Implement Micro-ROS Publisher/Subscriber on STM32F4 with FreeRTOS

Introduction

In this tutorial, we will implement a micro-ROS publisher/subscriber system on an STM32F4 microcontroller using FreeRTOS. This setup will enable efficient transmission of sensor data between different nodes in a robotics application. We’ll cover the prerequisites, necessary parts, tools, and provide step-by-step instructions to get your micro-ROS system up and running.

Prerequisites

• Basic knowledge of embedded systems and microcontrollers.
• Familiarity with FreeRTOS and ROS2 concepts.
• STM32F4 development board (e.g., STM32F4Discovery).
• Micro-ROS setup on your development machine.
• STM32CubeIDE or any compatible IDE installed.

Parts/Tools

• STM32F4 microcontroller board
• USB to UART converter
• Temperature or other sensor (e.g., DHT11, BMP280)
• Micro-ROS client library
• FreeRTOS
• STM32CubeMX for configuration

Steps

1. Set up your development environment:
   1. Install STM32CubeIDE and STM32CubeMX.
   2. Download and install the micro-ROS client library.
   3. Ensure you have the necessary toolchain for your STM32F4 board.
2. Configure the STM32F4 with STM32CubeMX:
   1. Open STM32CubeMX and create a new project for your STM32F4 board.
   2. Enable the FreeRTOS middleware:

   Middleware > FreeRTOS

   3. Configure the necessary peripherals (e.g., UART for communication).
   4. Generate the project files and open it in STM32CubeIDE.
3. Implement FreeRTOS tasks:
   1. Create a new task for the micro-ROS publisher:

   void publisher_task(void *argument) {
                   // Publisher setup code
                   while (1) {
                       // Publish sensor data
                       vTaskDelay(pdMS_TO_TICKS(1000));
                   }
               }

   2. Create another task for the micro-ROS subscriber:

   void subscriber_task(void *argument) {
                   // Subscriber setup code
                   while (1) {
                       // Handle received messages
                       vTaskDelay(pdMS_TO_TICKS(1000));
                   }
               }

4. Initialize the micro-ROS client:
   1. In your main function, initialize the micro-ROS client:

   micro_ros_init();

   2. Create publisher and subscriber with appropriate topic names:

   micro_ros_create_publisher(...);
   micro_ros_create_subscriber(...);

5. Publish and subscribe to sensor data:
   1. In the publisher task, read sensor data and publish it:

   sensor_data_t data;
   data.value = read_sensor();
   micro_ros_publish(&data);

   2. In the subscriber task, process the incoming data:

   sensor_data_t received_data;
   micro_ros_subscribe(&received_data);
   process_received_data(received_data);

6. Build and flash the firmware:
   1. Build the project in STM32CubeIDE.
   2. Connect your STM32F4 board via USB and flash the firmware.
   3. Open a terminal to view the output and ensure data transmission works.

Troubleshooting

• Connection issues: Ensure that the UART settings in your code match those of your terminal. Check wiring and connections.
• Data not received: Verify the topic names and ensure both publisher and subscriber are set up correctly.
• FreeRTOS task not running: Check the task priorities and ensure that the scheduler is running properly.
• Micro-ROS initialization failure: Recheck the micro-ROS setup and ensure all required libraries are included in the project.

Conclusion

In this tutorial, we successfully implemented a micro-ROS publisher/subscriber system on an STM32F4 microcontroller using FreeRTOS. By following the steps outlined, you can transmit sensor data effectively in a robotics application. With this foundation, you can expand your capabilities by integrating additional sensors or developing more complex communication patterns.