uC/OS-II互斥信号(OS_mutex)块

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

#ifndef  OS_MASTER_FILE
#include "includes.h"
#endif

/*
*********************************************************************************************************
*                                            LOCAL CONSTANTS
*********************************************************************************************************
*/

#define  OS_MUTEX_KEEP_LOWER_8   0x00FF
#define  OS_MUTEX_KEEP_UPPER_8   0xFF00

#define  OS_MUTEX_AVAILABLE      0x00FF

#if OS_MUTEX_EN > 0
/*
*********************************************************************************************************
*                                   ACCEPT MUTUAL EXCLUSION SEMAPHORE
*
* Description: This  function checks the mutual exclusion semaphore to see if a resource is available.
*              Unlike OSMutexPend(), OSMutexAccept() does not suspend the calling task if the resource is
*              not available or the event did not occur.
*
* Arguments  : pevent     is a pointer to the event control block
*
*              err        is a pointer to an error code which will be returned to your application:
*                            OS_NO_ERR          if the call was successful.
*                            OS_ERR_EVENT_TYPE  if 'pevent' is not a pointer to a mutex
*                            OS_ERR_PEVENT_NULL 'pevent' is a NULL pointer
*                            OS_ERR_PEND_ISR     if you called this function from an ISR
*
* Returns    : == 1       if the resource is available, the mutual exclusion semaphore is acquired
*              == 0       a) if the resource is not available
*                         b) you didn't pass a pointer to a mutual exclusion semaphore
*                         c) you called this function from an ISR
*
* Warning(s) : This function CANNOT be called from an ISR because mutual exclusion semaphores are
*              intended to be used by tasks only.
*********************************************************************************************************
*/
//This  function checks the mutual exclusion semaphore to see if a resource is available.
#if OS_MUTEX_ACCEPT_EN > 0
INT8U  OSMutexAccept (OS_EVENT *pevent, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                            /* Allocate storage for CPU status register     */
    OS_CPU_SR  cpu_sr;
#endif    
    
    
    if (OSIntNesting > 0) {                            /* Make sure it's not called from an ISR        */
        *err = OS_ERR_PEND_ISR;
        return (0);
    }
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                     /* Validate 'pevent'                            */
        *err = OS_ERR_PEVENT_NULL;
        return (0);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) {  /* Validate event block type                    */
        *err = OS_ERR_EVENT_TYPE;
        return (0);
    }
#endif                                                     
    OS_ENTER_CRITICAL();                               /* Get value (0 or 1) of Mutex                  */
    if ((pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8) == OS_MUTEX_AVAILABLE) {     
        pevent->OSEventCnt &= OS_MUTEX_KEEP_UPPER_8;   /*      Mask off LSByte (Acquire Mutex)         */
        pevent->OSEventCnt |= OSTCBCur->OSTCBPrio;     /*      Save current task priority in LSByte    */
        pevent->OSEventPtr  = (void *)OSTCBCur;        /*      Link TCB of task owning Mutex           */
        OS_EXIT_CRITICAL();
        *err = OS_NO_ERR;
        return (1);
    }
    OS_EXIT_CRITICAL();
    *err = OS_NO_ERR;
    return (0);
}
#endif                                                     

/*$PAGE*/
/*
*********************************************************************************************************
*                                  CREATE A MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function creates a mutual exclusion/排斥 semaphore.
*
* Arguments  : prio          is the priority to use when accessing the mutual exclusion semaphore.  In
*                            other words, when the semaphore is acquired and a higher priority task
*                            attempts to obtain the semaphore then the priority of the task owning the
*                            semaphore is raised to this priority.  It is assumed that you will specify
*                            a priority that is LOWER in value than ANY of the tasks competing for the
*                            mutex.
*
*              err           is a pointer to an error code which will be returned to your application:
*                               OS_NO_ERR           if the call was successful.
*                               OS_ERR_CREATE_ISR   if you attempted to create a MUTEX from an ISR
*                               OS_PRIO_EXIST       if a task at the priority inheritance priority
*                                                   already exist.
*                               OS_ERR_PEVENT_NULL  No more event control blocks available.
*                               OS_PRIO_INVALID     if the priority you specify is higher that the
*                                                   maximum allowed (i.e. > OS_LOWEST_PRIO)
*
* Returns    : != (void *)0  is a pointer to the event control clock (OS_EVENT) associated with the
*                            created mutex.
*              == (void *)0  if an error is detected.
*
* Note(s)    : 1) The LEAST significant 8 bits of '.OSEventCnt' are used to hold the priority number
*                 of the task owning the mutex or 0xFF if no task owns the mutex.
*              2) The MOST  significant 8 bits of '.OSEventCnt' are used to hold the priority number
*                 to use to reduce priority inversion.
*********************************************************************************************************
*/
//创建一个互斥信号量
OS_EVENT  *OSMutexCreate (INT8U prio, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
    OS_CPU_SR  cpu_sr;
#endif    
    OS_EVENT  *pevent;

