/*
*********************************************************************************************************
*                                                uC/OS-II
*                                          The Real-Time Kernel
*                                        MESSAGE QUEUE MANAGEMENT
*
*                          (c) Copyright 1992-2002, Jean J. Labrosse, Weston, FL
*                                           All Rights Reserved
*
* File : OS_Q.C
* By   : Jean J. Labrosse
*********************************************************************************************************
*/

#ifndef  OS_MASTER_FILE//防止編譯器包含一些代碼
#include "includes.h"
#endif

#if (OS_Q_EN > 0) && (OS_MAX_QS > 0)
/*
*********************************************************************************************************
*                                      ACCEPT MESSAGE FROM QUEUE
*
* Description: This function checks the queue to see if a message is available.  Unlike OSQPend(),
*              OSQAccept() does not suspend the calling task if a message is not available.
*
* Arguments  : pevent        is a pointer to the event control block
*
* Returns    : != (void *)0  is the message in the queue if one is available.  The message is removed
*                            from the so the next time OSQAccept() is called, the queue will contain
*                            one less entry.
*              == (void *)0  if the queue is empty or,
*                            if 'pevent' is a NULL pointer or,
*                            if you passed an invalid event type

*********************************************************************************************************
*/

#if OS_Q_ACCEPT_EN > 0
void  *OSQAccept (OS_EVENT *pevent)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif
    void      *msg;
    OS_Q      *pq;


#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {               /* Validate 'pevent'                                  */
        return ((void *)0);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_Q) {/* Validate event block type                          */
        return ((void *)0);
    }
#endif
    OS_ENTER_CRITICAL();
    pq = (OS_Q *)pevent->OSEventPtr;             /* Point at queue control block                       */
    if (pq->OSQEntries > 0) {                    /* See if any messages in the queue                   */
        msg = *pq->OSQOut++;                     /* Yes, extract oldest message from the queue         */
        pq->OSQEntries--;                        /* Update the number of entries in the queue          */
        if (pq->OSQOut == pq->OSQEnd) {          /* Wrap OUT pointer if we are at the end of the queue */
            pq->OSQOut = pq->OSQStart;
        }
    } else {
        msg = (void *)0;                         /* Queue is empty                                     */
    }
    OS_EXIT_CRITICAL();
    return (msg);                                /* Return message received (or NULL)                  */
}
#endif
/*$PAGE*/
/*
*********************************************************************************************************
*                                        CREATE A MESSAGE QUEUE
*
* Description: This function creates a message queue if free event control blocks are available.
*
* Arguments  : start         is a pointer to the base address of the message queue storage area.  The
*                            storage area MUST be declared as an array of pointers to 'void' as follows
*
*                            void *MessageStorage[size]
*
*              size          is the number of elements in the storage area
*
* Returns    : != (OS_EVENT *)0  is a pointer to the event control clock (OS_EVENT) associated with the
*                                created queue
*              == (OS_EVENT *)0  if no event control blocks were available or an error was detected
                                                      建立一個消息隊列
描述：如果有空余事件控制塊，就建立一個消息隊列
參數：start：指向消息隊列存儲空間基地址。存儲空間必須定義成void 型的
                            一系列指針，形式如右：void *MessageStorage[size]
                 size：存儲空間內單元的數目
返回：!= (OS_EVENT *)0  是指向結合建立的隊列的事件控制時鐘(OS_EVENT)的指針
                 == (OS_EVENT *)0如果沒有適合的事件控制塊或者有錯誤
*********************************************************************************************************
*/

OS_EVENT  *OSQCreate (void **start, INT16U size)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;//分配名為cpu_sr 的局部變量，用于支持OS_CRITICAL_METHOD方法3
#endif
    OS_EVENT  *pevent;
    OS_Q      *pq;


