Memory usage monitoring in FreeRTOS - Mini Project: Build & Apply

Memory Usage Monitoring in FreeRTOS

📖 Scenario: You are working on an embedded system using FreeRTOS. To ensure your system runs smoothly, you need to monitor the memory usage of your tasks. This helps prevent crashes caused by running out of memory.

🎯 Goal: Build a simple FreeRTOS program that tracks the free heap memory available and prints it periodically. You will create a variable to hold the heap size, configure a monitoring interval, write the code to get the free heap size, and finally print the result.

📋 What You'll Learn

Create a variable to store the free heap size

Add a configuration variable for the monitoring interval in milliseconds

Use the FreeRTOS API to get the current free heap size

Print the free heap size to the console

💡 Why This Matters

🌍 Real World

Monitoring memory usage helps embedded developers avoid crashes and optimize resource use in devices like IoT sensors, wearables, and controllers.

💼 Career

Understanding how to monitor and manage memory in FreeRTOS is essential for embedded systems engineers and firmware developers to ensure system reliability.

1

Create a variable to store free heap size

Create a variable called freeHeapSize of type size_t and initialize it to 0.

FreeRTOS

# Create a variable called freeHeapSize of type size_t and initialize it to 0
// Your code here

Hint

Use size_t for memory size variables in FreeRTOS.

2

Add a configuration variable for monitoring interval

Add a variable called monitorIntervalMs of type const TickType_t and set it to 1000 to represent 1000 milliseconds (1 second).

FreeRTOS

size_t freeHeapSize = 0;
// Add a variable called monitorIntervalMs of type const TickType_t set to 1000
// Your code here

Hint

Use const TickType_t for fixed time intervals in FreeRTOS.

3

Get the current free heap size

Use the FreeRTOS API function xPortGetFreeHeapSize() to assign the current free heap size to the variable freeHeapSize.

FreeRTOS

size_t freeHeapSize = 0;
const TickType_t monitorIntervalMs = 1000;
// Assign freeHeapSize using xPortGetFreeHeapSize()
// Your code here

Hint

Call xPortGetFreeHeapSize() without parameters to get free heap size.

4

Print the free heap size

Write a printf statement to display the text "Free heap size: " followed by the value of freeHeapSize and a newline.

FreeRTOS

size_t freeHeapSize = 0;
const TickType_t monitorIntervalMs = 1000;
freeHeapSize = xPortGetFreeHeapSize();
// Print the free heap size
// Your code here

Hint

Use printf("Free heap size: %u\n", (unsigned int)freeHeapSize); to print the value.

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