cortex-m 0.7.8

Low level access to Cortex-M processors
Documentation 
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use critical_section::{Impl, RawRestoreState, set_impl};

use crate::interrupt;
use crate::register::primask;

struct SingleCoreCriticalSection;
set_impl!(SingleCoreCriticalSection);

unsafe impl Impl for SingleCoreCriticalSection {
    unsafe fn acquire() -> RawRestoreState {
        // Backup previous state of PRIMASK register. We access the entire register directly as a
        // u32 instead of using the primask::read() function to minimize the number of processor
        // cycles during which interrupts are disabled.
        let restore_state = primask::read_raw();
        // NOTE: Fence guarantees are provided by interrupt::disable(), which performs a `compiler_fence(SeqCst)`.
        interrupt::disable();
        restore_state
    }

    unsafe fn release(restore_state: RawRestoreState) {
        // NOTE: Fence guarantees are provided by primask::write_raw(), which performs a `compiler_fence(SeqCst)`.
        unsafe { primask::write_raw(restore_state) };
    }
}