FreeRTOS之xTaskCreate实现分析

1 函数接口

1.1 函数接口

BaseType_t xTaskCreate( TaskFunction_t pxTaskCode,
const char * const pcName,
const configSTACK_DEPTH_TYPE uxStackDepth,
void * const pvParameters,
UBaseType_t uxPriority,
TaskHandle_t * const pxCreatedTask )

1.2 函数参数简介

• TaskFunction_t pxTaskCode 任务的处理函数
• const char * const pcName 任务的名字
• const configSTACK_DEPTH_TYPE uxStackDepth 当前任务栈的大小，栈的实际大小为uxStackDepth * sizeof(StackType_t)
• void * const pvParameters 传入到任务处理函数的参数
• UBaseType_t uxPriority 当前任务的优先级
• TaskHandle_t * const pxCreatedTask 任务句柄

2 xTaskCreate的调用关系

2.1 调用关系

|- xTaskCreate
|- prvCreateTask
|- pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );
|- pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );
|- prvInitialiseNewTask
|- vListInitialiseItem( &( pxNewTCB->xStateListItem ) );
|- vListInitialiseItem( &( pxNewTCB->xEventListItem ) );
|- pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
|- *pxCreatedTask = ( TaskHandle_t ) pxNewTCB;
|- prvAddNewTaskToReadyList
|- prvInitialiseTaskLists
|- prvAddTaskToReadyList
|- listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) );

2.2 调用关系示意图

根据上面的调用关系可以总结为下面简单的示意图示例

3 函数源码分析

3.1 xTaskCreate

• pxNewTCB = prvCreateTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask ); 创建并初始化当前要创建的任务TCB
• prvAddNewTaskToReadyList( pxNewTCB ); 将当前创建的任务插入到pxReadyTasksLists对应优先级的列表中

BaseType_t xTaskCreate( TaskFunction_t pxTaskCode,
const char * const pcName,
const configSTACK_DEPTH_TYPE uxStackDepth,
void * const pvParameters,
UBaseType_t uxPriority,
TaskHandle_t * const pxCreatedTask )
{
TCB_t * pxNewTCB;
BaseType_t xReturn;

traceENTER_xTaskCreate( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask );

pxNewTCB = prvCreateTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask );

if( pxNewTCB != NULL )
{
#if ( ( configNUMBER_OF_CORES > 1 ) && ( configUSE_CORE_AFFINITY == 1 ) )
{
/* Set the task's affinity before scheduling it. */
pxNewTCB->uxCoreAffinityMask = configTASK_DEFAULT_CORE_AFFINITY;
}
#endif

prvAddNewTaskToReadyList( pxNewTCB );
xReturn = pdPASS;
}
else
{
xReturn = errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY;
}

traceRETURN_xTaskCreate( xReturn );

return xReturn;
}

3.2 prvCreateTask

• pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) ); 申请当前任务的栈空间，栈的size为( ( size_t ) uxStackDepth ) * sizeof( StackType_t )
• pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); 申请TCB任务块
• prvInitialiseNewTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL ); 初始化当前任务的TCB

static TCB_t * prvCreateTask( TaskFunction_t pxTaskCode,
  const char * const pcName,
  const configSTACK_DEPTH_TYPE uxStackDepth,
  void * const pvParameters,
  UBaseType_t uxPriority,
  TaskHandle_t * const pxCreatedTask )
{
TCB_t * pxNewTCB;

/* If the stack grows down then allocate the stack then the TCB so the stack
 * does not grow into the TCB.  Likewise if the stack grows up then allocate
 * the TCB then the stack. */
#if ( portSTACK_GROWTH > 0 )
{
/* Allocate space for the TCB.  Where the memory comes from depends on
 * the implementation of the port malloc function and whether or not static
 * allocation is being used. */
/* MISRA Ref 11.5.1 [Malloc memory assignment] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/main/MISRA.md#rule-115 */
/* coverity[misra_c_2012_rule_11_5_violation] */
pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );

if( pxNewTCB != NULL )
{
( void ) memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) );

