doc/build/zephyr_cmake_package.rst - third_party/github/zephyrproject-rtos/zephyr - Git at Google

 .. _cmake_pkg:

 Zephyr CMake Package
 ####################

 The Zephyr `CMake package`_ is a convenient way to create a Zephyr-based application.

 .. note::
    The :ref:`zephyr-app-types` section introduces the application types
    used in this page.

 The Zephyr CMake package ensures that CMake can automatically select a Zephyr installation to use for building
 the application, whether it is a :ref:`Zephyr repository application <zephyr-repo-app>`,
 a :ref:`Zephyr workspace application <zephyr-workspace-app>`, or a
 :ref:`Zephyr freestanding application <zephyr-freestanding-app>`.

 When developing a Zephyr-based application, then a developer simply needs to write
 ``find_package(Zephyr)`` in the beginning of the application :file:`CMakeLists.txt` file.

 To use the Zephyr CMake package it must first be exported to the `CMake user package registry`_.
 This is means creating a reference to the current Zephyr installation inside the
 CMake user package registry.


 .. tabs::

    .. group-tab:: Ubuntu

       In Linux, the CMake user package registry is found in:

       ``~/.cmake/packages/Zephyr``

    .. group-tab:: macOS

       In macOS, the CMake user package registry is found in:

       ``~/.cmake/packages/Zephyr``

    .. group-tab:: Windows

       In Windows, the CMake user package registry is found in:

       ``HKEY_CURRENT_USER\Software\Kitware\CMake\Packages\Zephyr``


 The Zephyr CMake package allows CMake to automatically find a Zephyr base.
 One or more Zephyr installations must be exported.
 Exporting multiple Zephyr installations may be useful when developing or testing
 Zephyr freestanding applications, Zephyr workspace application with vendor forks, etc..


 Zephyr CMake package export (west)
 **********************************

 When installing Zephyr using :ref:`west <get_the_code>` then it is recommended
 to export Zephyr using ``west zephyr-export``.

 .. _zephyr_cmake_package_export:

 Zephyr CMake package export (without west)
 ******************************************

 Zephyr CMake package is exported to the CMake user package registry using the following commands:

 .. code-block:: bash

    cmake -P <PATH-TO-ZEPHYR>/share/zephyr-package/cmake/zephyr_export.cmake

 This will export the current Zephyr to the CMake user package registry.

 To also export the Zephyr Unittest CMake package, run the following command in addition:

 .. code-block:: bash

    cmake -P <PATH-TO-ZEPHYR>/share/zephyrunittest-package/cmake/zephyr_export.cmake

 .. _zephyr_cmake_package_zephyr_base:

 Zephyr Base Environment Setting
 *******************************

 The Zephyr CMake package search functionality allows for explicitly specifying
 a Zephyr base using an environment variable.

 To do this, use the following ``find_package()`` syntax:

 .. code-block:: cmake

    find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

 This syntax instructs CMake to first search for Zephyr using the Zephyr base environment setting
 :envvar:`ZEPHYR_BASE` and then use the normal search paths.

 .. _zephyr_cmake_search_order:

 Zephyr CMake Package Search Order
 *********************************

 When Zephyr base environment setting is not used for searching, the Zephyr installation matching
 the following criteria will be used:

 * A Zephyr repository application will use the Zephyr in which it is located.
   For example:

   .. code-block:: none

         <projects>/zephyr-workspace/zephyr
         └── samples
             └── hello_world

   in this example, ``hello_world`` will use ``<projects>/zephyr-workspace/zephyr``.


 * Zephyr workspace application will use the Zephyr that share the same workspace.
   For example:

   .. code-block:: none

      <projects>/zephyr-workspace
      ├── zephyr
      ├── ...
      └── my_applications
           └── my_first_app

   in this example, ``my_first_app`` will use ``<projects>/zephyr-workspace/zephyr`` as this Zephyr
   is located in the same workspace as the Zephyr workspace application.

