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Board Support Packages

lbuild module: modm:board

modm provides pre-configured BSPs for several commercial off-the-shelf development boards. There are two main components to the BPSs:

  1. An inheritable configuration board.xml containing the HAL target, options and the board module. This pre-defined configuration is aliased as a repo configuration so that your project.xml simply <extends>modm:{board-name}</extends>.
  2. A module modm:board:{board-name} that pulls in required dependencies, configures the modm library and provides the code to initialize the board. You can then #include <modm/board.hpp> in your project.

The BSPs all use a common interface within a top-level namespace Board:

  • Board::initialize(): Initializes the targets clock system, logger, LEDs and Buttons.
  • Board::initialize{subsystem}(): Initializes optional board subsystems.
  • Board::SystemClock: Provides the clock configuration for use in Peripheral::initialize<Board::SystemClock, ...>().
  • Board::Led{name}: Board-specific LEDs are initialized as outputs and off.
  • Board::Leds: A modm::platform::SoftwareGpioPort containing all board LEDs.
  • Board::Button: Board-specific input buttons are initialized as input with pull-up/down as required.
  • Board::{pin-name}: All board-specific pins are aliased to their respective modm::platform::Gpio{port}{pin}.

If the board supports a dedicated serial logging output the BSP redirects the modm:debug module debug stream MODM_LOG_INFO etc.

Please note that YOU must explicitly call the Board functions to initialize your hardware, just including the board module is not enough. Here is an example using the modm:disco-f469ni BSP:

#include <modm/board.hpp>

int main()
    // ALWAYS initialize the board first!
    // Then initialize the subsystems you want to use

    // Set LEDs via the GPIO port

    // Use the Arduino pin names

    // Use the boards serial logging
    MODM_LOG_INFO << "REBOOT!" << modm::endl;

    while (true) {
        // Link the LED to the button
    return 0;

Only select one BSP module

Even though some targets have multiple BSPs modules available (for example: Blue Pill and Black Pill), you can only use one module, since all define the same functions resulting in naming conflicts.


The BSPs contain an opinionated set of pre-defined functionality and settings. This is great for just quickly prototyping something, however, when you want to use custom hardware, or even just change a few settings, it's better to use your own BSP:

  1. Generate the BSP closest to your custom hardware, then copy the files from modm/src/modm/board/{name} to your own project and modify them.
  2. In your project.xml remove the board config inheritance (<extends>) and instead copy the pre-defined options into your own config.
  3. Check what modm modules you need to depend on and add them to your own project (check for module.depends(...) in the BSPs
  4. You may need to manually add the pre-defined collector values to your project configuration (check for env.collect(...) in the BSPs

Create the SystemClock struct

The easiest way using ST's CubeMX tool.

1. CubeMX Clock Graph

First we create a project in CubeMX with the desired microcontroller using the largest (pin-count, flash) variant. CubeMX displays something like this in the "Clock configuration" tab:

ST CubeMX Clock Configuration example

Then configure all clocks, muxes, multipliers and dividers to the highest allowed clock speeds (*).

(*) exceptions: E.g. USB usually requires exactly 48 MHz.

This settings are reflected in the constants static constexpr uint32_t Frequency, Apb1 and Apb2 as well as in const Rcc::PllFactors pllFactors{...} and the following lines. The PllFactors struct should be fairly self-explanatory.

2. Peripheral Mapping

As we can see in the graphic above, there are different clock ranges. Each peripheral is connected to a clock domain. Some peripherals have an upstream clock mux, this is currently ignored in modm and the default setting for the clock mux is assumed.

The figure shows the block diagram of the controller, which can be found at the beginning of the data sheet (not in the reference manual):

STM32 Block Diagram example

For each peripheral we create a static constexpr uint32_t member in the struct SystemClock and assign the value of the clock domain to which the peripheral is connected.


modm:board modm_board modm: board modm_architecture_assert modm: architecture: assert modm_board->modm_architecture_assert modm_architecture_delay modm: architecture: delay modm_board->modm_architecture_delay