What is the main reason that the MBR (0x7E) page is being to protected mode when the bootloader starts?

[attila-v]

I have to write this page in case of the application firmware update, so I have to unprotect it in the bootloader (in the nrf_bootloader_app_start_final() function).
won't this be a problem?

regards,
Attila

nRF52832, SDK 15.3

[Hung Bui]

Hi Attila, 
It's part of the Secure Boot sequence. You can read about that here: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/lib_secure_boot.html?cp=7_1_3_5_0_8

It's is to avoid malfunction/glitch or hacking of the application can cause any damage to the MBR hence brick the device. 
 
Could you give more information why you need to modify the MBR when doing DFU update ? 

[attila-v]

Hi,

you can see my problem here: https://devzone.nordicsemi.com/f/nordic-q-a/59594/what-is-the-right-way-of-the-dfu

OK, it's solved, but I'm confused about MBR. As you can see in the topic, I modified the 'MBR params page / BL settings backup' only, not the real MBR. My question refers to it.

[Hung Bui]

Please be aware that the NRF_MBR_PARAMS_PAGE_ADDRESS (0x7E000) is not the MBR itself. It's the page that stores the MBR settings (and bootloader_setting backup). It's located on top of the bootloader. 

My understanding is that you are doing DFU from application, and the bootloader only does the swapping part ? 

I don't think you would need to write to the MBR_PARAMS_PAGE in that case. But you need to define NRF_DFU_IN_APP in the bootloader. 

[attila-v]

thank you for your quick answer!

yes, my aim is to do the DFU form application, so I will check and try your suggestion.

regards, Attila

[Hung Bui]

There a similar case here that you may want to have a look: https://devzone.nordicsemi.com/f/nordic-q-a/52594/how-to-update-software-using-the-bootloader