vTaskPrioritySet() dynamic priority in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the priority of a FreeRTOS task.

FreeRTOS

vTaskPrioritySet([1], 3);

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

Apriority

BTaskHandle_t

CxTaskHandle

DtaskHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using the priority value as the first argument.

Using the type name instead of a variable.

Using an undefined variable.

The function vTaskPrioritySet() requires the task handle as the first argument. Here, taskHandle is the correct variable representing the task.

2fill in blank

medium

Complete the code to increase the priority of a task by 1.

FreeRTOS

vTaskPrioritySet(taskHandle, [1] + 1);

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

AuxTaskPriorityGet(taskHandle)

BtaskPriority

CpriorityLevel

DgetPriority()

Attempts:

3 left

💡 Hint

Common Mistakes

Using an undefined variable for priority.

Trying to call a method that does not exist.

Passing the priority value directly without getting current priority.

The function uxTaskPriorityGet() returns the current priority of the task. Adding 1 increases the priority by one level.

3fill in blank

hard

Fix the error in setting the task priority dynamically.

FreeRTOS

int newPriority = [1];
vTaskPrioritySet(taskHandle, newPriority);

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

ApriorityLevel + 1

BuxTaskPriorityGet(taskHandle) + 1

CgetPriority() + 1

DtaskPriority + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using variables that are not declared or initialized.

Using functions that do not exist in FreeRTOS.

Not adding 1 to the current priority.

To set a new priority, you must get the current priority using uxTaskPriorityGet() and then add 1. Other options use undefined variables or functions.

4fill in blank

hard

Fill both blanks to create a dictionary of task names and their priorities for tasks with priority greater than 2.

FreeRTOS

taskPriorities = { [1]: uxTaskPriorityGet([2]) for [1] in taskList if uxTaskPriorityGet([1]) > 2 }

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

Atask

BtaskHandle

Cpriority

DtaskName

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for key and value access.

Using undefined variables.

Confusing task names with task handles.

The variable task is used as the loop variable representing each task handle in taskList. We use it to get the priority and as the key in the dictionary.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping task names to their priorities for tasks with priority above 1.

FreeRTOS

taskPriorityDict = { [1]: [2] for [3] in tasks if [2] > 1 }

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

Atask.name

Btask.priority

Ctask

DuxTaskPriorityGet(task)

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined variables for keys or values.

Not calling the function to get priority.

Using the wrong variable in the loop.

We loop over task in tasks. The key is task.name and the value is the priority obtained by uxTaskPriorityGet(task). The condition checks if priority is greater than 1.

Practice

1.

What does the FreeRTOS function vTaskPrioritySet() do?

easy

A. It changes the priority of a task while the program is running.

B. It creates a new task with a fixed priority.

C. It deletes a task permanently.

D. It suspends a task temporarily.

Solution

1. Step 1: Understand the function purpose

   vTaskPrioritySet() is designed to change the priority of an existing task dynamically during runtime.

2. Step 2: Compare with other task functions

   Creating, deleting, or suspending tasks are done by different functions, not vTaskPrioritySet().

3. Final Answer:

   It changes the priority of a task while the program is running. -> Option A

4. Quick Check:

   vTaskPrioritySet() changes priority [OK]

Hint: Remember: vTaskPrioritySet changes priority dynamically [OK]

Common Mistakes:

• Confusing vTaskPrioritySet with task creation functions
• Thinking it deletes or suspends tasks
• Assuming priority is fixed at task creation

2.

Which of the following is the correct syntax to change a task's priority using vTaskPrioritySet()?

TaskHandle_t xTaskHandle;
// Change priority to 3
_____;

easy

A. vTaskPrioritySetPriority(xTaskHandle, 3);

B. vTaskPrioritySet(xTaskHandle, 3);

C. vTaskPrioritySet(3, xTaskHandle);

D. vTaskSetPriority(xTaskHandle, 3);

Solution

1. Step 1: Recall the function signature

   The correct function is vTaskPrioritySet(TaskHandle_t xTask, UBaseType_t uxNewPriority), so the task handle comes first, then the new priority.