 .. note::
    The root of a Zephyr workspace is identical to ``west topdir`` if the workspace was
    installed using ``west``

 * Zephyr freestanding application will use the Zephyr registered in the CMake user package registry.
   For example:

   .. code-block:: none

      <projects>/zephyr-workspace-1
      └── zephyr                       (Not exported to CMake)

      <projects>/zephyr-workspace-2
      └── zephyr                       (Exported to CMake)

      <home>/app
      ├── CMakeLists.txt
      ├── prj.conf
      └── src
          └── main.c

   in this example, only ``<projects>/zephyr-workspace-2/zephyr`` is exported to the CMake package
   registry and therefore this Zephyr will be used by the Zephyr freestanding application
   ``<home>/app``.

   If user wants to test the application with ``<projects>/zephyr-workspace-1/zephyr``, this can be
   done by using the Zephyr Base environment setting, meaning set
   ``ZEPHYR_BASE=<projects>/zephyr-workspace-1/zephyr``, before
   running CMake.

   .. note::

      The Zephyr package selected on the first CMake invocation will be used for all subsequent
      builds. To change the Zephyr package, for example to test the application using Zephyr base
      environment setting, then it is necessary to do a pristine build first
      (See :ref:`application_rebuild`).

 Zephyr CMake Package Version
 ****************************

 When writing an application then it is possible to specify a Zephyr version number ``x.y.z`` that
 must be used in order to build the application.

 Specifying a version is especially useful for a Zephyr freestanding application as it ensures the
 application is built with a minimal Zephyr version.

 It also helps CMake to select the correct Zephyr to use for building, when there are multiple
 Zephyr installations in the system.

 For example:

   .. code-block:: cmake

      find_package(Zephyr 2.2.0)
      project(app)

 will require ``app`` to be built with Zephyr 2.2.0 as minimum.
 CMake will search all exported candidates to find a Zephyr installation which matches this version
 criteria.

 Thus it is possible to have multiple Zephyr installations and have CMake automatically select
 between them based on the version number provided, see `CMake package version`_ for details.

 For example:

 .. code-block:: none

    <projects>/zephyr-workspace-2.a
    └── zephyr                       (Exported to CMake)

    <projects>/zephyr-workspace-2.b
    └── zephyr                       (Exported to CMake)

    <home>/app
    ├── CMakeLists.txt
    ├── prj.conf
    └── src
        └── main.c

 in this case, there are two released versions of Zephyr installed at their own workspaces.
 Workspace 2.a and 2.b, corresponding to the Zephyr version.

 To ensure ``app`` is built with minimum version ``2.a`` the following ``find_package``
 syntax may be used:

 .. code-block:: cmake

    find_package(Zephyr 2.a)
    project(app)


 Note that both ``2.a`` and ``2.b`` fulfill this requirement.

 CMake also supports the keyword ``EXACT``, to ensure an exact version is used, if that is required.
 In this case, the application CMakeLists.txt could be written as:

 .. code-block:: cmake

    find_package(Zephyr 2.a EXACT)
    project(app)

 In case no Zephyr is found which satisfies the version required, as example, the application specifies

 .. code-block:: cmake

    find_package(Zephyr 2.z)
    project(app)

 then an error similar to below will be printed:

 .. code-block:: none

    Could not find a configuration file for package "Zephyr" that is compatible
    with requested version "2.z".

    The following configuration files were considered but not accepted:

      <projects>/zephyr-workspace-2.a/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake, version: 2.a.0
      <projects>/zephyr-workspace-2.b/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake, version: 2.b.0


 .. note:: It can also be beneficial to specify a version number for Zephyr repository applications
           and Zephyr workspace applications. Specifying a version in those cases ensures the
 	  application will only build if the Zephyr repository or workspace is matching.
 	  This can be useful to avoid accidental builds when only part of a workspace has been
 	  updated.


 Multiple Zephyr Installations (Zephyr workspace)
 ************************************************

 Testing out a new Zephyr version, while at the same time keeping the existing Zephyr in the
 workspace untouched is sometimes beneficial.

 Or having both an upstream Zephyr, Vendor specific, and a custom Zephyr in same workspace.