    if (OSIntNesting > 0) {                      /* See if called from ISR ...                         */
        return ((OS_EVENT *)0);                  /* ... can't CREATE from an ISR                       */
    }//不能在ISR中建立消息隊列
    OS_ENTER_CRITICAL();
    pevent = OSEventFreeList;                    /* Get next free event control block                  */
	//從空余的ECB鏈表中取得一個事件控制塊。對剩下的作相應調整
	//ECB是單向鏈表
    if (OSEventFreeList != (OS_EVENT *)0) {      /* See if pool of free ECB pool was empty             */
        OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
    }//對剩下的進行相應的調整
    OS_EXIT_CRITICAL();
    if (pevent != (OS_EVENT *)0) {               /* See if we have an event control block              */
		//如果我們得到了事件控制塊
        OS_ENTER_CRITICAL();
        pq = OSQFreeList;                        /* Get a free queue control block                     */
		//得到一塊新的隊列控制塊
        if (pq != (OS_Q *)0) {                   /* Were we able to get a queue control block ?        */
			//如果得到的不為空，即真正得到了。
            OSQFreeList         = OSQFreeList->OSQPtr;    /* Yes, Adjust free list pointer to next free*/
			//調整表頭
            OS_EXIT_CRITICAL();
			//初始化新得到的隊列控制塊
            pq->OSQStart        = start;                  /*      Initialize the queue                 */
            pq->OSQEnd          = &start[size];
            pq->OSQIn           = start;
            pq->OSQOut          = start;
            pq->OSQSize         = size;
            pq->OSQEntries      = 0;//初始化消息數為零
            pevent->OSEventType = OS_EVENT_TYPE_Q;//設置事件控制塊類型
            pevent->OSEventCnt  = 0;//信號量
            pevent->OSEventPtr  = pq;//將此塊指向消息隊列結構指針
            OS_EventWaitListInit(pevent);   /*      Initalize the wait list  *///初始化等待列表
        } else {//如果沒有得到隊列控制塊
            pevent->OSEventPtr = (void *)OSEventFreeList; /* No,  Return event control block on error  */
			//以錯誤形式返回隊列控制塊
            OSEventFreeList    = pevent;//退回事件控制塊，不用了。
            OS_EXIT_CRITICAL();
            pevent = (OS_EVENT *)0;//清零，給下一次使用。
        }
    }
    return (pevent);//如果消息隊列建立成功，則會返回一個指針，否則，就返回空指針。
    //消息隊列成功后返回的這個指針用于以后對消息隊列的操作因此，該指針
    //可以看作是相應消息隊列的句柄。
}
/*$PAGE*/
/*
*********************************************************************************************************
*                                        DELETE A MESSAGE QUEUE
*
* Description: This function deletes a message queue and readies all tasks pending on the queue.
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired
*                            queue.
*
*              opt           determines delete options as follows:
*                            opt == OS_DEL_NO_PEND   Delete the queue ONLY if no task pending
*                            opt == OS_DEL_ALWAYS    Deletes the queue even if tasks are waiting.
*                                                    In this case, all the tasks pending will be readied.
*
*              err           is a pointer to an error code that can contain one of the following values:
*                            OS_NO_ERR               The call was successful and the queue was deleted
*                            OS_ERR_DEL_ISR          If you tried to delete the queue from an ISR
*                            OS_ERR_INVALID_OPT      An invalid option was specified
*                            OS_ERR_TASK_WAITING     One or more tasks were waiting on the queue
*                            OS_ERR_EVENT_TYPE       If you didn't pass a pointer to a queue
*                            OS_ERR_PEVENT_NULL      If 'pevent' is a NULL pointer.
*
* Returns    : pevent        upon error
*              (OS_EVENT *)0 if the queue was successfully deleted.
*
* Note(s)    : 1) This function must be used with care.  Tasks that would normally expect the presence of
*                 the queue MUST check the return code of OSQPend().
*              2) OSQAccept() callers will not know that the intended queue has been deleted unless
*                 they check 'pevent' to see that it's a NULL pointer.
*              3) This call can potentially disable interrupts for a long time.  The interrupt disable
*                 time is directly proportional to the number of tasks waiting on the queue.
*              4) Because ALL tasks pending on the queue will be readied, you MUST be careful in
*                 applications where the queue is used for mutual exclusion because the resource(s)
*                 will no longer be guarded by the queue.
*              5) If the storage for the message queue was allocated dynamically (i.e. using a malloc()
*                 type call) then your application MUST release the memory storage by call the counterpart
*                 call of the dynamic allocation scheme used.  If the queue storage was created statically
*                 then, the storage can be reused.
                                                  刪除一個消息隊列
描述：刪除一個隊列，使在隊列上掛起的任務全部就緒
參數：pevent ：指向事件控制塊和目標隊列的指針
                 opt:決定刪除選項，如下：
*                            opt == OS_DEL_NO_PEND   沒有任務掛起才刪除
*                            opt == OS_DEL_ALWAYS    有任務掛起也刪，掛起的任務全部就緒
*              err          指向包含如下錯誤信息的指針
*                            OS_NO_ERR              調用成功，隊列刪除
*                            OS_ERR_DEL_ISR         如果想從ISR中刪除
*                            OS_ERR_INVALID_OPT      指定了非法選項
*                            OS_ERR_TASK_WAITING     有任務在隊列中等待
*                            OS_ERR_EVENT_TYPE      如果你沒有傳遞消息給隊列
*                            OS_ERR_PEVENT_NULL     如果pevent是一個空指針
返回：pevent；有錯
                 (OS_EVENT *)0如果隊列成功刪除
備注：1、此函數要小心使用，任務希望現場隊列檢查OSQPend()的返回代碼，什么意思，不知道
                2、OSQAccept()的調用者不知道目標隊列是否刪除了，除非檢查pevent'是否為空指針
                3、此調用將潛在關中斷一段時間，時間長短與隊列中任務多少成正比
                4、因為所有隊列中掛起的任務就緒，在多任務的時候要小心，因為這些資源
                       隊列不再看管（因為刪除了）。
                5、如果消息存儲用動態分配（比如用malloc()），那么應用程序必須通過
                        調用相應的動態配置去釋放內存空間，如果隊列存儲是靜態建立，則可以再次
                利用
*********************************************************************************************************
*/

#if OS_Q_DEL_EN > 0
OS_EVENT  *OSQDel (OS_EVENT *pevent, INT8U opt, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
    OS_CPU_SR  cpu_sr;
#endif