    //各种判断
    if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
        *err = OS_ERR_CREATE_ISR;                          /* ... can't CREATE mutex from an ISR       */
        return ((OS_EVENT *)0);
    }
#if OS_ARG_CHK_EN > 0
    if (prio >= OS_LOWEST_PRIO) {                          /* Validate PIP                             */
        *err = OS_PRIO_INVALID;
        return ((OS_EVENT *)0);
    }
#endif
    OS_ENTER_CRITICAL();
    if (OSTCBPrioTbl[prio] != (OS_TCB *)0) {               /* Mutex priority must not already exist    */
        OS_EXIT_CRITICAL();                                /* Task already exist at priority ...       */
        *err = OS_PRIO_EXIST;                              /* ... inheritance priority                 */
        return ((OS_EVENT *)0);                            
    }
    //书包
    OSTCBPrioTbl[prio] = (OS_TCB *)1;                      /* Reserve the table entry                  */
    pevent             = OSEventFreeList;                  /* Get next free event control block        */
    //判断事件控制块是否可用
    if (pevent == (OS_EVENT *)0) {                         /* See if an ECB was available              */
        //还回去
        OSTCBPrioTbl[prio] = (OS_TCB *)0;                  /* No, Release the table entry              */
        OS_EXIT_CRITICAL();
        *err               = OS_ERR_PEVENT_NULL;           /* No more event control blocks             */
        return (pevent);
    }
    //否则
    OSEventFreeList     = (OS_EVENT *)OSEventFreeList->OSEventPtr;   /* Adjust the free list           */
    OS_EXIT_CRITICAL();
    //类型是互斥信息号量--4
    pevent->OSEventType = OS_EVENT_TYPE_MUTEX;
    //把优先级左移动8位 且低8位标记为11111111OSEventCnt的高八位是prio 低八位是8个1
    pevent->OSEventCnt  = (prio << 8) | OS_MUTEX_AVAILABLE;/* Resource is available                    */
    //表示任务没有使用本次信号量
    pevent->OSEventPtr  = (void *)0;                       /* No task owning the mutex                 */
    //然后对事件控制块进行初始化
    OS_EventWaitListInit(pevent);
    *err                = OS_NO_ERR;
    return (pevent);
}

/*$PAGE*/
/*
*********************************************************************************************************
*                                          DELETE A MUTEX
*
* Description: This function deletes a mutual exclusion semaphore and readies all tasks pending on the it.
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired mutex.
*
*              opt           determines delete options as follows:
*                            opt == OS_DEL_NO_PEND   Delete mutex ONLY if no task pending
*                            opt == OS_DEL_ALWAYS    Deletes the mutex 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 mutex was deleted
*                            OS_ERR_DEL_ISR          If you attempted to delete the MUTEX from an ISR
*                            OS_ERR_INVALID_OPT      An invalid option was specified
*                            OS_ERR_TASK_WAITING     One or more tasks were waiting on the mutex
*                            OS_ERR_EVENT_TYPE       If you didn't pass a pointer to a mutex
*                            OS_ERR_PEVENT_NULL      If 'pevent' is a NULL pointer.
*
* Returns    : pevent        upon error
*              (OS_EVENT *)0 if the mutex was successfully deleted.
*
* Note(s)    : 1) This function must be used with care.  Tasks that would normally expect the presence of
*                 the mutex MUST check the return code of OSMutexPend().
*              2) 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 mutex.
*              3) Because ALL tasks pending on the mutex will be readied, you MUST be careful because the
*                 resource(s) will no longer be guarded by the mutex.
*********************************************************************************************************
*/
//删除一个互斥信号量0000opt删除的方式--类似于信号量的删除
#if OS_MUTEX_DEL_EN
OS_EVENT  *OSMutexDel (OS_EVENT *pevent, INT8U opt, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif    
    BOOLEAN    tasks_waiting;
    INT8U      pip;

