Migrate STM32 Bare-Metal Firmware to FreeRTOS with MQTT for IoT Sensors

Introduction

In this tutorial, we will guide you through the process of migrating STM32 bare-metal firmware to FreeRTOS, incorporating MQTT for IoT sensor data transmission. This transition will allow for better task management, efficient resource utilization, and easier integration with networking protocols. Follow these steps carefully to ensure a smooth migration.

Prerequisites

• Basic understanding of C programming and embedded systems.
• Familiarity with STM32 microcontrollers.
• Experience with bare-metal firmware development.
• FreeRTOS library downloaded and configured for your STM32 project.
• An MQTT broker, such as Mosquitto, running on your local network or a cloud service.

Parts/Tools

• STM32 microcontroller development board.
• Development environment (e.g., STM32CubeIDE or Keil).
• FreeRTOS library.
• Paho MQTT C client library.
• Debugger for STM32 (optional, but recommended).

Steps

1. Set up FreeRTOS in your STM32 project:
   1. Download the FreeRTOS library from the official website.
   2. Include the FreeRTOS source files in your project directory.
   3. Configure the FreeRTOS settings in your project’s configuration file.
2. Modify the system initialization code:
   1. Replace the main function in your bare-metal code with the FreeRTOS task function:

   int main(void) {
       // System Initialization
       SystemInit();
       // Create FreeRTOS tasks
       xTaskCreate(vTaskSensorData, "SensorTask", configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL);
       // Start the scheduler
       vTaskStartScheduler();
       while(1);
   }

3. Create a FreeRTOS task for sensor data:
   1. Define the task function:

   void vTaskSensorData(void *pvParameters) {
       while(1) {
           // Read sensor data
           readSensorData();
           // Publish data via MQTT
           mqttPublish(sensorData);
           // Delay for a period
           vTaskDelay(pdMS_TO_TICKS(1000));
       }
   }

   2. Implement the readSensorData() function to gather data from your sensors.
   3. Implement the mqttPublish() function to send data via MQTT.
4. Integrate MQTT functionality:
   1. Add the Paho MQTT C client library to your project.
   2. Initialize the MQTT client in your task:

   MqttClient client;
   mqttClientInit(&client, &network);
   mqttConnect(&client, "broker.hivemq.com", 1883, "username", "password");

   3. Implement the mqttPublish() function:

   void mqttPublish(float sensorData) {
       char payload[50];
       snprintf(payload, sizeof(payload), "Sensor Data: %f", sensorData);
       mqttPublishMessage(&client, "sensor/topic", payload, strlen(payload), MQTT_PUBLISH_QOS_0);
   }

Troubleshooting

• MQTT connection issues: Ensure that the broker’s IP address and port are correctly specified. Check the network connection of your STM32 device.
• FreeRTOS Scheduler not running: Verify that the vTaskStartScheduler() function is called correctly and there are no blocking calls in your tasks.
• Sensor data not publishing: Double-check the implementation of the mqttPublish() function and ensure the topic is correct.

Conclusion

Congratulations! You have successfully migrated your STM32 bare-metal firmware to FreeRTOS with MQTT integration for IoT sensor data transmission. This migration opens up opportunities for utilizing advanced features of FreeRTOS and enhances your project’s capabilities through efficient task management and networking. Continue exploring more features of FreeRTOS and MQTT to further improve your IoT applications.