David[m]12: This is what I currently am doing

```rs
fn main() {
    // ...

    GLOBAL_STATE.lock(|s| s.borrow_mut().replace(my_t));
}

static GLOBAL_STATE: blocking_mutex::CriticalSectionMutex<RefCell<Option<&'static mut T>>> = ...;

#[interrupt]
fn PIO0_IRQ_0() {
    static mut INTERNAL_STATE: Option<&'static mut T> = None;

    let internal_state = INTERNAL_STATE.get_or_insert_with(|| GLOBAL_STATE.lock(|cell| cell.borrow_mut().take().unwrap()));

    // internal_state....
}
```

but it feels a bit dirty, so hoping someone has a better way haha