freertos 源码分析四 任务创建的简单分析

任务创建xTaskCreate
为TCB和TCB栈分配空间， 初始化，加入就绪任务链表

#if ( configSUPPORT_DYNAMIC_ALLOCATION == 1 )BaseType_t xTaskCreate( TaskFunction_t pxTaskCode,const char * const pcName,const configSTACK_DEPTH_TYPE usStackDepth,void * const pvParameters,UBaseType_t uxPriority,TaskHandle_t * const pxCreatedTask ){    TCB_t * pxNewTCB;BaseType_t xReturn;#if ( portSTACK_GROWTH > 0 ){pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); if( pxNewTCB != NULL ){memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) ); pxNewTCB->pxStack = ( StackType_t * ) pvPortMallocStack( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); if( pxNewTCB->pxStack == NULL ){vPortFree( pxNewTCB );pxNewTCB = NULL;}}}#else{StackType_t * pxStack;pxStack = pvPortMallocStack( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) );if( pxStack != NULL ){pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );                                                                            if( pxNewTCB != NULL ){memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) );pxNewTCB->pxStack = pxStack;}else{vPortFreeStack( pxStack );}}else{pxNewTCB = NULL;}}#endifif( pxNewTCB != NULL ){#if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 ){pxNewTCB->ucStaticallyAllocated = tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB;}#endifprvInitialiseNewTask( pxTaskCode, pcName, ( uint32_t ) usStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );prvAddNewTaskToReadyList( pxNewTCB );xReturn = pdPASS;}else{xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;}return xReturn;}
#endif

TCB初始化
设置栈顶栈底，任务名，优先级，初始化及填充状态消息表项。

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 )
{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 ) ) );                                                                                                                                                 configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );#if ( configRECORD_STACK_HIGH_ADDRESS == 1 ){pxNewTCB->pxEndOfStack = pxTopOfStack;}#endif}#else{pxTopOfStack = pxNewTCB->pxStack;configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxNewTCB->pxStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0UL ) );pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32_t ) 1 );}#endifif( pcName != NULL ){for( x = ( UBaseType_t ) 0; x < ( UBaseType_t ) configMAX_TASK_NAME_LEN; x++ ){pxNewTCB->pcTaskName[ x ] = pcName[ x ];if( pcName[ x ] == ( char ) 0x00 ){break;}}pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1 ] = '\0';}configASSERT( uxPriority < configMAX_PRIORITIES );if( uxPriority >= ( UBaseType_t ) configMAX_PRIORITIES )                                                                                       {uxPriority = ( UBaseType_t ) configMAX_PRIORITIES - ( UBaseType_t ) 1U;}pxNewTCB->uxPriority = uxPriority;#if ( configUSE_MUTEXES == 1 ){pxNewTCB->uxBasePriority = uxPriority;}#endifvListInitialiseItem( &( pxNewTCB->xStateListItem ) );vListInitialiseItem( &( pxNewTCB->xEventListItem ) );listSET_LIST_ITEM_OWNER( &( pxNewTCB->xStateListItem ), pxNewTCB );listSET_LIST_ITEM_VALUE( &( pxNewTCB->xEventListItem ), ( TickType_t ) configMAX_PRIORITIES - ( TickType_t ) uxPriority );listSET_LIST_ITEM_OWNER( &( pxNewTCB->xEventListItem ), pxNewTCB );if( pxCreatedTask != NULL ){*pxCreatedTask = ( TaskHandle_t ) pxNewTCB;}}

加入就绪态链表 禁中断 任务数加一，设为当前，开中断

static void prvAddNewTaskToReadyList( TCB_t * pxNewTCB )                                                                                           
{taskENTER_CRITICAL();  {uxCurrentNumberOfTasks++;if( pxCurrentTCB == NULL ){pxCurrentTCB = pxNewTCB;if( uxCurrentNumberOfTasks == ( UBaseType_t ) 1 ){prvInitialiseTaskLists();}}else{if( xSchedulerRunning == pdFALSE ){if( pxCurrentTCB->uxPriority <= pxNewTCB->uxPriority ){pxCurrentTCB = pxNewTCB;}}}uxTaskNumber++;prvAddTaskToReadyList( pxNewTCB );}taskEXIT_CRITICAL();if( xSchedulerRunning != pdFALSE ){if( pxCurrentTCB->uxPriority < pxNewTCB->uxPriority ){taskYIELD_IF_USING_PREEMPTION();}}
}

若是uxCurrentNumberOfTasks 为1,即第一个任务，初始化各链表

static void prvInitialiseTaskLists( void )
{UBaseType_t uxPriority;for( uxPriority = ( UBaseType_t ) 0U; uxPriority < ( UBaseType_t ) configMAX_PRIORITIES; uxPriority++ ){vListInitialise( &( pxReadyTasksLists[ uxPriority ] ) );}vListInitialise( &xDelayedTaskList1 );vListInitialise( &xDelayedTaskList2 );vListInitialise( &xPendingReadyList );#if ( INCLUDE_vTaskDelete == 1 ){vListInitialise( &xTasksWaitingTermination );}#endif#if ( INCLUDE_vTaskSuspend == 1 ){vListInitialise( &xSuspendedTaskList );}#endifpxDelayedTaskList = &xDelayedTaskList1;pxOverflowDelayedTaskList = &xDelayedTaskList2;
}  

prvAddTaskToReadyList宏定义

#define prvAddTaskToReadyList( pxTCB )                                                                 \traceMOVED_TASK_TO_READY_STATE( pxTCB );                                                           \taskRECORD_READY_PRIORITY( ( pxTCB )->uxPriority );                                                \listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) ); \tracePOST_MOVED_TASK_TO_READY_STATE( pxTCB )

记录最高优先级

#define taskRECORD_READY_PRIORITY( uxPriority ) \
{                                               \if( ( uxPriority ) > uxTopReadyPriority )   \{                                           \uxTopReadyPriority = ( uxPriority );    \}                                           \
}

listINSERT_END 加入链表

taskYIELD_IF_USING_PREEMPTION 定义 
#if ( configUSE_PREEMPTION == 0 )#define taskYIELD_IF_USING_PREEMPTION()
#else#define taskYIELD_IF_USING_PREEMPTION()    portYIELD_WITHIN_API()                                                                              
#endif#ifndef portYIELD_WITHIN_API#define portYIELD_WITHIN_API    portYIELD                                                                                                      
#endif
stm32对应portYIELD 定义 适配不同定义不同
#define portYIELD()||   |   |   |   __asm volatile ( "SWI 0" )