/* Allocate space for the stack used by the task being created.
 * The base of the stack memory stored in the TCB so the task can
 * be deleted later if required. */
/* MISRA Ref 11.5.1 [Malloc memory assignment] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/main/MISRA.md#rule-115 */
/* coverity[misra_c_2012_rule_11_5_violation] */
pxNewTCB->pxStack = ( StackType_t * ) pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );

if( pxNewTCB->pxStack == NULL )
{
/* Could not allocate the stack.  Delete the allocated TCB. */
vPortFree( pxNewTCB );
pxNewTCB = NULL;
}
}
}
#else /* portSTACK_GROWTH */
{
StackType_t * pxStack;

/* Allocate space for the stack used by the task being created. */
/* MISRA Ref 11.5.1 [Malloc memory assignment] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/main/MISRA.md#rule-115 */
/* coverity[misra_c_2012_rule_11_5_violation] */
pxStack = pvPortMallocStack( ( ( ( size_t ) uxStackDepth ) * sizeof( StackType_t ) ) );

if( pxStack != NULL )
{
/* Allocate space for the TCB. */
/* MISRA Ref 11.5.1 [Malloc memory assignment] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/main/MISRA.md#rule-115 */
/* coverity[misra_c_2012_rule_11_5_violation] */
pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) );

if( pxNewTCB != NULL )
{
( void ) memset( ( void * ) pxNewTCB, 0x00, sizeof( TCB_t ) );

/* 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. */
vPortFreeStack( pxStack );
}
}
else
{
pxNewTCB = NULL;
}
}
#endif /* portSTACK_GROWTH */

if( pxNewTCB != NULL )
{
#if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )
{
/* Tasks can be created statically or dynamically, so note this
 * task was created dynamically in case it is later deleted. */
pxNewTCB->ucStaticallyAllocated = tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB;
}
#endif /* tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE */

prvInitialiseNewTask( pxTaskCode, pcName, uxStackDepth, pvParameters, uxPriority, pxCreatedTask, pxNewTCB, NULL );
}

return pxNewTCB;
}

3.3 prvInitialiseNewTask

• memset( pxNewTCB->pxStack, ( int ) tskSTACK_FILL_BYTE, ( size_t ) uxStackDepth * sizeof( StackType_t ) ); 将栈内存都设置为0xa5的魔鬼数字
• pxTopOfStack = &( pxNewTCB->pxStack[ uxStackDepth - ( configSTACK_DEPTH_TYPE ) 1 ] );
  pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) ); 栈地址对齐设置
• pxNewTCB->pxEndOfStack = pxTopOfStack; 记录当前TCB的栈顶
• 记录当前任务的名字，如果传入的名字参数是有效的则记录任务的名字，需要注意的是任务的名字长度是有限制的，其长度受configMAX_TASK_NAME_LEN限制，所以任务的名字尽量区简短有效的字符串便于记录。

if( pcName != NULL )
    {
        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 ] == ( char ) 0x00 )
            {
                break;
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }

        /* Ensure the name string is terminated in the case that the string length
         * was greater or equal to configMAX_TASK_NAME_LEN. */
        pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1U ] = '\0';
    }

• pxNewTCB->uxPriority = uxPriority; 记录当前任务的优先级
• vListInitialiseItem( &( pxNewTCB->xStateListItem ) ); 需要注意pxItem->pxContainer = NULL;的处理，pxContainer 在后面的处理中会指向pxReadyTasksLists中对应优先级的地址。

void vListInitialiseItem( ListItem_t * const pxItem )
{
    traceENTER_vListInitialiseItem( pxItem );

    /* Make sure the list item is not recorded as being on a list. */
    pxItem->pxContainer = NULL;

    /* Write known values into the list item if
     * configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
    listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );
    listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );

    traceRETURN_vListInitialiseItem();
}

• vListInitialiseItem( &( pxNewTCB->xEventListItem ) ); 该处理和上面的处理流程是一样的。
• listSET_LIST_ITEM_OWNER( &( pxNewTCB->xStateListItem ), pxNewTCB ); 记录当前xStateListItem的pvOwner 为pxNewTCB 。#define listSET_LIST_ITEM_OWNER( pxListItem, pxOwner ) ( ( pxListItem )->pvOwner = ( void * ) ( pxOwner ) )
• pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters ); 初始化栈，这个栈的设置需要根据自己的任务调度去设置。
• *pxCreatedTask = ( TaskHandle_t ) pxNewTCB; 如果pxCreatedTask是有效的，则记录当前任务的TCB。

