pvPortMalloc and vPortFree in FreeRTOS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allocate memory dynamically using FreeRTOS.

FreeRTOS

void *ptr = [1](100);

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

AvPortFree

Bmalloc

CpvPortMalloc

Dfree

Attempts:

3 left

💡 Hint

Common Mistakes

Using standard malloc instead of pvPortMalloc.

Confusing allocation with freeing functions.

pvPortMalloc is the FreeRTOS function to allocate memory dynamically.

2fill in blank

medium

Complete the code to free the allocated memory using FreeRTOS.

FreeRTOS

void *ptr = pvPortMalloc(50);
[1](ptr);

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

AvPortFree

Bmalloc

Cfree

DpvPortMalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Using free instead of vPortFree.

Calling pvPortMalloc instead of freeing memory.

vPortFree is the FreeRTOS function to free memory allocated by pvPortMalloc.

3fill in blank

hard

Fix the error in the code to correctly allocate and free memory in FreeRTOS.

FreeRTOS

char *buffer = [1](256);
// Use buffer
vPortFree(buffer);

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

ApvPortMalloc

Bmalloc

CvPortFree

Dcalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing standard malloc/free with FreeRTOS memory functions.

Not using vPortFree to free pvPortMalloc memory.

Use pvPortMalloc to allocate memory and vPortFree to free it in FreeRTOS. The code incorrectly uses free instead of vPortFree.

4fill in blank

hard

Fill both blanks to create a buffer, check allocation success, and free it properly.

FreeRTOS

char *buf = [1](128);
if (buf == [2]) {
    // handle error
}
vPortFree(buf);

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

ApvPortMalloc

BNULL

Cmalloc

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking against 0 instead of NULL.

Using malloc instead of pvPortMalloc.

pvPortMalloc allocates memory, and NULL is used to check if allocation failed.

5fill in blank

hard

Fill all three blanks to allocate memory, check success, and free it correctly in FreeRTOS.

FreeRTOS

void *mem = [1](size);
if (mem == [2]) {
    return -1;
}
[3](mem);

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

Amalloc

BNULL

CvPortFree

DpvPortMalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Using standard malloc/free instead of FreeRTOS functions.

Not checking for NULL after allocation.

pvPortMalloc allocates memory, NULL checks failure, and vPortFree frees the memory in FreeRTOS.

Practice

1. What is the primary purpose of pvPortMalloc in FreeRTOS?

easy

A. To suspend a running task temporarily

B. To free allocated memory back to the system

C. To create a new task in FreeRTOS

D. To allocate memory safely for tasks and resources

Solution

1. Step 1: Understand the role of pvPortMalloc

   pvPortMalloc is designed to allocate memory safely in FreeRTOS, especially in multitasking environments.

2. Step 2: Differentiate from other functions

   Functions like vPortFree free memory, and task creation or suspension are unrelated to memory allocation.

3. Final Answer:

   To allocate memory safely for tasks and resources -> Option D

4. Quick Check:

   pvPortMalloc = allocate memory [OK]

Hint: pvPortMalloc always allocates memory safely [OK]

Common Mistakes:

• Confusing pvPortMalloc with vPortFree
• Thinking pvPortMalloc creates tasks
• Assuming it suspends tasks

2. Which of the following is the correct syntax to free memory allocated by pvPortMalloc?

easy

A. vPortFree(pointer);

B. pvPortMalloc(pointer);

C. free(pointer);

D. vPortMalloc(pointer);

Solution

1. Step 1: Identify the function to free memory

   Memory allocated by pvPortMalloc must be freed using vPortFree to avoid memory leaks.

2. Step 2: Check syntax correctness

   The correct syntax is vPortFree(pointer);. Other options either allocate memory or use standard C free, which is not recommended in FreeRTOS.

3. Final Answer:

   vPortFree(pointer); -> Option A

4. Quick Check:

   Free memory with vPortFree [OK]

Hint: Use vPortFree to release memory allocated by pvPortMalloc [OK]

Common Mistakes:

• Using free() instead of vPortFree()
• Calling pvPortMalloc to free memory
• Incorrect function names like vPortMalloc

3. Consider the following FreeRTOS code snippet:

void *ptr = pvPortMalloc(100);
if(ptr != NULL) {
    vPortFree(ptr);
    ptr = NULL;
}
printf("%p", ptr);

What will be the output of the printf statement?

medium

A. A memory address (non-NULL pointer)

B. Compilation error

C. NULL (0x0 or equivalent)

D. Random garbage value

Solution

1. Step 1: Analyze memory allocation and freeing

   pvPortMalloc(100) allocates memory and returns a pointer. Then vPortFree(ptr) frees it, and ptr is set to NULL.

2. Step 2: Understand the printf output

   Since ptr is explicitly set to NULL, printf will print 0x0 or equivalent NULL pointer representation.

3. Final Answer:

   NULL (0x0 or equivalent) -> Option C

4. Quick Check:

   Pointer set to NULL after free = NULL output [OK]

Hint: Pointer set to NULL after free prints NULL [OK]

Common Mistakes:

• Assuming pointer still holds address after free
• Expecting compilation error due to free
• Thinking printf prints garbage

4. Identify the error in the following FreeRTOS code snippet:

void *ptr = pvPortMalloc(50);
// Some code using ptr
vPortFree(ptr);
vPortFree(ptr);

medium

A. Double free of the same pointer

B. Missing check if pvPortMalloc returned NULL

C. Incorrect function name vPortFree

D. Memory leak due to not freeing ptr

Solution

1. Step 1: Review memory allocation and freeing

   pvPortMalloc(50) allocates memory and returns a pointer stored in ptr. The first vPortFree(ptr) frees this memory.

2. Step 2: Identify the problem with second free

   The second vPortFree(ptr) attempts to free the same memory again, causing a double free error which can crash or corrupt memory.

3. Final Answer:

   Double free of the same pointer -> Option A

4. Quick Check:

   Freeing pointer twice causes error [OK]

Hint: Never free the same pointer twice without resetting it [OK]

Common Mistakes:

• Ignoring double free risks
• Not checking for NULL after malloc
• Confusing function names

5. You want to allocate memory for an array of 10 integers using FreeRTOS memory management. Which code snippet correctly allocates and frees this memory?

hard

A. int *arr = (int *)pvPortMalloc(sizeof(int));
if(arr != NULL) {
// use arr
vPortFree(arr);
}

B. int *arr = (int *)pvPortMalloc(10 * sizeof(int));
if(arr != NULL) {
// use arr
vPortFree(arr);
}

C. int *arr = (int *)malloc(10 * sizeof(int));
if(arr != NULL) {
// use arr
free(arr);
}

D. int *arr = (int *)vPortFree(10 * sizeof(int));
if(arr != NULL) {
// use arr
pvPortMalloc(arr);
}

Solution

1. Step 1: Allocate correct memory size with pvPortMalloc

   To store 10 integers, allocate 10 times the size of int using pvPortMalloc(10 * sizeof(int)). This ensures enough space.

2. Step 2: Free memory properly with vPortFree

   After using the array, free the memory with vPortFree(arr). Also, check if allocation succeeded by verifying arr != NULL.

3. Final Answer:

   Correct allocation and freeing using pvPortMalloc and vPortFree -> Option B

4. Quick Check:

   Allocate 10 ints with pvPortMalloc, free with vPortFree [OK]

Hint: Multiply size by count in pvPortMalloc, free with vPortFree [OK]

Common Mistakes:

• Allocating only size of one int instead of 10
• Using standard malloc/free instead of pvPortMalloc/vPortFree
• Confusing allocation and free function calls