xTaskCreate函数：创建一个任务（动态内存分配）

BaseType_t xTaskCreate(	TaskFunction_t pxTaskCode,
							const char * const pcName,
							const uint16_t usStackDepth,
							void * const pvParameters,
							UBaseType_t uxPriority,
							TaskHandle_t * const pxCreatedTask ) /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
	{
	TCB_t *pxNewTCB;
	BaseType_t xReturn;
	{
		StackType_t *pxStack;

			/* Allocate space for the stack used by the task being created. */
			pxStack = ( StackType_t * ) pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */

			if( pxStack != NULL )
			{
				/* Allocate space for the TCB. */
				pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); /*lint !e961 MISRA exception as the casts are only redundant for some paths. */

				if( pxNewTCB != NULL )
				{
					/* Store the stack location in the TCB. */
					pxNewTCB->pxStack = pxStack;
				}
				else
				{
					/* The stack cannot be used as the TCB was not created.  Free
					it again. */
					vPortFree( pxStack );
				}
			}
			else
			{
				pxNewTCB = NULL;
			}
		}
		#endif /* portSTACK_GROWTH */

		if( pxNewTCB != NULL )
		{
		prvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
			prvAddNewTaskToReadyList( pxNewTCB );
			xReturn = pdPASS;
		}
		else
		{
			xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
		}

		return xReturn;
	}

1.动态申请usStackDepth大小的内存；

2.为任务控制块TCB申请内存

3.将任务控制块的任务栈指针指向申请好的任务栈内存地址。

	prvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
			prvAddNewTaskToReadyList( pxNewTCB );
			xReturn = pdPASS;

4.调用prvInitialiseNewTask函数。

static void prvInitialiseNewTask( 	TaskFunction_t pxTaskCode,
									const char * const pcName,
									const uint32_t ulStackDepth,
									void * const pvParameters,
									UBaseType_t uxPriority,
									TaskHandle_t * const pxCreatedTask,
									TCB_t *pxNewTCB,
									const MemoryRegion_t * const xRegions ) /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
{
StackType_t *pxTopOfStack;
UBaseType_t x;
	#if( portSTACK_GROWTH < 0 )
	{
		pxTopOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32_t ) 1 );
		pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) ); /*lint !e923 MISRA exception.  Avoiding casts between pointers and integers is not practical.  Size differences accounted for using portPOINTER_SIZE_TYPE type. */

		/* Check the alignment of the calculated top of stack is correct. */
		configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );
	}
	for( x = ( UBaseType_t ) 0; x < ( UBaseType_t ) configMAX_TASK_NAME_LEN; x++ )
	{
		pxNewTCB->pcTaskName[ x ] = pcName[ x ];

		/* Don't copy all configMAX_TASK_NAME_LEN if the string is shorter than
		configMAX_TASK_NAME_LEN characters just in case the memory after the
		string is not accessible (extremely unlikely). */
		if( pcName[ x ] == 0x00 )
		{
			break;
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1 ] = '\0';

	/* This is used as an array index so must ensure it's not too large.  First
	remove the privilege bit if one is present. */
	if( uxPriority >= ( UBaseType_t ) configMAX_PRIORITIES )
	{
		uxPriority = ( UBaseType_t ) configMAX_PRIORITIES - ( UBaseType_t ) 1U;
	}
	else
	{
		mtCOVERAGE_TEST_MARKER();
	}

	pxNewTCB->uxPriority = uxPriority;
		vListInitialiseItem( &( pxNewTCB->xStateListItem ) );
	vListInitialiseItem( &( pxNewTCB->xEventListItem ) );

	/* Set the pxNewTCB as a link back from the ListItem_t.  This is so we can get
	back to	the containing TCB from a generic item in a list. */
	listSET_LIST_ITEM_OWNER( &( pxNewTCB->xStateListItem ), pxNewTCB );

	/* Event lists are always in priority order. */
	listSET_LIST_ITEM_VALUE( &( pxNewTCB->xEventListItem ), ( TickType_t ) configMAX_PRIORITIES - ( TickType_t ) uxPriority ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */
	listSET_LIST_ITEM_OWNER( &( pxNewTCB->xEventListItem ), pxNewTCB );
	{
		/* Avoid compiler warning about unreferenced parameter. */
		( void ) xRegions;
	}
	#if ( configUSE_TASK_NOTIFICATIONS == 1 )
	{
		pxNewTCB->ulNotifiedValue = 0;
		pxNewTCB->ucNotifyState = taskNOT_WAITING_NOTIFICATION;
	}
		{
		pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
	}
	#endif /* portUSING_MPU_WRAPPERS */

	if( ( void * ) pxCreatedTask != NULL )
	{
		/* Pass the handle out in an anonymous way.  The handle can be used to
		change the created task's priority, delete the created task, etc.*/
		*pxCreatedTask = ( TaskHandle_t ) pxNewTCB;
	}
	else
	{
		mtCOVERAGE_TEST_MARKER();
	}
	}