Good insight! I guess I don't really understand why we can't use native types then. I don't want to keep having to write these:

  pub fn fir_q31(
    s: &mut sys::arm_fir_instance_q31,
    input: &[i32],
    output: &mut [i32],
    block_size: usize,

    compiler_fence(Ordering::SeqCst);
    unsafe {
        sys::arm_fir_q31(s, input.as_ptr(), output.as_mut_ptr(), block_size as u32);
    }
}