Ah! So this is an unfamiliarity issue on my part: I didn’t realize cortex_m::interrupt::Mutex has a different API than std::sync::Mutex or the various spinlock

Ah! So this is an unfamiliarity issue on my part: I didn’t realize cortex_m::interrupt::Mutex has a different API than std::sync::Mutex or the various spinlock mutices. It deliberately only provides immutability because they want you to be able to choose how to do the interior mutability yourself. Now this all seems reasonable. Tricky! (With hubris the interrupt stuff is abstracted away so you don’t need to access stuff this way, hence at least some of that unfamiliarity.)