sd_flash_page_erase() time execution on nRF52840

[era]

Hi!

We develop our product on nRF52840 using S113 softdevice, version 7.0.1. From time to time, we need to erase some part of flash, so we use sd_flash_page_erase() function. We measured time execution of this function and it usually takes about 50 us to be executed.

Also, there is an information in nRF52840 documentation that page erase takes 85 ms maximum.
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fnvmc.html

Does this function only schedule page erase, which is executed later in smaller parts? Is there any risk, that this function call would take much longer (e.g. 85 ms for whole page erase).

Best regards,
Michal

[era]

Thanks. After page erase scheduling, the erase is performed from priority 0, as Flash erase/write operations are defined as softdevice timing-critical. So this means that I cannot preempt this process and it takes up to 90 ms. Can anything be done about this? Or do I need to be prepared that after page erase scheduling my code can be completely halted for so long?

[Turbo J]

The nRF52840 has partial flash erase, around 1ms each time.

[era]

But does it work with softdevice enabled? I think the only way is to erase page in chunks using timeslots, right? SD has no api for partial erase.

[Turbo J]

I believe the SD already knows how to partially erase a flash page, otherwise it would be impossible in most BTLE timing setups - especially during a connection (for peer manager).

Edit: Wrong assumtion, see below.

[era]

OK. But my main problem is that after scheduling page erase with SD api, I get very high priority interrupt, which takes up to 90 ms. I try to find a workaround, because it is not acceptable for me to stop my application in random moments for so long. So to sum up:

- I have softdevice enabled (and I want it to be enabled all the time)

- I need to erase flash page from time to time

- I can't let my application to be stopped for tenths of milliseconds

Is there any workaround for this? Would erasing flash page by chunks in timeslots using NVMC api help?

[Jørgen Holmefjord]

I checked with the softdevice developers. The softdevice does not support partial page erase, and will disable all interrupts during the erase (up to 90 ms). You can implement partial erase in timeslots yourself.