liteos中event的使用

event的API的使用例程使用如下：
首先初始化一个event
static EVENT_CB_S  example_event;
uwRet = LOS_EventInit(&example_event);
然后读这个event
    uwEvent = LOS_EventRead(&example_event, event_wait, LOS_WAITMODE_AND, 100);
    if(uwEvent == event_wait)
    {
        dprintf("Example_Event,read event :0x%x\n",uwEvent);
        uwRet = LOS_InspectStatusSetByID(LOS_INSPECT_EVENT, LOS_INSPECT_STU_SUCCESS);
        if (LOS_OK != uwRet)
        {
            dprintf("Set Inspect Status Err\n");
        }
    }
    else
    {
        dprintf("Example_Event,read event timeout\n");
        uwRet = LOS_InspectStatusSetByID(LOS_INSPECT_EVENT, LOS_INSPECT_STU_ERROR);
        if (LOS_OK != uwRet)
        {
            dprintf("Set Inspect Status Err\n");
        }
    }

最后写这个event
    /* write event */
    dprintf("Example_TaskEntry_Event write event .\n");
    uwRet = LOS_EventWrite(&example_event, event_wait);
    if(uwRet != LOS_OK)
    {
        dprintf("event write failed .\n");
        return LOS_NOK;
    }
我们首先看看event的初始化
LITE_OS_SEC_TEXT_INIT UINT32 LOS_EventInit(PEVENT_CB_S pstEventCB)
{
#如果event id 为null，则返回，本例中event id是静态定义的
    if (pstEventCB == NULL)
    {
        return LOS_ERRNO_EVENT_PTR_NULL;
    }
#将eventId 赋值为零
    pstEventCB->uwEventID = 0;
#每个event 有个list，这里将list置空
    LOS_ListInit(&pstEventCB->stEventList);
    return LOS_OK;
}
可以看到list将next和prev都指向了自己
LITE_OS_SEC_ALW_INLINE STATIC_INLINE VOID LOS_ListInit(LOS_DL_LIST *pstList)
{
    pstList->pstNext = pstList;
    pstList->pstPrev = pstList;
}
下来我们看看event的read函数
LITE_OS_SEC_TEXT UINT32 LOS_EventRead(PEVENT_CB_S pstEventCB, UINT32 uwEventMask, UINT32 uwMode, UINT32 uwTimeOut)
{
    UINT32      uwRet = 0;
    UINTPTR     uvIntSave;
    LOS_TASK_CB *pstRunTsk;
#保存中断
    uvIntSave = LOS_IntLock();
#这里的poll其实就是判断pstEventCB->uwEventID 和 uwEventMask, 以及uwMode直接的关系，并没有任何poll的动作
    uwRet = LOS_EventPoll(&(pstEventCB->uwEventID), uwEventMask, uwMode);

    if (uwRet == 0)
    {
        

        pstRunTsk = g_stLosTask.pstRunTask;
        pstRunTsk->uwEventMask = uwEventMask;
        pstRunTsk->uwEventMode = uwMode;
#将当前task加到event的srEventList中，这里的uwTimeOut 如果不等于forever的话，还会建立一个timer在uwTimeOut到期后
#唤醒这个task
        osTaskWait(&pstEventCB->stEventList, OS_TASK_STATUS_PEND, uwTimeOut);
#恢复中断
        (VOID)LOS_IntRestore(uvIntSave);
#当前task让出cpu
        LOS_Schedule();
#当再次执行task时判断这个task是否在timeout后才被唤醒的
        if (pstRunTsk->usTaskStatus & OS_TASK_STATUS_TIMEOUT)
        {
            uvIntSave = LOS_IntLock();
            pstRunTsk->usTaskStatus &= (~OS_TASK_STATUS_TIMEOUT);
            (VOID)LOS_IntRestore(uvIntSave);
            return LOS_ERRNO_EVENT_READ_TIMEOUT;
        }

        uvIntSave = LOS_IntLock();
#如果不是timeout唤醒的，说明已经调用过event write，才被唤醒的，说明>uwEventID已经被更新了
#再次判断这三者>uwEventID,uwEventMask,uwMode的关系后退出。
        uwRet = LOS_EventPoll(&pstEventCB->uwEventID,uwEventMask,uwMode);
        (VOID)LOS_IntRestore(uvIntSave);
    }
    else
    {
        (VOID)LOS_IntRestore(uvIntSave);
    }

    return uwRet;
}

最后再在看看event write函数
LITE_OS_SEC_TEXT UINT32 LOS_EventWrite(PEVENT_CB_S pstEventCB, UINT32 uwEvents)
{
    LOS_TASK_CB *pstResumedTask;
    LOS_TASK_CB *pstNextTask = (LOS_TASK_CB *)NULL;
    UINTPTR     uvIntSave;
    UINT8       ucExitFlag = 0;


    uvIntSave = LOS_IntLock();

    pstEventCB->uwEventID |= uwEvents;
#首先检测event的list是否为null，因为前面已经调用过event read函数了，所以这里肯定不为null
    if (!LOS_ListEmpty(&pstEventCB->stEventList))
    {

        for (pstResumedTask = LOS_DL_LIST_ENTRY((&pstEventCB->stEventList)->pstNext, LOS_TASK_CB, stPendList);/*lint !e413*/
            &pstResumedTask->stPendList != (&pstEventCB->stEventList);)
        {
#找到event list中第一个需要wakeup的task
            pstNextTask = LOS_DL_LIST_ENTRY(pstResumedTask->stPendList.pstNext, LOS_TASK_CB, stPendList); /*lint !e413*/

            if (((pstResumedTask->uwEventMode & LOS_WAITMODE_OR) && (pstResumedTask->uwEventMask & uwEvents) != 0) ||
                ((pstResumedTask->uwEventMode & LOS_WAITMODE_AND) && (pstResumedTask->uwEventMask & pstEventCB->uwEventID) == pstResumedTask->uwEventMask))
            {
#设置flags，后面用于调度
                ucExitFlag = 1;
#wakeup这个task
                osTaskWake(pstResumedTask, OS_TASK_STATUS_PEND);
            }
            pstResumedTask = pstNextTask;
        }

        if (ucExitFlag == 1)
        {
            (VOID)LOS_IntRestore(uvIntSave);
#由于flag被置为1，说明有task 要被唤醒，开始调度
            LOS_Schedule();
            return LOS_OK;
        }
    }

    (VOID)LOS_IntRestore(uvIntSave);
    return LOS_OK;
}