if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) {       /* Validate event block type                */
        *err = OS_ERR_EVENT_TYPE;
        return (pevent);//如果事件不是郵箱模式
    }
#endif
    OS_ENTER_CRITICAL();
    if (pevent->OSEventGrp != 0x00) {                      /* See if any tasks waiting on mailbox      */
		//看郵箱中有沒有任務(wù)在等待
        tasks_waiting = TRUE;                              /* Yes                                      */
    } else {
        tasks_waiting = FALSE;                             /* No                                       */
    }
    switch (opt) {
        case OS_DEL_NO_PEND:                               /* Delete mailbox only if no task waiting   */
			//沒有任務(wù)等待的情況下才刪除郵箱
             if (tasks_waiting == FALSE) {//如果沒有任務(wù)等待
                 pevent->OSEventType = OS_EVENT_TYPE_UNUSED;//將事件標(biāo)志為沒有用的
                 pevent->OSEventPtr  = OSEventFreeList;    /* Return Event Control Block to free list  */
				 //將ECB返回給空閑列表
                 OSEventFreeList     = pevent;             /* Get next free event control block        */
				 //它指向新的空閑列表
                 OS_EXIT_CRITICAL();
                 *err = OS_NO_ERR;//成功刪除
                 return ((OS_EVENT *)0);                   /* Mailbox has been deleted                 */
             } else {
                 OS_EXIT_CRITICAL();
                 *err = OS_ERR_TASK_WAITING;//如果有任務(wù)在等待
                 return (pevent);
             }

        case OS_DEL_ALWAYS:                                /* Always delete the mailbox                */
             while (pevent->OSEventGrp != 0x00) {          /* Ready ALL tasks waiting for mailbox      */
                 OS_EventTaskRdy(pevent, (void *)0, OS_STAT_MBOX);
             }//所以等待該信號(hào)的任務(wù)都進(jìn)入就緒態(tài)，每個(gè)任務(wù)都以為自己得到了
             //NULL指針，每個(gè)任務(wù)必須檢查返回的指針，看是不是非NULL，另外，
             //當(dāng)每個(gè)任務(wù)都進(jìn)入就緒態(tài)，中斷是關(guān)的，也延長(zhǎng)了中斷響應(yīng)時(shí)間。
             pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
             pevent->OSEventPtr  = OSEventFreeList;        /* Return Event Control Block to free list  */
             OSEventFreeList     = pevent;                 /* Get next free event control block        */
			 //同上面一樣，將ECB返回給空閑列表，并指向新的表頭
             OS_EXIT_CRITICAL();
             if (tasks_waiting == TRUE) {                  /* Reschedule only if task(s) were waiting  */
			 	//只有有任務(wù)等待的時(shí)候才需要任務(wù)調(diào)度
                 OS_Sched();                               /* Find highest priority task ready to run  */
             }
             *err = OS_NO_ERR;
             return ((OS_EVENT *)0);                       /* Mailbox has been deleted                 */

        default:
             OS_EXIT_CRITICAL();
             *err = OS_ERR_INVALID_OPT;//如果有其它不合理的選項(xiàng)。
             return (pevent);
    }
}
#endif

/*$PAGE*/
/*
*********************************************************************************************************
*                                      PEND ON MAILBOX FOR A MESSAGE
*
* Description: This function waits for a message to be sent to a mailbox
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired mailbox
*
*              timeout       is an optional timeout period (in clock ticks).  If non-zero, your task will
*                            wait for a message to arrive at the mailbox up to the amount of time
*                            specified by this argument.  If you specify 0, however, your task will wait
*                            forever at the specified mailbox or, until a message arrives.
*
*              err           is a pointer to where an error message will be deposited.  Possible error
*                            messages are:
*
*                            OS_NO_ERR           The call was successful and your task received a
*                                                message.
*                            OS_TIMEOUT          A message was not received within the specified timeout
*                            OS_ERR_EVENT_TYPE   Invalid event type
*                            OS_ERR_PEND_ISR     If you called this function from an ISR and the result
*                                                would lead to a suspension.
*                            OS_ERR_PEVENT_NULL  If 'pevent' is a NULL pointer
*
* Returns    : != (void *)0  is a pointer to the message received
*              == (void *)0  if no message was received or,
*                            if 'pevent' is a NULL pointer or,
*                            if you didn't pass the proper pointer to the event control block.
                                                 等待郵箱中的消息
描述：等待將要送到郵箱中的消息
參數(shù)：pevent：指向目標(biāo)郵箱ECB的指針
                 timeout：超時(shí)階段的選項(xiàng)，如果非零，事件將在郵箱中等待消息的到來
                 直到這個(gè)值的時(shí)間到；如果是零，消息將永遠(yuǎn)等待，直到消息到來。
                 err：指向?qū)⒁獋鬟f的錯(cuò)誤消息指針。可能如下：
                            OS_NO_ERR          操作成功，任務(wù)得到消息
*                            OS_TIMEOUT          規(guī)定時(shí)間內(nèi)沒有收到消息
*                            OS_ERR_EVENT_TYPE  非法事件類型
*                            OS_ERR_PEND_ISR     如果在中斷中調(diào)用，結(jié)果將中止
*                            OS_ERR_PEVENT_NULL  如果pevent 是空指針
*********************************************************************************************************
*/

void  *OSMboxPend (OS_EVENT *pevent, INT16U timeout, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif    
    void      *msg;


