l0calh05t What happens if you set a board that isn't present / available (i.e., Bela when only a Beast/Face is used or BelaMini on a Bela)?
it will fail and not start. See https://github.com/BelaPlatform/Bela/blob/master/core/RTAudio.cpp#L452-L479
l0calh05t Ok, but can any value in [0, 128) actually be used? What if something else is assigned to the pin as well?
It will let you do that ... if you end up picking one of the pins that the Bela Digital channels are on and you set it to an output, this will affect the readings, but if it's used as an input, it will work. There are no checks to avoid any such clashes, we just make sure it doesn't crash. It's up to the user to select a pin that makes sense. Again, most likely this is just for those who want to spin their own board or something like that, not really for day-to-day usage ...