Choosing the right heap scheme in FreeRTOS - Step-by-Step Execution

Concept Flow - Choosing the right heap scheme

Start: Need dynamic memory?

↓

Check memory constraints

↓

Choose heap scheme

↓

heap_1

↓

Allocate/Free memory

↓

Monitor fragmentation & performance

↓

Adjust scheme if needed

↓

End

This flow shows how to pick a FreeRTOS heap scheme based on memory needs and constraints, then allocate memory and monitor performance.

Execution Sample

FreeRTOS

void *ptr = pvPortMalloc(100);
if(ptr != NULL) {
  // Use memory
  vPortFree(ptr);
}

This code allocates 100 bytes using the chosen heap scheme and frees it after use.

Execution Table

Step	Action	Heap Scheme Selected	Memory Allocated	Fragmentation Status	Notes
1	Start allocation request	None	0 bytes	N/A	No heap chosen yet
2	Check system memory constraints	heap_4	0 bytes	N/A	heap_4 chosen for best fragmentation control
3	Call pvPortMalloc(100)	heap_4	100 bytes	Low	Memory allocated successfully
4	Use allocated memory	heap_4	100 bytes	Low	Memory in use
5	Call vPortFree(ptr)	heap_4	0 bytes	Low	Memory freed
6	Monitor fragmentation	heap_4	0 bytes	Low	Fragmentation remains low
7	End	heap_4	0 bytes	Low	Allocation cycle complete

💡 Allocation and free complete with heap_4 scheme maintaining low fragmentation

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
ptr	NULL	Address 0x20001000	NULL	NULL
Memory Allocated	0 bytes	100 bytes	0 bytes	0 bytes
Fragmentation	N/A	Low	Low	Low

Key Moments - 3 Insights

Why choose heap_4 over heap_1 or heap_2?

heap_4 offers better fragmentation control and is suitable for systems with limited memory, as shown in execution_table step 2 where heap_4 is selected for low fragmentation.

What happens if pvPortMalloc fails?

If pvPortMalloc returns NULL (not shown in this trace), it means memory allocation failed due to insufficient free memory or fragmentation, so the program should handle this gracefully.

Does freeing memory immediately reduce fragmentation?

Freeing memory returns it to the heap, but fragmentation depends on how memory blocks are arranged; heap_4 manages fragmentation better as seen in step 6 where fragmentation remains low after free.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of 'ptr'?

A 100 bytes

B NULL

C Address 0x20001000

D heap_4

💡 Hint

Check variable_tracker row for 'ptr' after step 3

At which step does the memory get freed?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look at execution_table action column for 'vPortFree(ptr)'

If the system had very limited memory and fragmentation was high, which heap scheme might be better than heap_1?

A heap_2

B heap_4

C heap_3

D None

💡 Hint

Refer to concept_flow where heap_4 is chosen for fragmentation control

Concept Snapshot

FreeRTOS offers multiple heap schemes (heap_1 to heap_5).
Choose based on memory constraints and fragmentation needs.
heap_1 is simple but no free support.
heap_4 manages fragmentation well.
Use pvPortMalloc and vPortFree to allocate and free memory.
Monitor fragmentation to adjust scheme if needed.

Full Transcript

This visual trace shows how FreeRTOS chooses a heap scheme for dynamic memory allocation. It starts by checking system memory constraints, then selects heap_4 for its good fragmentation control. The code allocates 100 bytes using pvPortMalloc, uses the memory, then frees it with vPortFree. Fragmentation remains low throughout. Key points include why heap_4 is chosen, what happens if allocation fails, and how freeing memory affects fragmentation. The quiz tests understanding of pointer values, freeing steps, and heap scheme choices.