secure bootloader preserve custom data in flash during DFU

[vist]

I noticed that the secure bootloader by default protects bond information during FOTA. In earlier SDK versions there was something called preserved pages right below the bootloader in memory but I can't find it in SDK v15.1. 

How do I preserve my custom data during FOTA?

[Einar Thorsrud]

Hi,

You can reserve more flash pages by modifying the definition of DFU_APP_DATA_RESERVED in nrf_dfu_types.h. By default, 3 pages is set aside, which matches the 3 pages typically used for FDS in most BLE examples in the SDK.

[vist]

Thank you for your answer. I have some follow up questions.

If I want to be able to have about 80 bonds simultaneously I need all those three pages for bond information according to https://devzone.nordicsemi.com/f/nordic-q-a/34879/flash-memory-and-bonding-data-from-peer-manager

What do I need to change in order to add 2 pages of personal data to be stored by the FDS in addition to changing the DFU_APP_DATA_RESERVED?

[Einar Thorsrud]

Hi,

The size of each bond can varya byt, but a typical bond with one CCCD requires 38 words (152 bytes). This means that you need at least 3 FDS virtual pages (assuming 1024 words per page) for data in order to get abot 80 bonds, so you need to set 4 in total. If you need to store additional data (you wrote 2 pages), then it totals to 6 pages.

To achieve this, set FDS_VIRTUAL_PAGES in the projects sdk_config.h to 6 and set DFU_APP_DATA_RESERVED in nrf_dfu_types.h to resolve 6 pages as well (so that the bootloader stays away).