FreeRTOS动态内存分配管理

/* Allocate the memory for the heap. */
#if( configAPPLICATION_ALLOCATED_HEAP == 1 )
//这种情况是可以把待管理的数组分配在外部SRAM、SDRAM中
	extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#else
//这种情况是把待管理的数组分配在内部RAM，由编译器决定地址
	static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#endif /* configAPPLICATION_ALLOCATED_HEAP */

//因为需要字节对齐，所以实际能使用的内存字节数要减去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

//已经分配了的字节数，也就是下一个空闲内存相对于首址(pucAlignedHeap)的偏移量
static size_t xNextFreeByte = ( size_t ) 0;

void *pvPortMalloc( size_t xWantedSize )
{
void *pvReturn = NULL;//待返回给用户分配地址
static uint8_t *pucAlignedHeap = NULL;//实际管理的数组首地址
	/* Ensure that blocks are always aligned to the required number of bytes. */
    //如果不是1字节对齐则先需要portBYTE_ALIGNMENT字节对齐
	#if( portBYTE_ALIGNMENT != 1 )
	{
		if( xWantedSize & portBYTE_ALIGNMENT_MASK )
		{			/* Byte alignment required. */
		//如果用户申请字节数不是portBYTE_ALIGNMENT_MASK字节对齐的，先要调整到portBYTE_ALIGNMENT_MASK字节对齐
		//比如申请13字节，要求portBYTE_ALIGNMENT = 8，
		//则xWantedSize = 13+(8-(13&7))=13+(8-5)=16，
		//最终申请16字节
			xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
		}
	}
	#endif
//挂起调度器，防止函数重入
	vTaskSuspendAll();
	{
		if( pucAlignedHeap == NULL )
		//说明是第一次调用此函数需要对对内存堆初始化确保内存堆首址也是8字节对齐
		{
			/* Ensure the heap starts on a correctly aligned boundary. */
		    //假设&ucHeap是0x20000C64，
		    //则&ucHeap[ portBYTE_ALIGNMENT ]是 0x20000C64+7=0x20000C6B
		    //pucAlignedHeap = 0x20000C6B & (~0x00000007) = 0x20000C68
		    //pucAlignedHeap才是实际操作的堆首址
			pucAlignedHeap = ( uint8_t * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );
		}
		/* Check there is enough room left for the allocation. */
		//已经分配的字节数xNextFreeByte + 将要分配的字节数xWantedSize
		//要小于总共有的字节数configADJUSTED_HEAP_SIZE
		if( ( ( xNextFreeByte + xWantedSize ) < configADJUSTED_HEAP_SIZE ) &&
		//此条件是防止溢出，因为内存是地址是单调增长
			( ( xNextFreeByte + xWantedSize ) > xNextFreeByte )	)/* Check for overflow. */
		{
			/* Return the next free byte then increment the index past this
			block. */
			//返回地址给用户
			pvReturn = pucAlignedHeap + xNextFreeByte;
			//更新已经分配了的内存字节数
			xNextFreeByte += xWantedSize;
		}
		traceMALLOC( pvReturn, xWantedSize );
	}
	( void ) xTaskResumeAll();
//解挂调度器
//如果使能的内存申请失败的钩子函数当申请失败时会执行申请失败钩子函数
	#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 );
}