CMake for Mbed OS

In order to replace the traditional Mbed tools, we are adding CMake support to allow the generation of build systems instructions to build Mbed OS as a library.

This is still at the experimental stage and still in development. It does not yet completely replace our current build tools. If you find a bug, please report it or raise a pull request as contributions are welcome!

Mbed OS is built as collection of all core libraries. Application project executables can be linked with the mbed-os library (which includes the core libraries of Mbed OS) and optional mbed-os- prefixed libraries depending on the additional features required by the projects and supported by the Mbed target.

The list of optional libraries for each component can be seen in the CMake input source file at the root of each component directory.

The following features are not yet supported and will be progressively added:

• Application profile selection (bare metal)
• Features that require altering compiler/linker command line options (except for printf library and C selections)

The full profile with the selected printf and C libraries.

Supported targets

Only a limited set of targets is supported at the moment.

The following targets are supported:

• Ambiq Micro targets
• Analog Devices targets
• ARM FM targets
• ARM SSG targets
• Cypress targets
• Freescale targets
• GigaDevice targets
• MAXIM targets
• Nordic targets
• NXP targets
• Renesas targets
• Samsung targets
• Silicon Labs targets
• STM targets
• Toshiba targets

The post build operations is only supported for the following Mbed boards: LPC1114, LPC1768, ARCH_PRO, LPC54114, LPC546XX, FF_LPC546XX, CY8CKIT064B0S2_4343W, CYTFM_064B0S2_4343W, CYSBSYSKIT_01.

The following Mbed boards do not have post build operations support as TFM is not yet supported: ARM_MUSCA_B1, ARM_MUSCA_B1_NS, ARM_MUSCA_S1, ARM_MUSCA_S1_NS.

Supported toolchains

Arm Compiler 6 and GNU Arm Embedded toolchains are supported.

Examples

Supported examples can be identified by the presence of a top level CMakeLists.txt input source file.

Known issues

• Ninja: ARMClang6 response files require unix paths on Windows. Reference: https://gitlab.kitware.com/cmake/cmake/-/issues/21093. We disabled response files for Ninja on Windows until CMake is fixed.

How to build an application

Prerequisities:

• CMake >=3.19.0
• mbed-tools >=4.0.0
• Python modules defined in tools/cmake/requirements.txt

From the application root or wherever mbed-os.lib is found, run the following command to:

• create the Mbed OS configuration CMake module
• create a build directory
• generate the project configuration
• build the project using the Ninja build system

   mbedtools compile -m <mbed-target> -t <toolchain>

CMAKE_BUILD_TYPE can overridden with Mbed specific values: Develop (default value), Release and Debug.

mbed-tools will pass -DCMAKE_BUILD_TYPE=<supported-build-type> for you when using the --build-type optional argument of the build subcommand as follows:

mbedtools compile -m <mbed-target> -t <toolchain> -b <supported-build-type>

If you're running CMake directly, you may need to pass it in yourself as follows:

cmake -S <source-dir> -B <build-dir> -DCMAKE_BUILD_TYPE=debug

How to build a greentea test

Install prerequisites suggested in the previous section and follow the below steps to build:

• Set your current directory to the test suite directory

• CMake MBED_TEST_LINK_LIBRARIES command-line argument config must be passed either mbed-os or mbed-baremetal when you are building a greentea test. In addition to that, you must pass any extra library along if that library source is not maintained as part of mbed os source tree.

  For example:
  kvstore greentea test is dependent on mbed-storage and mbed-storage-filesystemstore library however you don't need to pass it via MBED_TEST_LINK_LIBRARIES as it is already target linked in greentea test CMakeLists.txt, at the same time some libraries and test cases are private to the application and if you want to use it with kvstore test then pass it with MBED_TEST_LINK_LIBRARIES command-line argument.

• Run the following command for the test suite to be recognised as a valid Mbed application

  touch mbed-os.lib && ln -s /path/to/mbed-os mbed-os

• Run the following command for the configuration CMake module to be generated

  mbedtools configure -t <TOOLCHAIN> -m <MBED_TARGET>

• Build the test binary with the full profile

  cd cmake_build/<MBED_TARGET>/<PROFILE>/<TOOLCHAIN>/ && cmake ../../../.. -G Ninja -DMBED_TEST_LINK_LIBRARIES=mbed-os && cmake --build .

  To build the test binary with the baremetal profile

  cd cmake_build/<MBED_TARGET>/<PROFILE>/<TOOLCHAIN>/ && cmake ../../../.. -G Ninja -DMBED_TEST_LINK_LIBRARIES=mbed-baremetal && cmake --build .

  To build the test binary with the full profile and a "XYZ" library

  cd cmake_build/<MBED_TARGET>/<PROFILE>/<TOOLCHAIN>/ && cmake ../../../.. -G Ninja -D"MBED_TEST_LINK_LIBRARIES=mbed-os XYZ" && cmake --build .

Notes:

• These steps will change when mbedtools implements a sub-command to invoke Greentea tests
• Some Greentea tests require specific application configuration files in order to build and run successfully. For example, the connectivity/mbedtls/tests/TESTS/mbedtls/sanity test requires the configuration file found at TESTs/configs/experimental.json.

Naming convention

• mbed namespace: Mbed CMake targets must have mbed- prefix
• all characters are lower case
• words separated by hyphens

For example: mbed-ble-cordio