    if (OSIntNesting > 0) {                           /* See if called from ISR ...                    */
        *err = OS_ERR_PEND_ISR;                       /* ... can't PEND from an ISR                    */
        return ((void *)0);
    }//中斷服務(wù)子程序不能等待。
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */
        *err = OS_ERR_PEVENT_NULL;
        return ((void *)0);//目標(biāo)郵箱ECB指針為零，不合理
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) {  /* Validate event block type                     */
		//事件類型不是郵箱類型
        *err = OS_ERR_EVENT_TYPE;
        return ((void *)0);
    }
#endif
    OS_ENTER_CRITICAL();
    msg = pevent->OSEventPtr;
    if (msg != (void *)0) {                           /* See if there is already a message */
//如果郵箱中有消息，則從中取出消息，返回給調(diào)用函數(shù)，并將NULL存入郵箱，
//同時(shí)返回?zé)o錯(cuò)代碼給它的調(diào)用函數(shù)，這個(gè)返回結(jié)果表示，已由另一個(gè)任務(wù)或者中斷
//服務(wù)子程序?qū)⑿畔l(fā)送到郵箱中。如果為空的話，調(diào)用此函數(shù)的任務(wù)將進(jìn)入睡眠狀態(tài)
//等待另一個(gè)任務(wù)（可中斷服務(wù)程序）通過郵箱發(fā)送消息，OSMboxPend（）允許定義一個(gè)
//最長(zhǎng)等待時(shí)間作為它的參數(shù)，防止任務(wù)無期限等待
        pevent->OSEventPtr = (void *)0;               /* Clear the mailbox                             */
        OS_EXIT_CRITICAL();
        *err = OS_NO_ERR;
        return (msg);                                 /* Return the message received (or NULL)         */
		//返回得到的消息
    }
    OSTCBCur->OSTCBStat |= OS_STAT_MBOX;              /* Message not available, task will pend         */
	//消息無效，掛起任務(wù)，進(jìn)入睡眠，等待其它郵箱消息喚醒
    OSTCBCur->OSTCBDly   = timeout;                   /* Load timeout in TCB                           */
	//等待時(shí)間也放入任務(wù)控制塊中，該址在OSTimeTick()中被逐次減一
    OS_EventTaskWait(pevent);                         /* Suspend task until event or timeout occurs    */
	//真正將任務(wù)進(jìn)入睡眠，
    OS_EXIT_CRITICAL();
    OS_Sched();                                       /* Find next highest priority task ready to run  */
	//任務(wù)調(diào)度，下一個(gè)優(yōu)先級(jí)的任務(wù)運(yùn)行。
    OS_ENTER_CRITICAL();
    msg = OSTCBCur->OSTCBMsg;//取出消息
    if (msg != (void *)0) {                           /* See if we were given the message              */
        OSTCBCur->OSTCBMsg      = (void *)0;          /* Yes, clear message received                   */
        OSTCBCur->OSTCBStat     = OS_STAT_RDY;
        OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;      /* No longer waiting for event                   */
        OS_EXIT_CRITICAL();
		//是否真正接收到消息，如果是，進(jìn)入就緒態(tài)，不再等待事件，
        *err                    = OS_NO_ERR;
        return (msg);                                 /* Return the message received                   */
		//將收到的消息返回
    }
    OS_EventTO(pevent);                               /* Timed out, Make task ready                    */
	//如果超時(shí)，讓任務(wù)就緒
    OS_EXIT_CRITICAL();
    *err = OS_TIMEOUT;                                /* Indicate that a timeout occured               */
    return ((void *)0);                               /* Return a NULL message                         */
	//返回空指針
}
/*$PAGE*/
/*
*********************************************************************************************************
*                                       POST MESSAGE TO A MAILBOX
*
* Description: This function sends a message to a mailbox
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired mailbox
*
*              msg           is a pointer to the message to send.  You MUST NOT send a NULL pointer.
*
* Returns    : OS_NO_ERR            The call was successful and the message was sent
*              OS_MBOX_FULL         If the mailbox already contains a message.  You can can only send one
*                                   message at a time and thus, the message MUST be consumed before you
*                                   are allowed to send another one.
*              OS_ERR_EVENT_TYPE    If you are attempting to post to a non mailbox.
*              OS_ERR_PEVENT_NULL   If 'pevent' is a NULL pointer
*              OS_ERR_POST_NULL_PTR If you are attempting to post a NULL pointer
                                                       向郵箱發(fā)送一則消息
描述：向郵箱發(fā)送一則消息
參數(shù)：pevent：指向目標(biāo)郵箱的ECB的指針
                 msg:將要發(fā)送的消息指針，不能發(fā)送空指針
 返回：OS_NO_ERR：消息發(fā)送成功
                OS_MBOX_FULL ：如果郵箱中已經(jīng)有消息了，一次只能發(fā)送一條消息，
                在你允許發(fā)送另一條前，消息必須用掉
                OS_ERR_EVENT_TYPE：如果你要發(fā)送到的不是郵箱
                 OS_ERR_PEVENT_NULL：如果目標(biāo)ECB是空指針
                 OS_ERR_POST_NULL_PTR：如果你想發(fā)空指針
*********************************************************************************************************
*/

#if OS_MBOX_POST_EN > 0
INT8U  OSMboxPost (OS_EVENT *pevent, void *msg)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif    
    
    
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */
        return (OS_ERR_PEVENT_NULL);
    }//合理的目標(biāo)ECB
    if (msg == (void *)0) {                           /* Make sure we are not posting a NULL pointer   */