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

//因為需要字節對齊，所以實際能使用的內存字節數要減去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

//已經分配了的字節數，也就是下一個空閑內存相對于首址(pucAlignedHeap)的偏移量
static size_t xNextFreeByte = ( size_t ) 0;

void *pvPortMalloc( size_t xWantedSize )
{
void *pvReturn = NULL;//待返回給用戶分配地址
static uint8_t *pucAlignedHeap = NULL;//實際管理的數組首地址
	/* Ensure that blocks are always aligned to the required number of bytes. */
    //如果不是1字節對齊則先需要portBYTE_ALIGNMENT字節對齊
	#if( portBYTE_ALIGNMENT != 1 )
	{
		if( xWantedSize & portBYTE_ALIGNMENT_MASK )
		{			/* Byte alignment required. */
		//如果用戶申請字節數不是portBYTE_ALIGNMENT_MASK字節對齊的，先要調整到portBYTE_ALIGNMENT_MASK字節對齊
		//比如申請13字節，要求portBYTE_ALIGNMENT = 8，
		//則xWantedSize = 13+(8-(13&7))=13+(8-5)=16，
		//最終申請16字節
			xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
		}
	}
	#endif
//掛起調度器，防止函數重入
	vTaskSuspendAll();
	{
		if( pucAlignedHeap == NULL )
		//說明是第一次調用此函數需要對對內存堆初始化確保內存堆首址也是8字節對齊
		{
			/* 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. */
		//已經分配的字節數xNextFreeByte + 將要分配的字節數xWantedSize
		//要小于總共有的字節數configADJUSTED_HEAP_SIZE
		if( ( ( xNextFreeByte + xWantedSize ) < configADJUSTED_HEAP_SIZE ) &&
		//此條件是防止溢出，因為內存是地址是單調增長
			( ( xNextFreeByte + xWantedSize ) > xNextFreeByte )	)/* Check for overflow. */
		{
			/* Return the next free byte then increment the index past this
			block. */
			//返回地址給用戶
			pvReturn = pucAlignedHeap + xNextFreeByte;
			//更新已經分配了的內存字節數
			xNextFreeByte += xWantedSize;
		}
		traceMALLOC( pvReturn, xWantedSize );
	}
	( void ) xTaskResumeAll();
//解掛調度器
//如果使能的內存申請失敗的鉤子函數當申請失敗時會執行申請失敗鉤子函數
	#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 );
}