Suggestions for customizing NCS immutable and MCUBoot boot loaders?

[denis]

Are there any suggestions for creating slightly customized versions of the immutable and MCUBoot boot loaders?

Currently I'm using CONFIG_SECURE_BOOT=y & CONFIG_BOOTLOADER_MCUBOOT=y to get the immutable and MCUBoot boot loaders.  I would like to add some code to those boot loaders to show various states of the boot loader on our custom board (via LED & Display).  What would be the easiest approach to do this?

Ideally, I'd like to use as much of the current immutable and MCUBoot as possible and just have a custom "main" with my changes.  And have those boot loaders be used in the multi-image build instead.

[Simon]

There's no problem modifying the MCUboot and the immutable bootloader. 

• Setting the option CONFIG_SECURE_BOOT=y will use the sample located in ncs/nrf/samples/bootloader/src/main.c, so just modify that.
• Setting the option CONFIG_BOOTLOADER_MCUBOOT=y will use the sample located in ncs\bootloader\mcuboot\boot\zephyr\main.c, so just modify that

Best regards,

Simon

[denis]

Is there a way to do it out of tree?

[Simon]

One way of going about this is to fork the nrf and bootloader repositories and modify the mentioned samples, then upload it to your personal GitHub and add the urls to those repos into a west.yml located in your application.

You have to make your application the manifest repository (instead of the nrf repository), by running west init -m <url to manifest> and west update to get all the other repos (including the modified nrf and mcuboo repos).

Check out how it's done here: https://github.com/OeySa/nRF9160-Hello_Board (this will import the west.yml file from the nrf repo, since import is set to true)

Does that suffice?

There may be some other ways of going about this. I can look into it if the above approach is not what you're looking for.

[denis]

Ideally, I would like to create a new boot loader application in my repo.  That application would use ncs and include mcuboot libraries.  So with just a custom main (and a few other support files) build the custom boot loader.  Then tell ncs with a conf option to use that instead of the default mcuboot.

[Simon]

I talked with a developer about this. What you're explaining is not possible unfortunately, or it requires a lot of work. You would have to modify nrf/modules/mcuboot/CMakeLists.txt. I would recommend you to just create a file mcuboot.patch file inside the application, that contains all the changes you've applied to the mcuboot. Then just run git -C <path to mcuboot> apply from the application folder. This is less work that the approach I suggested (maintaining your own west module).

Best regards,

Simon

[denis]

I ended up using the MCUBoot repository (not the NCS fork) and can now build a custom boot loader.