FreeRTOS heap implementations (heap_1 to heap_5) - Step-by-Step Execution

Concept Flow - FreeRTOS heap implementations (heap_1 to heap_5)

Start: Choose heap implementation

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heap_1: Simple malloc/free

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heap_2: malloc/free with coalescing

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heap_3: Uses standard malloc/free

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heap_4: malloc/free with best fit + coalescing

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heap_5: Multiple memory regions

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End

The flow shows selecting one of the five FreeRTOS heap implementations, each with different memory management features.

Execution Sample

FreeRTOS

/* Example: Using heap_4.c */
void *ptr = pvPortMalloc(100);  // Allocate 100 bytes
vPortFree(ptr);                 // Free allocated memory

This code allocates 100 bytes using heap_4 and then frees it, showing basic allocation and deallocation.

Execution Table

Step	Action	Heap Implementation	Memory State	Notes
1	Call pvPortMalloc(100)	heap_4	Block of 100 bytes allocated, free blocks adjusted	Best fit block chosen, free blocks coalesced if needed
2	Call vPortFree(ptr)	heap_4	Block of 100 bytes freed, adjacent free blocks merged	Memory coalescing reduces fragmentation
3	Call pvPortMalloc(50)	heap_1	Block of 50 bytes allocated, no coalescing	Simple allocation, no merging of free blocks
4	Call vPortFree(ptr)	heap_1	Block of 50 bytes freed, no coalescing	Memory fragmentation possible
5	Call pvPortMalloc(200)	heap_3	Standard malloc allocates 200 bytes	Uses system malloc/free
6	Call vPortFree(ptr)	heap_3	Standard free called	Relies on system heap
7	Call pvPortMalloc(150)	heap_5	Allocates 150 bytes from multiple regions	Supports multiple memory regions
8	Call vPortFree(ptr)	heap_5	Block freed in correct region	Memory managed per region
9	Exit	-	-	All allocations and frees completed

💡 All memory allocations and frees completed for different heap implementations

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	Final
ptr	NULL	Pointer to 100-byte block (heap_4)	NULL (freed)	Pointer to 50-byte block (heap_1)	NULL (freed)	Pointer to 200-byte block (heap_3)	NULL (freed)	Pointer to 150-byte block (heap_5)	NULL (freed)	NULL

Key Moments - 3 Insights

Why does heap_1 not merge free blocks after freeing memory?

heap_1 only frees memory but does not coalesce adjacent free blocks, so fragmentation can occur as shown in steps 3 and 4 of the execution_table.

How does heap_4 reduce fragmentation compared to heap_1?

heap_4 uses best fit allocation and merges adjacent free blocks when freeing memory, reducing fragmentation as seen in steps 1 and 2.

What is special about heap_5 compared to other heap implementations?

heap_5 manages multiple separate memory regions, allocating and freeing memory in the correct region, demonstrated in steps 7 and 8.

Visual Quiz - 3 Questions

Look at the execution_table, what happens to the pointer 'ptr' after step 2?

A It points to the freed 100-byte block

B It points to a new allocated block

C It becomes NULL after freeing

D It remains unchanged

💡 Hint

Check variable_tracker column 'After Step 2' for 'ptr' value

At which step does the heap implementation use system malloc/free?

A Step 1

B Step 5

C Step 3

D Step 7

💡 Hint

Look at execution_table 'Heap Implementation' column for 'heap_3'

If heap_1 was changed to coalesce free blocks, which step's memory state would change?

A Step 4

B Step 2

C Step 6

D Step 8

💡 Hint

Refer to key_moments about heap_1 behavior and execution_table step 4

Concept Snapshot

FreeRTOS offers 5 heap implementations:
heap_1: Simple malloc/free, no coalescing
heap_2: malloc/free with coalescing
heap_3: Uses system malloc/free
heap_4: Best fit malloc/free with coalescing
heap_5: Supports multiple memory regions
Choose based on fragmentation and memory needs.

Full Transcript

This visual execution shows how FreeRTOS heap implementations manage memory differently. Starting from choosing a heap type, heap_1 simply allocates and frees memory without merging free blocks, which can cause fragmentation. heap_2 improves by coalescing adjacent free blocks. heap_3 relies on the system's malloc and free functions. heap_4 uses a best fit strategy and merges free blocks to reduce fragmentation. heap_5 supports multiple memory regions, allocating and freeing memory in the correct region. The execution table traces allocation and freeing steps for each heap type, showing pointer changes and memory state. Variable tracking follows the pointer 'ptr' through allocations and frees. Key moments clarify why coalescing matters and how heap_5 differs. The quiz tests understanding of pointer states, heap types, and effects of coalescing. The snapshot summarizes the five heap implementations and their key features.