    if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
        *err = OS_ERR_DEL_ISR;                             /* ... can't DELETE from an ISR             */
        return (pevent);
    }
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                         /* Validate 'pevent'                        */
        *err = OS_ERR_PEVENT_NULL;
        return ((OS_EVENT *)0);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) {      /* Validate event block type                */
        *err = OS_ERR_EVENT_TYPE;
        return (pevent);
    }
#endif
    OS_ENTER_CRITICAL();
    if (pevent->OSEventGrp != 0x00) {                      /* See if any tasks waiting on mutex        */
        tasks_waiting = TRUE;                              /* Yes                                      */
    } else {
        tasks_waiting = FALSE;                             /* No                                       */
    }
    switch (opt) {
        /* Delete mutex only if no task waiting     */
        case OS_DEL_NO_PEND:                               /* Delete mutex only if no task waiting     */
             if (tasks_waiting == FALSE) {
                 pip                 = (INT8U)(pevent->OSEventCnt >> 8);
                 OSTCBPrioTbl[pip]   = (OS_TCB *)0;        /* Free up the PIP                          */
                 pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
                 pevent->OSEventPtr  = OSEventFreeList;    /* Return Event Control Block to free list  */
                 OSEventFreeList     = pevent;
                 OS_EXIT_CRITICAL();
                 *err = OS_NO_ERR;
                 return ((OS_EVENT *)0);                   /* Mutex has been deleted                   */
             } else {
                 OS_EXIT_CRITICAL();
                 *err = OS_ERR_TASK_WAITING;
                 return (pevent);
             }

        case OS_DEL_ALWAYS:                                /* Always delete the mutex                  */
             while (pevent->OSEventGrp != 0x00) {          /* Ready ALL tasks waiting for mutex        */
                 OS_EventTaskRdy(pevent, (void *)0, OS_STAT_MUTEX);
             }
             pip                 = (INT8U)(pevent->OSEventCnt >> 8);
             OSTCBPrioTbl[pip]   = (OS_TCB *)0;            /* Free up the PIP                          */
             pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
             pevent->OSEventPtr  = OSEventFreeList;        /* Return Event Control Block to free list  */
             OSEventFreeList     = pevent;                 /* Get next free event control block        */
             OS_EXIT_CRITICAL();
             if (tasks_waiting == TRUE) {                  /* Reschedule only if task(s) were waiting  */
                 OS_Sched();                               /* Find highest priority task ready to run  */
             }
             *err = OS_NO_ERR;
             return ((OS_EVENT *)0);                       /* Mutex has been deleted                   */

        default:
             OS_EXIT_CRITICAL();
             *err = OS_ERR_INVALID_OPT;
             return (pevent);
    }
}
#endif

/*$PAGE*/
/*
*********************************************************************************************************
*                                  PEND ON MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function waits for a mutual exclusion semaphore.
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired
*                            mutex.
*
*              timeout       is an optional timeout period (in clock ticks).  If non-zero, your task will
*                            wait for the resource up to the amount of time specified by this argument.
*                            If you specify 0, however, your task will wait forever at the specified
*                            mutex or, until the resource becomes available.
*
*              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 owns the mutex
*                               OS_TIMEOUT         The mutex was not available within the specified time.
*                               OS_ERR_EVENT_TYPE  If you didn't pass a pointer to a mutex
*                               OS_ERR_PEVENT_NULL 'pevent' is a NULL pointer
*                               OS_ERR_PEND_ISR    If you called this function from an ISR and the result
*                                                  would lead to a suspension.
*
* Returns    : none
*
* Note(s)    : 1) The task that owns the Mutex MUST NOT pend on any other event while it owns the mutex.
*              2) You MUST NOT change the priority of the task that owns the mutex
*********************************************************************************************************
*/
//请求一个互斥信号量---timeout延时时间  This function waits for a mutual exclusion semaphore.
void  OSMutexPend (OS_EVENT *pevent, INT16U timeout, INT8U *err)
{
#if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
    OS_CPU_SR  cpu_sr;
#endif    
    //优先级继承优先级
    INT8U      pip;                                        /* Priority Inheritance Priority (PIP)      */
    INT8U      mprio;                                      /* Mutex owner priority                     */
    //任务是否就绪标志
    BOOLEAN    rdy;                                        /* Flag indicating task was ready           */
    OS_TCB    *ptcb;

