====== Power Management ======

[[https://devzone.nordicsemi.com/f/nordic-q-a/10424/nrf51422-won-t-sleep#post-id-58214]]
===== WFE =====
**Wait For Event**

It is only hint and depends on implementation.
The ''WFE'' instruction allows (but does not require) the processor to enter a low-power state
until some event occurs such as a ''SEV'' being issued by another processor.

If the Event Register is not set, WFE suspends execution until one of the following events occurs:
  * an IRQ interrupt, unless masked by the CPSR I-bit
  * an FIQ interrupt, unless masked by the CPSR F-bit
  * an Imprecise Data abort, unless masked by the CPSR A-bit
  * a Debug Entry request, if Debug is enabled
  * an Event signaled by another processor using the SEV instruction.
If the Event Register is set, WFE clears it and returns immediately.
If WFE is implemented, SEV must also be implemented.

===== SEV =====
**Set Event**

Generates a SEV (send a global event) hint instruction.

''SEV'' causes an event to be signalled to all cores within a multiprocessor system.
It is a NOP on a uniprocessor system.
If ''SEV'' is implemented, ''WFE'' must also be implemented.