Why priority design matters in FreeRTOS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the task priority correctly.

FreeRTOS

xTaskCreate(TaskFunction, "Task1", 1000, NULL, [1], NULL);

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

AconfigMAX_PRIORITIES + 1

B0

CtskIDLE_PRIORITY + 1

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting priority to 0 causes the task to have idle priority.

Using negative or out-of-range priorities causes errors.

The task priority must be set above the idle priority to ensure it runs.

2fill in blank

medium

Complete the code to create a high priority task.

FreeRTOS

xTaskCreate(TaskFunction, "HighPriorityTask", 1000, NULL, [1], NULL);

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

A1

BtskIDLE_PRIORITY

CconfigMAX_PRIORITIES + 1

DconfigMAX_PRIORITIES - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using configMAX_PRIORITIES causes invalid priority error.

Using idle priority for high priority tasks causes scheduling issues.

High priority tasks use the highest valid priority, which is configMAX_PRIORITIES - 1.

3fill in blank

hard

Fix the error in the priority assignment.

FreeRTOS

vTaskPrioritySet(TaskHandle, [1]);

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

AtskIDLE_PRIORITY + 2

BconfigMAX_PRIORITIES

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting priority to configMAX_PRIORITIES causes errors.

Negative priorities are invalid.

Priority must be within valid range: 0 to configMAX_PRIORITIES - 1.

4fill in blank

hard

Fill both blanks to create a medium priority task and set its priority.

FreeRTOS

xTaskCreate(TaskFunction, "MediumTask", 1000, NULL, [1], &TaskHandle);
vTaskPrioritySet(TaskHandle, [2]);

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

AtskIDLE_PRIORITY + 2

BtskIDLE_PRIORITY + 1

DconfigMAX_PRIORITIES

Attempts:

3 left

💡 Hint

Common Mistakes

Using different priorities for creation and setting causes confusion.

Using invalid priority values causes runtime errors.

Both creation and priority set use the same valid medium priority.

5fill in blank

hard

Fill all three blanks to create a task, set its priority, and delete it properly.

FreeRTOS

xTaskCreate(TaskFunction, "TempTask", 1000, NULL, [1], &TaskHandle);
vTaskPrioritySet(TaskHandle, [2]);
vTaskDelete([3]);

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

AtskIDLE_PRIORITY + 1

CTaskHandle

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Deleting task with NULL handle does nothing.

Using inconsistent priorities causes unexpected behavior.

Create and set priority with valid value, then delete the task using its handle.

Practice

1.

Why is task priority important in FreeRTOS?

easy

A. It determines which task runs first when multiple are ready.

B. It changes the task's memory size automatically.

C. It controls the task's stack overflow protection.

D. It sets the task's execution time limit.

Solution

1. Step 1: Understand task scheduling in FreeRTOS

   FreeRTOS uses task priorities to decide which task runs when multiple tasks are ready.

2. Step 2: Identify the role of priority

   The highest priority ready task gets CPU time first, ensuring important tasks run promptly.

3. Final Answer:

   It determines which task runs first when multiple are ready. -> Option A

4. Quick Check:

   Priority controls task execution order = A [OK]

Hint: Priority decides task run order, highest runs first [OK]

Common Mistakes:

• Confusing priority with memory size
• Thinking priority limits execution time
• Assuming priority controls stack protection

2.

Which of the following is the correct way to set a task priority in FreeRTOS?

vTaskPrioritySet(

easy

A. vTaskPrioritySet(TaskHandle_t xTask);

B. vTaskPrioritySet(TaskHandle_t xTask, UBaseType_t uxNewPriority);

C. vTaskPrioritySet(UBaseType_t uxNewPriority, TaskHandle_t xTask);

D. vTaskPrioritySet(UBaseType_t uxNewPriority);

Solution

1. Step 1: Recall FreeRTOS API for setting priority

   The function vTaskPrioritySet requires the task handle and the new priority as parameters.

2. Step 2: Check parameter order

   The correct order is first the task handle, then the new priority value.

3. Final Answer:

   vTaskPrioritySet(TaskHandle_t xTask, UBaseType_t uxNewPriority); -> Option B

4. Quick Check:

   Correct parameter order = C [OK]

Hint: Task handle first, then priority in vTaskPrioritySet [OK]

Common Mistakes:

• Swapping parameter order
• Missing one parameter
• Using wrong parameter types

3.

Given two tasks, TaskA with priority 3 and TaskB with priority 2, both ready to run, which task will FreeRTOS run first?

medium

A. TaskB

B. Depends on task creation order

C. Both run simultaneously

D. TaskA

Solution

1. Step 1: Compare task priorities

   TaskA has priority 3, TaskB has priority 2. Higher number means higher priority.

2. Step 2: Determine which task runs first

   FreeRTOS runs the highest priority ready task first, so TaskA runs before TaskB.

3. Final Answer:

   TaskA -> Option D

4. Quick Check:

   Higher priority runs first = B [OK]

Hint: Higher priority number runs first in FreeRTOS [OK]

Common Mistakes:

• Thinking lower number means higher priority
• Assuming tasks run simultaneously
• Believing creation order affects scheduling

4.

What is wrong with this code snippet?

vTaskPrioritySet(3, TaskHandle);

medium

A. Parameters are in wrong order.

B. Priority value 3 is invalid.

C. TaskHandle should be a number.

D. Function name is incorrect.

Solution

1. Step 1: Check function parameter order

   The correct order is (TaskHandle_t xTask, UBaseType_t uxNewPriority), but here it is reversed.

2. Step 2: Validate parameter types

   TaskHandle should be first, priority second. The code swaps them causing error.

3. Final Answer:

   Parameters are in wrong order. -> Option A

4. Quick Check:

   Correct parameter order matters = A [OK]

Hint: Task handle first, priority second in vTaskPrioritySet [OK]

Common Mistakes:

• Swapping parameters
• Using wrong data types
• Misnaming the function

5.

You have three tasks: Task1 (priority 2), Task2 (priority 2), and Task3 (priority 3). Task1 and Task2 share a resource and must not run simultaneously. How should you design priorities to keep the system responsive and safe?

hard

A. Use no priorities and rely on task delays.

B. Set all tasks to same priority to avoid conflicts.

C. Set Task3 highest priority, Task1 and Task2 equal lower priorities, use mutex for resource.

D. Set Task1 highest priority, Task2 medium, Task3 lowest.

Solution

1. Step 1: Assign highest priority to critical task

   Task3 has highest priority (3) to keep system responsive.

2. Step 2: Use equal lower priorities and mutex for shared resource

   Task1 and Task2 have same priority (2) and use a mutex to prevent simultaneous access.

3. Step 3: Avoid equal priorities without synchronization

   Equal priorities without mutex risk resource conflicts; delays reduce responsiveness.

4. Final Answer:

   Set Task3 highest priority, Task1 and Task2 equal lower priorities, use mutex for resource. -> Option C

5. Quick Check:

   Priority + mutex ensures safety and responsiveness = D [OK]

Hint: Use highest priority for critical task, mutex for shared resource [OK]

Common Mistakes:

• Ignoring resource protection
• Setting all tasks same priority without sync
• Using delays instead of priorities