static void prvInitialiseNewTask( TaskFunction_t pxTaskCode,
                                  const char * const pcName,
                                  const configSTACK_DEPTH_TYPE uxStackDepth,
                                  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 ( portUSING_MPU_WRAPPERS == 1 )
        /* Should the task be created in privileged mode? */
        BaseType_t xRunPrivileged;

        if( ( uxPriority & portPRIVILEGE_BIT ) != 0U )
        {
            xRunPrivileged = pdTRUE;
        }
        else
        {
            xRunPrivileged = pdFALSE;
        }
        uxPriority &= ~portPRIVILEGE_BIT;
    #endif /* portUSING_MPU_WRAPPERS == 1 */

    /* Avoid dependency on memset() if it is not required. */
    #if ( tskSET_NEW_STACKS_TO_KNOWN_VALUE == 1 )
    {
        /* Fill the stack with a known value to assist debugging. */
        ( void ) memset( pxNewTCB->pxStack, ( int ) tskSTACK_FILL_BYTE, ( size_t ) uxStackDepth * sizeof( StackType_t ) );
    }
    #endif /* tskSET_NEW_STACKS_TO_KNOWN_VALUE */

    /* Calculate the top of stack address.  This depends on whether the stack
     * grows from high memory to low (as per the 80x86) or vice versa.
     * portSTACK_GROWTH is used to make the result positive or negative as required
     * by the port. */
    #if ( portSTACK_GROWTH < 0 )
    {
        pxTopOfStack = &( pxNewTCB->pxStack[ uxStackDepth - ( configSTACK_DEPTH_TYPE ) 1 ] );
        pxTopOfStack = ( StackType_t * ) ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );

        /* Check the alignment of the calculated top of stack is correct. */
        configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0U ) );

        #if ( configRECORD_STACK_HIGH_ADDRESS == 1 )
        {
            /* Also record the stack's high address, which may assist
             * debugging. */
            pxNewTCB->pxEndOfStack = pxTopOfStack;
        }
        #endif /* configRECORD_STACK_HIGH_ADDRESS */
    }
    #else /* portSTACK_GROWTH */
    {
        pxTopOfStack = pxNewTCB->pxStack;
        pxTopOfStack = ( StackType_t * ) ( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack ) + portBYTE_ALIGNMENT_MASK ) & ( ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) ) );

        /* Check the alignment of the calculated top of stack is correct. */
        configASSERT( ( ( ( portPOINTER_SIZE_TYPE ) pxTopOfStack & ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK ) == 0U ) );

        /* The other extreme of the stack space is required if stack checking is
         * performed. */
        pxNewTCB->pxEndOfStack = pxNewTCB->pxStack + ( uxStackDepth - ( configSTACK_DEPTH_TYPE ) 1 );
    }
    #endif /* portSTACK_GROWTH */

    /* Store the task name in the TCB. */
    if( pcName != NULL )
    {
        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 ] == ( char ) 0x00 )
            {
                break;
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }

        /* Ensure the name string is terminated in the case that the string length
         * was greater or equal to configMAX_TASK_NAME_LEN. */
        pxNewTCB->pcTaskName[ configMAX_TASK_NAME_LEN - 1U ] = '\0';
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    /* This is used as an array index so must ensure it's not too large. */
    configASSERT( uxPriority < configMAX_PRIORITIES );

    if( uxPriority >= ( UBaseType_t ) configMAX_PRIORITIES )
    {
        uxPriority = ( UBaseType_t ) configMAX_PRIORITIES - ( UBaseType_t ) 1U;
    }
    else
    {
        mtCOVERAGE_TEST_MARKER();
    }

    pxNewTCB->uxPriority = uxPriority;
    #if ( configUSE_MUTEXES == 1 )
    {
        pxNewTCB->uxBasePriority = uxPriority;
    }
    #endif /* configUSE_MUTEXES */

    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 );
    listSET_LIST_ITEM_OWNER( &( pxNewTCB->xEventListItem ), pxNewTCB );

