NRF52 Bootloader - Application Data Preserve

[Ankit Bhatnagar]

Hi,

I am using NRF52832 with secure bootloader to OTA my application in the field using Dual Bank updates and everything is working fine. In my application, I am using FDS library with 12 pages (48kb) reserved for my application data. 

I was going through the bootloader code and noticed that at some point I had set 

DFU_APP_DATA_RESERVED               (CODE_PAGE_SIZE * 0)

That would mean my FDS data should not be preserved after an OTA update. However with test I found that it definitely is being preserved. 

Confused, I look through the bootloader code, specifically where it checks the flash for space and allocates data for the new image in the function nrf_dfu_cache_prepare. From what I understood, this function does not actually delete the content of Bank 1. It simply overwrites it's content with the new image data. Since my new image size is small enough, my FDS data is not touched (but eventually will be when my new image size if big enough). 

Here is the logging information from this function

required_size: 0x199F0.
single_bank: F.
keep_app: T.
keep_softdevice: T.
SD_PRESENT: T.
Bank contents:
Bank 0 code: 0x01: Size: 0x18F30
Bank 1 code: 0x00: Size: 0x0
pass: 0.
cache add: 0x3F000.
cache_too_small: F.
keep_firmware: T.
delete_more: F.

Can someone confirm that what I have understood is correct?

[Edvin]

Hello,

NRF_DFU_APP_DATA_AREA_SIZE is set from DFU_APP_DATA_RESERVED, and is used in cache_too_small in nrf_dfu_cache_prepare.

As you say, the reason it was not erased is that your application wasn't that large that it overwrote the FDS pages. 

You should really set DFU_APP_DATA_RESERVED according to the size of your FDS requirements to avoid corrupted data in your FDS pages. You should update the bootloader.

Best regards,

Edvin

[Ankit Bhatnagar]

Thanks Edvin. Yes I have now set DFU_APP_DATA_RESERVED accordingly to avoid data loss. I just wanted to confirm that I understood was correct :)