uc/os-ii事件控制塊

任務間的同步依賴於任務間的通信。在μC/OS-II中，使用信號量、互斥信號量、消息郵箱、消息隊列、事件標誌組這些被稱作事件的中間環節來實現任務之間的通信的。爲了把描述事件的數據結構統一起來，μC/OS-II使用叫做事件控制塊ECB的數據結構來描述諸如信號量、互斥信號量、消息郵箱、消息隊列、事件標誌組這些事件。

事件控制塊中包含包括等待任務表在內的所有有關事件的數據 。

#if (OS_EVENT_EN) && (OS_MAX_EVENTS > 0)
typedef struct os_event {
    INT8U    OSEventType;                    /* Type of event control block (see OS_EVENT_TYPE_xxxx)    */
    void    *OSEventPtr;                     /* Pointer to message or queue structure                   */
    INT16U   OSEventCnt;                     /* Semaphore Count (not used if other EVENT type)          */
#if OS_LOWEST_PRIO <= 63
    INT8U    OSEventGrp;                     /* Group corresponding to tasks waiting for event to occur */
    INT8U    OSEventTbl[OS_EVENT_TBL_SIZE];  /* List of tasks waiting for event to occur                */
#else
    INT16U   OSEventGrp;                     /* Group corresponding to tasks waiting for event to occur */
    INT16U   OSEventTbl[OS_EVENT_TBL_SIZE];  /* List of tasks waiting for event to occur                */
#endif

#if OS_EVENT_NAME_SIZE > 1
    INT8U    OSEventName[OS_EVENT_NAME_SIZE];
#endif
} OS_EVENT;

圖示爲事件控制塊的內存結構圖。

一般地，對於事件控制塊進行如下一些通用操作：

• OS_EventWaitListInit()：初始化事件控制塊。
  初始化等待任務列表爲全0，沒有任務在等待事件。

void  OS_EventWaitListInit (OS_EVENT *pevent)
{
#if OS_LOWEST_PRIO <= 63
    INT8U  *ptbl;
#else
    INT16U *ptbl;
#endif
    INT8U   i;


    pevent->OSEventGrp = 0;                      /* No task waiting on event                           */
    ptbl               = &pevent->OSEventTbl[0];

    for (i = 0; i < OS_EVENT_TBL_SIZE; i++) {
        *ptbl++ = 0;
    }
}

• OS_EventTaskRdy()：使任務進入就緒態。
  當某個事件發生後，就要使等待任務列表中優先級最高的任務脫離等待，並置於就緒狀態。

INT8U  OS_EventTaskRdy (OS_EVENT *pevent, void *pmsg, INT8U msk, INT8U pend_stat)
{
    OS_TCB  *ptcb;
    INT8U    y;
    INT8U    x;
    INT8U    prio;
#if OS_LOWEST_PRIO > 63
    INT16U  *ptbl;
#endif


#if OS_LOWEST_PRIO <= 63
    y    = OSUnMapTbl[pevent->OSEventGrp];              /* Find HPT waiting for message                */
    x    = OSUnMapTbl[pevent->OSEventTbl[y]];
    prio = (INT8U)((y << 3) + x);                       /* Find priority of task getting the msg       */
#else
    if ((pevent->OSEventGrp & 0xFF) != 0) {             /* Find HPT waiting for message                */
        y = OSUnMapTbl[ pevent->OSEventGrp & 0xFF];
    } else {
        y = OSUnMapTbl[(pevent->OSEventGrp >> 8) & 0xFF] + 8;
    }
    ptbl = &pevent->OSEventTbl[y];
    if ((*ptbl & 0xFF) != 0) {
        x = OSUnMapTbl[*ptbl & 0xFF];
    } else {
        x = OSUnMapTbl[(*ptbl >> 8) & 0xFF] + 8;
    }
    prio = (INT8U)((y << 4) + x);                       /* Find priority of task getting the msg       */
#endif

    ptcb                  =  OSTCBPrioTbl[prio];        /* Point to this task's OS_TCB                 */
    ptcb->OSTCBDly        =  0;                         /* Prevent OSTimeTick() from readying task     */
#if ((OS_Q_EN > 0) && (OS_MAX_QS > 0)) || (OS_MBOX_EN > 0)
    ptcb->OSTCBMsg        =  pmsg;                      /* Send message directly to waiting task       */
#else
    pmsg                  =  pmsg;                      /* Prevent compiler warning if not used        */
#endif
    ptcb->OSTCBStat      &= ~msk;                       /* Clear bit associated with event type        */
    ptcb->OSTCBStatPend   =  pend_stat;                 /* Set pend status of post or abort            */
                                                        /* See if task is ready (could be susp'd)      */
    if ((ptcb->OSTCBStat &   OS_STAT_SUSPEND) == OS_STAT_RDY) {
        OSRdyGrp         |=  ptcb->OSTCBBitY;           /* Put task in the ready to run list           */
        OSRdyTbl[y]      |=  ptcb->OSTCBBitX;
    }

    OS_EventTaskRemove(ptcb, pevent);                   /* Remove this task from event   wait list     */
#if (OS_EVENT_MULTI_EN > 0)
    if (ptcb->OSTCBEventMultiPtr != (OS_EVENT **)0) {   /* Remove this task from events' wait lists    */
        OS_EventTaskRemoveMulti(ptcb, ptcb->OSTCBEventMultiPtr);
        ptcb->OSTCBEventPtr       = (OS_EVENT  *)pevent;/* Return event as first multi-pend event ready*/
    }
#endif

    return (prio);
}

• OS_EventTaskWait()：使任務進入等待某事件發生狀態
  當某個任務要等待一個事件發生時，相應OSSemPend()、OSMutexPend()、OSMboxPend()或OSQPend()函數會調用OSEventTaskWait()函數將當前任務從任務就緒表中刪除，並放到相應事件的事件控制塊的等待任務列表中。

void  OS_EventTaskWait (OS_EVENT *pevent)
{
    INT8U  y;
    OSTCBCur->OSTCBEventPtr               = pevent;                 /* Store ptr to ECB in TCB         */

    pevent->OSEventTbl[OSTCBCur->OSTCBY] |= OSTCBCur->OSTCBBitX;    /* Put task in waiting list        */
    pevent->OSEventGrp                   |= OSTCBCur->OSTCBBitY;

    y             =  OSTCBCur->OSTCBY;            /* Task no longer ready                              */
    OSRdyTbl[y]  &= ~OSTCBCur->OSTCBBitX;
    if (OSRdyTbl[y] == 0) {
        OSRdyGrp &= ~OSTCBCur->OSTCBBitY;         /* Clear event grp bit if this was only task pending */
    }
}

• OS_EventTaskRemove() : 刪除任務對某時間的等待狀態

void  OS_EventTaskRemove (OS_TCB   *ptcb,
                          OS_EVENT *pevent)
{
    INT8U  y;
    y                       =  ptcb->OSTCBY;
    pevent->OSEventTbl[y]  &= ~ptcb->OSTCBBitX;         /* Remove task from wait list                  */
    if (pevent->OSEventTbl[y] == 0) {
        pevent->OSEventGrp &= ~ptcb->OSTCBBitY;
    }
}