    #if ( portUSING_MPU_WRAPPERS == 1 )
    {
        vPortStoreTaskMPUSettings( &( pxNewTCB->xMPUSettings ), xRegions, pxNewTCB->pxStack, uxStackDepth );
    }
    #else
    {
        /* Avoid compiler warning about unreferenced parameter. */
        ( void ) xRegions;
    }
    #endif

    #if ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 )
    {
        /* Allocate and initialize memory for the task's TLS Block. */
        configINIT_TLS_BLOCK( pxNewTCB->xTLSBlock, pxTopOfStack );
    }
    #endif

    /* Initialize the TCB stack to look as if the task was already running,
     * but had been interrupted by the scheduler.  The return address is set
     * to the start of the task function. Once the stack has been initialised
     * the top of stack variable is updated. */
    #if ( portUSING_MPU_WRAPPERS == 1 )
    {
        /* If the port has capability to detect stack overflow,
         * pass the stack end address to the stack initialization
         * function as well. */
        #if ( portHAS_STACK_OVERFLOW_CHECKING == 1 )
        {
            #if ( portSTACK_GROWTH < 0 )
            {
                pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxStack, pxTaskCode, pvParameters, xRunPrivileged, &( pxNewTCB->xMPUSettings ) );
            }
            #else /* portSTACK_GROWTH */
            {
                pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxEndOfStack, pxTaskCode, pvParameters, xRunPrivileged, &( pxNewTCB->xMPUSettings ) );
            }
            #endif /* portSTACK_GROWTH */
        }
        #else /* portHAS_STACK_OVERFLOW_CHECKING */
        {
            pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters, xRunPrivileged, &( pxNewTCB->xMPUSettings ) );
        }
        #endif /* portHAS_STACK_OVERFLOW_CHECKING */
    }
    #else /* portUSING_MPU_WRAPPERS */
    {
        /* If the port has capability to detect stack overflow,
         * pass the stack end address to the stack initialization
         * function as well. */
        #if ( portHAS_STACK_OVERFLOW_CHECKING == 1 )
        {
            #if ( portSTACK_GROWTH < 0 )
            {
                pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxStack, pxTaskCode, pvParameters );
            }
            #else /* portSTACK_GROWTH */
            {
                pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxNewTCB->pxEndOfStack, pxTaskCode, pvParameters );
            }
            #endif /* portSTACK_GROWTH */
        }
        #else /* portHAS_STACK_OVERFLOW_CHECKING */
        {
            pxNewTCB->pxTopOfStack = pxPortInitialiseStack( pxTopOfStack, pxTaskCode, pvParameters );
        }
        #endif /* portHAS_STACK_OVERFLOW_CHECKING */
    }
    #endif /* portUSING_MPU_WRAPPERS */

    /* Initialize task state and task attributes. */
    #if ( configNUMBER_OF_CORES > 1 )
    {
        pxNewTCB->xTaskRunState = taskTASK_NOT_RUNNING;

        /* Is this an idle task? */
        if( ( ( TaskFunction_t ) pxTaskCode == ( TaskFunction_t ) prvIdleTask ) || ( ( TaskFunction_t ) pxTaskCode == ( TaskFunction_t ) prvPassiveIdleTask ) )
        {
            pxNewTCB->uxTaskAttributes |= taskATTRIBUTE_IS_IDLE;
        }
    }
    #endif /* #if ( configNUMBER_OF_CORES > 1 ) */

    if( 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();
    }
}

3.4 prvAddNewTaskToReadyList

该函数的实现需要考虑core的数量，分别core 0的处理和多核的处理。
单核的处理流程：

• uxCurrentNumberOfTasks = ( UBaseType_t ) ( uxCurrentNumberOfTasks + 1U ); 将当前任务的数量加1
• 记录当前任务的TCB：对于单核，pxCurrentTCB = pxNewTCB;
• 如果当前的任务是链表的第一个任务，则调用prvInitialiseTaskLists();做链表的初始化工作。
• uxTaskNumber++;
• prvAddTaskToReadyList( pxNewTCB ); 将当前任务的TCB插入到pxReadyTasksLists链表中。

