So. I somehow need to pass mutable references to an interrupt routine.
Option 1 is static THING: Mutex<Refcell<T>>.
Option 2 is to have a static pointer and turn it to a mutable reference within the ISR.
I'd like advice about the merits and demerits of each option. In particular, I'd like information about what code the Mutex<Refcell<T>> thingummy leads to: are both of those data-types compiled to no-ops?
Of particular note: The Mutex in this case is based on critical sections. There is only a single processor, and the “threads” in question are merely the main thread + the ISRs.