FDS record write lock

[Tim Adu]

Hello,

I am experimenting with the Flash Device Storage (FDS) API. Specifically, I'm using the nfc_writable_ndef_msg project as a starting point. It's a really good example.

I would like to eventually use the FDS to store the device serial number as a record (this should be generated only once and stored in flash forever). How can I use the FDS (or other means) to ensure that this particular record never gets erased (especially when a firmware update is done)?

Thanks.

[Kenneth]

Hi,

My suggestion is that persistent data that never is changed can be stored to UICR (without FDS).

Best regards,
Kenneth

[Tim Adu]

Thanks Kenneth.
1. Is it possible to use the FDS mechanism to write to UICR? Or would you simply use the low level functions?
2. Any examples/references you could point me to?
3. How do I program the chip (nrf52840) without wiping the UICR?

[Kenneth]

1. You would need to use low level functions yes.

2. I believe fstorage example should show this, it also depends on whether the softdevice is enabled or not at the time. 

3. Don't use --eraseall or --eraseuicr after UICR is programmed with the configuration you want to keep.

Best regards,
Kenneth

[Tim Adu]

Great! I think I have all I need. You mentioned that the usage of  fstorage depends on whether softdevice is enabled or not.
1. What impact does softdevice have on fstorage?

2. Any considerations I need to have in mind when I want to implement DFU/OTA while also keeping UICR data intact?

[Kenneth]

Hi,

When softdevice is disabled, you have direct control/access to the NVMC of the nRF52840, and all flash operations will be executed directly. While when the softdevice is enabled, then all flash operations will be scheduled:

https://infocenter.nordicsemi.com/topic/sds_s140/SDS/s1xx/flash_mem_api/flash_mem_api.html?cp=3_4_2_0_7

DFU/OTA don't alter UICR no.

Best regards,
Kenneth