Multiple tasks running concurrently in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a FreeRTOS task named "Task1".

FreeRTOS

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

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

AvTaskFunction

BvTaskStartScheduler

CvTaskDelete

DvTaskDelay

Attempts:

3 left

💡 Hint

Common Mistakes

Using scheduler or delay functions instead of the task function.

Passing NULL instead of a function.

The function vTaskFunction is the task function passed to xTaskCreate to define the task's behavior.

2fill in blank

medium

Complete the code to start the FreeRTOS scheduler.

FreeRTOS

int main() {
    // Create tasks here
    [1]();
    for(;;);
}

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AvTaskDelete

BvTaskStartScheduler

CxTaskCreate

DvTaskDelay

Attempts:

3 left

💡 Hint

Common Mistakes

Calling task creation functions instead of starting the scheduler.

Forgetting to start the scheduler.

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

3fill in blank

hard

Fix the error in the task delay call to delay for 1000 milliseconds.

FreeRTOS

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

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ApdMS_TO_TICKS(1000)

B1000

C1000 / portTICK_PERIOD_MS

D1000 * portTICK_PERIOD_MS

Attempts:

3 left

💡 Hint

Common Mistakes

Passing raw milliseconds directly to vTaskDelay.

Multiplying instead of converting properly.

The macro pdMS_TO_TICKS(1000) converts 1000 milliseconds to the correct tick count for vTaskDelay.

4fill in blank

hard

Fill both blanks to create two tasks with different priorities.

FreeRTOS

xTaskCreate(Task1Function, "Task1", 1000, NULL, [1], NULL);
xTaskCreate(Task2Function, "Task2", 1000, NULL, [2], NULL);

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A2

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same priority for both tasks.

Assigning lower priority to the task that should run first.

Task1 has priority 1 and Task2 has priority 2, so Task2 runs with higher priority.

5fill in blank

hard

Fill all three blanks to create a task that deletes itself after running once.

FreeRTOS

void vOneShotTask(void *pvParameters) {
    // Task code here
    [1](pdMS_TO_TICKS(1000));
    [2](NULL);
    for(;;) {
        [3](NULL);
    }
}

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

AvTaskDelay

BvTaskDelete

CvTaskSuspend

DvTaskStartScheduler

Attempts:

3 left

💡 Hint

Common Mistakes

Calling delete without NULL parameter.

Not delaying before deleting.

Using start scheduler inside a task.

The task delays briefly, then deletes itself with vTaskDelete(NULL).

Practice

1. What is the main purpose of running multiple tasks concurrently in FreeRTOS?

easy

A. To allow the program to perform several operations at the same time

B. To make the program run slower

C. To use more memory without benefit

D. To avoid using any delays in the code

Solution

1. Step 1: Understand task concurrency

   Multiple tasks let the program handle different jobs at once, improving efficiency.

2. Step 2: Identify the purpose in FreeRTOS

   FreeRTOS switches between tasks automatically, enabling multitasking.

3. Final Answer:

   To allow the program to perform several operations at the same time -> Option A

4. Quick Check:

   Multiple tasks = multitasking = To allow the program to perform several operations at the same time [OK]

Hint: Multiple tasks mean doing many things at once [OK]

Common Mistakes:

• Thinking tasks slow down the program
• Believing tasks waste memory
• Ignoring the role of delays

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

easy

A. TaskCreate(TaskFunction, "TaskName", stackSize, NULL, priority, NULL);

B. createTask(TaskFunction, "TaskName", stackSize, NULL, priority, NULL);

C. xTaskCreate(TaskFunction, "TaskName", stackSize, NULL, priority, NULL);

D. xCreateTask(TaskFunction, "TaskName", stackSize, NULL, priority, NULL);

Solution

1. Step 1: Recall FreeRTOS task creation function

   The correct function to create a task is xTaskCreate.

2. Step 2: Match the exact syntax

   xTaskCreate(TaskFunction, "TaskName", stackSize, NULL, priority, NULL); matches the correct function name and parameters.

