PPI with WFE/WFI

RE: PPI with WFE/WFI

Einar Thorsrud — Wed, 15 Nov 2023 14:30:17 GMT

See this post.

RE: PPI with WFE/WFI

pungent1188 — Wed, 15 Nov 2023 13:29:42 GMT

Why is __WFE needed twice? Wouldn't that mean losing first event?

RE: PPI with WFE/WFI

eric ding — Mon, 14 May 2018 10:42:04 GMT

Got it. Big thanks.

RE: PPI with WFE/WFI

Einar Thorsrud — Mon, 14 May 2018 08:44:21 GMT

The difference between WFI and WFE is described in the ARM Cortex-M4 Devices Generic User Guide. Interrupts also cause wake-up from WFE, so WFE and WFI can be used interchangeably in most cases. Note that SEV can be used together with WFE as shown below to ensure that the device goes to sleep also when the event register is already set.

Most SDK examples and the SoftDevice use code similar to this to go to sleep:

// Make sure the event register is cleared
__SEV();
__WFE();
// Enter System ON sleep mode
__WFE();

RE: PPI with WFE/WFI

eric ding — Mon, 14 May 2018 07:50:19 GMT

okay, understood, thanks.

Then , one more question, what's the difference between WFI and WFE in the nRF serial platform?

or in which case should the WFI be used and in which case using WFE?

Thanks

Eric

RE: PPI with WFE/WFI

Einar Thorsrud — Mon, 14 May 2018 07:45:22 GMT

Yes, that is correct. The CPU will only we waken up if there is an event and the event is configured to generate an interrupt in the INTENSET register.

RE: PPI with WFE/WFI

eric ding — Mon, 14 May 2018 07:37:09 GMT

Hi Einar,

Either the CPU is halted by WFI or WFE, as long as the event is not enabled and connected to NVIC, the CPU will not be woke up, is this the correct understanding?

Thanks.

Eric.

RE: PPI with WFE/WFI

Einar Thorsrud — Mon, 14 May 2018 07:25:20 GMT

Hi Eric,

PPI is independent of the CPU and will not wake up the CPU. However, the same event that can be connected to a PPI channel can also be configured to generate an interrupt if you want to wake the CPU. The figure in the beginning of the Peripheral interface chapter in the Product specification shows how this is related.

Cheers,

Einar