多核的处理流程：

• uxCurrentNumberOfTasks++;
• 如果当前创建的这个任务是链表的第一个任务，则调用prvInitialiseTaskLists();做链表的初始化工作。
• uxTaskNumber++;
• prvAddTaskToReadyList( pxNewTCB ); 将当前任务的TCB插入到pxReadyTasksLists链表中。

#if ( configNUMBER_OF_CORES == 1 )

    static void prvAddNewTaskToReadyList( TCB_t * pxNewTCB )
    {
        /* Ensure interrupts don't access the task lists while the lists are being
         * updated. */
        taskENTER_CRITICAL();
        {
            uxCurrentNumberOfTasks = ( UBaseType_t ) ( uxCurrentNumberOfTasks + 1U );

            if( pxCurrentTCB == NULL )
            {
                /* There are no other tasks, or all the other tasks are in
                 * the suspended state - make this the current task. */
                pxCurrentTCB = pxNewTCB;

                if( uxCurrentNumberOfTasks == ( UBaseType_t ) 1 )
                {
                    /* This is the first task to be created so do the preliminary
                     * initialisation required.  We will not recover if this call
                     * fails, but we will report the failure. */
                    prvInitialiseTaskLists();
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }
            }
            else
            {
                /* If the scheduler is not already running, make this task the
                 * current task if it is the highest priority task to be created
                 * so far. */
                if( xSchedulerRunning == pdFALSE )
                {
                    if( pxCurrentTCB->uxPriority <= pxNewTCB->uxPriority )
                    {
                        pxCurrentTCB = pxNewTCB;
                    }
                    else
                    {
                        mtCOVERAGE_TEST_MARKER();
                    }
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }
            }

            uxTaskNumber++;

            #if ( configUSE_TRACE_FACILITY == 1 )
            {
                /* Add a counter into the TCB for tracing only. */
                pxNewTCB->uxTCBNumber = uxTaskNumber;
            }
            #endif /* configUSE_TRACE_FACILITY */
            traceTASK_CREATE( pxNewTCB );

            prvAddTaskToReadyList( pxNewTCB );

            portSETUP_TCB( pxNewTCB );
        }
        taskEXIT_CRITICAL();

        if( xSchedulerRunning != pdFALSE )
        {
            /* If the created task is of a higher priority than the current task
             * then it should run now. */
            taskYIELD_ANY_CORE_IF_USING_PREEMPTION( pxNewTCB );
        }
        else
        {
            mtCOVERAGE_TEST_MARKER();
        }
    }

#else /* #if ( configNUMBER_OF_CORES == 1 ) */

    static void prvAddNewTaskToReadyList( TCB_t * pxNewTCB )
    {
        /* Ensure interrupts don't access the task lists while the lists are being
         * updated. */
        taskENTER_CRITICAL();
        {
            uxCurrentNumberOfTasks++;

            if( xSchedulerRunning == pdFALSE )
            {
                if( uxCurrentNumberOfTasks == ( UBaseType_t ) 1 )
                {
                    /* This is the first task to be created so do the preliminary
                     * initialisation required.  We will not recover if this call
                     * fails, but we will report the failure. */
                    prvInitialiseTaskLists();
                }
                else
                {
                    mtCOVERAGE_TEST_MARKER();
                }

                /* All the cores start with idle tasks before the SMP scheduler
                 * is running. Idle tasks are assigned to cores when they are
                 * created in prvCreateIdleTasks(). */
            }

            uxTaskNumber++;

            #if ( configUSE_TRACE_FACILITY == 1 )
            {
                /* Add a counter into the TCB for tracing only. */
                pxNewTCB->uxTCBNumber = uxTaskNumber;
            }
            #endif /* configUSE_TRACE_FACILITY */
            traceTASK_CREATE( pxNewTCB );

            prvAddTaskToReadyList( pxNewTCB );

            portSETUP_TCB( pxNewTCB );

            if( xSchedulerRunning != pdFALSE )
            {
                /* If the created task is of a higher priority than another
                 * currently running task and preemption is on then it should
                 * run now. */
                taskYIELD_ANY_CORE_IF_USING_PREEMPTION( pxNewTCB );
            }
            else
            {
                mtCOVERAGE_TEST_MARKER();
            }
        }
        taskEXIT_CRITICAL();
    }

