How to Implement DVFS Firmware on ESP32 with FreeRTOS for IoT Energy Efficiency

Introduction

Dynamic Voltage and Frequency Scaling (DVFS) is a technique used to optimize energy consumption in electronic devices. By dynamically adjusting the operating voltage and frequency according to the workload, devices can achieve significant power savings. In this tutorial, we will implement DVFS firmware on the ESP32 microcontroller using FreeRTOS, making it ideal for energy-efficient IoT applications.

Prerequisites

• Basic knowledge of C programming.
• Familiarity with FreeRTOS concepts.
• ESP32 development board.
• Arduino IDE or ESP-IDF installed on your computer.
• USB cable to connect the ESP32 to your computer.

Parts/Tools

• ESP32 Development Board
• USB Cable
• Arduino IDE or ESP-IDF
• Basic electronic components (optional for additional sensors)

Steps

1. Set Up Your Development Environment
   1. Download and install the Arduino IDE or ESP-IDF.
   2. Install the ESP32 board package:

      Tools > Board > Board Manager > search for "ESP32" and install

2. Create a New Project
   1. Open Arduino IDE or your ESP-IDF workspace.
   2. Create a new file and name it dvfs_example.ino.
3. Include Necessary Libraries

   In your project, include the essential FreeRTOS and ESP32 libraries:

   #include <freertos/FreeRTOS.h>
   #include <freertos/task.h>
   #include <driver/ledc.h>
   #include <esp_system.h>

4. Initialize DVFS Settings

   Configure the DVFS settings for the ESP32:

   void initDVFS() {
       // Set frequency and voltage scaling parameters
       ledc_set_freq(LEDC_LOW_SPEED_MODE, LEDC_TIMER_0, 1000); // 1 kHz
       ledc_set_duty(LEDC_LOW_SPEED_MODE, LEDC_CHANNEL_0, 128); // 50% duty cycle
       ledc_update_duty(LEDC_LOW_SPEED_MODE, LEDC_CHANNEL_0);
   }

5. Implement the DVFS Control Logic

   Write logic to adjust voltage and frequency based on the system load:

   void adjustDVFS(int load) {
       if (load < 20) {
           // Low load, reduce frequency and voltage
           ledc_set_freq(LEDC_LOW_SPEED_MODE, LEDC_TIMER_0, 500); // 500 Hz
       } else if (load < 70) {
           // Medium load, maintain frequency
           ledc_set_freq(LEDC_LOW_SPEED_MODE, LEDC_TIMER_0, 1000); // 1 kHz
       } else {
           // High load, increase frequency
           ledc_set_freq(LEDC_LOW_SPEED_MODE, LEDC_TIMER_0, 2000); // 2 kHz
       }
   }

6. Create a Task to Monitor Load

   Implement a FreeRTOS task that monitors the system load and adjusts DVFS:

   void loadMonitoringTask(void *pvParameters) {
       while (1) {
           int currentLoad = getSystemLoad(); // Function to retrieve system load
           adjustDVFS(currentLoad);
           vTaskDelay(pdMS_TO_TICKS(1000)); // Delay for 1 second
       }
   }
   

7. Initialize FreeRTOS and Start the Task

   Finally, initialize FreeRTOS and start the load monitoring task:

   void setup() {
       Serial.begin(115200);
       initDVFS();
       xTaskCreate(loadMonitoringTask, "Load Monitor", 2048, NULL, 1, NULL);
   }
   
   void loop() {
       // Main loop can be left empty
   }

Troubleshooting

• ESP32 Not Responding: Check your USB connection and ensure the correct board is selected in the Arduino IDE.
• DVFS Not Working: Verify that the frequency and duty cycle settings are correctly configured.
• Task Not Running: Ensure that you have enough stack size allocated for the FreeRTOS task.
• Compilation Errors: Ensure that all necessary libraries are included and correctly referenced.

Conclusion

By implementing DVFS on the ESP32 using FreeRTOS, you can significantly enhance the energy efficiency of your IoT applications. This tutorial provided a step-by-step guide to set up and run DVFS on your ESP32. Experiment with different load conditions and frequency settings to find the optimal configuration for your specific use case.