2. Step 2: Check the options

   vTaskPrioritySet(xTaskHandle, 3); matches the correct syntax exactly. Options A, B, and D either swap parameters or use incorrect function names.

3. Final Answer:

   vTaskPrioritySet(xTaskHandle, 3); -> Option B

4. Quick Check:

   Correct syntax = vTaskPrioritySet(task, priority) [OK]

Hint: Function name and parameter order matter: task handle first [OK]

Common Mistakes:

• Swapping the order of parameters
• Using incorrect function names
• Passing priority before task handle

3.

Consider the following code snippet:

TaskHandle_t xTask1;
// Assume xTask1 is created with priority 2
vTaskPrioritySet(xTask1, 5);
UBaseType_t newPriority = uxTaskPriorityGet(xTask1);
printf("%u", newPriority);

What will be printed?

medium

A. 0

B. 2

C. 5

D. Compilation error

Solution

1. Step 1: Understand priority change

   The call vTaskPrioritySet(xTask1, 5) changes the task's priority from 2 to 5.

2. Step 2: Check the priority retrieval

   uxTaskPriorityGet(xTask1) returns the current priority, which is now 5.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   Priority updated to 5, so output is 5 [OK]

Hint: Priority changes immediately, so get returns new value [OK]

Common Mistakes:

• Assuming priority stays the same after set
• Confusing priority with task handle
• Thinking printf prints task handle

4.

What is wrong with this code snippet?

TaskHandle_t xTask2 = NULL;
vTaskPrioritySet(xTask2, 4);

medium

A. The function vTaskPrioritySet returns a value that is ignored.

B. Priority 4 is invalid; priorities must be 0 or 1 only.

C. vTaskPrioritySet requires a pointer to the task, not the handle.

D. xTask2 is NULL, so setting priority causes undefined behavior.

Solution

1. Step 1: Check the task handle value

   The variable xTask2 is set to NULL, meaning it does not point to a valid task.

2. Step 2: Understand effect of NULL handle

   Calling vTaskPrioritySet() with a NULL handle leads to undefined behavior or runtime error because no valid task exists to change priority.

3. Final Answer:

   xTask2 is NULL, so setting priority causes undefined behavior. -> Option D

4. Quick Check:

   NULL task handle causes error [OK]

Hint: Never pass NULL as task handle to vTaskPrioritySet [OK]

Common Mistakes:

• Ignoring NULL task handle
• Assuming priority range is only 0 or 1
• Confusing handle with pointer to handle

5.

You have two tasks: TaskA with priority 3 and TaskB with priority 5. You want TaskA to temporarily run with higher priority than TaskB during a critical section. Which code snippet correctly achieves this?

TaskHandle_t xTaskA, xTaskB;
// Initially priorities: TaskA=3, TaskB=5
// Critical section starts
_____;
// Critical section ends
vTaskPrioritySet(xTaskA, 3);

hard

A. vTaskPrioritySet(xTaskA, 6);

B. vTaskPrioritySet(xTaskB, 2);

C. vTaskPrioritySet(xTaskA, 5);

D. vTaskPrioritySet(xTaskB, 3);

Solution

1. Step 1: Identify priority requirements

   TaskA must have higher priority than TaskB (which is 5) during the critical section.

2. Step 2: Choose correct priority change

   Setting TaskA to 6 makes it higher than TaskB's 5. Options A and D lower TaskB's priority instead. vTaskPrioritySet(xTaskA, 5); sets TaskA to 5, equal to TaskB, not higher.

3. Step 3: Restore original priority after critical section

   After the critical section, TaskA's priority is reset to 3 as shown.

4. Final Answer:

   vTaskPrioritySet(xTaskA, 6); -> Option A

5. Quick Check:

   TaskA priority > TaskB priority during critical section [OK]

Hint: Raise TaskA priority above TaskB, then restore after [OK]

Common Mistakes:

• Setting TaskA priority equal to TaskB
• Lowering TaskB priority instead of raising TaskA
• Not restoring original priority after critical section