Flight Controller Porting Guide

This topic is for developers who want to port PX4 to work with new flight controller hardware.

PX4 Architecture

PX4 consists of two main layers: The board support and middleware layer on top of the host OS (NuttX, Linux or any other POSIX platform like Mac OS), and the applications (Flight Stack in src/modules). Please reference the PX4 Architectural Overview for more information.

This guide is focused only on the host OS and middleware as the applications/flight stack will run on any board target.

Flight Controller Configuration File Layout

Board startup and configuration files are located under /boards in each board's vendor-specific directory (i.e. boards/VENDOR/MODEL/)).

For example, for FMUv5:

  • (All) Board-specific files: /boards/px4/fmu-v5.
  • Build configuration: /boards/px4/fmu-v5/default.cmake.
  • Board-specific initialisation file: /boards/px4/fmu-v5/init/rc.board
    • A board-specific initialisation file is automatically included in startup scripts if found under the boards directory at init/rc.board.
    • The file is used to start sensors (and other things) that only exist on a particular board. It may also be used to set a board's default parameters, UART mappings, and any other special cases.
    • For FMUv5 you can see all the Pixhawk 4 sensors being started, and it also sets a larger LOGGER_BUF, and in AUTOCNF section (fresh setups) it sets the SYS_FMU_TASK parameter.

In addition there are several groups of configuration files for each board located throughout the code base:

Host Operating System Configuration

This section describes the purpose and location of the configuration files required for each supported host operating system to port them to new flight controller hardware.

NuttX

In order to port PX4 on NuttX to a new hardware target, that hardware target must be supported by NuttX. The NuttX project maintains an excellent porting guide for porting NuttX to a new computing platform.

For all NuttX based flight controllers (e.g. the Pixhawk series) the OS is loaded as part of the application build.

The configuration files for all boards, including linker scripts and other required settings, are located under /boards in a vendor- and board-specific directory (i.e. boards/VENDOR/MODEL/)).

The following example uses FMUv5 as it is a recent reference configuration for NuttX based flight controllers:

The function of each of these files, and perhaps more, will need to be duplicated for a new flight controller board.

NuttX Menuconfig

If you need to modify the NuttX OS configuration, you can do this via menuconfig using the PX4 shortcuts:

make px4_fmu-v5_default menuconfig
make px4_fmu-v5_default qconfig

For fresh installs of PX4 onto Ubuntu using ubuntu_sim_nuttx.sh you will also need to install kconfig tools from NuttX tools.

The following steps are not required if using the px4-dev-nuttx docker container or have installed to macOS using our normal instructions (as these includekconfig-mconf).

Run the following commands from any directory:

git clone https://bitbucket.org/nuttx/tools.git
cd tools/kconfig-frontends
sudo apt install gperf
./configure --enable-mconf --disable-nconf --disable-gconf --enable-qconf --prefix=/usr
make
sudo make install

The --prefix=/usr is essential as it determines the specific installation location where PX4 is hardcoded to look for kconfig-tools. The --enable-mconf and --enable-qconf options will enable the menuconfig and qconfig options respectively.

To run qconfig you may need to install additional Qt dependencies.

Linux

Linux boards do not include the OS and kernel configuration. These are already provided by the Linux image available for the board (which needs to support the inertial sensors out of the box).

Middleware Components and Configuration

This section describes the various middleware components, and the configuration file updates needed to port them to new flight controller hardware.

QuRT / Hexagon

  • The start script is located in posix-configs/.
  • The OS configuration is part of the default Linux image (TODO: Provide location of LINUX IMAGE and flash instructions).
  • The PX4 middleware configuration is located in src/drivers/boards. TODO: ADD BUS CONFIG
  • Drivers: DriverFramework.
  • Reference config: Running make eagle_default builds the Snapdragon Flight reference config.

RC UART Wiring Recommendations

It is generally recommended to connect RC via separate RX and TX pins to the microcontroller. If however RX and TX are connected together, the UART has to be put into singlewire mode to prevent any contention. This is done via board config and manifest files. One example is px4fmu-v5.

Officially Supported Hardware

The PX4 project supports and maintains the FMU standard reference hardware and any boards that are compatible with the standard. This includes the Pixhawk-series (see the user guide for a full list of officially supported hardware).

Every officially supported board benefits from:

  • PX4 Port available in the PX4 repository
  • Automatic firmware builds that are accessible from QGroundControl
  • Compatibility with the rest of the ecosystem
  • Automated checks via CI - safety remains paramount to this community
  • Flight testing

We encourage board manufacturers to aim for full compatibility with the FMU spec. With full compatibility you benefit from the ongoing day-to-day development of PX4, but have none of the maintenance costs that come from supporting deviations from the specification.

Manufacturers should carefully consider the cost of maintenance before deviating from the specification (the cost to the manufacturer is proportional to the level of divergence).

We welcome any individual or company to submit their port for inclusion in our supported hardware, provided they are willing to follow our Code of Conduct and work with the Dev Team to provide a safe and fulfilling PX4 experience to their customers.

It's also important to note that the PX4 dev team has a responsibility to release safe software, and as such we require any board manufacturer to commit any resources necessary to keep their port up-to-date, and in a working state.

If you want to have your board officially supported in PX4:

  • Your hardware must be available in the market (i.e. it can be purchased by any developer without restriction).
  • Hardware must be made available to the PX4 Dev Team so that they can validate the port (contact lorenz@px4.io for guidance on where to ship hardware for testing).
  • The board must pass full test suite and flight testing.

The PX4 project reserves the right to refuse acceptance of new ports (or remove current ports) for failure to meet the requirements set by the project.

You can reach out to the core developer team and community on the official Forums and Chat.

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