 For example:

 .. code-block:: none

    <projects>/zephyr-workspace
    ├── zephyr
    ├── zephyr-vendor
    ├── zephyr-custom
    ├── ...
    └── my_applications
         └── my_first_app


 in this setup, ``find_package(Zephyr)`` has the following order of precedence for selecting
 which Zephyr to use:

 * Project name: ``zephyr``
 * First project, when Zephyr projects are ordered lexicographical, in this case.

   * ``zephyr-custom``
   * ``zephyr-vendor``

 This means that ``my_first_app`` will use ``<projects>/zephyr-workspace/zephyr``.

 It is possible to specify a Zephyr preference list in the application.

 A Zephyr preference list can be specified as:

 .. code-block:: cmake

    set(ZEPHYR_PREFER "zephyr-custom" "zephyr-vendor")
    find_package(Zephyr)

    project(my_first_app)


 the ``ZEPHYR_PREFER`` is a list, allowing for multiple Zephyrs.
 If a Zephyr is specified in the list, but not found in the system, it is simply ignored and
 ``find_package(Zephyr)`` will continue to the next candidate.


 This allows for temporary creation of a new Zephyr release to be tested, without touching current
 Zephyr. When testing is done, the ``zephyr-test`` folder can simply be removed.
 Such a CMakeLists.txt could look as:

 .. code-block:: cmake

    set(ZEPHYR_PREFER "zephyr-test")
    find_package(Zephyr)

    project(my_first_app)

 .. _cmake_build_config_package:

 Zephyr Build Configuration CMake packages
 *****************************************

 There are two Zephyr Build configuration packages which provide control over the build
 settings in Zephyr in a more generic way. These packages are:

 * **ZephyrBuildConfiguration**: Applies to all Zephyr applications in the workspace
 * **ZephyrAppConfiguration**: Applies only to the application you are currently building

 They are similar to the per-user :file:`.zephyrrc` file that can be used to set :ref:`env_vars`,
 but they set CMake variables instead. They also allow you to automatically share the build
 configuration among all users through the project repository. They also allow more advanced use
 cases, such as loading of additional CMake boilerplate code.

 The Zephyr Build Configuration CMake packages will be loaded in the Zephyr boilerplate code after
 initial properties and ``ZEPHYR_BASE`` has been defined, but before CMake code execution. The
 ZephyrBuildConfiguration is included first and ZephyrAppConfiguration afterwards. That means the
 application-specific package could override the workspace settings, if needed.
 This allows the Zephyr Build Configuration CMake packages to setup or extend properties such as:
 ``DTS_ROOT``, ``BOARD_ROOT``, ``TOOLCHAIN_ROOT`` / other toolchain setup, fixed overlays, and any
 other property that can be controlled. It also allows inclusion of additional boilerplate code.

 To provide a ZephyrBuildConfiguration or ZephyrAppConfiguration, create
 :file:`ZephyrBuildConfig.cmake` and/or :file:`ZephyrAppConfig.cmake` respectively and place them
 in the appropriate location. The CMake ``find_package`` mechanism will search for these files with
 the steps below. Other default CMake package search paths and hints are disabled and there is no
 version checking implemented for these packages. This also means that these packages cannot be
 installed in the CMake package registry. The search steps are:

 1. If ``ZephyrBuildConfiguration_ROOT``, or ``ZephyrAppConfiguration_ROOT`` respectively, is set,
    search within this prefix path. If a matching file is found, execute this file. If no matching
    file is found, go to step 2.
 2. Search within ``${ZEPHYR_BASE}/../*``, or ``${APPLICATION_SOURCE_DIR}`` respectively. If a
    matching file is found, execute this file. If no matching file is found, abort the search.

 It is recommended to place the files in the default paths from step 2, but with the
 ``<PackageName>_ROOT`` variables you have the flexibility to place them anywhere. This is
 especially necessary for freestanding applications, for which the default path to
 ZephyrBuildConfiguration usually does not work. In this case the ``<PackageName>_ROOT`` variables
 can be set on the CMake command line, **before** ``find_package(Zephyr ...)``, as environment
 variable or from a CMake cache initialization file with the ``-C`` command line option.

