Why scheduling determines real-time behavior in FreeRTOS - See It in Action

Why Scheduling Determines Real-Time Behavior

📖 Scenario: You are working on a small embedded system that controls two tasks: one that blinks an LED and another that reads a sensor. Both tasks need to run repeatedly, but the sensor reading must happen more frequently to keep the system responsive.

🎯 Goal: Build a simple FreeRTOS program that creates two tasks with different priorities and observe how the scheduler decides which task runs first, showing how scheduling affects real-time behavior.

📋 What You'll Learn

Create two tasks named vTaskBlink and vTaskSensor.

Set the priority of vTaskSensor higher than vTaskBlink.

Use vTaskDelay to simulate task work and periodic execution.

Print messages from each task to show which runs when.

Observe the output to understand scheduling impact.

💡 Why This Matters

🌍 Real World

Embedded systems often run multiple tasks that must respond quickly. Scheduling ensures critical tasks get CPU time first.

💼 Career

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

1

Create two FreeRTOS tasks

Write code to create two tasks named vTaskBlink and vTaskSensor using xTaskCreate. Use empty task functions for now.

FreeRTOS

// Your code here to create vTaskBlink and vTaskSensor tasks

Need a hint?

Use xTaskCreate to make tasks. Give vTaskSensor a higher priority number than vTaskBlink.

2

Add print statements and delays

Inside vTaskBlink and vTaskSensor, add printf statements to print "Blink task running" and "Sensor task running" respectively. Keep the vTaskDelay calls to simulate work.

FreeRTOS

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

void vTaskBlink(void *pvParameters) {
    for(;;) {
        // Add printf here
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void vTaskSensor(void *pvParameters) {
    for(;;) {
        // Add printf here
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main(void) {
    xTaskCreate(vTaskBlink, "Blink", 1000, NULL, 1, NULL);
    xTaskCreate(vTaskSensor, "Sensor", 1000, NULL, 2, NULL);
    vTaskStartScheduler();
    for(;;);
}

Need a hint?

Use printf inside each task's infinite loop before the delay.

3

Explain scheduling effect with priorities

Add comments in the main function explaining that vTaskSensor has higher priority and will run more often, showing how scheduling affects real-time behavior.

FreeRTOS

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

void vTaskBlink(void *pvParameters) {
    for(;;) {
        printf("Blink task running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void vTaskSensor(void *pvParameters) {
    for(;;) {
        printf("Sensor task running\n");
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main(void) {
    // Explain priority effect here
    xTaskCreate(vTaskBlink, "Blink", 1000, NULL, 1, NULL);
    xTaskCreate(vTaskSensor, "Sensor", 1000, NULL, 2, NULL);
    vTaskStartScheduler();
    for(;;);
}

Need a hint?

Add comments in main explaining the priority difference and its effect on scheduling.

4

Run and observe output

Run the program and observe the printed output. Write a printf statement in main before starting the scheduler that says "Starting scheduler".

FreeRTOS

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

void vTaskBlink(void *pvParameters) {
    for(;;) {
        printf("Blink task running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void vTaskSensor(void *pvParameters) {
    for(;;) {
        printf("Sensor task running\n");
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main(void) {
    // Print starting message here
    xTaskCreate(vTaskBlink, "Blink", 1000, NULL, 1, NULL);
    xTaskCreate(vTaskSensor, "Sensor", 1000, NULL, 2, NULL);
    vTaskStartScheduler();
    for(;;);
}

Need a hint?

Print "Starting scheduler" before calling vTaskStartScheduler() to confirm program start.