Memory usage monitoring in FreeRTOS

Introduction

Memory usage monitoring helps you see how much memory your FreeRTOS program uses. It keeps your system running smoothly by avoiding memory problems.

When you want to check if your tasks have enough memory to run.

When your system crashes and you suspect memory is full.

When you add new features and want to make sure memory is still enough.

When debugging memory leaks or unexpected behavior.

When optimizing your program to use less memory.

Syntax

FreeRTOS

size_t uxTaskGetStackHighWaterMark(TaskHandle_t xTask);

This function returns the minimum amount of stack space that has remained for the task since it started.

You need to pass the task handle to check its stack usage.

Examples

Check the stack space left for the current task by passing NULL.

FreeRTOS

size_t freeStack = uxTaskGetStackHighWaterMark(NULL);

Check the stack space left for a specific task using its handle.

FreeRTOS

size_t freeStack = uxTaskGetStackHighWaterMark(myTaskHandle);

Sample Program

This program creates a task that prints its free stack space every second. It helps monitor memory usage live.

FreeRTOS

#include "FreeRTOS.h"
#include "task.h"
#include <stdio.h>

void vTaskFunction(void *pvParameters) {
    for (;;) {
        size_t freeStack = uxTaskGetStackHighWaterMark(NULL);
        printf("Free stack space: %u words\n", (unsigned int)freeStack);
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

int main(void) {
    xTaskCreate(vTaskFunction, "Task1", 100, NULL, 1, NULL);
    vTaskStartScheduler();
    return 0;
}

Important Notes

Stack space is measured in words, not bytes. One word is usually 4 bytes on many systems.

Low free stack values mean your task is close to running out of memory.

Use this monitoring to avoid stack overflow crashes.

Summary

Memory usage monitoring in FreeRTOS helps keep your system stable.

Use uxTaskGetStackHighWaterMark() to check free stack space per task.

Regular monitoring prevents crashes and helps optimize memory use.

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