 .. note:: The ``<PackageName>_ROOT`` variables, as well as the default paths, are just the prefixes
    to the search path. These prefixes get combined with additional path suffixes, which together
    form the actual search path. Any combination that honors the
    `CMake package search procedure`_ is valid and will work.

 If you want to completely disable the search for these packages, you can use the special CMake
 ``CMAKE_DISABLE_FIND_PACKAGE_<PackageName>`` variable for that. Just set
 ``CMAKE_DISABLE_FIND_PACKAGE_ZephyrBuildConfiguration`` or
 ``CMAKE_DISABLE_FIND_PACKAGE_ZephyrAppConfiguration`` to ``TRUE`` to disable the package.

 An example folder structure could look like this:

 .. code-block:: none

    <projects>/zephyr-workspace
    ├── zephyr
    ├── ...
    ├── manifest repo (can be named anything)
    │    └── cmake/ZephyrBuildConfig.cmake
    ├── ...
    └── zephyr application
         └── share/zephyrapp-package/cmake/ZephyrAppConfig.cmake

 A sample :file:`ZephyrBuildConfig.cmake` can be seen below.

 .. code-block:: cmake

    # ZephyrBuildConfig.cmake sample code

    # To ensure final path is absolute and does not contain ../.. in variable.
    get_filename_component(APPLICATION_PROJECT_DIR
                           ${CMAKE_CURRENT_LIST_DIR}/../../..
                           ABSOLUTE
    )

    # Add this project to list of board roots
    list(APPEND BOARD_ROOT ${APPLICATION_PROJECT_DIR})

    # Default to GNU Arm Embedded toolchain if no toolchain is set
    if(NOT ENV{ZEPHYR_TOOLCHAIN_VARIANT})
        set(ZEPHYR_TOOLCHAIN_VARIANT gnuarmemb)
        find_program(GNU_ARM_GCC arm-none-eabi-gcc)
        if(NOT ${GNU_ARM_GCC} STREQUAL GNU_ARM_GCC-NOTFOUND)
            # The toolchain root is located above the path to the compiler.
            get_filename_component(GNUARMEMB_TOOLCHAIN_PATH ${GNU_ARM_GCC}/../.. ABSOLUTE)
        endif()
    endif()

 Zephyr CMake package source code
 ********************************

 The Zephyr CMake package source code in
 :zephyr_file:`share/zephyr-package/cmake` and
 :zephyr_file:`share/zephyrunittest-package/cmake` contains the CMake config
 package which is used by the CMake ``find_package`` function.

 It also contains code for exporting Zephyr as a CMake config package.

 The following is an overview of the files in these directories:

 :file:`ZephyrConfigVersion.cmake`
     The Zephyr package version file. This file is called by CMake to determine
     if this installation fulfils the requirements specified by user when calling
     ``find_package(Zephyr ...)``. It is also responsible for detection of Zephyr
     repository or workspace only installations.

 :file:`ZephyrUnittestConfigVersion.cmake`
     Same responsibility as ``ZephyrConfigVersion.cmake``, but for unit tests.
     Includes ``ZephyrConfigVersion.cmake``.

 :file:`ZephyrConfig.cmake`
     The Zephyr package file. This file is called by CMake to for the package
     meeting which fulfils the requirements specified by user when calling
     ``find_package(Zephyr ...)``. This file is responsible for sourcing of
     boilerplate code.

 :file:`ZephyrUnittestConfig.cmake`
     Same responsibility as ``ZephyrConfig.cmake``, but for unit tests.
     Includes ``ZephyrConfig.cmake``.

 :file:`zephyr_package_search.cmake`
    Common file used for detection of Zephyr repository and workspace candidates.
    Used by ``ZephyrConfigVersion.cmake`` and ``ZephyrConfig.cmake`` for common code.

 :file:`zephyr_export.cmake`
    See :ref:`zephyr_cmake_package_export`.

