This intrinsic disables FIQ interrupts.
int __disable_fiq(void)
Note
On ARMv7 and ARMv7‑M, the __disable_fiq intrinsic has prototype:
void __disable_fiq(void)
__fiq returns the value the FIQ interrupt mask has in the PSR prior to the disabling of FIQ interrupts.
The __disable_fiq intrinsic can only be executed in privileged modes, that is, in non user modes. In User mode this intrinsic does not change the interrupt flags in the CPSR.
void foo(void)
{
int was_masked = __disable_fiq();
/* ... */
if (!was_masked)
__enable_fiq();
}