further enhancement that would be worth considering (since you mentioned CRSF;GHOST) would be for it to be somehow blocked - whether unelectable or error msg shown - until internal RF is disabled (since it will effectively kill internal RF if you enable GHOST after the internal RF is enabled - which you can do still on the X9D+ - you just can't enable the internal RF after enabling GHST). The internal RF is also currently not re-enabled if it was originally active, and GHOST is then enabled. and disabled. I've not tried with CRSF, but assume it would be the same.