FreeRTOS architecture overview - Mini Project: Build & Apply

FreeRTOS Architecture Overview

📖 Scenario: You are learning how FreeRTOS works inside an embedded system. Understanding its architecture helps you write better multitasking programs.

🎯 Goal: Build a simple FreeRTOS program that creates tasks and uses the basic architecture components like tasks, scheduler, and queues.

📋 What You'll Learn

Create task functions with exact names

Create task handles with exact names

Use FreeRTOS API functions with correct parameters

Print output to show task execution order

💡 Why This Matters

🌍 Real World

FreeRTOS is used in embedded devices like IoT gadgets, wearables, and industrial controllers to manage multiple tasks efficiently.

💼 Career

Understanding FreeRTOS architecture is essential for embedded software engineers working on real-time systems and multitasking applications.

1

Create two FreeRTOS tasks

Create two task functions called Task1 and Task2 that each take a void *pvParameters argument. Also, declare two task handles called Task1Handle and Task2Handle initialized to NULL.

FreeRTOS

// Define Task1 and Task2 functions
// Declare Task1Handle and Task2Handle as TaskHandle_t initialized to NULL
// Your code here

Hint

Define two functions with the exact names and parameters. Declare two task handles as TaskHandle_t variables set to NULL.

2

Create tasks in main and start scheduler

In the main function, create the two tasks using xTaskCreate with the exact names Task1 and Task2, stack size 100, priority 1, and store their handles in Task1Handle and Task2Handle. Then start the scheduler with vTaskStartScheduler().

FreeRTOS

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

TaskHandle_t Task1Handle = NULL;
TaskHandle_t Task2Handle = NULL;

void Task1(void *pvParameters) {
    for(;;) {
        // Task1 code
    }
}

void Task2(void *pvParameters) {
    for(;;) {
        // Task2 code
    }
}

int main(void) {
    // Create Task1 and Task2 with xTaskCreate
    // Start the scheduler with vTaskStartScheduler
    // Your code here
}

Hint

Use xTaskCreate to create each task with the exact parameters. Then call vTaskStartScheduler() to start running tasks.

3

Add task code to print messages

Inside the infinite loop of Task1 and Task2, add code to print "Task1 is running" and "Task2 is running" respectively using printf. Add a call to vTaskDelay(1000 / portTICK_PERIOD_MS) after each print to delay for 1 second.

FreeRTOS

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

TaskHandle_t Task1Handle = NULL;
TaskHandle_t Task2Handle = NULL;

void Task1(void *pvParameters) {
    for(;;) {
        // Print "Task1 is running"
        // Delay 1 second
        // Your code here
    }
}

void Task2(void *pvParameters) {
    for(;;) {
        // Print "Task2 is running"
        // Delay 1 second
        // Your code here
    }
}

int main(void) {
    xTaskCreate(Task1, "Task1", 100, NULL, 1, &Task1Handle);
    xTaskCreate(Task2, "Task2", 100, NULL, 1, &Task2Handle);
    vTaskStartScheduler();
    for(;;) {}
}

Hint

Use printf to show the task running message. Use vTaskDelay to pause the task for 1 second.

4

Run and observe task output

Run the program and observe the output. It should print alternating lines "Task1 is running" and "Task2 is running" every second.

FreeRTOS

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

TaskHandle_t Task1Handle = NULL;
TaskHandle_t Task2Handle = NULL;

void Task1(void *pvParameters) {
    for(;;) {
        printf("Task1 is running\n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

void Task2(void *pvParameters) {
    for(;;) {
        printf("Task2 is running\n");
        vTaskDelay(1000 / portTICK_PERIOD_MS);
    }
}

int main(void) {
    xTaskCreate(Task1, "Task1", 100, NULL, 1, &Task1Handle);
    xTaskCreate(Task2, "Task2", 100, NULL, 1, &Task2Handle);
    vTaskStartScheduler();
    for(;;) {}
}

// Run the program and observe the output

Hint

Run the program on your FreeRTOS environment or simulator. You should see the two messages printed repeatedly every second.

Practice

1. What is the main role of the FreeRTOS scheduler in its architecture?

easy

A. To store data permanently

B. To decide which task runs and when

C. To compile the code

D. To manage hardware interrupts only

Solution

1. Step 1: Understand the scheduler's purpose

   The scheduler controls task execution order and timing in FreeRTOS.

2. Step 2: Compare with other options

   Storing data, compiling code, or only managing interrupts are not scheduler roles.