    //是否在中断
    if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
        *err = OS_ERR_PEND_ISR;                            /* ... can't PEND from an ISR               */
        return;
    }
#if OS_ARG_CHK_EN > 0
    //事件指针是否可用
    if (pevent == (OS_EVENT *)0) {                         /* Validate 'pevent'                        */
        *err = OS_ERR_PEVENT_NULL;
        return;
    }
    //是否是互斥信号量
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) {      /* Validate event block type                */
        *err = OS_ERR_EVENT_TYPE;
        return;
    }
#endif
    OS_ENTER_CRITICAL();                                   /* Is Mutex available?                      */
    //查看互斥信号量有效
    //若有信号OSEventCnt的低八位是8个1 说明该信号量未被占用   与OS_MUTEX_KEEP_LOWER_8进行与 若为111111111
    if ((INT8U)(pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8) == OS_MUTEX_AVAILABLE) {
        //与OS_MUTEX_KEEP_UPPER_8保存到高八位
        //把低八位置0 表示资源被占用 这时OSEventCnt高八位为pip 低八位为0
        pevent->OSEventCnt &= OS_MUTEX_KEEP_UPPER_8;       /*      Yes, Acquire the resource                */
        //这时OSEventCnt高八位为pip 低八位为任务的优先级
        pevent->OSEventCnt |= OSTCBCur->OSTCBPrio;         /*      Save priority of owning task        */
        //OSEventPtr指向任务控制块
        pevent->OSEventPtr  = (void *)OSTCBCur;            /*      Point to owning task's OS_TCB       */
        OS_EXIT_CRITICAL();
        *err  = OS_NO_ERR;
        return;
    }
    //取出优先级继承优先级pip
    pip   = (INT8U)(pevent->OSEventCnt >> 8);                     /* No, Get PIP from mutex            */
    //否则信号量被占用--取出互斥信号量所有者的优先级 赋值给mprio
    mprio = (INT8U)(pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8);  /*     Get priority of mutex owner   */
    //取出互斥信号量所有者的tcb地址 赋值给ptcb
    ptcb  = (OS_TCB *)(pevent->OSEventPtr);                       /*     Point to TCB of mutex owner   */
    //判断当前的是否等觘cb优先级  且 请求的任务块大于当前的优先级
    if (ptcb->OSTCBPrio != pip && mprio > OSTCBCur->OSTCBPrio) {  /*     Need to promote prio of owner?*/
        //查看互斥信号量所有者是否就绪--若就绪
        if ((OSRdyTbl[ptcb->OSTCBY] & ptcb->OSTCBBitX) != 0x00) { /*     See if mutex owner is ready   */
                                                                  /*     Yes, Remove owner from Rdy ...*/
              //是否在就绪表中取消互斥信号量所有者的就绪标志                                                    /*          ... list at current prio */
            if ((OSRdyTbl[ptcb->OSTCBY] &= ~ptcb->OSTCBBitX) == 0x00) {
                //已取消---就直接把就绪组中对应置0
                OSRdyGrp &= ~ptcb->OSTCBBitY;
            }
            //就绪
            rdy = TRUE;
        } else {
            rdy = FALSE;                                          /* No                                */
        }
        //对互斥信号量所有者做优先级升级，改变TCB中所有者关于优先级域
        ptcb->OSTCBPrio         = pip;                     /* Change owner task prio to PIP            */
        ptcb->OSTCBY            = ptcb->OSTCBPrio >> 3;