 .. _CMake package: https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html
 .. _CMake user package registry: https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html#user-package-registry
 .. _CMake package version: https://cmake.org/cmake/help/latest/command/find_package.html#version-selection
 .. _CMake package search procedure: https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure
	.. _cmake_pkg:

	Zephyr CMake Package
	####################

	The Zephyr `CMake package`_ is a convenient way to create a Zephyr-based application.

	.. note::
	The :ref:`zephyr-app-types` section introduces the application types
	used in this page.

	The Zephyr CMake package ensures that CMake can automatically select a Zephyr installation to use for building
	the application, whether it is a :ref:`Zephyr repository application <zephyr-repo-app>`,
	a :ref:`Zephyr workspace application <zephyr-workspace-app>`, or a
	:ref:`Zephyr freestanding application <zephyr-freestanding-app>`.

	When developing a Zephyr-based application, then a developer simply needs to write
	``find_package(Zephyr)`` in the beginning of the application :file:`CMakeLists.txt` file.

	To use the Zephyr CMake package it must first be exported to the `CMake user package registry`_.
	This is means creating a reference to the current Zephyr installation inside the
	CMake user package registry.


	.. tabs::

	.. group-tab:: Ubuntu

	In Linux, the CMake user package registry is found in:

	``~/.cmake/packages/Zephyr``

	.. group-tab:: macOS

	In macOS, the CMake user package registry is found in:

	``~/.cmake/packages/Zephyr``

	.. group-tab:: Windows

	In Windows, the CMake user package registry is found in:

	``HKEY_CURRENT_USER\Software\Kitware\CMake\Packages\Zephyr``


	The Zephyr CMake package allows CMake to automatically find a Zephyr base.
	One or more Zephyr installations must be exported.
	Exporting multiple Zephyr installations may be useful when developing or testing
	Zephyr freestanding applications, Zephyr workspace application with vendor forks, etc..


	Zephyr CMake package export (west)
	**********************************

	When installing Zephyr using :ref:`west <get_the_code>` then it is recommended
	to export Zephyr using ``west zephyr-export``.

	.. _zephyr_cmake_package_export:

	Zephyr CMake package export (without west)
	******************************************

	Zephyr CMake package is exported to the CMake user package registry using the following commands:

	.. code-block:: bash

	cmake -P <PATH-TO-ZEPHYR>/share/zephyr-package/cmake/zephyr_export.cmake

	This will export the current Zephyr to the CMake user package registry.

	To also export the Zephyr Unittest CMake package, run the following command in addition:

	.. code-block:: bash

	cmake -P <PATH-TO-ZEPHYR>/share/zephyrunittest-package/cmake/zephyr_export.cmake

	.. _zephyr_cmake_package_zephyr_base:

	Zephyr Base Environment Setting
	*******************************

	The Zephyr CMake package search functionality allows for explicitly specifying
	a Zephyr base using an environment variable.

	To do this, use the following ``find_package()`` syntax:

	.. code-block:: cmake

	find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

	This syntax instructs CMake to first search for Zephyr using the Zephyr base environment setting
	:envvar:`ZEPHYR_BASE` and then use the normal search paths.

	.. _zephyr_cmake_search_order:

	Zephyr CMake Package Search Order
	*********************************

	When Zephyr base environment setting is not used for searching, the Zephyr installation matching
	the following criteria will be used:

	* A Zephyr repository application will use the Zephyr in which it is located.
	For example:

	.. code-block:: none

	<projects>/zephyr-workspace/zephyr
	└── samples
	└── hello_world

	in this example, ``hello_world`` will use ``<projects>/zephyr-workspace/zephyr``.


	* Zephyr workspace application will use the Zephyr that share the same workspace.
	For example:

	.. code-block:: none

	<projects>/zephyr-workspace
	├── zephyr
	├── ...
	└── my_applications
	└── my_first_app

	in this example, ``my_first_app`` will use ``<projects>/zephyr-workspace/zephyr`` as this Zephyr
	is located in the same workspace as the Zephyr workspace application.

