# 9. Miscellaneous instructions

- nop() `pass` no operation.

- wfi() Suspend execution in a low power state until an interrupt occurs.

- cpsid(flags) set the Priority Mask Register - disable interrupts.

- cpsie(flags) clear the Priority Mask Register - enable interrupts.

- mrs(Rd, special_reg) `Rd = special_reg` copy a special register to a general register. The special register may be IPSR (Interrupt Status Register) or BASEPRI (Base Priority Register). The IPSR provides a means of determining the exception number of an interrupt being processed. It contains zero if no interrupt is being processed.

Currently the `cpsie()` and `cpsid()` functions are partially implemented. They require but ignore the flags argument and serve as a means of enabling and disabling interrupts.

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