Why priority design matters in FreeRTOS - See It in Action

Why Priority Design Matters in FreeRTOS

📖 Scenario: Imagine you are building a simple embedded system using FreeRTOS. This system has multiple tasks like reading sensors, controlling motors, and sending data over communication. Each task has a different importance level. To make sure the most important tasks run first, you need to assign priorities correctly.

🎯 Goal: You will create three FreeRTOS tasks with different priorities and observe how priority affects which task runs first. This will help you understand why designing task priorities carefully is important in real-time systems.

📋 What You'll Learn

Create three FreeRTOS tasks named SensorTask, MotorTask, and CommTask

Assign priorities: SensorTask highest, MotorTask medium, CommTask lowest

Each task should print its name when running

Observe the order of task execution based on priority

💡 Why This Matters

🌍 Real World

In embedded systems like robots or IoT devices, tasks have different importance. Priority design ensures critical tasks run on time.

💼 Career

Understanding task priorities is essential for embedded software engineers working with real-time operating systems like FreeRTOS.

1

Create three FreeRTOS tasks

Write code to create three FreeRTOS tasks named SensorTask, MotorTask, and CommTask. Each task should run a simple function that prints its name once and then deletes itself.

FreeRTOS

// Create three tasks: SensorTask, MotorTask, CommTask
// Each task prints its name and deletes itself
// Your code here

Need a hint?

Use xTaskCreate to create each task. Each task function should print its name and then call vTaskDelete(NULL) to end.

2

Assign different priorities to tasks

Change the task creation code to assign priorities: SensorTask priority 3, MotorTask priority 2, and CommTask priority 1.

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include 

void SensorTask(void *pvParameters) {
    printf("SensorTask is running\n");
    vTaskDelete(NULL);
}

void MotorTask(void *pvParameters) {
    printf("MotorTask is running\n");
    vTaskDelete(NULL);
}

void CommTask(void *pvParameters) {
    printf("CommTask is running\n");
    vTaskDelete(NULL);
}

int main(void) {
    // Change priorities here
    xTaskCreate(SensorTask, "SensorTask", 1000, NULL, 3, NULL);
    xTaskCreate(MotorTask, "MotorTask", 1000, NULL, 2, NULL);
    xTaskCreate(CommTask, "CommTask", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}
// Your code here

Need a hint?

Set the priority argument in xTaskCreate to 3 for SensorTask, 2 for MotorTask, and 1 for CommTask.

3

Observe task execution order

Add code to each task to print its name repeatedly in a loop with a small delay. This will help you see which task runs first based on priority.

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include 

void SensorTask(void *pvParameters) {
    while(1) {
        printf("SensorTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void MotorTask(void *pvParameters) {
    while(1) {
        printf("MotorTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void CommTask(void *pvParameters) {
    while(1) {
        printf("CommTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

int main(void) {
    xTaskCreate(SensorTask, "SensorTask", 1000, NULL, 3, NULL);
    xTaskCreate(MotorTask, "MotorTask", 1000, NULL, 2, NULL);
    xTaskCreate(CommTask, "CommTask", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}
// Your code here

Need a hint?

Use an infinite loop while(1) in each task. Inside the loop, print the task name and call vTaskDelay(pdMS_TO_TICKS(1000)) to pause for 1 second.

4

Print the observed task execution order

Run the program and observe the printed output. Write a print statement outside the tasks that explains which task runs first based on priority.

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include 

void SensorTask(void *pvParameters) {
    while(1) {
        printf("SensorTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void MotorTask(void *pvParameters) {
    while(1) {
        printf("MotorTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void CommTask(void *pvParameters) {
    while(1) {
        printf("CommTask is running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

int main(void) {
    xTaskCreate(SensorTask, "SensorTask", 1000, NULL, 3, NULL);
    xTaskCreate(MotorTask, "MotorTask", 1000, NULL, 2, NULL);
    xTaskCreate(CommTask, "CommTask", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    // Print explanation below
    printf("SensorTask runs first because it has the highest priority.\n");
    // Your code here
}

Need a hint?

After starting the scheduler, add a printf statement explaining that SensorTask runs first due to its highest priority.