FreeRTOS architecture overview - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a FreeRTOS task.

FreeRTOS

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

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

AvTaskFunction

BvTaskDelay

CvTaskStartScheduler

DvTaskDelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using scheduler or delay functions instead of the task function.

Passing NULL instead of a function name.

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(void) {
    // Setup code
    [1]();
    for(;;); // Should never reach here
}

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

AvTaskDelay

BvTaskDelete

CxTaskCreate

DvTaskStartScheduler

Attempts:

3 left

💡 Hint

Common Mistakes

Calling task creation functions instead of starting the scheduler.

Using delay functions to start the scheduler.

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

3fill in blank

hard

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

FreeRTOS

void vTaskFunction(void *pvParameters) {
    for(;;) {
        [1](1000 / portTICK_PERIOD_MS);
    }
}

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

AvTaskDelay(1000)

BvTaskDelayMs

CvTaskDelay

Ddelay

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-FreeRTOS delay functions.

Passing the delay time inside the function call in the blank.

vTaskDelay() delays a task for a number of tick periods. The argument is in ticks, so 1000 milliseconds must be converted to ticks using 1000 / portTICK_PERIOD_MS.

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.name

B<=

C>

D.id

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like .id instead of .name.

Using wrong comparison operators like <= instead of >.

Access the task's name with .name and filter priorities greater than 2 with >.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase task names to their priorities if priority is greater than 0.

FreeRTOS

task_map = [1]: [2] for task, priority in tasks.items() if priority [3] 0}}

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

Atask.upper()

Bpriority

C>

Dtask.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase instead of uppercase for task names.

Using wrong comparison operators like < instead of >.

Use task.upper() for uppercase keys, priority as values, and filter with > 0.

Practice

1. What is the main role of the FreeRTOS scheduler in its architecture?

easy

A. To store data permanently

B. To decide which task runs and when

C. To compile the code

D. To manage hardware interrupts only

Solution

1. Step 1: Understand the scheduler's purpose

   The scheduler controls task execution order and timing in FreeRTOS.

2. Step 2: Compare with other options

   Storing data, compiling code, or only managing interrupts are not scheduler roles.

3. Final Answer:

   To decide which task runs and when -> Option B

4. Quick Check:

   Scheduler controls task timing = To decide which task runs and when [OK]

Hint: Scheduler manages task timing and switching [OK]

Common Mistakes:

• Confusing scheduler with memory storage
• Thinking scheduler compiles code
• Assuming scheduler only handles interrupts

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

easy

A. task_create(TaskFunction, StackSize);

B. CreateTask(TaskFunction, Priority);

C. xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle);

D. StartTask(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 handle.

2. Step 2: Check options for exact match

   Only xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); matches the correct FreeRTOS API call syntax.

3. Final Answer:

   xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); -> Option C

4. Quick Check:

   Use xTaskCreate with full parameters = xTaskCreate(TaskFunction, "TaskName", StackSize, NULL, Priority, &TaskHandle); [OK]

Hint: Remember xTaskCreate needs 6 parameters [OK]

Common Mistakes:

• Using incorrect function names
• Omitting required parameters
• Confusing task creation with starting tasks

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

void vTask1(void *pvParameters) {
    for (;;) {
        printf("Task 1 running\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void vTask2(void *pvParameters) {
    for (;;) {
        printf("Task 2 running\n");
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main() {
    xTaskCreate(vTask1, "Task1", 1000, NULL, 1, NULL);
    xTaskCreate(vTask2, "Task2", 1000, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}

medium

A. Task 1 running every 1 second, Task 2 running every 0.5 seconds

B. Task 1 and Task 2 run simultaneously without delay

C. Only Task 1 runs, Task 2 never runs

D. No output because scheduler is not started

Solution

1. Step 1: Analyze task delays

   Task 1 delays 1000 ms (1 second), Task 2 delays 500 ms (0.5 seconds) between prints.

2. Step 2: Understand scheduler behavior

   Both tasks have same priority and run repeatedly with their delays, so Task 2 prints twice as often.

3. Final Answer:

   Task 1 running every 1 second, Task 2 running every 0.5 seconds -> Option A

4. Quick Check:

   Delays control print frequency = Task 1 running every 1 second, Task 2 running every 0.5 seconds [OK]

Hint: Check vTaskDelay times to predict print frequency [OK]

Common Mistakes:

• Assuming tasks run simultaneously without delay
• Thinking only one task runs
• Ignoring vTaskStartScheduler call

4. Identify the error in this FreeRTOS task creation code snippet:

void vTask(void *pvParameters) {
    for (;;) {
        // Task code
    }
}

int main() {
    xTaskCreate(vTask, "Task", 1000, NULL, 2);
    vTaskStartScheduler();
    return 0;
}

medium

A. Missing task handle parameter in xTaskCreate

B. Task function should not have an infinite loop

C. Priority value 2 is invalid

D. vTaskStartScheduler() should be called before xTaskCreate

Solution

1. Step 1: Check xTaskCreate parameters

   xTaskCreate requires 6 parameters; here only 5 are provided, missing the task handle pointer.

2. Step 2: Verify other parts

   Infinite loop in task is normal, priority 2 is valid, scheduler must start after task creation.

3. Final Answer:

   Missing task handle parameter in xTaskCreate -> Option A

4. Quick Check:

   xTaskCreate needs 6 params = Missing handle param [OK]

Hint: Count xTaskCreate parameters; must be six [OK]

Common Mistakes:

• Omitting task handle parameter
• Misunderstanding infinite loops in tasks
• Incorrect order of scheduler start

5. You want to design a FreeRTOS system where a high-priority task waits for data from a low-priority task without wasting CPU time. Which FreeRTOS feature best supports this design?

hard

A. Running both tasks at the same priority to share CPU equally

B. Using vTaskDelay in the high-priority task to wait

C. Using global variables with busy-wait loops

D. Using a queue to send data and block the high-priority task until data arrives

Solution

1. Step 1: Understand task synchronization needs

   The high-priority task must wait efficiently without wasting CPU cycles.

2. Step 2: Evaluate FreeRTOS features

   Queues allow blocking the high-priority task until data is available, avoiding busy-waiting.

3. Step 3: Rule out other options

   vTaskDelay wastes time, busy-wait loops waste CPU, equal priority doesn't guarantee waiting.

4. Final Answer:

   Using a queue to send data and block the high-priority task until data arrives -> Option D

5. Quick Check:

   Queue blocks task efficiently = Using a queue to send data and block the high-priority task until data arrives [OK]

Hint: Use queues to block and wait without CPU waste [OK]

Common Mistakes:

• Using delays instead of blocking
• Busy-waiting wastes CPU
• Ignoring priority differences