How to avoid interrupt handling is not missed with sd_app_evt_wait()?

RE: How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Jarmo — Tue, 07 Feb 2017 08:35:42 GMT

Thanks for comment, I have to check the documents some day :)

RE: How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Susheel Nuguru — Mon, 06 Feb 2017 18:43:52 GMT

single WFI would have been enough to make sure that it makes the chip to sleep. But then there could be race conditions with WFI. WFE is not guarenteed to sleep because of its internal event set register. You can read more about the difference in this forum or ARM infocenter. It is well documented i think.

RE: How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Jarmo — Sun, 05 Feb 2017 18:12:16 GMT

Yeah, it sounds like there's no problem with that, then. However, I don't quite understand why a single __WFE() call is not enough?

RE: How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Susheel Nuguru — Sun, 05 Feb 2017 16:41:19 GMT

please update this thread, with new info Jarmo

RE: How to avoid interrupt handling is not missed with sd_app_evt_wait()?

Susheel Nuguru — Thu, 26 Jan 2017 17:13:39 GMT

Hi Jarmo,

sd_app_evt_wait() calls wait in the sequence of __WFE() __SEV() __WFE()

This way if the interrupt happened just before calling sd_app_evt_wait, then the above sequence will not sleep because
__WFE() -> The internal event was set as an interrupt occured just before this , now the event is cleared and this _WFE does nothing, means it wont go to sleep

__SEV()-> Set the event register explicitly

__WFE-> since we set event register explicitly, this __WFE will also not do anything apart from clearing the event register.

The above sequence will also work perfectly if no interrupt happened before calling sd_app_evt_wait
__WFE()-> since no internal event is set, this will make chip go to sleep (system idle)

__SEV -> executing this means the chip has woken up now or before in other context, we are setting internal event just to make sure

__WFE -> clear the internal event and do nothing, so now we are awake and all events handled and cleared.

sd_app_evt_wait also keeps track of application interrupts forwarded and acked by softdevice. So it avoids any race condition.