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    //! Interrupts

    // use core::sync::atomic::{self, Ordering};

    pub use bare_metal::{CriticalSection, Mutex, Nr};

    /// Disables all interrupts
    #[inline]
    pub fn disable() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe {
                asm!("cpsid i" ::: "memory" : "volatile");
            },

            #[cfg(all(cortex_m, not(feature = "inline-asm")))]
            () => unsafe {
                extern "C" {
                    fn __cpsid();
                }

                // XXX do we need a explicit compiler barrier here?
                __cpsid();
            },

            #[cfg(not(cortex_m))]
            () => unimplemented!(),
        }
    }

    /// Enables all the interrupts
    ///
    /// # Safety
    ///
    /// - Do not call this function inside an `interrupt::free` critical section
    #[inline]
    pub unsafe fn enable() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => asm!("cpsie i" ::: "memory" : "volatile"),

            #[cfg(all(cortex_m, not(feature = "inline-asm")))]
            () => {
                extern "C" {
                    fn __cpsie();
                }

                // XXX do we need a explicit compiler barrier here?
                __cpsie();
            }

            #[cfg(not(cortex_m))]
            () => unimplemented!(),
        }
    }

    /// Execute closure `f` in an interrupt-free context.
    ///
    /// This as also known as a "critical section".
    pub fn free<F, R>(f: F) -> R
    where
        F: FnOnce(&CriticalSection) -> R,
    {
        let primask = ::register::primask::read();

        // disable interrupts
        disable();

        let r = f(unsafe { &CriticalSection::new() });

        // If the interrupts were active before our `disable` call, then re-enable
        // them. Otherwise, keep them disabled
        if primask.is_active() {
            unsafe { enable() }
        }

        r
    }

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