3. Final Answer:

   To decide which task runs and when -> Option B

4. Quick Check:

   Scheduler controls task timing = To decide which task runs and when [OK]

Hint: Scheduler manages task timing and switching [OK]

Common Mistakes:

• Confusing scheduler with memory storage
• Thinking scheduler compiles code
• Assuming scheduler only handles interrupts

2. Which of the following is the correct way to create a task in FreeRTOS?

easy

A. task_create(TaskFunction, StackSize);

B. CreateTask(TaskFunction, Priority);

C. xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle);

D. StartTask(TaskFunction, "TaskName");

Solution

1. Step 1: Recall FreeRTOS task creation syntax

   The correct function is xTaskCreate with parameters: function, name, stack size, parameters, priority, and handle.

2. Step 2: Check options for exact match

   Only xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); matches the correct FreeRTOS API call syntax.

3. Final Answer:

   xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); -> Option C

4. Quick Check:

   Use xTaskCreate with full parameters = xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); [OK]

Hint: Remember xTaskCreate needs 6 parameters [OK]

Common Mistakes:

• Using incorrect function names
• Omitting required parameters
• Confusing task creation with starting tasks

3. Given the following FreeRTOS code snippet, what will be the output on the serial console?

void vTask1(void *pvParameters) {
    for (;;) {
        printf("Task 1 running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void vTask2(void *pvParameters) {
    for (;;) {
        printf("Task 2 running\n");
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main() {
    xTaskCreate(vTask1, "Task1", 1000, NULL, 1, NULL);
    xTaskCreate(vTask2, "Task2", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}

medium

A. Task 1 running every 1 second, Task 2 running every 0.5 seconds

B. Task 1 and Task 2 run simultaneously without delay

C. Only Task 1 runs, Task 2 never runs

D. No output because scheduler is not started

Solution

1. Step 1: Analyze task delays

   Task 1 delays 1000 ms (1 second), Task 2 delays 500 ms (0.5 seconds) between prints.

2. Step 2: Understand scheduler behavior

   Both tasks have same priority and run repeatedly with their delays, so Task 2 prints twice as often.

3. Final Answer:

   Task 1 running every 1 second, Task 2 running every 0.5 seconds -> Option A

4. Quick Check:

   Delays control print frequency = Task 1 running every 1 second, Task 2 running every 0.5 seconds [OK]

Hint: Check vTaskDelay times to predict print frequency [OK]

Common Mistakes:

• Assuming tasks run simultaneously without delay
• Thinking only one task runs
• Ignoring vTaskStartScheduler call

4. Identify the error in this FreeRTOS task creation code snippet:

void vTask(void *pvParameters) {
    for (;;) {
        // Task code
    }
}

int main() {
    xTaskCreate(vTask, "Task", 1000, NULL, 2);
    vTaskStartScheduler();
    return 0;
}

medium

A. Missing task handle parameter in xTaskCreate

B. Task function should not have an infinite loop

C. Priority value 2 is invalid

D. vTaskStartScheduler() should be called before xTaskCreate

Solution

1. Step 1: Check xTaskCreate parameters

   xTaskCreate requires 6 parameters; here only 5 are provided, missing the task handle pointer.

2. Step 2: Verify other parts

   Infinite loop in task is normal, priority 2 is valid, scheduler must start after task creation.

3. Final Answer:

   Missing task handle parameter in xTaskCreate -> Option A

4. Quick Check:

   xTaskCreate needs 6 params = Missing handle param [OK]

Hint: Count xTaskCreate parameters; must be six [OK]

Common Mistakes:

• Omitting task handle parameter
• Misunderstanding infinite loops in tasks
• Incorrect order of scheduler start

5. You want to design a FreeRTOS system where a high-priority task waits for data from a low-priority task without wasting CPU time. Which FreeRTOS feature best supports this design?

hard

A. Running both tasks at the same priority to share CPU equally

B. Using vTaskDelay in the high-priority task to wait

C. Using global variables with busy-wait loops

D. Using a queue to send data and block the high-priority task until data arrives

Solution

1. Step 1: Understand task synchronization needs

   The high-priority task must wait efficiently without wasting CPU cycles.

2. Step 2: Evaluate FreeRTOS features

   Queues allow blocking the high-priority task until data is available, avoiding busy-waiting.

3. Step 3: Rule out other options

   vTaskDelay wastes time, busy-wait loops waste CPU, equal priority doesn't guarantee waiting.

4. Final Answer:

   Using a queue to send data and block the high-priority task until data arrives -> Option D

5. Quick Check:

   Queue blocks task efficiently = Using a queue to send data and block the high-priority task until data arrives [OK]

Hint: Use queues to block and wait without CPU waste [OK]

Common Mistakes:

• Using delays instead of blocking
• Busy-waiting wastes CPU
• Ignoring priority differences