Why RTOS over bare-metal in FreeRTOS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a FreeRTOS task that prints "Hello".

FreeRTOS

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

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

AvTaskStartScheduler

BvTaskDelay

CvTaskPrintHello

DvTaskDelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using scheduler start function instead of task function

Using delay or delete functions incorrectly

The function vTaskPrintHello is the task function that prints "Hello". It is passed to xTaskCreate to create the task.

2fill in blank

medium

Complete the code to start the FreeRTOS scheduler.

FreeRTOS

int main() {
    // Setup code
    [1]();
    while(1) {}
}

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

AvTaskSuspend

BvTaskDelete

CvTaskDelay

DvTaskStartScheduler

Attempts:

3 left

💡 Hint

Common Mistakes

Calling delay or delete functions instead of starting scheduler

The function vTaskStartScheduler() starts the FreeRTOS scheduler, which begins running tasks.

3fill in blank

hard

Fix the error in the task function to yield control to other tasks.

FreeRTOS

void vTaskFunction(void *pvParameters) {
    while(1) {
        // Do work
        [1](1);
    }
}

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

AvTaskSuspend

BvTaskDelay

CvTaskStartScheduler

DvTaskDelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete or suspend which stops the task

Starting scheduler inside task

Using vTaskDelay(1) inside the loop allows the task to yield and lets other tasks run.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps task names to their priorities if priority is greater than 2.

FreeRTOS

task_priorities = {task[1]: priority for task, priority in tasks.items() if priority [2] 2}

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

A.upper()

B>

C<

D.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operator

Not changing case of task names

The task names are converted to uppercase with .upper(), and only tasks with priority greater than 2 are included.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase task names to their priorities if priority is less than 5.

FreeRTOS

filtered_tasks = [1]: [2] for task, [3] in tasks.items() if priority < 5}}

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

Atask.upper()

Bpriority

Dtask

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names

Not converting task names to uppercase

The dictionary maps uppercase task names (task.upper()) to their priorities, filtering tasks with priority less than 5.

Practice

1. Why is using an RTOS often better than programming on bare-metal for complex embedded systems?

easy

A. Because bare-metal code runs faster without any overhead

B. Because RTOS requires no knowledge of hardware

C. Because RTOS handles multiple tasks with scheduling and timing automatically

D. Because bare-metal systems never crash

Solution

1. Step 1: Understand task management differences

   RTOS automatically manages multiple tasks with scheduling and timing, while bare-metal requires manual handling.

2. Step 2: Compare complexity and reliability

   RTOS improves reliability by handling task switching and timing, reducing manual errors common in bare-metal.

3. Final Answer:

   Because RTOS handles multiple tasks with scheduling and timing automatically -> Option C

4. Quick Check:

   RTOS manages tasks automatically [OK]

Hint: RTOS automates multitasking; bare-metal needs manual control [OK]

Common Mistakes:

• Thinking bare-metal is always faster without considering complexity
• Assuming RTOS removes need for hardware knowledge
• Believing bare-metal systems never crash

2. Which of the following is the correct way to create a task in FreeRTOS?

easy

A. xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, NULL);

B. createTask(TaskFunction, Priority);

C. TaskCreate(TaskFunction, StackSize);

D. xCreateTask(TaskFunction, "TaskName");

Solution

1. Step 1: Recall FreeRTOS task creation syntax

   The correct function is xTaskCreate with parameters: function, name, stack size, parameters, priority, and task handle.

2. Step 2: Match options to syntax

   Only xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, NULL); matches the correct FreeRTOS API call with all required parameters.

3. Final Answer:

   xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, NULL); -> Option A

4. Quick Check:

   FreeRTOS task creation = xTaskCreate(...) [OK]

Hint: Remember FreeRTOS uses xTaskCreate with 6 parameters [OK]

Common Mistakes:

• Using incorrect function names like createTask
• Omitting required parameters
• Confusing parameter order

3. Given this FreeRTOS code snippet, what will be the output on the serial console?

void Task1(void *pvParameters) {
  for (;;) {
    printf("Task1 running\n");
    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

void Task2(void *pvParameters) {
  for (;;) {
    printf("Task2 running\n");
    vTaskDelay(pdMS_TO_TICKS(500));
  }
}

int main() {
  xTaskCreate(Task1, "Task1", 1000, NULL, 1, NULL);
  xTaskCreate(Task2, "Task2", 1000, NULL, 1, NULL);
  vTaskStartScheduler();
  return 0;
}

medium

A. Both tasks print at the same rate

B. Task1 prints twice as often as Task2

C. No output because scheduler is not started

D. Task2 prints twice as often as Task1

Solution

1. Step 1: Analyze delay times for each task

   Task1 delays 1000 ms between prints; Task2 delays 500 ms between prints.

2. Step 2: Compare print frequencies

   Task2 runs twice as often because 500 ms delay is half of 1000 ms delay.

3. Final Answer:

   Task2 prints twice as often as Task1 -> Option D

4. Quick Check:

   Shorter delay means more prints [OK]

Hint: Shorter vTaskDelay means more frequent prints [OK]

Common Mistakes:

• Confusing which task has shorter delay
• Assuming tasks run sequentially, not concurrently
• Ignoring vTaskStartScheduler call

4. This FreeRTOS code snippet does not behave as expected. What is the main problem?

void Task(void *pvParameters) {
  while(1) {
    // Do some work
    vTaskDelay(1000);
  }
}

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

medium

A. vTaskStartScheduler should be called before creating tasks

B. vTaskDelay needs pdMS_TO_TICKS macro for delay time

C. xTaskCreate missing priority parameter

D. Task function must return an int

Solution

1. Step 1: Check vTaskDelay usage

   vTaskDelay expects ticks, but 1000 is milliseconds; pdMS_TO_TICKS converts ms to ticks.

2. Step 2: Identify correct delay call

   Correct call is vTaskDelay(pdMS_TO_TICKS(1000)) to delay 1000 ms properly.

3. Final Answer:

   vTaskDelay needs pdMS_TO_TICKS macro for delay time -> Option B

4. Quick Check:

   Delay in ticks, not ms [OK]

Hint: Always convert ms to ticks with pdMS_TO_TICKS [OK]

Common Mistakes:

• Passing milliseconds directly to vTaskDelay
• Thinking task functions must return int
• Calling scheduler before creating tasks

5. You want to improve responsiveness in a sensor monitoring system by switching from bare-metal to FreeRTOS. Which approach best uses FreeRTOS features to achieve this?

hard

A. Create separate tasks for sensor reading, data processing, and communication with different priorities

B. Run all code sequentially in one task with long delays

C. Use FreeRTOS only to replace delay functions but keep one big task

D. Disable interrupts and rely on polling in a single task

Solution

1. Step 1: Identify how RTOS improves responsiveness

   RTOS allows multiple tasks with priorities, so critical tasks run promptly.

2. Step 2: Evaluate options for task design

   Creating separate tasks for sensor reading, processing, and communication with priorities uses RTOS strengths best.

3. Final Answer:

   Create separate tasks for sensor reading, data processing, and communication with different priorities -> Option A

4. Quick Check:

   Separate prioritized tasks improve responsiveness [OK]

Hint: Use multiple prioritized tasks for better responsiveness [OK]

Common Mistakes:

• Keeping all code in one task with delays
• Using RTOS only for delays, not multitasking
• Disabling interrupts reduces responsiveness