How to forward a CMake cache variable when using sysbuild?

[TorstenRobitzki]

I try to use sysbuild to build a firmware for nrf5340. I need a CMake cache variable in the CMakeLists.txt in my application (to emulate multiple build targets).

I use CMake to create the build system and want to have CACHE_VAR to be set to Value with in CMakeLists.txt

> cmake -DBOARD=<board> -DAPP_DIR=.. -DCACHE_VAR=Value ../../zephyr/share/sysbuild

Does not work (variable not set in CMakeLists.txt). According to the documentation, I thought, changing the variable name to either app_CACHE_VAR or APP_CACHE_VAR should do the trick, but unfortunately that's not the case.

How to forward a CMake cache variable when using sysbuild?

[merethan]

Hey Torsten,

There's an undocumented feature for this purpose, called zephyr_get(). The source tree is littered with it but as of yet no documentation has been written for it.

In your application CMakeLists.txt:

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

test_sysbuild()

# Must appear after find_package(Zephyr)
zephyr_get(CACHE_VAR SYSBUILD GLOBAL)

...and you're in business.

[TorstenRobitzki]

Hi @merethan
will try that! Thank you!