FreeRTOS - TCB

FreeRTOS为了实现任务调度。首先就需要定义任务调度的数据结构，来保存任务堆栈结构、任务状态、任务ID、任务的优先级等信息。这些信息集中存放在Task control block，即TCB，每个Task被分配唯一的TCB：

TCB结构体定义。

typedef struct tskTaskControlBlock       /* The old naming convention is used to prevent breaking kernel aware debuggers. */
{
    volatile StackType_t * pxTopOfStack; /**< Points to the location of the last item placed on the tasks stack.  THIS MUST BE THE FIRST MEMBER OF THE TCB STRUCT. */

    #if ( portUSING_MPU_WRAPPERS == 1 )
        xMPU_SETTINGS xMPUSettings; /**< The MPU settings are defined as part of the port layer.  THIS MUST BE THE SECOND MEMBER OF THE TCB STRUCT. */
    #endif

    #if ( configUSE_CORE_AFFINITY == 1 ) && ( configNUMBER_OF_CORES > 1 )
        UBaseType_t uxCoreAffinityMask; /**< Used to link the task to certain cores.  UBaseType_t must have greater than or equal to the number of bits as configNUMBER_OF_CORES. */
    #endif

    ListItem_t xStateListItem;                  /**< The list that the state list item of a task is reference from denotes the state of that task (Ready, Blocked, Suspended ). */
    ListItem_t xEventListItem;                  /**< Used to reference a task from an event list. */
    UBaseType_t uxPriority;                     /**< The priority of the task.  0 is the lowest priority. */
    StackType_t * pxStack;                      /**< Points to the start of the stack. */
    #if ( configNUMBER_OF_CORES > 1 )
        volatile BaseType_t xTaskRunState;      /**< Used to identify the core the task is running on, if the task is running. Otherwise, identifies the task's state - not running or yielding. */
        UBaseType_t uxTaskAttributes;           /**< Task's attributes - currently used to identify the idle tasks. */
    #endif
    char pcTaskName[ configMAX_TASK_NAME_LEN ]; /**< Descriptive name given to the task when created.  Facilitates debugging only. */ /*lint !e971 Unqualified char types are allowed for strings and single characters only. */

    #if ( configUSE_TASK_PREEMPTION_DISABLE == 1 )
        BaseType_t xPreemptionDisable; /**< Used to prevent the task from being preempted. */
    #endif

    #if ( ( portSTACK_GROWTH > 0 ) || ( configRECORD_STACK_HIGH_ADDRESS == 1 ) )
        StackType_t * pxEndOfStack; /**< Points to the highest valid address for the stack. */
    #endif

    #if ( portCRITICAL_NESTING_IN_TCB == 1 )
        UBaseType_t uxCriticalNesting; /**< Holds the critical section nesting depth for ports that do not maintain their own count in the port layer. */
    #endif

    #if ( configUSE_TRACE_FACILITY == 1 )
        UBaseType_t uxTCBNumber;  /**< Stores a number that increments each time a TCB is created.  It allows debuggers to determine when a task has been deleted and then recreated. */
        UBaseType_t uxTaskNumber; /**< Stores a number specifically for use by third party trace code. */
    #endif

    #if ( configUSE_MUTEXES == 1 )
        UBaseType_t uxBasePriority; /**< The priority last assigned to the task - used by the priority inheritance mechanism. */
        UBaseType_t uxMutexesHeld;
    #endif

    #if ( configUSE_APPLICATION_TASK_TAG == 1 )
        TaskHookFunction_t pxTaskTag;
    #endif

    #if ( configNUM_THREAD_LOCAL_STORAGE_POINTERS > 0 )
        void * pvThreadLocalStoragePointers[ configNUM_THREAD_LOCAL_STORAGE_POINTERS ];
    #endif

    #if ( configGENERATE_RUN_TIME_STATS == 1 )
        configRUN_TIME_COUNTER_TYPE ulRunTimeCounter; /**< Stores the amount of time the task has spent in the Running state. */
    #endif

    #if ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 )
        configTLS_BLOCK_TYPE xTLSBlock; /**< Memory block used as Thread Local Storage (TLS) Block for the task. */
    #endif

    #if ( configUSE_TASK_NOTIFICATIONS == 1 )
        volatile uint32_t ulNotifiedValue[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
        volatile uint8_t ucNotifyState[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
    #endif

    /* See the comments in FreeRTOS.h with the definition of
     * tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE. */
    #if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 ) /*lint !e731 !e9029 Macro has been consolidated for readability reasons. */
        uint8_t ucStaticallyAllocated;                     /**< Set to pdTRUE if the task is a statically allocated to ensure no attempt is made to free the memory. */
    #endif

    #if ( INCLUDE_xTaskAbortDelay == 1 )
        uint8_t ucDelayAborted;
    #endif

    #if ( configUSE_POSIX_ERRNO == 1 )
        int iTaskErrno;
    #endif
} tskTCB;

pxTopOfStack

 Points to the location of the last item placed on the tasks stack.  THIS MUST BE THE FIRST MEMBER OF THE TCB STRUCT.

必须放在结构体的最前面。指向了task 栈的最后面，也就是栈的结束位置。

xStateListItem

存放task的状态。运行、就绪、挂起等。

xEventListItem

存放关联到task的事件。

uxPriority

task的优先级，值越大优先级越高。

pxStack

指向栈的开始位置

pcTaskName

task的名字。

uxTCBNumber

每次创建tcb的时候都++。

uxTaskNumber

task的编号。

uxBasePriority

task上一次运行的优先级。

uxMutexesHeld

被信号量阻塞。

ulRunTimeCounter

记录task运行的事件。