/* Allocate the memory for the heap. */
#if( configAPPLICATION_ALLOCATED_HEAP == 1 )
//這種情況是可以把待管理的數(shù)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(shù)組分配在內(nèi)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(jié)對齊，所以實際能使用的內(nèi)存字節(jié)數(shù)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(jīng)分配了的字節(jié)數(shù)，也就是下一個空閑內(nèi)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(shù)組首地址
	/* Ensure that blocks are always aligned to the required number of bytes. */
    //如果不是1字節(jié)對齊則先需要portBYTE_ALIGNMENT字節(jié)對齊
	#if( portBYTE_ALIGNMENT != 1 )
	{
		if( xWantedSize & portBYTE_ALIGNMENT_MASK )
		{			/* Byte alignment required. */
		//如果用戶申請字節(jié)數(shù)不是portBYTE_ALIGNMENT_MASK字節(jié)對齊的，先要調(diào)整到portBYTE_ALIGNMENT_MASK字節(jié)對齊
		//比如申請13字節(jié)，要求portBYTE_ALIGNMENT = 8，
		//則xWantedSize = 13+(8-(13&7))=13+(8-5)=16，
		//最終申請16字節(jié)
			xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
		}
	}
	#endif
//掛起調(diào)度器，防止函數(shù)重入
	vTaskSuspendAll();
	{
		if( pucAlignedHeap == NULL )
		//說明是第一次調(diào)用此函數(shù)需要對對內(nèi)存堆初始化確保內(nèi)存堆首址也是8字節(jié)對齊
		{
			/* Ensure the heap starts on a correctly aligned boundary. */
		    //假設(shè)&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(jīng)分配的字節(jié)數(shù)xNextFreeByte + 將要分配的字節(jié)數(shù)xWantedSize
		//要小于總共有的字節(jié)數(shù)configADJUSTED_HEAP_SIZE
		if( ( ( xNextFreeByte + xWantedSize ) < configADJUSTED_HEAP_SIZE ) &&
		//此條件是防止溢出，因為內(nèi)存是地址是單調(diào)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(jīng)分配了的內(nèi)存字節(jié)數(shù)
			xNextFreeByte += xWantedSize;
		}
		traceMALLOC( pvReturn, xWantedSize );
	}
	( void ) xTaskResumeAll();
//解掛調(diào)度器
//如果使能的內(nèi)存申請失敗的鉤子函數(shù)當(dāng)申請失敗時會執(zhí)行申請失敗鉤子函數(shù)
	#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 );
}