xTaskCreate() function in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this FreeRTOS task creation code?

Consider the following FreeRTOS code snippet that creates a task. What will be the output printed by the task?

FreeRTOS

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

void vTaskCode(void * pvParameters) {
    printf("Task running with parameter: %d\n", (int)(intptr_t)pvParameters);
    vTaskDelete(NULL);
}

int main() {
    BaseType_t xReturned;
    TaskHandle_t xHandle = NULL;

    xReturned = xTaskCreate(
                    vTaskCode,       /* Function that implements the task. */
                    "Task1",         /* Text name for the task. */
                    1000,             /* Stack size in words, not bytes. */
                    (void *)42,       /* Parameter passed into the task. */
                    1,                /* Priority at which the task is created. */
                    &xHandle);        /* Used to pass out the created task's handle. */

    if(xReturned == pdPASS) {
        vTaskStartScheduler();
    } else {
        printf("Task creation failed!\n");
    }
    return 0;
}

A Task running with parameter: 0

B Task running with parameter: 42

C Task creation failed!

D Compilation error due to cast

💡 Hint

Look at the parameter passed to the task and how it is printed.

The task is created with parameter (void *)42, which is cast back to int inside the task and printed. So the output is "Task running with parameter: 42".

🧠 Conceptual

intermediate

What does the 'uxPriority' parameter in xTaskCreate() control?

In the xTaskCreate() function, what is the role of the 'uxPriority' parameter?

A It specifies the maximum number of times the task can run.

B It defines the stack size allocated to the task in bytes.

C It sets the priority level of the created task, determining its scheduling order.

D It is used to pass parameters to the task function.

💡 Hint

Think about how FreeRTOS decides which task to run first.

The 'uxPriority' parameter sets the task's priority. Higher priority tasks run before lower priority ones.

🔧 Debug

advanced

Why does this xTaskCreate() call fail to create a task?

Examine the following code snippet. Why does the task creation fail?

FreeRTOS

void vTaskCode(void * pvParameters) {
    for(;;) {}
}

int main() {
    BaseType_t xReturned;
    TaskHandle_t xHandle = NULL;

    xReturned = xTaskCreate(
                    vTaskCode,
                    "Task2",
                    0,          /* Stack size is zero */
                    NULL,
                    1,
                    &xHandle);

    if(xReturned == pdPASS) {
        vTaskStartScheduler();
    } else {
        printf("Task creation failed due to stack size!\n");
    }
    return 0;
}

A Because the stack size parameter is zero, which is invalid.

B Because the task function does not call vTaskDelete().

C Because the task priority is set to 1, which is too low.

D Because the task handle pointer is NULL.

💡 Hint

Check the stack size argument passed to xTaskCreate().

A stack size of zero is invalid and causes xTaskCreate() to fail.

📝 Syntax

advanced

Which xTaskCreate() call is syntactically correct?

Identify the syntactically correct xTaskCreate() call from the options below.

FreeRTOS

void vTaskCode(void * pvParameters) { for(;;) {} }

A xTaskCreate(vTaskCode, "Task", 1000, NULL, 2, NULL);

B xTaskCreate(vTaskCode, Task, 1000, NULL, 2, NULL);

C xTaskCreate(vTaskCode, "Task", 1000, NULL, "2", NULL);

D xTaskCreate(vTaskCode, "Task", 1000, NULL, 2);

💡 Hint

Check the types of each argument required by xTaskCreate().

Option A uses correct types: function pointer, string, stack size (uint16_t), void pointer, priority (UBaseType_t), and task handle pointer.

🚀 Application

expert

How many tasks are created and running after this code executes?

Given the following code, how many tasks will be created and running after vTaskStartScheduler() is called?

FreeRTOS

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

void vTaskCode(void * pvParameters) {
    printf("Task %d started\n", (int)(intptr_t)pvParameters);
    vTaskDelete(NULL);
}

int main() {
    BaseType_t xReturned;
    TaskHandle_t xHandle1 = NULL, xHandle2 = NULL;

    xReturned = xTaskCreate(vTaskCode, "Task1", 1000, (void *)1, 1, &xHandle1);
    if(xReturned != pdPASS) {
        printf("Failed to create Task1\n");
    }

    xReturned = xTaskCreate(vTaskCode, "Task2", 1000, (void *)2, 1, &xHandle2);
    if(xReturned != pdPASS) {
        printf("Failed to create Task2\n");
    }

    vTaskStartScheduler();
    return 0;
}

A No tasks run because the scheduler is never started.

B Only one task runs because the second creation fails.

C Two tasks are created but never run because of missing infinite loops.

D Two tasks are created and run briefly before deleting themselves.

💡 Hint

Look at how tasks delete themselves after printing and the scheduler start.

Both tasks are created successfully and run once, printing their message, then delete themselves.