some datas is updated from flash 0xFE000 and 0xFF000 when nrf_dfu_mbr_copy_bl function is called

[NordicChao]

When I use nrf_dfu_mbr_copy_bl  to do bootloader updating, the data is copied sucessfully, but I find some flash data are updated from 0xFE000 and 0xFF000：

The data is the same thought from different start address. :

0xFE000:
6B 78 88 DF 02 00 00 00 ......

0xFF000:
6B 78 88 DF 02 00 00 00 ......

1.please let me know why this happens?
2.and actually I plan to use the flash area start from 0xFF000 to 0xFFFFF for my project,  can i still use this area for project development?

[Hung Bui]

Hi Chao, 
You shouldn't use the address 0xFE000 , it's most likely the MBR parameter page. 
Please check in your bootloader what's the configuration of 
NRF_MBR_PARAMS_PAGE_ADDRESS

If you want to allocate a page for your own application, you need to put it before the bootloader. Have you considered using our fstorage library to store data ? 

[NordicChao]

NRF_MBR_PARAMS_PAGE_ADDRESS
BOOTLOADER_SETTINGS_ADDRESS

after nrf_dfu_mbr_copy_bl is called, flash data is updated both from address 0xFE000 and 0xFF000.It seems MBR code updates information to these two areas. 
so my understand is that 0xFE000-0xFF000 area can not be used for my own project.

now I use area from 0xFD000 to 0xFE0000, it works. My question is that  if I use this area, is there any risk?

[Hung Bui]

Hi Chao, 
I don't think it's a good idea. Please take a look here: https://docs.nordicsemi.com/bundle/sdk_nrf5_v17.1.0/page/lib_bootloader.html

The application data should be put into the space before the bootloader address. Which is BOOTLOADER_START_ADDR. But you also need to check if your application is already using a storage library, for example fstorage or not. You should avoid overwriting the fstorage space.