Adding extra_post_build step from out of tree application

[Anthony Ambuehl]

I'm using NCS v2.3.0.

I am trying to add an additional step for post build processing.  My application is out of tree, and if possible I'm trying to keep my changes limited to the application folder.

I found other tickets recommending extra_post_build_commands, however I do not find any examples of using this extra_post_build_command from the application directory.

As a test I inserted my commands into zephyr/modules/trusted-firmware-m/CmakeLists.txt  and found that it was running but not at the conclusion of building the application.  It was being run during mcuboot generation.

Is there a way to add post build steps from an out of tree application?

Is it necessary to modify the NCS repo/source to use the extra_post_build_commands?  

If so, which CMakeLists.txt should I change to run a step after all child images are built?

[Anthony Ambuehl]

Its been almost a week.  Is it possible to add additional post build processing steps from the application directory?

[Anthony Ambuehl]

Any help?

[Raoul]

Hi Anthony,

I apologise for the wait, I've been sick for the past couple of days. I should have passed this case on to a colleague.

You might have come across this case, pointing to examples of extra_post_build_commands being used in the NCS codebase. You could use any of them as a template, and it turns out that it works fine in your application's CMakeLists.txt.

In its simplest form, it looks like this:

set_property(GLOBAL APPEND PROPERTY extra_post_build_commands
  COMMAND echo "hello world"
  )

Although as far as I understand, it's important that this gets placed before zephyr gets pulled in (with "find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})"):

When I add the above to the CMakeLists.txt of a freestanding hello world sample, it seems to work well:

When I add mcuboot (CONFIG_BOOTLOADER_MCUBOOT=y) to introduce a child image, I see that the "extra command" still gets executed after the compiling and linking steps:

Although as you can see, there are now other steps occurring afterwards. I believe they are also executed through the extra_post_build_commands mechanism.

Is this acceptable for you? Or do you need your command to be executed at the very last? In that case I will have to research what determines the ordering of the post build commands.

Best regards,

Raoul

[Anthony Ambuehl]

Thanks for the response, I'm glad you are feeling better!

Our purpose for the additional post build step would be to perform some processing on the generated app_update.bin to prepare it for a proprietary FOTA service.  

Based on your example, the app_update.bin and app_signed.bin is also generated by a post build step and is generated after your hello_world.  This is probably happening because the application cmake appends at the beginning of the cmake file.  

Is there any way to append on to the extra_post_build steps after the find_package has added the steps for app_update.bin generation?

[Raoul]

Not completely, but almost, thanks!

I see, that makes a lot of sense. I've now spent an hour digging through CMake seeing if I can change the order (without modifying the Zephyr tree, like you said). No luck.

I've asked the NCS team for advice, and will let you know when I hear from them!

Best regards,

Raoul