	.. note::
	The root of a Zephyr workspace is identical to ``west topdir`` if the workspace was
	installed using ``west``

	* Zephyr freestanding application will use the Zephyr registered in the CMake user package registry.
	For example:

	.. code-block:: none

	<projects>/zephyr-workspace-1
	└── zephyr (Not exported to CMake)

	<projects>/zephyr-workspace-2
	└── zephyr (Exported to CMake)

	<home>/app
	├── CMakeLists.txt
	├── prj.conf
	└── src
	└── main.c

	in this example, only ``<projects>/zephyr-workspace-2/zephyr`` is exported to the CMake package
	registry and therefore this Zephyr will be used by the Zephyr freestanding application
	``<home>/app``.

	If user wants to test the application with ``<projects>/zephyr-workspace-1/zephyr``, this can be
	done by using the Zephyr Base environment setting, meaning set
	``ZEPHYR_BASE=<projects>/zephyr-workspace-1/zephyr``, before
	running CMake.

	.. note::

	The Zephyr package selected on the first CMake invocation will be used for all subsequent
	builds. To change the Zephyr package, for example to test the application using Zephyr base
	environment setting, then it is necessary to do a pristine build first
	(See :ref:`application_rebuild`).

	Zephyr CMake Package Version
	****************************

	When writing an application then it is possible to specify a Zephyr version number ``x.y.z`` that
	must be used in order to build the application.

	Specifying a version is especially useful for a Zephyr freestanding application as it ensures the
	application is built with a minimal Zephyr version.

	It also helps CMake to select the correct Zephyr to use for building, when there are multiple
	Zephyr installations in the system.

	For example:

	.. code-block:: cmake

	find_package(Zephyr 2.2.0)
	project(app)

	will require ``app`` to be built with Zephyr 2.2.0 as minimum.
	CMake will search all exported candidates to find a Zephyr installation which matches this version
	criteria.

	Thus it is possible to have multiple Zephyr installations and have CMake automatically select
	between them based on the version number provided, see `CMake package version`_ for details.

	For example:

	.. code-block:: none

	<projects>/zephyr-workspace-2.a
	└── zephyr (Exported to CMake)

	<projects>/zephyr-workspace-2.b
	└── zephyr (Exported to CMake)

	<home>/app
	├── CMakeLists.txt
	├── prj.conf
	└── src
	└── main.c

	in this case, there are two released versions of Zephyr installed at their own workspaces.
	Workspace 2.a and 2.b, corresponding to the Zephyr version.

	To ensure ``app`` is built with minimum version ``2.a`` the following ``find_package``
	syntax may be used:

	.. code-block:: cmake

	find_package(Zephyr 2.a)
	project(app)


	Note that both ``2.a`` and ``2.b`` fulfill this requirement.

	CMake also supports the keyword ``EXACT``, to ensure an exact version is used, if that is required.
	In this case, the application CMakeLists.txt could be written as:

	.. code-block:: cmake

	find_package(Zephyr 2.a EXACT)
	project(app)

	In case no Zephyr is found which satisfies the version required, as example, the application specifies

	.. code-block:: cmake

	find_package(Zephyr 2.z)
	project(app)

	then an error similar to below will be printed:

	.. code-block:: none

	Could not find a configuration file for package "Zephyr" that is compatible
	with requested version "2.z".

	The following configuration files were considered but not accepted:

	<projects>/zephyr-workspace-2.a/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake, version: 2.a.0
	<projects>/zephyr-workspace-2.b/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake, version: 2.b.0


	.. note:: It can also be beneficial to specify a version number for Zephyr repository applications
	and Zephyr workspace applications. Specifying a version in those cases ensures the
	application will only build if the Zephyr repository or workspace is matching.
	This can be useful to avoid accidental builds when only part of a workspace has been
	updated.


	Multiple Zephyr Installations (Zephyr workspace)
	************************************************

	Testing out a new Zephyr version, while at the same time keeping the existing Zephyr in the
	workspace untouched is sometimes beneficial.

	Or having both an upstream Zephyr, Vendor specific, and a custom Zephyr in same workspace.

