Stack high water mark monitoring in FreeRTOS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Stack High Water Mark Purpose

What does the stack high water mark value represent in FreeRTOS?

A The maximum amount of stack space that has been used by the task since it started.

B The total stack size allocated to the task at creation.

C The current free stack space available for the task.

D The number of context switches the task has performed.

💡 Hint

Think about what 'high water mark' means in terms of usage.

The stack high water mark shows the minimum amount of free stack space left, indicating the maximum stack usage so far.

💻 Command Output

intermediate

Interpreting uxTaskGetStackHighWaterMark Output

Given the following FreeRTOS code snippet, what is the output of uxTaskGetStackHighWaterMark(NULL) if the task stack size is 200 words and the function returns 50?

FreeRTOS

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

A High water mark: 200

B High water mark: 50

C High water mark: 0

D High water mark: 150

💡 Hint

The function returns the minimum free stack space in words.

The function returns the minimum free stack space left, so it prints 50.

❓ Configuration

advanced

Configuring Stack Overflow Checking

Which FreeRTOS configuration option enables stack overflow checking at runtime?

A configUSE_PREEMPTION

B configUSE_IDLE_HOOK

C configMAX_PRIORITIES

D configCHECK_FOR_STACK_OVERFLOW

💡 Hint

Look for the option related to stack overflow detection.

configCHECK_FOR_STACK_OVERFLOW enables runtime stack overflow checking in FreeRTOS.

❓ Troubleshoot

advanced

Diagnosing Unexpected Low Stack High Water Mark

A task with a stack size of 256 words shows a high water mark of 5. What is the most likely cause?

A The task is using almost all its stack space, risking overflow.

B The task has just started and has not used much stack yet.

C The stack size is too large for the task's needs.

D The high water mark function is returning the total stack size.

💡 Hint

Low high water mark means low free stack space.

A low high water mark means the task has used most of its stack, which risks overflow.

🔀 Workflow

expert

Steps to Monitor Stack Usage in a Running FreeRTOS System

What is the correct sequence of steps to monitor stack high water mark for a task in FreeRTOS?

A 2,1,3,4

B 1,3,2,4

C 1,2,3,4

D 1,2,4,3

💡 Hint

Think about the logical order from getting data to acting on it.

You first get the value, then interpret it, then compare to threshold, then log or alert.