        ptcb->OSTCBBitY         = OSMapTbl[ptcb->OSTCBY];
        ptcb->OSTCBX            = ptcb->OSTCBPrio & 0x07;
        ptcb->OSTCBBitX         = OSMapTbl[ptcb->OSTCBX];
        //就绪
        if (rdy == TRUE) {                                 /* If task was ready at owner's priority ...*/
            //在就绪表和就绪组中重新提升后的优先级设置就绪标志
            OSRdyGrp               |= ptcb->OSTCBBitY;     /* ... make it ready at new priority.       */
            OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
        }
        //互斥信号量原来未就绪
        OSTCBPrioTbl[pip]       = (OS_TCB *)ptcb;
    }
    //完成对优先级升级，继续对本任务就绪操作--设置等待互斥信号量的标志
    OSTCBCur->OSTCBStat |= OS_STAT_MUTEX;             /* Mutex not available, pend current task        */
    //存储超时
    OSTCBCur->OSTCBDly   = timeout;                   /* Store timeout in current task's TCB           */
    //取消本任务就绪状态
    OS_EventTaskWait(pevent);                         /* Suspend task until event or timeout occurs    */
    OS_EXIT_CRITICAL();
    OS_Sched();                                        /* Find next highest priority task ready         */
    OS_ENTER_CRITICAL();
    //若延时时间到了
    if (OSTCBCur->OSTCBStat & OS_STAT_MUTEX) {        /* Must have timed out if still waiting for event*/
        //结束等待状态  转去执行延时时间到 的函数
        OS_EventTO(pevent);
        OS_EXIT_CRITICAL();
        *err = OS_TIMEOUT;                            /* Indicate that we didn't get mutex within TO   */
        return;
    }
    //否则把当前指针指向0
    OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
    OS_EXIT_CRITICAL();
    *err = OS_NO_ERR;
}
/*$PAGE*/
/*
*********************************************************************************************************
*                                  POST TO A MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function signals a mutual exclusion semaphore
*
* Arguments  : pevent              is a pointer to the event control block associated with the desired
*                                  mutex.
*
* Returns    : OS_NO_ERR               The call was successful and the mutex was signaled.
*              OS_ERR_EVENT_TYPE       If you didn't pass a pointer to a mutex
*              OS_ERR_PEVENT_NULL      'pevent' is a NULL pointer
*              OS_ERR_POST_ISR         Attempted to post from an ISR (not valid for MUTEXes)
*              OS_ERR_NOT_MUTEX_OWNER  The task that did the post is NOT the owner of the MUTEX.
*********************************************************************************************************
*/
//发送互斥信号量---释放一个互斥信号量
INT8U  OSMutexPost (OS_EVENT *pevent)
{
#if OS_CRITICAL_METHOD == 3                           /* Allocate storage for CPU status register      */
    OS_CPU_SR  cpu_sr;
#endif    
    //优先级继承优先级
    INT8U      pip;                                   /* Priority inheritance priority                 */
    INT8U      prio;
    