	For example:

	.. code-block:: none

	<projects>/zephyr-workspace
	├── zephyr
	├── zephyr-vendor
	├── zephyr-custom
	├── ...
	└── my_applications
	└── my_first_app


	in this setup, ``find_package(Zephyr)`` has the following order of precedence for selecting
	which Zephyr to use:

	* Project name: ``zephyr``
	* First project, when Zephyr projects are ordered lexicographical, in this case.

	* ``zephyr-custom``
	* ``zephyr-vendor``

	This means that ``my_first_app`` will use ``<projects>/zephyr-workspace/zephyr``.

	It is possible to specify a Zephyr preference list in the application.

	A Zephyr preference list can be specified as:

	.. code-block:: cmake

	set(ZEPHYR_PREFER "zephyr-custom" "zephyr-vendor")
	find_package(Zephyr)

	project(my_first_app)


	the ``ZEPHYR_PREFER`` is a list, allowing for multiple Zephyrs.
	If a Zephyr is specified in the list, but not found in the system, it is simply ignored and
	``find_package(Zephyr)`` will continue to the next candidate.


	This allows for temporary creation of a new Zephyr release to be tested, without touching current
	Zephyr. When testing is done, the ``zephyr-test`` folder can simply be removed.
	Such a CMakeLists.txt could look as:

	.. code-block:: cmake

	set(ZEPHYR_PREFER "zephyr-test")
	find_package(Zephyr)

	project(my_first_app)

	.. _cmake_build_config_package:

	Zephyr Build Configuration CMake packages
	*****************************************

	There are two Zephyr Build configuration packages which provide control over the build
	settings in Zephyr in a more generic way. These packages are:

	* ZephyrBuildConfiguration: Applies to all Zephyr applications in the workspace
	* ZephyrAppConfiguration: Applies only to the application you are currently building

	They are similar to the per-user :file:`.zephyrrc` file that can be used to set :ref:`env_vars`,
	but they set CMake variables instead. They also allow you to automatically share the build
	configuration among all users through the project repository. They also allow more advanced use
	cases, such as loading of additional CMake boilerplate code.

	The Zephyr Build Configuration CMake packages will be loaded in the Zephyr boilerplate code after
	initial properties and ``ZEPHYR_BASE`` has been defined, but before CMake code execution. The
	ZephyrBuildConfiguration is included first and ZephyrAppConfiguration afterwards. That means the
	application-specific package could override the workspace settings, if needed.
	This allows the Zephyr Build Configuration CMake packages to setup or extend properties such as:
	``DTS_ROOT``, ``BOARD_ROOT``, ``TOOLCHAIN_ROOT`` / other toolchain setup, fixed overlays, and any
	other property that can be controlled. It also allows inclusion of additional boilerplate code.

	To provide a ZephyrBuildConfiguration or ZephyrAppConfiguration, create
	:file:`ZephyrBuildConfig.cmake` and/or :file:`ZephyrAppConfig.cmake` respectively and place them
	in the appropriate location. The CMake ``find_package`` mechanism will search for these files with
	the steps below. Other default CMake package search paths and hints are disabled and there is no
	version checking implemented for these packages. This also means that these packages cannot be
	installed in the CMake package registry. The search steps are:

	1. If ``ZephyrBuildConfiguration_ROOT``, or ``ZephyrAppConfiguration_ROOT`` respectively, is set,
	search within this prefix path. If a matching file is found, execute this file. If no matching
	file is found, go to step 2.
	2. Search within ``${ZEPHYR_BASE}/../*``, or ``${APPLICATION_SOURCE_DIR}`` respectively. If a
	matching file is found, execute this file. If no matching file is found, abort the search.

	It is recommended to place the files in the default paths from step 2, but with the
	``<PackageName>_ROOT`` variables you have the flexibility to place them anywhere. This is
	especially necessary for freestanding applications, for which the default path to
	ZephyrBuildConfiguration usually does not work. In this case the ``<PackageName>_ROOT`` variables
	can be set on the CMake command line, before ``find_package(Zephyr ...)``, as environment
	variable or from a CMake cache initialization file with the ``-C`` command line option.

