feat: add trainer virtual switch

[3djc]

Asked for on RCGroups

This provide a virtual switch indicating when a trainer link is active.

The switch is functionality does not depend of trainer type (all work), and can only be ON on the master radio (as the slave radio has no way to know if a master is listening to it)

[elecpower]

Is there any need to write this to yaml as I interpret it as being a condition and there is no need for persistence?

[3djc]

I think there is a need for yaml:

you can also use it to change rates for example when trainer is active

[elecpower]

Use cases help my understanding. Therefore if

can only be ON on master radio (slave radio have no way to know if a master is there listening to it)

then should the switch not be listed/available when trainer mode set to slave?

[3djc]

I wondered about that too, but I felt there was more risk of confusion if a switch was to disappear based on trainer setup (especially in mixers lines). If you are slave, it will just never come true, but remains valid nonetheless

[pfeerick]

I tried the hard-wired trainer on X9D+2019, TX16S and Zorro, with a special function that beeps while the trainer is active... worked perfectly, as well as companion read/write. So now I get some form of audio prompt when the trainer connects, while it's active, and when it disconnects (if the audio files are present).

I just had a thought... we protect the user against being able to power down while USB connected or a telemetry RF link active... but not with the trainer active? Something to think about?