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Building Amazon FreeRTOS with CMake

CMake targets your host operating system as the target system by default. To use it for cross compiling, CMake requires a toolchain file, which specifies the compiler that you want to use. In Amazon FreeRTOS, we provide default toolchain files in <amazon-freertos>/tools/cmake/toolchains. The way to provide this file to CMake depends on whether you’re using the CMake commandline interface or GUI. For more details, follow the Generating Build Files (CMake Command-Line Tool) instructions below. For more information about cross-compiling in CMake, see CrossCompiling in the official CMake wiki.

To build a CMake-based project

  1. Run CMake to generate the build files for a native build system, like Make or Ninja.

    You can use either the CMake command-line tool or the CMake GUI to generate the build files for your native build system.

    For information about generating Amazon FreeRTOS build files, see Generating Build Files (CMake Command-Line Tool) and Generating Build Files (CMake GUI).

  2. Invoke the native build system to make the project into an executable.

    For information about making Amazon FreeRTOS build files, see Building Amazon FreeRTOS from Generated Build Files.

Generating Build Files (CMake Command-Line Tool)

You can use the CMake command-line tool (cmake) to generate build files for Amazon FreeRTOS. To generate the build files, you need to specify a target board, a compiler and the location of the source code and build directory. Specify the target board using the -DVENDOR option. Specify the compiler with the -DCOMPILER option. Use the -S option to specify the location of the source code. Use the -Boption to specify the location of generated build files.

Note
The compiler must be in the system's PATH variable, or you must specify the location of the compiler.

For example, if the vendor is Texas Instruments, and the board is the CC3220 Launchpad, and the compiler is GCC for ARM, you can issue the following command to build the source files from the current directory to a directory named build:

cmake -DVENDOR=ti -DBOARD=cc3220_launchpad -DCOMPILER=arm-ti -S . -B build

Note
If you are using Windows, you must specify the native build system because CMake uses Visual Studio by default. For example:

cmake -DVENDOR=ti -DBOARD=cc3220_launchpad -DCOMPILER=arm-ti -S . -B build -G Ninja

Or:

cmake -DVENDOR=ti -DBOARD=cc3220_launchpad -DCOMPILER=arm-ti -S . -B build -G "MinGW Makefiles"

The regular expressions ${VENDOR}.* and ${BOARD}.* are used to search for a matching board, so you don't have to use the full names of the vendor and board for the VENDOR and BOARD options. Partial names work, provided there is a single match. For example, the following commands generate the same build files from the same source:

cmake -DVENDOR=ti -DCOMPILER=arm-ti -S . -B build

cmake -DBOARD=cc3220 -DCOMPILER=arm-ti -S . -B build

cmake -DVENDOR=t -DBOARD=cc -DCOMPILER=arm-ti -S . -B build

You can use the CMAKE_TOOLCHAIN_FILE option if you want to use a toolchain file that is not located in the default directory cmake/toolchains. For example:

cmake -DBOARD=cc3220 -DCMAKE_TOOLCHAIN_FILE='/path/to/toolchain_file.cmake' -S . -B build

If the toolchain file does not use absolute paths for your compiler, and you didn't add your compiler to the PATH environment variable, CMake might not be able to find it. To make sure that CMake finds your toolchain file, you can use the AFR_TOOLCHAIN_PATH option. This option searches the specified toolchain directory path and the toolchain's subfolder under bin. For example:

cmake -DBOARD=cc3220 -DCMAKE_TOOLCHAIN_FILE='/path/to/toolchain_file.cmake' -DAFR_TOOLCHAIN_PATH='/path/to/toolchain/' -S . -B build

To enable debugging, set the CMAKE_BUILD_TYPE to debug. With this option enabled, CMake adds debug flags to the compile options, and builds Amazon FreeRTOS with debug symbols.

# Build with debug symbols
cmake -DBOARD=cc3220 -DCOMPILER=arm-ti -DCMAKE_BUILD_TYPE=debug -S . -B build

You can also set the CMAKE_BUILD_TYPE to release to add optimization flags to the compile options.

Generating Build Files (CMake GUI)

You can use the CMake GUI to generate Amazon FreeRTOS build files.

To generate build files with the CMake GUI

  1. From the command line, issue cmake-gui to start the GUI.

  2. Choose Browse Source and specify the source input, and then choose Browse Build and specify the build output.
    [Image NOT FOUND]

  3. Choose Configure, and under Specify the build generator for this project, find and choose the build system that you want to use to build the generated build files. if you do not see the pop up window, you might be reusing an existing build directory. In this case, delete the CMake cache by choosing Delete Cache from the File menu.
    [Image NOT FOUND]

  4. Choose Specify toolchain file for cross-compiling, and then choose Next.

  5. Choose the toolchain file (for example, amazon-freertos/tools/cmake/toolchains/arm-ti.cmake), and then choose Finish.

    The default configuration for Amazon FreeRTOS is the template board, which does not provide any portable layer targets. As a result, a window appears with the message Error in configuration process. Note
    If you are seeing the following error:

    CMake Error at tools/cmake/toolchains/find_compiler.cmake:23 (message):
Compiler not found, you can specify search path with AFR_TOOLCHAIN_PATH.

    It means the compiler is not in your PATH environment variable. You can set the AFR_TOOLCHAIN_PATH variable in the GUI to tell CMake where you installed your compiler. If you do not see the AFR_TOOLCHAIN_PATH variable, choose Add Entry. In the pop up window, under Name, type AFR_TOOLCHAIN_PATH. Under Compiler Path type the path to your compiler. for example, C:/toolchains/arm-none-eabi-gcc.

  6. The GUI should now look like this:
    [Image NOT FOUND]

    Choose AFR_BOARD, choose your board, and then choose Configure again.

  7. Choose Generate. CMake generates the build system files (for example, makefiles or ninja files), and these files appear in the build directory you specified in the first step. Follow the instructions in the next section to generate the binary image.

Building Amazon FreeRTOS from Generated Build Files

Building with Native Build System

You can build Amazon FreeRTOS with a native build system by calling the build system command from the output binaries directory.

For example, if your build file output directory is <build_dir>, and you are using Make as your native build system, run the following commands:

cd <build_dir>
make -j4

Building with CMake

You can also use the CMake command-line tool to build Amazon FreeRTOS. CMake provides an abstraction layer for calling native build systems. For example:

cmake --build <build_dir>

Here are some other common uses of the CMake command-line tool's build mode:

# Take advantage of CPU cores.
cmake --build <build_dir> --parallel 8

# Build specific targets.
cmake --build <build_dir> --target afr_kernel

# Clean first, then build.
cmake --build <build_dir> --clean-first

For more information about the CMake build mode, see the CMake documentation.