Tasks: IdleTasks

Running a generic IdleTask function when all your priority tasks are in the blocked state

Notes

Check the entire code examples at the ESP32-Repo

Setting up your project to use vApplicationIdleHook for the ESP32

• make menuconfig
• Enter component config
• FreeRTOS
• Use FreeRTOS legacy hooks > Press y/Y
• Enable legacy idle hook > Press y/Y
• Save your changes

NOTE: In your main.c file do not forget to add the function void vApplicationIdleHook(void)

Why do we need “Idle Tasks”

Most of the priority tasks have a fixed duration or time to run. Most of the time apart from serving these priority tasks is spent in an idle state by the microcontroller.

However, this idle state can be utilized to get generic information about the system and run continuously when the other tasks are in a blocked state.

It is important to note that the IdleTask has a priority of 0 assigned by the FreeRTOS kernel. Hence even a Task having a priority of 1 will be given priority instead of the IdleTask.

Using the API

There is no API for IdleTask

This needs to be added to your main.c file

void vApplicationIdleHook(void)
{
  // Write your code here
  // NOTE, Make sure it is compact
}

Code Example

In this code example we will use a counter variable to store the number of cycles spent by the controller in the idle state.

static uint32_t ulIdleCycleCount;

void print_idle(void *ignore);

void app_main()
{
  xTaskCreate(&print_idle, "print task", 2048, NULL, 1, NULL);
}

// Create a periodic task that prints the idleCount value
void print_idle(void *ignore)
{
  while(1)
  {
    printf("IdleCount: %u\n", ulIdleCycleCount);
    vTaskDelay(pdMS_TO_TICKS(500));
  }
}

// Increments the idleCount variable
void vApplicationIdleHook(void)
{
  ulIdleCycleCount++;
}

Output

Since my kernel is set to a speed of 100Hz this is my output

IdleCount: 0
IdleCount: 50
IdleCount: 100

Conclusion

In this tutorial we have learnt about IdleTasks, how they can be implemented in FreeRTOS and where they can be beneficial.

In the next tutorial we shall learn about how to dynamically change the priority of different tasks.

Meanwhile, have fun and keep learning!