freertos创建函数xTaskCreate( v

signed portBASE_TYPE xTaskGenericCreate( pdTASK_CODE pxTaskCode, const signed char * const pcName, unsigned short usStackDepth, void *pvParameters, unsigned portBASE_TYPE uxPriority, xTaskHandle *pxCreatedTask, portSTACK_TYPE *puxStackBuffer, const xMemoryRegion * const xRegions )

{

signed portBASE_TYPE xReturn;

tskTCB * pxNewTCB;

 configASSERT( pxTaskCode );

 configASSERT( ( uxPriority < configMAX_PRIORITIES ) );

 //分配任务TCB和堆栈

 pxNewTCB = prvAllocateTCBAndStack( usStackDepth, puxStackBuffer );

 if( pxNewTCB != NULL )

 {

  portSTACK_TYPE *pxTopOfStack;

  #if( portUSING_MPU_WRAPPERS == 1 )

   portBASE_TYPE xRunPrivileged;

   if( ( uxPriority & portPRIVILEGE_BIT ) != 0U )

   {

    xRunPrivileged = pdTRUE;

   }

   else

   {

    xRunPrivileged = pdFALSE;

   }

   uxPriority &= ~portPRIVILEGE_BIT;

  #endif

//判断堆栈增长方式是否是由高到低增长

  #if( portSTACK_GROWTH < 0 )

  {

   pxTopOfStack = pxNewTCB->pxStack + ( usStackDepth - ( unsigned short ) 1 );

//保持堆栈为字节对齐？

   pxTopOfStack = ( portSTACK_TYPE * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ( portPOINTER_SIZE_TYPE ) ~portBYTE_ALIGNMENT_MASK  ) );

   configASSERT( ( ( ( unsigned long ) pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );

  }

  #else

  {

   pxTopOfStack = pxNewTCB->pxStack;

   configASSERT( ( ( ( unsigned long ) pxNewTCB->pxStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );

   pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( usStackDepth - 1 );

  }

  #endif

  //TCB初始化

  prvInitialiseTCBVariables( pxNewTCB, pcName, uxPriority, xRegions, usStackDepth );

  #if( portUSING_MPU_WRAPPERS == 1 )

  {

   pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters, xRunPrivileged );

  }

  #else

  {

//汇编语言对堆栈进行初始化

   pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );

  }

  #endif

  portALIGNMENT_ASSERT_pxCurrentTCB( ( ( ( unsigned long ) pxNewTCB->pxTopOfStack & ( unsigned long ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );

  if( ( void * ) pxCreatedTask != NULL )

  {

   *pxCreatedTask = ( xTaskHandle ) pxNewTCB;

  }

  taskENTER_CRITICAL();

  {

   uxCurrentNumberOfTasks++;//更新系统任务数

   if( pxCurrentTCB == NULL )

   {

    pxCurrentTCB =  pxNewTCB;

    if( uxCurrentNumberOfTasks == ( unsigned portBASE_TYPE ) 1 )

    {

     //如果当前任务数为1的话，则证明米有初始化就绪列表，等待列表，挂起列表等

    //初始化就绪列表的时候，定义优先级为一个数据数组，则每个数据数组的元素代表一个优先级

//其他列表则没有这么复杂 直接定义 不区分优先级

     prvInitialiseTaskLists();

    }

   }

   else

   {

    //比较，将当前最高的优先级赋给pxCurrentTCB

    if( xSchedulerRunning == pdFALSE )

    {

     if( pxCurrentTCB->uxPriority <= uxPriority )

     {

      pxCurrentTCB = pxNewTCB;

     }

    }

   }

   //更新uxTopUsedPriority，方便查询的时候直接从uxTopUsedPriority开始查询

   if( pxNewTCB->uxPriority > uxTopUsedPriority )

   {

    uxTopUsedPriority = pxNewTCB->uxPriority;

   }

   #if ( configUSE_TRACE_FACILITY == 1 )

   {

    pxNewTCB->uxTCBNumber = uxTCBNumber;

   }

   #endif

   uxTCBNumber++;

//将任务添加到就绪列表中。当任务处于阻塞态的时候，从就绪列表中删除，加入到阻塞列表中。

   prvAddTaskToReadyQueue( pxNewTCB );

   xReturn = pdPASS;

   traceTASK_CREATE( pxNewTCB );

  }

  taskEXIT_CRITICAL();

 }

 else

 {

  xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;

  traceTASK_CREATE_FAILED();

 }

 if( xReturn == pdPASS )

 {

  if( xSchedulerRunning != pdFALSE )

  {

   if( pxCurrentTCB->uxPriority < uxPriority )

   {

    portYIELD_WITHIN_API();

   }

  }

 }

 return xReturn;

}