Task priority assignment in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a task with priority 2.

FreeRTOS

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

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

A2

B0

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as priority which is the idle priority.

Confusing stack size with priority.

The fifth parameter sets the task priority. Here, priority 2 is correct.

2fill in blank

medium

Complete the code to set the priority of an existing task to 3.

FreeRTOS

vTaskPrioritySet([1], 3);

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

AxTaskHandle

BNULL

CtaskFunction

DxQueueHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL which changes the priority of the current task.

Passing the task function name instead of the handle.

The first parameter is the handle of the task whose priority you want to change.

3fill in blank

hard

Fix the error in setting the task priority to 4 for a task handle named myTaskHandle.

FreeRTOS

vTaskPrioritySet(myTaskHandle, [1]);

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

A"4"

B4

CHIGH

Dpriority

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an integer for priority.

Using undefined constants.

The priority must be an integer value, not a string or undefined variable.

4fill in blank

hard

Fill both blanks to create a task with priority 5 and stack size 2000.

FreeRTOS

xTaskCreate(taskFunction, "Task2", [1], NULL, [2], NULL);

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

A2000

B1000

C5

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping stack size and priority parameters.

Using too small stack size for the task.

The third parameter is stack size, and the fifth is priority.

5fill in blank

hard

Fill all three blanks to create a task with name "Logger", priority 3, and stack size 1500.

FreeRTOS

xTaskCreate([1], [2], [3], NULL, 3, NULL);

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

AloggerTask

B"Logger"

C1500

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Using stack size as a string.

Confusing task name and function name.

Using wrong priority value.

The first argument is the task function name, second is the task name string, third is stack size.

Practice

1.

In FreeRTOS, what does a higher task priority number mean?

easy

A. The task runs only when idle

B. The task runs after lower priority tasks

C. The task runs before lower priority tasks

D. The task is deleted automatically

Solution

1. Step 1: Understand task priority meaning

   In FreeRTOS, tasks with higher priority numbers get CPU time before lower priority tasks.

2. Step 2: Relate priority number to execution order

   A higher number means the task is more important and runs first.

3. Final Answer:

   The task runs before lower priority tasks -> Option C

4. Quick Check:

   Higher priority = runs first [OK]

Hint: Higher number means higher priority, runs first [OK]

Common Mistakes:

• Thinking lower number means higher priority
• Confusing priority with task state
• Assuming priority controls memory usage

2.

Which of the following is the correct way to assign a priority of 3 to a task in FreeRTOS using xTaskCreate?

void vTaskFunction(void *pvParameters) { /* Task code */ }

xTaskCreate(vTaskFunction, "Task1", 1000, NULL, ?, NULL);

easy

A. taskPriority = 3

B. "3"

C. priority = 3

D. 3

Solution

1. Step 1: Check xTaskCreate parameters

   The fifth parameter is the task priority and expects an integer value.

2. Step 2: Identify correct priority assignment

   Passing 3 directly as an integer is correct; strings or assignments are invalid here.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   Priority parameter = integer value [OK]

Hint: Priority is an integer, no quotes or assignments [OK]

Common Mistakes:

• Using quotes around priority number
• Writing assignment expressions inside parameters
• Passing variable names without declaration

3.

Given the following FreeRTOS code snippet, which task will run first?

void TaskA(void *pvParameters) { while(1) {} }
void TaskB(void *pvParameters) { while(1) {} }

xTaskCreate(TaskA, "A", 1000, NULL, 2, NULL);
xTaskCreate(TaskB, "B", 1000, NULL, 4, NULL);

medium

A. TaskB

B. TaskA

C. Both run simultaneously

D. Neither runs

Solution

1. Step 1: Identify task priorities

   TaskA has priority 2, TaskB has priority 4.

2. Step 2: Determine which runs first

   TaskB has higher priority, so it runs before TaskA.

3. Final Answer:

   TaskB -> Option A

4. Quick Check:

   Higher priority task runs first [OK]

Hint: Higher priority number runs first [OK]

Common Mistakes:

• Assuming tasks run in creation order
• Thinking equal priority means simultaneous run
• Ignoring priority values

4.

What is wrong with this FreeRTOS task creation code snippet?

void vTask(void *pvParameters) { /* code */ }

xTaskCreate(vTask, "Task", 1000, NULL, 5, NULL);
xTaskCreate(vTask, "Task", 1000, NULL, -1, NULL);

medium

A. Priority cannot be negative

B. Task name must be unique

C. Stack size must be zero

D. Task function must return int

Solution

1. Step 1: Check priority values

   FreeRTOS priorities must be zero or positive integers; negative values are invalid.

2. Step 2: Validate other parameters

   Task name can be reused, stack size 1000 is valid, and task function returns void as required.

3. Final Answer:

   Priority cannot be negative -> Option A

4. Quick Check:

   Priority >= 0 required [OK]

Hint: Priority must be zero or positive [OK]

Common Mistakes:

• Using negative priority values
• Thinking task names must be unique
• Expecting task function to return int

5.

You have three tasks with priorities 1, 3, and 3. How should you assign priorities to ensure the most important task runs first and the least important runs last?

Choose the best priority assignment:

• A: Task1=1, Task2=3, Task3=3
• B: Task1=3, Task2=3, Task3=1
• C: Task1=3, Task2=1, Task3=3
• D: Task1=1, Task2=1, Task3=3

hard

A. Task1=1 (lowest), Task2=3, Task3=3 (highest)

B. Task1=3 (highest), Task2=3, Task3=1 (lowest)

C. Task1=3 (highest), Task2=1, Task3=3 (highest)

D. Task1=1, Task2=1, Task3=3 (highest)

Solution

1. Step 1: Identify importance order

   The most important task should have highest priority (3), least important lowest (1).

2. Step 2: Match priorities to tasks

   Task1=3 (highest), Task2=3, Task3=1 (lowest) assigns highest priority (3) to Task1 and Task2, and lowest (1) to Task3, ensuring important tasks run first.

3. Final Answer:

   Task1=3 (highest), Task2=3, Task3=1 (lowest) -> Option B

4. Quick Check:

   Highest priority = most important task [OK]

Hint: Assign highest number to most important task [OK]

Common Mistakes:

• Assigning same priority to all tasks
• Giving lowest priority to important tasks
• Ignoring task importance order