__WFE() returned even if there was no event. Can you help?

RE: __WFE() returned even if there was no event. Can you help?

Vidar Berg — Thu, 01 Jun 2023 09:18:34 GMT

__WFE() should not be called directly in Zephyr. Instead, you should let your program return to the idle thread when there is no more work to do (see System Threads).

EDIT: Note that masked interrupts can also trigger wakeup. https://developer.arm.com/documentation/dui0552/a/the-cortex-m3-processor/power-management/wakeup-from-sleep-mode

RE: __WFE() returned even if there was no event. Can you help?

thang47 — Thu, 01 Jun 2023 09:01:19 GMT

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When I use the command:
__SEV();
__WFE();
__WFE();
to enter sleep mode. Then it wakes up every 4 minutes, even though no interrupt occurs

RE: __WFE() returned even if there was no event. Can you help?

Vidar Berg — Thu, 01 Jun 2023 08:42:51 GMT

Hi,

Please describe your setup and the exact problem you are facing.

Thanks,

Vidar

RE: __WFE() returned even if there was no event. Can you help?

thang47 — Thu, 01 Jun 2023 08:06:06 GMT

Hi, I also had the same problem. Don't know if you have solved it yet?

Thanks.

RE: __WFE() returned even if there was no event. Can you help?

Vidar Berg — Tue, 23 Nov 2021 05:41:15 GMT

Interrupts which are enabled will be serviced immediately after wakeup and will therefore never be read as pending from the main context. If you want that, you either have to mask or disable your interrupt(s).

e.g.,

__disable_irq();
__WFI();

for (int8 i=-15; i<39; i++)
{

if (NVIC_GetPendingIRQ(i) == 1)
    NRF_LOG_ERROR ("Pending IRQ = %d\r\n", i);
}
__enable_irq(); // Allow interrupts to be serviced again

RE: __WFE() returned even if there was no event. Can you help?

joojoo5 — Tue, 23 Nov 2021 00:33:42 GMT

To Vidar,

Thank you for your comments.

And, I tried both __SEV(); __WFE(); __WFE(); and __WFE(); __SEV(); __WFE(); but unfortunately it didn't work.

And, I tried __WFI() as well but no luck.

As you can see my original question, after __WFE() there is no pending IRQ.

I still don't understand why it went out from the __WFE() or series of __WFE() or __WFI().

I think that is the key issue here.

Please assist.

Thanks.

RE: __WFE() returned even if there was no event. Can you help?

Vidar Berg — Mon, 22 Nov 2021 12:29:44 GMT

Hello,

The __WFE instruction needs to be executed twice to put the system in sleep after an interrupt has been serviced, please see this answer by Anders here in this post for more details: https://devzone.nordicsemi.com/f/nordic-q-a/490/how-do-you-put-the-nrf51822-chip-to-sleep/2571#2571. It looks like a __WFI might be better suited for your current implementation.

Best regards,

Vidar