Stack high water mark monitoring in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the stack high water mark of a task.

FreeRTOS

UBaseType_t highWaterMark = uxTaskGetStackHighWaterMark([1]);

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

ATaskHandle_t

BNULL

CxTaskHandle

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Passing NULL instead of the task handle.

Using the type name instead of a variable.

Passing void or unrelated values.

The function uxTaskGetStackHighWaterMark() requires the task handle as argument to return the stack high water mark.

2fill in blank

medium

Complete the code to print the stack high water mark value.

FreeRTOS

printf("Stack high water mark: %u\n", [1]);

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

AhighWaterMark

BTaskHandle_t

CuxTaskGetStackHighWaterMark(xTaskHandle)

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function inside printf instead of using the variable.

Passing the task handle or NULL instead of the value.

Using the type name instead of a variable.

The variable highWaterMark stores the value returned by uxTaskGetStackHighWaterMark() and should be printed.

3fill in blank

hard

Fix the error in the code to correctly get the stack high water mark.

FreeRTOS

UBaseType_t highWaterMark = uxTaskGetStackHighWaterMark([1]);

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

ATaskHandle

BNULL

CNULLHandle

DxTaskHandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL or invalid variable names.

Confusing type names with variables.

The function requires a valid task handle variable like xTaskHandle. Passing NULL or invalid names causes errors.

4fill in blank

hard

Fill both blanks to create a function that returns the stack high water mark of a task.

FreeRTOS

UBaseType_t getStackHighWaterMark([1] task) {
    return uxTaskGetStackHighWaterMark([2]);
}

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

ATaskHandle_t

BxTaskHandle

Ctask

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using void as parameter type.

Passing a variable not declared as parameter.

Mismatching parameter names.

The function parameter should be of type TaskHandle_t and the same parameter task is passed to uxTaskGetStackHighWaterMark().

5fill in blank

hard

Fill all three blanks to complete the for loop that populates the highWaterMarks array using the corresponding task handles.

FreeRTOS

const char* taskNames[] = {"Task1", "Task2", "Task3"};
UBaseType_t highWaterMarks[] = {0, 0, 0};
for (int [1] = 0; [2] < 3; [3]++) {
    highWaterMarks[i] = uxTaskGetStackHighWaterMark(xTaskHandles[i]);
}

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

Ai

Bj

Ck

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in loop parts.

Using undefined variables.

The loop variable i is used consistently for initialization, condition, and increment.

Practice

1.

What does the stack high water mark indicate in FreeRTOS?

easy

A. The total stack size allocated to a task

B. The minimum amount of free stack space a task has had

C. The maximum CPU usage of a task

D. The number of tasks currently running

Solution

1. Step 1: Understand stack high water mark meaning

   The stack high water mark shows the smallest amount of unused stack space a task has had since it started.

2. Step 2: Compare with other options

   Other options describe CPU usage, total stack size, or task count, which are unrelated to stack high water mark.

3. Final Answer:

   The minimum amount of free stack space a task has had -> Option B

4. Quick Check:

   Stack high water mark = minimum free stack space [OK]

Hint: Remember: 'high water mark' means lowest free stack left [OK]

Common Mistakes:

• Confusing stack size with stack usage
• Thinking it measures CPU or task count
• Assuming it shows maximum stack used

2.

Which is the correct way to get the stack high water mark of the current task in FreeRTOS?

?

easy

A. uxTaskGetStackHighWaterMark(NULL);

B. uxTaskGetStackHighWaterMark(currentTask);

C. getStackHighWaterMark(NULL);

D. uxGetStackHighWaterMark();

Solution

1. Step 1: Recall function signature

   The FreeRTOS function to get stack high water mark is uxTaskGetStackHighWaterMark, which takes a task handle or NULL for current task.

2. Step 2: Identify correct usage

   Passing NULL gets the current task's high water mark. Other options use wrong function names or parameters.

3. Final Answer:

   uxTaskGetStackHighWaterMark(NULL); -> Option A

4. Quick Check:

   Use NULL for current task in uxTaskGetStackHighWaterMark [OK]

Hint: Use NULL to refer to current task handle [OK]

Common Mistakes:

• Using wrong function names
• Passing invalid parameters instead of NULL
• Assuming no parameter needed

3.

Given the following code snippet, what will be the output if the task's minimum free stack space was 50 words?

UBaseType_t highWaterMark = uxTaskGetStackHighWaterMark(NULL);
printf("High water mark: %u\n", highWaterMark);

medium

A. High water mark: 50

B. High water mark: 0

C. High water mark: Stack overflow

D. Compilation error

Solution

1. Step 1: Understand uxTaskGetStackHighWaterMark output

   This function returns the minimum free stack space (in words) the task had, which is 50 in this case.

2. Step 2: Analyze printf output

   The printf prints the unsigned integer value returned, so output will be "High water mark: 50".

3. Final Answer:

   High water mark: 50 -> Option A

4. Quick Check:

   Function returns minimum free stack, printed as number [OK]

Hint: Function returns minimum free stack words, print as unsigned int [OK]

Common Mistakes:

• Assuming it returns zero on no overflow
• Thinking it returns error string
• Confusing with stack size or usage

4.

Identify the error in this code snippet intended to get the stack high water mark of a task named myTaskHandle:

UBaseType_t mark = uxTaskGetStackHighWaterMark(myTaskHandle);

Assume myTaskHandle is a valid task handle.

medium

A. Return type should be int, not UBaseType_t

B. Function name is incorrect, should be uxGetStackHighWaterMark

C. Parameter should be NULL to get any task's high water mark

D. No error, code is correct

Solution

1. Step 1: Verify function and parameter usage

   uxTaskGetStackHighWaterMark takes a task handle to get that task's high water mark. Using myTaskHandle is valid.

2. Step 2: Check return type and function name

   Return type UBaseType_t is correct. Function name is correct as per FreeRTOS API.

3. Final Answer:

   No error, code is correct -> Option D

4. Quick Check:

   Correct function and parameter usage means no error [OK]

Hint: Use task handle parameter for specific task, NULL for current task [OK]

Common Mistakes:

• Thinking NULL is required for all tasks
• Using wrong function names
• Confusing return types

5.

You want to monitor stack usage of multiple tasks and log a warning if any task's stack high water mark falls below 20 words. Which approach is best?

hard

A. Only check the current task's stack high water mark using NULL parameter

B. Increase all task stack sizes to 20 words to avoid overflow

C. Periodically call uxTaskGetStackHighWaterMark for each task handle and check if value < 20

D. Use vTaskDelete to remove tasks with low stack

Solution

1. Step 1: Understand monitoring multiple tasks

   To monitor multiple tasks, you must check each task's stack high water mark individually using their task handles.

2. Step 2: Implement threshold check

   Calling uxTaskGetStackHighWaterMark for each task and comparing to 20 words allows detecting low stack and logging warnings.

3. Final Answer:

   Periodically call uxTaskGetStackHighWaterMark for each task handle and check if value < 20 -> Option C

4. Quick Check:

   Check each task's high water mark against threshold [OK]

Hint: Check each task's high water mark, compare to threshold [OK]

Common Mistakes:

• Checking only current task misses others
• Assuming increasing stack size fixes monitoring
• Deleting tasks instead of warning