Task function signature in FreeRTOS

Introduction

Task functions are the main code blocks that run in FreeRTOS tasks. They need a specific format so the system can run them properly.

When creating a new task to run code concurrently.

When defining what a task should do when it starts.

When passing a function to FreeRTOS to manage as a task.

When organizing code to run in separate threads on a microcontroller.

Syntax

FreeRTOS

void TaskName(void *pvParameters)

The function must return void because tasks do not return values.

The parameter void *pvParameters allows passing any data to the task.

Examples

Basic task function with no return and a generic parameter pointer.

FreeRTOS

void vTaskCode(void *pvParameters) {
    // Task code here
}

Task function that receives a pointer to an integer parameter and uses it.

FreeRTOS

void SensorTask(void *pvParameters) {
    int sensorId = *(int *)pvParameters;
    // Use sensorId in task
}

Sample Program

This program creates a FreeRTOS task named "ExampleTask" that prints its name every second. The task function uses the parameter to know its name.

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include <stdio.h>

void vTaskExample(void *pvParameters) {
    const char *taskName = (const char *)pvParameters;
    for (;;) {
        printf("Running task: %s\n", taskName);
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

int main(void) {
    const char *name = "Task1";
    xTaskCreate(vTaskExample, "ExampleTask", 1000, (void *)name, 1, NULL);
    vTaskStartScheduler();
    for(;;); // Should never reach here
    return 0;
}

Important Notes

Task functions must never return; they usually run an infinite loop.

Always cast pvParameters to the correct pointer type before use.

Summary

Task functions have the signature void TaskName(void *pvParameters).

They run code inside an infinite loop and do not return.

The pvParameters pointer lets you pass any data to the task.

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