Static INTERRUPT_COUNT

pub static INTERRUPT_COUNT: AtomicUsize

Reference count for the number of GPIO interrupts currently active.

This is used to determine if it’s possible for the SAM4L to go into WAIT/RETENTION mode, since those modes will not be woken up by GPIO interrupts.

This is an AtomicUsize because it has to be a Sync type to live in a global—Rust has no way of knowing we’re not going to use it across threads. Use Ordering::Relaxed when reading/writing the value to get LLVM to just use plain loads and stores instead of atomic operations.