atomic_swap_8
return (atomic_swap_8(&pwp->scratch_locked, 1));
while ((rval = atomic_swap_8(&pwp->scratch_locked, 1)) != 0) {
extern uint8_t atomic_swap_8(volatile uint8_t *, uint8_t);
__ATOMIC_OPXX(atomic_swap_8, uint8_t, "xchg" SUF_8, "q")