Task function signature in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this FreeRTOS task function signature code?

Consider this FreeRTOS task function signature and its usage. What will be the output when the task runs?

FreeRTOS

void vTaskCode(void *pvParameters) {
    int *p = (int *)pvParameters;
    printf("Value: %d\n", *p);
}

int main() {
    int x = 10;
    vTaskCode(&x);
    return 0;
}

A Runtime error due to invalid pointer

B Value: 0

C Compilation error due to wrong function signature

D Value: 10

💡 Hint

Remember the task function takes a void pointer parameter which can be cast to any type.

The task function receives a void pointer which is cast to int pointer. The value pointed to is printed correctly as 10.

❓ Predict Output

intermediate

What error occurs with this incorrect FreeRTOS task function signature?

What error will this code produce when compiled or run?

FreeRTOS

void vTaskCode(int pvParameters) {
    printf("Value: %d\n", pvParameters);
}

int main() {
    int x = 5;
    vTaskCode(x);
    return 0;
}

A Compilation error due to wrong parameter type

B Prints: Value: 5

C Runtime error due to invalid pointer

D No output

💡 Hint

Check the parameter type expected by FreeRTOS task functions.

Although the signature is not the standard FreeRTOS task signature, this code compiles and prints 5 because the function is called directly.

🧠 Conceptual

advanced

Which is the correct FreeRTOS task function signature?

Select the correct function signature for a FreeRTOS task function.

A void TaskFunction()

B int TaskFunction(int pvParameters)

C void TaskFunction(void *pvParameters)

D void TaskFunction(int *pvParameters)

💡 Hint

FreeRTOS task functions always take a void pointer parameter and return void.

FreeRTOS task functions must have the signature void function(void *pvParameters) to be compatible with the scheduler.

❓ Predict Output

advanced

What is the output of this FreeRTOS task function with pointer parameter?

What will this code print when the task function runs?

FreeRTOS

void vTaskCode(void *pvParameters) {
    char *msg = (char *)pvParameters;
    printf("Message: %s\n", msg);
}

int main() {
    char message[] = "Hello FreeRTOS";
    vTaskCode(message);
    return 0;
}

A Message: Hello FreeRTOS

B Compilation error due to wrong cast

C Message: (null)

D Runtime error due to invalid pointer

💡 Hint

Casting void pointer to char pointer is valid for string parameters.

The void pointer is cast to char pointer correctly and prints the string.

🧠 Conceptual

expert

Why must FreeRTOS task functions have the signature void function(void *pvParameters)?

Choose the best explanation for why FreeRTOS task functions require this signature.

A Because the scheduler expects a function returning void and taking a generic pointer to pass any data.

B Because void return type allows returning task status codes to the scheduler.

C Because the parameter must always be an integer representing task ID.

D Because FreeRTOS tasks cannot accept any parameters.

💡 Hint

Think about how the scheduler manages tasks and passes data.

The scheduler calls task functions expecting void return and a void pointer parameter to pass any user data generically.

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