FreeRTOS動態記憶體分配管理heap_1範例

/* Allocate the memory for the heap. */
#if( configAPPLICATION_ALLOCATED_HEAP == 1 )
//這種情況是可以把待管理的陣列分配在外部SRAM、SDRAM中
	extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#else
//這種情況是把待管理的陣列分配在內部RAM，由編譯器決定地址
	static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#endif /* configAPPLICATION_ALLOCATED_HEAP */

//因為需要位元組對齊，所以實際能使用的記憶體位元組數要減去portBYTE_ALIGNMENT
/* A few bytes might be lost to byte aligning the heap start address. */
#define configADJUSTED_HEAP_SIZE	( configTOTAL_HEAP_SIZE - portBYTE_ALIGNMENT )

#define portBYTE_ALIGNMENT8

//已經分配了的位元組數，也就是下一個空閒記憶體相對於首址(pucAlignedHeap)的偏移量
static size_t xNextFreeByte = ( size_t ) 0;

void *pvPortMalloc( size_t xWantedSize )
{
void *pvReturn = NULL;//待返回給使用者分配地址
static uint8_t *pucAlignedHeap = NULL;//實際管理的陣列首地址
	/* Ensure that blocks are always aligned to the required number of bytes. */
    //如果不是1位元組對齊則先需要portBYTE_ALIGNMENT位元組對齊
	#if( portBYTE_ALIGNMENT != 1 )
	{
		if( xWantedSize & portBYTE_ALIGNMENT_MASK )
		{			/* Byte alignment required. */
		//如果使用者申請位元組數不是portBYTE_ALIGNMENT_MASK位元組對齊的，先要調整到portBYTE_ALIGNMENT_MASK位元組對齊
		//比如申請13位元組，要求portBYTE_ALIGNMENT = 8，
		//則xWantedSize = 13+(8-(13&7))=13+(8-5)=16，
		//最終申請16位元組
			xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
		}
	}
	#endif
//掛起排程器，防止函數重入
	vTaskSuspendAll();
	{
		if( pucAlignedHeap == NULL )
		//說明是第一次呼叫此函數需要對對記憶體堆初始化確保記憶體堆首址也是8位元組對齊
		{
			/* Ensure the heap starts on a correctly aligned boundary. */
		    //假設&ucHeap是0x20000C64，
		    //則&ucHeap[ portBYTE_ALIGNMENT ]是 0x20000C64+7=0x20000C6B
		    //pucAlignedHeap = 0x20000C6B & (~0x00000007) = 0x20000C68
		    //pucAlignedHeap才是實際操作的堆首址
			pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
		}
		/* Check there is enough room left for the allocation. */
		//已經分配的位元組數xNextFreeByte + 將要分配的位元組數xWantedSize
		//要小於總共有的位元組數configADJUSTED_HEAP_SIZE
		if( ( ( xNextFreeByte + xWantedSize ) < configADJUSTED_HEAP_SIZE ) &&
		//此條件是防止溢位，因為記憶體是地址是單調增長
			( ( xNextFreeByte + xWantedSize ) > xNextFreeByte )	)/* Check for overflow. */
		{
			/* Return the next free byte then increment the index past this
			block. */
			//返回地址給使用者
			pvReturn = pucAlignedHeap + xNextFreeByte;
			//更新已經分配了的記憶體位元組數
			xNextFreeByte += xWantedSize;
		}
		traceMALLOC( pvReturn, xWantedSize );
	}
	( void ) xTaskResumeAll();
//解掛排程器
//如果使能的記憶體申請失敗的勾點函數當申請失敗時會執行申請失敗勾點函數
	#if( configUSE_MALLOC_FAILED_HOOK == 1 )
	{
		if( pvReturn == NULL )
		{
			extern void vApplicationMallocFailedHook( void );
			vApplicationMallocFailedHook();
		}
	}
	#endif
	return pvReturn;
}

#if portBYTE_ALIGNMENT == 8
	#define portBYTE_ALIGNMENT_MASK ( 0x0007 )
#endif

void vPortFree( void *pv )
{
	/* Memory cannot be freed using this scheme.  See heap_2.c, heap_3.c and
	heap_4.c for alternative implementations, and the memory management pages of
	http://www.FreeRTOS.org for more information. */
	( void ) pv;
	/* Force an assert as it is invalid to call this function. */
	configASSERT( pv == NULL );
}

size_t xPortGetFreeHeapSize( void )
{
	return ( configADJUSTED_HEAP_SIZE - xNextFreeByte );
}