Memory usage monitoring in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the current free heap size in FreeRTOS.

FreeRTOS

size_t freeHeap = [1]();

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

AvTaskDelay

BxPortGetFreeHeapSize

CxTaskGetTickCount

DxQueueCreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using task-related functions like xTaskGetTickCount instead of heap functions.

Confusing delay functions with memory functions.

The function xPortGetFreeHeapSize() returns the current free heap size in bytes.

2fill in blank

medium

Complete the code to print the minimum ever free heap size in FreeRTOS.

FreeRTOS

printf("Min free heap: %u bytes\n", [1]());

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

AvTaskDelay

BxTaskGetTickCount

CxPortGetMinimumEverFreeHeapSize

DxPortGetFreeHeapSize

Attempts:

3 left

💡 Hint

Common Mistakes

Using the current free heap size function instead of minimum ever.

Using unrelated task or delay functions.

xPortGetMinimumEverFreeHeapSize() returns the smallest amount of free heap ever recorded, useful for checking memory usage peaks.

3fill in blank

hard

Fix the error in the code to correctly get the free heap size.

FreeRTOS

size_t freeHeap = [1]();

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

AxPortGetFreeHeapSize

BvTaskGetHeapSize

CxTaskGetFreeHeapSize

DxPortGetFreeHeap

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect or non-existent function names.

Confusing task or delay functions with heap functions.

The correct function to get free heap size is xPortGetFreeHeapSize(). Other options are invalid or do not exist.

4fill in blank

hard

Fill both blanks to create a dictionary of task names and their stack high water marks.

FreeRTOS

TaskStatus_t taskStatusArray[[1]];
for (int i = 0; i < [2]; i++) {
    printf("Task: %s, Stack high water mark: %u\n", taskStatusArray[i].pcTaskName, taskStatusArray[i].usStackHighWaterMark);
}

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

AuxTaskGetNumberOfTasks

BvTaskDelay

CconfigMAX_PRIORITIES

DxPortGetFreeHeapSize

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated functions for array size or loop count.

Using constants instead of dynamic task count.

uxTaskGetNumberOfTasks() returns the number of tasks, used to size the array and loop count.

5fill in blank

hard

Fill all three blanks to create a filtered dictionary of tasks with stack high water mark below a threshold.

FreeRTOS

for (int i = 0; i < [1]; i++) {
    if (taskStatusArray[i].usStackHighWaterMark [2] [3]) {
        printf("Low stack task: %s, Water mark: %u\n", taskStatusArray[i].pcTaskName, taskStatusArray[i].usStackHighWaterMark);
    }
}

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

AuxTaskGetNumberOfTasks

B<

C100

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Using incorrect loop limits.

Confusing threshold values.

The loop runs over all tasks using uxTaskGetNumberOfTasks(). The condition checks if the stack high water mark is less than 100 bytes to find tasks with low stack.

Practice

1. What is the primary purpose of memory usage monitoring in FreeRTOS?

easy

A. To keep the system stable by tracking free stack space

B. To increase CPU clock speed automatically

C. To disable unused tasks permanently

D. To reduce the size of the kernel

Solution

1. Step 1: Understand memory monitoring role

   Memory usage monitoring helps detect low memory conditions to avoid crashes.

2. Step 2: Identify the main goal in FreeRTOS

   Tracking free stack space per task ensures system stability and prevents overflow.

3. Final Answer:

   To keep the system stable by tracking free stack space -> Option A

4. Quick Check:

   Memory monitoring = system stability [OK]

Hint: Memory monitoring prevents crashes by tracking stack space [OK]

Common Mistakes:

• Confusing memory monitoring with CPU speed control
• Thinking it disables tasks automatically
• Assuming it reduces kernel size

2. Which FreeRTOS function is used to check the minimum amount of stack space left for a task?

easy

A. uxTaskGetStackHighWaterMark()

B. vTaskDelete()

C. xTaskCreate()

D. vTaskDelay()

Solution

1. Step 1: Identify stack monitoring function

   uxTaskGetStackHighWaterMark() returns the minimum free stack space for a task.

2. Step 2: Differentiate from other task functions

   Other functions manage tasks but do not report stack usage.

3. Final Answer:

   uxTaskGetStackHighWaterMark() -> Option A

4. Quick Check:

   Stack check function = uxTaskGetStackHighWaterMark() [OK]

Hint: Stack water mark means free stack space left [OK]

Common Mistakes:

• Choosing task creation or deletion functions
• Confusing delay function with memory check

3. Given the code snippet:

UBaseType_t freeStack = uxTaskGetStackHighWaterMark(NULL);
printf("Free stack: %u\n", freeStack);

What does this code output?

medium

A. The total stack size of the current task

B. The current CPU usage percentage

C. The minimum free stack space left in the current task

D. The number of tasks running

Solution

1. Step 1: Analyze uxTaskGetStackHighWaterMark(NULL)

   Passing NULL gets the current task's minimum free stack space since start.

2. Step 2: Understand printf output

   It prints the free stack space value, not total stack or CPU info.

3. Final Answer:

   The minimum free stack space left in the current task -> Option C

4. Quick Check:

   NULL param = current task stack free space [OK]

Hint: NULL means current task in FreeRTOS stack check [OK]

Common Mistakes:

• Thinking it returns total stack size
• Confusing with task count or CPU usage

4. You wrote this code to monitor stack usage:

UBaseType_t freeStack = uxTaskGetStackHighWaterMark(taskHandle);
if(freeStack == 0)
{
  printf("Stack overflow detected!\n");
}

But it never prints the warning even when the system crashes. What is the likely issue?

medium

A. Using taskHandle instead of NULL for current task

B. Checking for zero instead of a low threshold

C. Not calling vTaskStartScheduler() before monitoring

D. Using printf instead of a logging function

Solution

1. Step 1: Understand uxTaskGetStackHighWaterMark() return

   It returns minimum free stack space, zero means no free space left.

2. Step 2: Check condition logic

   Waiting for exactly zero misses low free space warnings; better to check below a threshold.

3. Final Answer:

   Checking for zero instead of a low threshold -> Option B

4. Quick Check:

   Zero check misses low stack warnings [OK]

Hint: Check for low stack threshold, not just zero [OK]

Common Mistakes:

• Assuming zero is the only danger point
• Confusing taskHandle usage
• Blaming printf for missing output

5. You want to monitor stack usage for multiple tasks and log warnings if any task's free stack falls below 50 words. Which approach is best?

hard

A. Call uxTaskGetStackHighWaterMark(NULL) once and assume all tasks are safe

B. Increase total heap size instead of monitoring stack

C. Only monitor the highest priority task's stack usage

D. Loop through all task handles, call uxTaskGetStackHighWaterMark(), compare to 50, log if below

Solution

1. Step 1: Understand monitoring multiple tasks

   Each task has its own stack; checking all ensures no task is overlooked.

2. Step 2: Implement threshold check per task

   Looping through tasks and comparing free stack to 50 words allows targeted warnings.

3. Step 3: Evaluate other options

   Checking only current or highest priority task misses others; increasing heap doesn't solve stack issues.

4. Final Answer:

   Loop through all task handles, call uxTaskGetStackHighWaterMark(), compare to 50, log if below -> Option D

5. Quick Check:

   Check all tasks individually for stack [OK]

Hint: Check each task's stack individually for accurate monitoring [OK]

Common Mistakes:

• Assuming one check covers all tasks
• Ignoring lower priority tasks
• Confusing heap size with stack size