	.. note:: The ``<PackageName>_ROOT`` variables, as well as the default paths, are just the prefixes
	to the search path. These prefixes get combined with additional path suffixes, which together
	form the actual search path. Any combination that honors the
	`CMake package search procedure`_ is valid and will work.

	If you want to completely disable the search for these packages, you can use the special CMake
	``CMAKE_DISABLE_FIND_PACKAGE_<PackageName>`` variable for that. Just set
	``CMAKE_DISABLE_FIND_PACKAGE_ZephyrBuildConfiguration`` or
	``CMAKE_DISABLE_FIND_PACKAGE_ZephyrAppConfiguration`` to ``TRUE`` to disable the package.

	An example folder structure could look like this:

	.. code-block:: none

	<projects>/zephyr-workspace
	├── zephyr
	├── ...
	├── manifest repo (can be named anything)
	│ └── cmake/ZephyrBuildConfig.cmake
	├── ...
	└── zephyr application
	└── share/zephyrapp-package/cmake/ZephyrAppConfig.cmake

	A sample :file:`ZephyrBuildConfig.cmake` can be seen below.

	.. code-block:: cmake

	# ZephyrBuildConfig.cmake sample code

	# To ensure final path is absolute and does not contain ../.. in variable.
	get_filename_component(APPLICATION_PROJECT_DIR
	${CMAKE_CURRENT_LIST_DIR}/../../..
	ABSOLUTE
	)

	# Add this project to list of board roots
	list(APPEND BOARD_ROOT ${APPLICATION_PROJECT_DIR})

	# Default to GNU Arm Embedded toolchain if no toolchain is set
	if(NOT ENV{ZEPHYR_TOOLCHAIN_VARIANT})
	set(ZEPHYR_TOOLCHAIN_VARIANT gnuarmemb)
	find_program(GNU_ARM_GCC arm-none-eabi-gcc)
	if(NOT ${GNU_ARM_GCC} STREQUAL GNU_ARM_GCC-NOTFOUND)
	# The toolchain root is located above the path to the compiler.
	get_filename_component(GNUARMEMB_TOOLCHAIN_PATH ${GNU_ARM_GCC}/../.. ABSOLUTE)
	endif()
	endif()

	Zephyr CMake package source code
	********************************

	The Zephyr CMake package source code in
	:zephyr_file:`share/zephyr-package/cmake` and
	:zephyr_file:`share/zephyrunittest-package/cmake` contains the CMake config
	package which is used by the CMake ``find_package`` function.

	It also contains code for exporting Zephyr as a CMake config package.

	The following is an overview of the files in these directories:

	:file:`ZephyrConfigVersion.cmake`
	The Zephyr package version file. This file is called by CMake to determine
	if this installation fulfils the requirements specified by user when calling
	``find_package(Zephyr ...)``. It is also responsible for detection of Zephyr
	repository or workspace only installations.

	:file:`ZephyrUnittestConfigVersion.cmake`
	Same responsibility as ``ZephyrConfigVersion.cmake``, but for unit tests.
	Includes ``ZephyrConfigVersion.cmake``.

	:file:`ZephyrConfig.cmake`
	The Zephyr package file. This file is called by CMake to for the package
	meeting which fulfils the requirements specified by user when calling
	``find_package(Zephyr ...)``. This file is responsible for sourcing of
	boilerplate code.

	:file:`ZephyrUnittestConfig.cmake`
	Same responsibility as ``ZephyrConfig.cmake``, but for unit tests.
	Includes ``ZephyrConfig.cmake``.

	:file:`zephyr_package_search.cmake`
	Common file used for detection of Zephyr repository and workspace candidates.
	Used by ``ZephyrConfigVersion.cmake`` and ``ZephyrConfig.cmake`` for common code.

	:file:`zephyr_export.cmake`
	See :ref:`zephyr_cmake_package_export`.

	.. _CMake package: https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html
	.. _CMake user package registry: https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html#user-package-registry
	.. _CMake package version: https://cmake.org/cmake/help/latest/command/find_package.html#version-selection
	.. _CMake package search procedure: https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure