Task handle usage in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a task and store its handle.

FreeRTOS

TaskHandle_t [1] = NULL;
xTaskCreate(taskFunction, "Task1", 1000, NULL, 1, &handle);

Drag options to blanks, or click blank then click option'

Ahandle

BtaskHandle

Ctask1Handle

DxHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name not matching the one passed to xTaskCreate.

Not declaring the handle variable before use.

The variable 'handle' is used to store the task handle when creating a task.

2fill in blank

medium

Complete the code to delete a task using its handle.

FreeRTOS

vTaskDelete([1]);

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ANULL

BxHandle

Chandle

DtaskHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL to vTaskDelete deletes the current task, not the target task.

Using an undefined variable.

To delete a specific task, pass its handle to vTaskDelete.

3fill in blank

hard

Fix the error in the code to suspend a task using its handle.

FreeRTOS

vTaskSuspend([1]);

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AtaskHandle

Bhandle

CNULL

DxHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL instead of the task handle.

Using a different variable name than the one storing the handle.

The correct handle variable 'handle' must be passed to vTaskSuspend to suspend the task.

4fill in blank

hard

Fill both blanks to resume a suspended task using its handle and check if the handle is valid.

FreeRTOS

if ([1] != NULL) {
    vTaskResume([2]);
}

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Ahandle

BtaskHandle

CNULL

DxHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for the check and resume call.

Not checking if the handle is NULL before resuming.

Check if 'handle' is not NULL before resuming the task using the same handle.

5fill in blank

hard

Fill all three blanks to create a task, store its handle, and then delete it.

FreeRTOS

TaskHandle_t [1] = NULL;
xTaskCreate(taskFunction, "Task2", 1000, NULL, 1, &[2]);
vTaskDelete([3]);

Drag options to blanks, or click blank then click option'

Ahandle2

DtaskHandle2

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for declaration, creation, and deletion.

Not passing the address of the handle variable to xTaskCreate.

Use the same variable 'handle2' to declare, pass to xTaskCreate, and delete the task.

Practice

1.

What is the main purpose of a task handle in FreeRTOS?

easy

A. To allocate memory for tasks

B. To store task priority values

C. To identify and control a specific task

D. To define the task's stack size

Solution

1. Step 1: Understand what a task handle represents

   A task handle is a reference used to identify a task uniquely in FreeRTOS.

2. Step 2: Identify the purpose of the handle

   The handle allows you to control the task, such as suspending or deleting it.

3. Final Answer:

   To identify and control a specific task -> Option C

4. Quick Check:

   Task handle = task control reference [OK]

Hint: Task handles let you control tasks by their ID [OK]

Common Mistakes:

• Confusing handle with task priority
• Thinking handle allocates memory
• Mixing handle with stack size

2.

Which of the following is the correct way to declare a task handle variable in FreeRTOS?

?

easy

A. TaskHandle_t xTaskHandle;

B. TaskHandle xTaskHandle;

C. HandleTask_t xTaskHandle;

D. Task_Handle xTaskHandle;

Solution

1. Step 1: Recall the FreeRTOS type for task handles

   The correct type defined by FreeRTOS for task handles is TaskHandle_t.

2. Step 2: Check the syntax of declaration

   Declaring a variable as TaskHandle_t xTaskHandle; is the correct syntax.

3. Final Answer:

   TaskHandle_t xTaskHandle; -> Option A

4. Quick Check:

   Task handle type = TaskHandle_t [OK]

Hint: Use TaskHandle_t to declare task handles [OK]

Common Mistakes:

• Using incorrect type names
• Adding underscores wrongly
• Confusing with other handle types

3.

What will be the output of the following code snippet?

TaskHandle_t xHandle = NULL;

void vTaskFunction(void *pvParameters) {
    for (;;) {
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

int main() {
    xTaskCreate(vTaskFunction, "Task1", 1000, NULL, 1, &xHandle);
    if (xHandle != NULL) {
        printf("Task created successfully\n");
    } else {
        printf("Task creation failed\n");
    }
    return 0;
}

medium

A. Task creation failed

B. Task created successfully

C. Compilation error due to missing includes

D. No output, program hangs

Solution

1. Step 1: Analyze task creation and handle assignment

   The function xTaskCreate assigns the created task's handle to xHandle. If successful, xHandle is not NULL.

2. Step 2: Check the condition and output

   The code checks if xHandle != NULL and prints "Task created successfully" if true.

3. Final Answer:

   Task created successfully -> Option B

4. Quick Check:

   xHandle != NULL means success [OK]

Hint: Check if handle is NULL to confirm task creation [OK]

Common Mistakes:

• Assuming handle is NULL on success
• Ignoring handle assignment
• Confusing task creation return value

4.

Identify the error in the following code snippet related to task handle usage:

TaskHandle_t xTaskHandle;

void vTaskFunction(void *pvParameters) {
    for (;;) {
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main() {
    xTaskCreate(vTaskFunction, "Task", 1000, NULL, 1, xTaskHandle);
    vTaskSuspend(xTaskHandle);
    return 0;
}

medium

A. xTaskCreate should pass &xTaskHandle, not xTaskHandle

B. vTaskSuspend cannot suspend a task

C. Task handle must be initialized to NULL before use

D. Task priority is missing in xTaskCreate

Solution

1. Step 1: Check how task handle is passed to xTaskCreate

   The last parameter of xTaskCreate expects a pointer to the task handle variable, so it should be &xTaskHandle.

2. Step 2: Identify the error in the code

   The code passes xTaskHandle instead of its address, causing incorrect handle assignment.

3. Final Answer:

   xTaskCreate should pass &xTaskHandle, not xTaskHandle -> Option A

4. Quick Check:

   Pass handle address to xTaskCreate [OK]

Hint: Always pass &handle to xTaskCreate [OK]

Common Mistakes:

• Passing handle instead of its address
• Assuming vTaskSuspend needs no handle
• Ignoring task priority parameter

5.

You want to create two tasks and suspend the first one after creation using task handles. Which code snippet correctly achieves this?

void vTask1(void *pvParameters) { for(;;) {} }
void vTask2(void *pvParameters) { for(;;) {} }

int main() {
    TaskHandle_t xHandle1 = NULL, xHandle2 = NULL;
    // Create tasks here
    // Suspend first task here
    return 0;
}

hard

A. xTaskCreate(vTask1, "Task1", 1000, NULL, 1, &xHandle1);
xTaskCreate(vTask2, "Task2", 1000, NULL, 1, &xHandle2);
vTaskSuspend(NULL);

B. xTaskCreate(vTask1, "Task1", 1000, NULL, 1, xHandle1);
xTaskCreate(vTask2, "Task2", 1000, NULL, 1, xHandle2);
vTaskSuspend(xHandle1);

C. xTaskCreate(vTask1, "Task1", 1000, NULL, 1, &xHandle1);
xTaskCreate(vTask2, "Task2", 1000, NULL, 1, &xHandle2);
vTaskSuspend(&xHandle1);

D. xTaskCreate(vTask1, "Task1", 1000, NULL, 1, &xHandle1);
xTaskCreate(vTask2, "Task2", 1000, NULL, 1, &xHandle2);
vTaskSuspend(xHandle1);

Solution

1. Step 1: Correctly create tasks with handles

   Use &xHandle1 and &xHandle2 to store task handles during creation.

2. Step 2: Suspend the first task using its handle

   Call vTaskSuspend(xHandle1); to suspend the first task by passing the handle itself, not its address or NULL.

3. Final Answer:

   Correct creation with &xHandle and suspend with xHandle1 -> Option D

4. Quick Check:

   Create with &handle, suspend with handle [OK]

Hint: Create tasks with &handle, suspend using handle [OK]

Common Mistakes:

• Passing handle instead of &handle to xTaskCreate
• Passing &handle to vTaskSuspend instead of handle
• Suspending with NULL handle