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    //! Miscellaneous assembly instructions

    /// Puts the processor in Debug state. Debuggers can pick this up as a "breakpoint".
    ///
    /// **NOTE** calling `bkpt` when the processor is not connected to a debugger will cause an
    /// exception.
    #[inline(always)]
    pub fn bkpt() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("bkpt" :::: "volatile") },

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

                __bkpt();
            },

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

    /// Blocks the program for *at least* `n` instruction cycles
    ///
    /// This is implemented in assembly so its execution time is the same regardless of the optimization
    /// level.
    ///
    /// NOTE that the delay can take much longer if interrupts are serviced during its execution.
    #[inline]
    pub fn delay(_n: u32) {
        // NOTE(divide by 4) is easier to compute than `/ 3` is it's just a shift (`>> 2`).
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe {
                asm!("1:
                      nop
                      subs $0, $$1
                      bne.n 1b"
                     : "+r"(_n / 4 + 1)
                     :
                     :
                     : "volatile");
            },

            #[cfg(all(cortex_m, not(feature = "inline-asm")))]
            () => unsafe {
                extern "C" {
                    fn __delay(n: u32);
                }

                __delay(_n / 4 + 1);
            },

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

    /// A no-operation. Useful to prevent delay loops from being optimized away.
    #[inline]
    pub fn nop() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("nop" :::: "volatile") },

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

                __nop()
            },

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

    /// Wait For Event
    #[inline]
    pub fn wfe() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("wfe" :::: "volatile") },

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

                __wfe()
            },

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

    /// Wait For Interrupt
    #[inline]
    pub fn wfi() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("wfi" :::: "volatile") },

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

                __wfi()
            },

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

    /// Send Event
    #[inline]
    pub fn sev() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("sev" :::: "volatile") },

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

                __sev()
            },

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

    /// Instruction Synchronization Barrier
    ///
    /// Flushes the pipeline in the processor, so that all instructions following the `ISB` are fetched
    /// from cache or memory, after the instruction has been completed.
    #[inline]
    pub fn isb() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("isb 0xF" ::: "memory" : "volatile") },

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

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

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

    /// Data Synchronization Barrier
    ///
    /// Acts as a special kind of memory barrier. No instruction in program order after this instruction
    /// can execute until this instruction completes. This instruction completes only when both:
    ///
    ///  * any explicit memory access made before this instruction is complete
    ///  * all cache and branch predictor maintenance operations before this instruction complete
    #[inline]
    pub fn dsb() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("dsb 0xF" ::: "memory" : "volatile") },

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

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

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

    /// Data Memory Barrier
    ///
    /// Ensures that all explicit memory accesses that appear in program order before the `DMB`
    /// instruction are observed before any explicit memory accesses that appear in program order
    /// after the `DMB` instruction.
    #[inline]
    pub fn dmb() {
        match () {
            #[cfg(all(cortex_m, feature = "inline-asm"))]
            () => unsafe { asm!("dmb 0xF" ::: "memory" : "volatile") },

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

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

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

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