Comment 10 for bug 1722849

Regarding the "intrinsic" functions for getting the PRIMASK or for setting/clearing the PRIMASK, I should have probably used the term "builtin functions" for the GNU-ARM, such as the collection listed at https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html. Unfortunately, the built-in collection has no functions for getting/setting the PRIMASK or for setting/clearing it.

The CMSIS functions __get_PRIMASK(), __disable_irq() and __set_PRIMASK() are not really "built in", because they are simply defined by means of in-line assembly in the "cmsis_gcc.h" header file. Therefore they don't work.

Quite specifically, the following textbook recipe for disabling interrupts by "saving and restoring" the interrupt context (PRIMASK in this case) will NOT work:

/* critical section (save and restore interrupt status) -- DOES NOT WORK! */
#define CRIT_ENTRY(primask_) do { \
    (primask_) = __get_PRIMASK(); \
    __disable_irq(); \
} while (0)

#define CRIT_EXIT(primask_) __set_PRIMASK((primask_))

--MMS