#endif

3.5 prvInitialiseTaskLists

在prvInitialiseTaskLists函数中分别会初始化pxReadyTasksLists、xDelayedTaskList1、xDelayedTaskList2 、xPendingReadyList 、xTasksWaitingTermination 以及xSuspendedTaskList等链表。

• vListInitialise

void vListInitialise( List_t * const pxList )
{
    traceENTER_vListInitialise( pxList );

    /* The list structure contains a list item which is used to mark the
     * end of the list.  To initialise the list the list end is inserted
     * as the only list entry. */
    pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );

    listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );

    /* The list end value is the highest possible value in the list to
     * ensure it remains at the end of the list. */
    pxList->xListEnd.xItemValue = portMAX_DELAY;

    /* The list end next and previous pointers point to itself so we know
     * when the list is empty. */
    pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );
    pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );

    /* Initialize the remaining fields of xListEnd when it is a proper ListItem_t */
    #if ( configUSE_MINI_LIST_ITEM == 0 )
    {
        pxList->xListEnd.pvOwner = NULL;
        pxList->xListEnd.pxContainer = NULL;
        listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );
    }
    #endif

    pxList->uxNumberOfItems = ( UBaseType_t ) 0U;

    /* Write known values into the list if
     * configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
    listSET_LIST_INTEGRITY_CHECK_1_VALUE( pxList );
    listSET_LIST_INTEGRITY_CHECK_2_VALUE( pxList );

    traceRETURN_vListInitialise();
}

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 /* INCLUDE_vTaskDelete */

    #if ( INCLUDE_vTaskSuspend == 1 )
    {
        vListInitialise( &xSuspendedTaskList );
    }
    #endif /* INCLUDE_vTaskSuspend */

    /* Start with pxDelayedTaskList using list1 and the pxOverflowDelayedTaskList
     * using list2. */
    pxDelayedTaskList = &xDelayedTaskList1;
    pxOverflowDelayedTaskList = &xDelayedTaskList2;
}

3.6 prvAddTaskToReadyList

• listINSERT_END( &( pxReadyTasksLists[ ( pxTCB )->uxPriority ] ), &( ( pxTCB )->xStateListItem ) ); 将当前任务的TCB插入到pxReadyTasksLists对应优先级的链表中，

#define prvAddTaskToReadyList( pxTCB )                                                                     \
    do {                                                                                                   \
        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 );                                                      \
    } while( 0 )

3.7 listINSERT_END

• ( pxNewListItem )->pxContainer = ( pxList ); 该处理便于通过任务的TCB找到对应优先级的链表头。

#define listINSERT_END( pxList, pxNewListItem )           \
    do {                                                  \
        ListItem_t * const pxIndex = ( pxList )->pxIndex; \
                                                          \
        /* Only effective when configASSERT() is also defined, these tests may catch \
         * the list data structures being overwritten in memory.  They will not catch \
         * data errors caused by incorrect configuration or use of FreeRTOS. */ \
        listTEST_LIST_INTEGRITY( ( pxList ) );                                  \
        listTEST_LIST_ITEM_INTEGRITY( ( pxNewListItem ) );                      \
                                                                                \
        /* Insert a new list item into ( pxList ), but rather than sort the list, \
         * makes the new list item the last item to be removed by a call to \
         * listGET_OWNER_OF_NEXT_ENTRY(). */                                                        \
        ( pxNewListItem )->pxNext = pxIndex;                                                        \
        ( pxNewListItem )->pxPrevious = pxIndex->pxPrevious;                                        \
                                                                                                    \
        pxIndex->pxPrevious->pxNext = ( pxNewListItem );                                            \
        pxIndex->pxPrevious = ( pxNewListItem );                                                    \
                                                                                                    \
        /* Remember which list the item is in. */                                                   \
        ( pxNewListItem )->pxContainer = ( pxList );                                                \
                                                                                                    \
        ( ( pxList )->uxNumberOfItems ) = ( UBaseType_t ) ( ( ( pxList )->uxNumberOfItems ) + 1U ); \
    } while( 0 )

原文地址：https://blog.csdn.net/u014100559/article/details/143956642

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