Sysbuild - Merge Images into Single .hex File

[SetZero]

Hello,

I'm currently trying to merge the outputs of a sysbuild, which are multiple non-overlapping .hex files into a single hex file for easier handling. But i couldn't find a lot of information on how to do that, so that west flash will also work with a single file.

On the Sysbuild Docs I found this sentence:

Instead, you may use the outputs of this domain for other purposes - for example, to produce a secondary image for DFU, or to merge multiple images together.

I tried to add BUILD_ONLY TRUE to my ExternalZephyrProject_Add, but I can't add that to the root level application, which also creates a hex file. When I try to move my root level application to a subproject, so that i have two ExternalZephyrProject_Add it will now complain that the root level has no sources, which makes sense, as I now only have a merge step in the CMakeFile of the root.

And if all of that would work i still would have the question how I would pass the merged hex file to west flash.

I'm looking forward for any help on how this can be done

Edit: for clarification, I'm not using an nRF chip, therefore i can't (as far as I understand) use their merge tool.

[TK5095]

You can use mergehex.py Afterwards
https://github.com/zephyrproject-rtos/zephyr/tree/main/scripts/build

[SetZero]

Thanks. That helps a bit.
I also found out that there is HEX_FILES_TO_MERGE. But that seems to be partially broken. As it could, at one point, directly be flashed using west flash, which is not working anymore. It should be an easy fix to just edit cmake/flash/CMakeLists.txt and add another case to enable flashing again, but the usage of it seems rather inconvenient, as you have to define it before any zephyr includes. Therefore, you can't use it in the sysbuild.cmake and you have to set it before ExternalZephyrProject_Add.
Another option i found was using set_property(GLOBAL APPEND PROPERTY extra_post_build_commands, but that also suffers the same issues as HEX_FILES_TO_MERGE.
It would be a lot more convenient to have something like CONFIG_BUILD_OUTPUT_HEX or some command which you can use at after including zephyr.

[pdgendt]

Take a look at #83085, not available in a released version though.