Using CMake with FreeRTOS

Important

This page refers to the Amazon-FreeRTOS repository which is deprecated. We recommend that you start here when you create a new project. If you already have an existing FreeRTOS project based on the now deprecated Amazon-FreeRTOS repository, see the Amazon-FreeRTOS Github Repository Migration Guide.

You can use CMake to generate project build files from FreeRTOS application source code, and to build and run the source code.

You can also use an IDE to edit, debug, compile, flash, and run code on FreeRTOS-qualified devices. Each board-specific Getting Started guide includes instructions for setting up the IDE for a particular platform. If you prefer working without an IDE, you can use other third-party code editing and debugging tools for developing and debugging your code, and then use CMake to build and run the applications.

The following boards support CMake:

• Espressif ESP32-DevKitC

• Espressif ESP-WROVER-KIT

• Infineon XMC4800 IoT Connectivity Kit

• Marvell MW320 AWS IoT Starter Kit

• Marvell MW322 AWS IoT Starter Kit

• Microchip Curiosity PIC32MZEF Bundle

• Nordic nRF52840 DK Development kit

• STMicroelectronicsSTM32L4 Discovery Kit IoT Node

• Texas Instruments CC3220SF-LAUNCHXL

• Microsoft Windows Simulator

See the topics below for more information about using CMake with FreeRTOS.

Prerequisites

Make sure that your host machine meets the following prerequisites before continuing:

• Your device's compilation toolchain must support the machine's operating system. CMake supports all versions of Windows, macOS, and Linux

  Windows subsystem for Linux (WSL) is not supported. Use native CMake on Windows machines.

• You must have CMake version 3.13 or higher installed.

  You can download the binary distribution of CMake from CMake.org.

  Note

  If you download the binary distribution of CMake, make sure that you add the CMake executable to the PATH environment variable before you using CMake from command line.

  You can also download and install CMake using a package manager, like homebrew on macOS, and scoop or chocolatey on Windows.

  Note

  The CMake package versions provided in the package managers for many Linux distributions are out-of-date. If your distribution's package manager does not provide the latest version of CMake, you can try alternative package managers, like linuxbrew or nix.

• You must have a compatible native build system.

  CMake can target many native build systems, including GNU Make or Ninja. Both Make and Ninja can be installed with package managers on Linux, macOS and Windows. If you are using Make on Windows, you can install a standalone version from Equation, or you can install MinGW, which bundles make.

  Note

  The Make executable in MinGW is called mingw32-make.exe, instead of make.exe.

  We recommend that you use Ninja, as it is faster than Make and also provides native support to all desktop operating systems.

Developing FreeRTOS applications with third-party code editors and debugging tools

You can use a code editor and a debugging extension or a third-party debugging tool to develop applications for FreeRTOS.

If, for example, you use Visual Studio Code as your code editor, you can install the Cortex-Debug VS Code extension as a debugger. When you finish developing your application, you can invoke the CMake command-line tool to build your project from within VS Code. For more information about using CMake to build FreeRTOS applications, see Building FreeRTOS with CMake.

For debugging, you can provide a VS Code with debug configuration similar to the following:

"configurations": [
    {
        "name": "Cortex Debug",
        "cwd": "${workspaceRoot}",
        "executable": "./build/st/stm32l475_discovery/aws_demos.elf",
        "request": "launch",
        "type": "cortex-debug",
        "servertype": "stutil"
    }
]

Building 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 FreeRTOS, we provide default toolchain files in freertos/tools/cmake/toolchains. The way to provide this file to CMake depends on whether you’re using the CMake command line 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 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 FreeRTOS build files, see Building 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 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.

You can use the following options for cmake:

• -DVENDOR – Specifies the target board.

• -DCOMPILER – Specifies the compiler.

• -S – Specifies the location of the source code.

• -B – Specifies 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-directory:

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

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-directory -G Ninja

Or:

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

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

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

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-directory

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-directory

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

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

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 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.

   

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.

   

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

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

   The default configuration for FreeRTOS is the template board, which does not provide any portable layer targets. As a result, a window appears with the message .

   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:

   

   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 FreeRTOS from generated build files

Building with native build system

You can build 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 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.