One application with MCUboot and overwrite image upgrades?

[SebastianA]

I'm trying to build an app with MCUboot and overwrite-based image upgrades.

We use NCS v2.5.0, and in my experiments the nRF52840 DK board.

First I tried to test this with samples/application_development/sysbuild/with_mcuboot. It has
 CONFIG_BOOT_UPGRADE_ONLY=y
 CONFIG_MCUBOOT_DOWNGRADE_PREVENTION=y
for its mcuboot.conf

I built a new version of its application. The build system didn't give me a file to upgrade with. I noticed in nrf/modules/mcuboot/CMakeList.txt that there is a check in the beginning for SYSBUILD and then returning, so I tried to create the upgrade image myself:

objcopy -O ihex --change-addresses 0x86000 -I binary build/with_mcuboot/zephyr/zephyr.signed.bin --gap-fill 0xff --pad-to 0x100000 app_moved.hex

The addresses are from the partition_manager_report. I flashed that file, but the bootloader didn't update the application to it, nor write any error messages. I guess that file isn't correct to use for upgrades.

My next try was to not use sysbuild and change the hello_world sample instead. I updated the prj.conf to:

CONFIG_BOOTLOADER_MCUBOOT=y
CONFIG_MCUBOOT_BOOTLOADER_MODE_OVERWRITE_ONLY=y
CONFIG_MCUBOOT_BOOTLOADER_NO_DOWNGRADE=y
CONFIG_BOOT_UPGRADE_ONLY=y
CONFIG_MCUBOOT_DOWNGRADE_PREVENTION=y

Then the build system complains that the last two keys are unknown (I had copied them from the sysbuild sample), so I removed them. This made me get the app_moved_test_update.hex file.

I tried to just flash that one and then the bootloader from the first sample used it and did an overwriting upgrade, just like I want it. Great!

Then I tried to use the newly built bootloader from the hello_world sample instead, but then it does a swap upgrade.

How do I get one project to both build MCUboot with the overwrite support as well as getting an app_moved_test_update.hex file for the application?

I don't really care if the project uses sysbuild or not, but it would be great if both ways could be used as this is supposed to be a sample for other applications to copy.

[Vidar Berg]

Hi,

A solution, if not using sysbuild, is to create a 'child_image' directory in your project source directory containing a Kconfig fragment for MCUBoot where you can place the specific Kconfig symbols for MCUBoot that you want to override. Expected naming and placement of the Kconfif files in the child image folder is illustrated here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.5.0/nrf/config_and_build/multi_image.html#permanent-configuration-changes-to-child-images 

Here is a simple example if you want to build MCUBOOT with CONFIG_BOOT_UPGRADE_ONLY=y:

5875.child_image.zip

Please note that you must perform a pristine build after adding the child image folder to the project for it to be picked up by the build system. After the build is complete, you can verify that your settings were applied by checking the .config file located in your build directory under mcuboot/zephyr/.

[SebastianA]

That works fine! Thank you!