Variables

Variable mechanism is introduced to facilitate data record in both CMake and Kconfig for MCUXpresso SDK.

For example in a cmake file with a board variable in the BASE_PATH, one copy of the following project segment data can be shared by all boards examples without any duplication.

if(CONFIG_MCUX_PRJSEG_module.board.suite)
    mcux_add_source(
        BASE_PATH ${SdkRootDirPath}/examples/_boards/${board} # "board" variable shall be defined in each board so that each board can use this project segment
        SOURCES dcd.c dcd.h
    )
endif()

In Kconfig, the same board variable can set the board Kconfig path for all boards.

rsource "${board}/Kconfig"

There are some required variables which must be provided for each build to make the CMake configuration process run passed.

Besides, customized variables are allowed for some software data recorded although not suggested.

Required Variables

There are some required variables which shall be defined in advance to make the build workable. These variables are generally related to hardware related information. All these required variables can be defined in cmake files, but to enable the switch across device parts in run time with Kconfig, most hardware related variables are moved into Kconfig.chip because Kconfig mechanism can make sure that when you switch device part, all related variables can be switch at the same time.

Here is the cmake files stored variable table:

Variable Name	Explanation	Acquisition	Used in
SdkRootDirPath	SDK root directory Specify sdk root path	Automatically set by build system	CMake
board	board name, like evkbmimxrt1170	Provided in cli argument, also need to record it in board variable cmake	CMake and Kconfig
board_root	board root folder For public boards, it is `examples/_boards` For internal boards, it is `examples_int/_boards`	Board variable cmake	CMake and Kconfig
device	device name, like MIMXRT1176	Device variable cmake	CMake and Kconfig
device_root	device root folder For public devices, it is `devices` For internal devices, it is `devices_int`	Device variable cmake	CMake and Kconfig
soc_series	soc series, like RT1170	Device variable cmake	CMake and Kconfig
soc_portfolio	soc portfolio, like RT	Soc portfolio variable cmake	CMake and Kconfig
soc_periph	soc periph, like periph	Device variable cmake	CMake and Kconfig
core_id	Core id, like cm33_core0	Device variable cmake. This is only required for multicore device.	Kconfig
core_id_suffix_name	Core id suffix name	Device variable cmake	CMake
multicore_foldername	multicore folder name	Device variable cmake	CMake

The above variables shall anyway be provided in CMake because they are used by Kconfig process.

Customized Variables

Besides above variables, you can set your own variables in CMake to facilitate your data record with extension mcux_set_variable.

For the required variables, build system will guarantee that they are defined before used.
For you customized variables, please make sure that your variables are defined before used.

Tips For Variable Usage

Variable value replacement is invisible in CMake process, to avoid potential issues, please minimize the usage of variable.
To make Kconfig integrable for other Kconfig system, please don’t use variables in Kconfig data other than rsource. rsource is only to load Kconfig files and it only support required variables, not customized ones.