This intrinsic enables IRQ interrupts.
Typically, this intrinsic enables IRQ interrupts by clearing the I-bit in the CPSR. However, for Cortex M-profile processors, it clears the exception mask register (PRIMASK).
__enable_irq 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