3. Final Answer:

   xTaskCreate(TaskFunction, "TaskName", stackSize, NULL, priority, NULL); -> Option C

4. Quick Check:

   Task creation function = xTaskCreate = xTaskCreate(TaskFunction, "TaskName", stackSize, NULL, priority, NULL); [OK]

Hint: Remember the function starts with 'xTaskCreate' [OK]

Common Mistakes:

• Using incorrect function names like createTask
• Mixing up parameter order
• Missing the 'x' prefix in function name

3. Consider this FreeRTOS code snippet:

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));
  }
}

What will be the output pattern when both tasks run concurrently?

medium

A. Task1 prints every 1 second; Task2 prints every 0.5 seconds

B. Task1 and Task2 print at the same time every 1 second

C. Task1 prints every 0.5 seconds; Task2 prints every 1 second

D. Only Task1 prints because Task2 is blocked

Solution

1. Step 1: Analyze vTaskDelay timing for Task1

   Task1 delays 1000 ms (1 second) between prints.

2. Step 2: Analyze vTaskDelay timing for Task2

   Task2 delays 500 ms (0.5 seconds) between prints.

3. Step 3: Understand concurrent execution

   Both tasks run independently, so Task2 prints twice as often as Task1.

4. Final Answer:

   Task1 prints every 1 second; Task2 prints every 0.5 seconds -> Option A

5. Quick Check:

   Delays control print rate = Task1 prints every 1 second; Task2 prints every 0.5 seconds [OK]

Hint: Check each task's delay time to predict print frequency [OK]

Common Mistakes:

• Assuming tasks print simultaneously
• Mixing up delay times
• Thinking one task blocks the other

4. Given this code snippet, what is the error?

void TaskA(void *pvParameters) {
  while(1) {
    // Do something
    vTaskDelay(1000);
  }
}

xTaskCreate(TaskA, "TaskA", 1000, NULL, 1, NULL);

medium

A. Task function must return int, not void

B. vTaskDelay requires delay in ticks, not milliseconds

C. Stack size 1000 is too small

D. Task name must be longer than 5 characters

Solution

1. Step 1: Check vTaskDelay parameter

   vTaskDelay expects delay in ticks, not milliseconds.

2. Step 2: Identify correct delay usage

   Use pdMS_TO_TICKS(1000) to convert 1000 ms to ticks.

3. Final Answer:

   vTaskDelay requires delay in ticks, not milliseconds -> Option B

4. Quick Check:

   Delay unit must be ticks = vTaskDelay requires delay in ticks, not milliseconds [OK]

Hint: Use pdMS_TO_TICKS() to convert ms to ticks for vTaskDelay [OK]

Common Mistakes:

• Passing milliseconds directly to vTaskDelay
• Wrong return type for task function
• Incorrect stack size assumptions

5. You want two tasks to print messages alternately every 500 ms without overlapping prints. Which approach ensures this behavior in FreeRTOS?

hard

A. Use global variables without any synchronization

B. Use vTaskDelay with different delay times for each task

C. Run both tasks at the same priority without synchronization

D. Use a binary semaphore to synchronize tasks before printing

Solution

1. Step 1: Understand the need for synchronization

   To avoid overlapping prints, tasks must coordinate access to the printing resource.

2. Step 2: Identify synchronization method

   A binary semaphore allows one task to print while the other waits, alternating access.

3. Step 3: Evaluate other options

   Different delays or same priority without sync can cause overlapping prints; global variables alone don't prevent conflicts.

4. Final Answer:

   Use a binary semaphore to synchronize tasks before printing -> Option D

5. Quick Check:

   Synchronization via semaphore = Use a binary semaphore to synchronize tasks before printing [OK]

Hint: Use semaphores to control shared resource access [OK]

Common Mistakes:

• Relying only on delays for synchronization
• Ignoring task priority effects
• Not using any synchronization mechanism