Power Management

https://devzone.nordicsemi.com/f/nordic-q-a/10424/nrf51422-won-t-sleep#post-id-58214

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.

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.