    if (OSIntNesting > 0) {                           /* See if called from ISR ...                    */
        return (OS_ERR_POST_ISR);                     /* ... can't POST mutex from an ISR              */
    }
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */
        return (OS_ERR_PEVENT_NULL);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) { /* Validate event block type                     */
        return (OS_ERR_EVENT_TYPE);
    }                                                 
#endif
    OS_ENTER_CRITICAL();
    pip  = (INT8U)(pevent->OSEventCnt >> 8);          /* Get priority inheritance priority of mutex    */
    //获取原来任务的优先级
    prio = (INT8U)(pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8);  /* Get owner's original priority      */
    
    if (OSTCBCur->OSTCBPrio != pip &&
        OSTCBCur->OSTCBPrio != prio) {                /* See if posting task owns the MUTEX            */
        OS_EXIT_CRITICAL();
        return (OS_ERR_NOT_MUTEX_OWNER);
    }
    //如果本任务是由于继承机制提高的优先级----恢复原来的优先级
    if (OSTCBCur->OSTCBPrio == pip) {                 /* Did we have to raise current task's priority? */
                                                      /* Yes, Return to original priority              */
                                                      /*      Remove owner from ready list at 'pip'    */
        if ((OSRdyTbl[OSTCBCur->OSTCBY] &= ~OSTCBCur->OSTCBBitX) == 0) {
            OSRdyGrp &= ~OSTCBCur->OSTCBBitY;
        }
        OSTCBCur->OSTCBPrio         = prio;
        OSTCBCur->OSTCBY            = prio >> 3;
        OSTCBCur->OSTCBBitY         = OSMapTbl[OSTCBCur->OSTCBY];
        OSTCBCur->OSTCBX            = prio & 0x07;
        OSTCBCur->OSTCBBitX         = OSMapTbl[OSTCBCur->OSTCBX];
        OSRdyGrp                   |= OSTCBCur->OSTCBBitY;
        OSRdyTbl[OSTCBCur->OSTCBY] |= OSTCBCur->OSTCBBitX;
        OSTCBPrioTbl[prio]          = (OS_TCB *)OSTCBCur;
    }
    //先占优先级指针表中的pip项
    OSTCBPrioTbl[pip] = (OS_TCB *)1;                  /* Reserve table entry                           */
    if (pevent->OSEventGrp != 0x00) {                 /* Any task waiting for the mutex?               */
                                                      /* Yes, Make HPT waiting for mutex ready         */
        //将事件等待表中的优先级最高任务就绪
        prio                = OS_EventTaskRdy(pevent, (void *)0, OS_STAT_MUTEX);
        pevent->OSEventCnt &= OS_MUTEX_KEEP_UPPER_8;  /*      Save priority of mutex's new owner       */
        pevent->OSEventCnt |= prio;
        //OSEventPtr指向新的互斥信号量所有者的tcb
        pevent->OSEventPtr  = OSTCBPrioTbl[prio];     /*      Link to mutex owner's OS_TCB             */
        OS_EXIT_CRITICAL();
        OS_Sched();                                   /*      Find highest priority task ready to run  */
        return (OS_NO_ERR);
    }
    //没有任务等待互斥信号量时就运行到这
    //Mutex is now available   
    pevent->OSEventCnt |= OS_MUTEX_AVAILABLE;         /* No,  Mutex is now available                   */
    pevent->OSEventPtr  = (void *)0;
    OS_EXIT_CRITICAL();
    return (OS_NO_ERR);
}
/*$PAGE*/
/*
*********************************************************************************************************
*                                     QUERY A MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function obtains information about a mutex
*
* Arguments  : pevent        is a pointer to the event control block associated with the desired mutex
*
*              pdata         is a pointer to a structure that will contain information about the mutex
*
* Returns    : OS_NO_ERR            The call was successful and the message was sent
*              OS_ERR_QUERY_ISR     If you called this function from an ISR
*              OS_ERR_PEVENT_NULL   'pevent' is a NULL pointer
*              OS_ERR_EVENT_TYPE    If you are attempting to obtain data from a non mutex.
*********************************************************************************************************
*/
//This function obtains information about a mutex  OS_MUTEX_DATA结构体  用于保存互斥信号量的 信息
#if OS_MUTEX_QUERY_EN > 0
INT8U  OSMutexQuery (OS_EVENT *pevent, OS_MUTEX_DATA *pdata)
{
#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */
    OS_CPU_SR  cpu_sr;
#endif    
    INT8U     *psrc;
    INT8U     *pdest;
    //各种判断

    if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
        return (OS_ERR_QUERY_ISR);                         /* ... can't QUERY mutex from an ISR        */
    }
#if OS_ARG_CHK_EN > 0
    if (pevent == (OS_EVENT *)0) {                         /* Validate 'pevent'                        */
        return (OS_ERR_PEVENT_NULL);
    }
    if (pevent->OSEventType != OS_EVENT_TYPE_MUTEX) {      /* Validate event block type                */
        return (OS_ERR_EVENT_TYPE);
    }
#endif
    OS_ENTER_CRITICAL();
    pdata->OSMutexPIP  = (INT8U)(pevent->OSEventCnt >> 8);
    pdata->OSOwnerPrio = (INT8U)(pevent->OSEventCnt & OS_MUTEX_KEEP_LOWER_8);
    if (pdata->OSOwnerPrio == 0xFF) {
        pdata->OSValue = 1;//可用的一个互斥信号量
    } else {
        pdata->OSValue = 0;
    }
    pdata->OSEventGrp  = pevent->OSEventGrp;               /* Copy wait list                           */
    psrc               = &pevent->OSEventTbl[0];
    pdest              = &pdata->OSEventTbl[0];
#if OS_EVENT_TBL_SIZE > 0
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 1
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 2
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 3
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 4
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 5
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 6
    *pdest++           = *psrc++;
#endif

#if OS_EVENT_TBL_SIZE > 7
    *pdest             = *psrc;
#endif
    OS_EXIT_CRITICAL();
    return (OS_NO_ERR);
}
#endif                                                     /* OS_MUTEX_QUERY_EN                        */
#endif                                                     /* OS_MUTEX_EN                              */