Can firmware write to FLASH directly, not using fstorage, without bothering the SoftDevice?

[riceman0]

Hello, I just want to clarify a secondary takeaway from my post:

https://devzone.nordicsemi.com/f/nordic-q-a/60714/best-approach-to-store-nonvolatile-data

I would like to confirm that we can access our nrf52832 registers to write to FLASH (ie not using nordic drivers, eg fstorage) without bothering the SoftDevice?  Meaning, will this work and do we need to be careful not to conflict with, for example, SoftDevice register actions or flash access?

Thanks.

[Jørgen Holmefjord]

Hi,

If you do not use a softdevice in your application, or the softdevice is disabled, you can access the NVMC registers as much as you want to write/erase flash.

If a softdevice is enabled, you can only do flash operations through the softdevice flash API. BLE has critical timing requirements. If the softdevice fails to handle the events within time, the radio link may be lost. During a flash write/erase operation, the CPU is halted, preventing the softdevice from handling events. 

Through the softdevice flash API, flash operations are performed asynchronously between BLE events, determined by the internal scheduler in the softdevice.

Accessing the NVMC registers directly with a softdevice enabled will likely lead to a softdevice assert.

Best regards,
Jørgen

[Jørgen Holmefjord]

Fstorage comes with two separate Backends, the softdevice backend and the NVMC backed. If you look into the softdevice backend implementation (components\libraries\fstorage\nrf_fstorage_sd.c), you will see that it uses the softdevice APIs for writing/erasing flash.

[rsoc16]

Hi, I was eavesdropping on this question because I was working through something similar. When you say

Jørgen Holmefjord said:

BLE has critical timing requirements. If the softdevice fails to handle the events within time, the radio link may be lost.

Does that mean that if the soft device is used for other things, i.e. app timers, and not ble connectivity, this is ok? I have been using the NVMC methodology for flash erase/write, while only using the soft device for my service loop (the app timer) and flash memory jumps. I have not run into any soft device asserts, which I wanted to know if it was expected or not.

[Jørgen Holmefjord]

Hi,

I'm not sure what you mean by this:

rsoc16 said:

while only using the soft device for my service loop (the app timer) and flash memory jumps

App_timer is running on RTC1, which is not related to the softdevice. Softdevice is only required when doing BLE/ANT connectivity. 

I have not tested if the softdevice will assert if you access the NVMC peripheral when the softdevice is enabled but not doing any radio-activity. Anyway, I do not see the gain from not using the softdevice API, if no other softdevice activity is scheduled, the flash operations should be granted by the softdevice quite immediately. If you do not require the features of the softdevice, I would recommend you to not enable it at all.

Best regards,
Jørgen