RE: Methods to put the nRF52 to sleep in a "spinlock loop"

m.wagner — Thu, 03 Sep 2020 14:54:22 GMT

I only posted the question in the community forums, but there was no satisfying answer, unfortunately.

RE: Methods to put the nRF52 to sleep in a "spinlock loop"

dfer — Thu, 03 Sep 2020 14:03:39 GMT

I would be interested to know what Arm replied.

RE: Methods to put the nRF52 to sleep in a "spinlock loop"

m.wagner — Fri, 28 Jun 2019 09:20:47 GMT

Thank you. I'll try to contact ARM to get a statement for first question.

RE: Methods to put the nRF52 to sleep in a "spinlock loop"

Einar Thorsrud — Fri, 28 Jun 2019 09:16:06 GMT

Hi,

This is a bit intricate, so I have discussed it with a few colleagues before answering. I suggest you ask ARM directly if you need more details.

[quote user=""]An IRQn will only set the event register if it changes from "not pending" to "pending". (e.g. if a RADIO IRQ occurred but was not served (i.e. the pending bit was never cleared), and then a second RADIO IRQ occurrs, the event register will not be set.[/quote]

This is a good question. This is in line with my understanding, so I believe you are correct. I cannot guarantee it, though.

[quote user=""]__WFI-based sleep needs masking interrupts when a flag is set from the IRQ_Handler.[/quote]

I believe you are correct. We do not use WFI in the SoftDevice though and have less experience with it.

[quote user=""]Relevant interrupts must not be masked when using __WFE-based sleep, otherwise the system may not wake up.[/quote]

Yes. If you use buy_flag that is set form higher priority, then you cannot mask the interrupts that set the busy_flag.

[quote user=""]Care must be taken on the order of __WFE and __SEV calls in any case...[/quote]

Yes. So the code snippet you have under the "WFE-based sleep function (wrong)" heading is definitely wrong.

[quote user=""]The more elaborate sleep function with __WFE(); __SEV(); __WFE(); is a power optimisation, requiring one loop iteration less to go to sleep than just calling __WFE();[/quote]

Yes.