Task function signature in FreeRTOS - Mini Project: Build & Apply

Understanding Task Function Signature in FreeRTOS

📖 Scenario: You are working on a small embedded system project using FreeRTOS. To run tasks properly, you need to write task functions with the correct signature so the operating system can manage them.

🎯 Goal: Learn how to write a FreeRTOS task function with the correct signature and create a simple task that prints a message.

📋 What You'll Learn

Create a task function with the correct FreeRTOS signature

Use the void *pvParameters parameter

Call vTaskDelete(NULL) at the end of the task

Print a message inside the task function

💡 Why This Matters

🌍 Real World

Embedded systems often use FreeRTOS to manage multiple tasks like sensor reading, communication, and control. Writing task functions correctly is essential for system stability.

💼 Career

Understanding FreeRTOS task function signatures is important for embedded software engineers working on real-time applications in industries like automotive, robotics, and IoT.

1

Create a FreeRTOS task function skeleton

Write a function called vTaskFunction that takes a single parameter void *pvParameters and returns void. Inside the function, add an empty infinite loop for(;;).

FreeRTOS

void vTaskFunction(void *pvParameters) {
    // Your code here
}

Hint

Remember, FreeRTOS task functions always have the signature void functionName(void *pvParameters) and usually run an infinite loop.

2

Add a print statement inside the task loop

Inside the infinite loop of vTaskFunction, add a call to printf that prints the exact message "Task is running\n".

FreeRTOS

void vTaskFunction(void *pvParameters) {
    for(;;) {
        // Add printf statement here
    }
}

Hint

Use printf inside the loop to show the task is running.

3

Add task deletion to end the task properly

After the infinite loop in vTaskFunction, add a call to vTaskDelete(NULL) to delete the current task when it finishes.

FreeRTOS

void vTaskFunction(void *pvParameters) {
    for(;;) {
        printf("Task is running\n");
    }
    // Add vTaskDelete(NULL) here
}

Hint

Use vTaskDelete(NULL) to delete the current task safely.

4

Print a message to confirm task function is defined

Write a main function that calls printf with the exact message "Task function signature ready" to confirm your task function is defined correctly.

FreeRTOS

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

int main(void) {
    // Your code here
}

Hint

Use printf in main to print the confirmation message.

Practice

1.

What is the correct signature for a FreeRTOS task function?

easy

A. int TaskName(int param)

B. void TaskName(void *pvParameters)

C. void TaskName()

D. void TaskName(int *param)

Solution

1. Step 1: Recall FreeRTOS task function signature

   FreeRTOS tasks must have the signature with return type void and a single void pointer parameter.

2. Step 2: Match the signature with options

   Only void TaskName(void *pvParameters) matches void TaskName(void *pvParameters) exactly.

3. Final Answer:

   void TaskName(void *pvParameters) -> Option B

4. Quick Check:

   Task signature = void TaskName(void *pvParameters) [OK]

Hint: Task functions always return void and take void* parameter [OK]

Common Mistakes:

• Using int return type instead of void
• Omitting the void* parameter
• Using incorrect parameter types

2.

Which of the following is a syntactically correct FreeRTOS task function declaration?

void MyTask(_____)

easy

A. void *pvParameters

B. int param

C. char *name

D. void

Solution

1. Step 1: Understand parameter type for FreeRTOS tasks

   Task functions must accept a single parameter of type void *.

2. Step 2: Check each option

   Only void *pvParameters uses void *pvParameters, which is correct syntax.

3. Final Answer:

   void *pvParameters -> Option A

4. Quick Check:

   Parameter type = void *pvParameters [OK]

Hint: Task parameter must be void pointer (void*) [OK]

Common Mistakes:

• Using int or char pointer instead of void pointer
• Using void without pointer
• Missing parameter entirely

3.

What will happen if you run this FreeRTOS task function?

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

medium

A. The task will return a value causing runtime error.

B. The task will run once and then exit.

C. The task will cause a compile error.

D. The task will run repeatedly in an infinite loop.

Solution

1. Step 1: Analyze the task function loop

   The task contains a for(;;) infinite loop, so it runs repeatedly.

2. Step 2: Understand FreeRTOS task behavior

   Tasks should not return; they run inside infinite loops to keep running.

3. Final Answer:

   The task will run repeatedly in an infinite loop. -> Option D

4. Quick Check:

   Infinite loop in task = runs repeatedly [OK]

Hint: FreeRTOS tasks run inside infinite loops [OK]

Common Mistakes:

• Thinking task runs once and exits
• Expecting return value from task
• Confusing infinite loop with error

4.

Identify the error in this FreeRTOS task function:

void FaultyTask(void *pvParameters) {
    int count = 0;
    while(count < 5) {
        count++;
    }
    return;
}

medium

A. The function should not return; it must loop forever.

B. The parameter type is incorrect.

C. The variable count should be a pointer.

D. The while loop condition is invalid syntax.

Solution

1. Step 1: Check task function return behavior

   FreeRTOS tasks must not return; they should run inside infinite loops.

2. Step 2: Analyze the code flow

   This task loops 5 times then returns, which is incorrect for FreeRTOS tasks.

3. Final Answer:

   The function should not return; it must loop forever. -> Option A

4. Quick Check:

   Tasks must not return, use infinite loop [OK]

Hint: Tasks must never return; use infinite loops [OK]

Common Mistakes:

• Allowing task to return
• Changing parameter type incorrectly
• Misunderstanding loop conditions

5.

You want to pass an integer value to a FreeRTOS task. Which is the correct way to define and use the task function?

void NumberTask(_____)
{
    int received = *(int *)pvParameters;
    for(;;) {
        // Use received value
    }
}

hard

A. void pvParameters

B. int pvParameters

C. void *pvParameters

D. int *pvParameters

Solution

1. Step 1: Recall task function parameter type

   Task functions must accept a void * parameter to allow any data type.

2. Step 2: Understand data passing

   The integer is passed via pointer cast from void *, so parameter must be void *pvParameters.

3. Final Answer:

   void *pvParameters -> Option C

4. Quick Check:

   Use void* parameter to pass any data type [OK]

Hint: Always use void* parameter to pass data to tasks [OK]

Common Mistakes:

• Using int instead of void* parameter
• Using void without pointer
• Not casting void* to correct type inside task