• uC/OS-II信号(OS_sem)块


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

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

    #if OS_SEM_EN > 0
    /*
    *********************************************************************************************************
    *                                           ACCEPT SEMAPHORE
    *
    * Description: This function checks the semaphore to see if a resource is available or, if an event
    *              occurred.  Unlike OSSemPend(), OSSemAccept() 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
    *
    * Returns    : >  0       if the resource is available or the event did not occur the semaphore is
    *                         decremented to obtain the resource.
    *              == 0       if the resource is not available or the event did not occur or,
    *                         if 'pevent' is a NULL pointer or,
    *                         if you didn't pass a pointer to a semaphore
    *********************************************************************************************************
    */
    //无等待请求信号量--这函数function:当一个任务请求信号量时,如果希望在信
    //量无效时准许任务不进入等待状态而继续运行,则不调用函数OSSPend 而是调用本函数OSSemAccept
    #if OS_SEM_ACCEPT_EN > 0
    INT16U  OSSemAccept (OS_EVENT *pevent)
    {
    #if OS_CRITICAL_METHOD == 3                           /* Allocate storage for CPU status register      */
        OS_CPU_SR  cpu_sr;
    #endif    
        INT16U     cnt;


    #if OS_ARG_CHK_EN > 0
        if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */
            return (0);
        }
        if (pevent->OSEventType != OS_EVENT_TYPE_SEM) {   /* Validate event block type                     */
            return (0);
        }
    #endif
        OS_ENTER_CRITICAL();
        cnt = pevent->OSEventCnt;
        //See if resource is available
        if (cnt > 0) {                                    /* See if resource is available                  */
            pevent->OSEventCnt--;                         /* Yes, decrement semaphore and notify caller    */
        }
        OS_EXIT_CRITICAL();
        return (cnt);                                     /* Return semaphore count                        */
    }
    #endif    

    /*$PAGE*/
    /*
    *********************************************************************************************************
    *                                           CREATE A SEMAPHORE
    *
    * Description: This function creates a semaphore.
    *
    * Arguments  : cnt           is the initial value for the semaphore.  If the value is 0, no resource is
    *                            available (or no event has occurred).  You initialize the semaphore to a
    *                            non-zero value to specify how many resources are available (e.g. if you have
    *                            10 resources, you would initialize the semaphore to 10).
    *
    * Returns    : != (void *)0  is a pointer to the event control clock (OS_EVENT) associated with the
    *                            created semaphore
    *              == (void *)0  if no event control blocks were available
    *********************************************************************************************************
    */
    //This function creates a semaphore.
    OS_EVENT  *OSSemCreate (INT16U cnt)
    {
    #if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
        OS_CPU_SR  cpu_sr;
    #endif    
        OS_EVENT  *pevent;

        
        if (OSIntNesting > 0) {                                /* See if called from ISR ...               */
            return ((OS_EVENT *)0);                            /* ... can't CREATE from an ISR             */
        }
        OS_ENTER_CRITICAL();
        /* Get next free event control block        */
        pevent = OSEventFreeList;                              /* Get next free event control block        */
        if (OSEventFreeList != (OS_EVENT *)0) {                /* See if pool of free ECB pool was empty   */
            OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
        }
        OS_EXIT_CRITICAL();
        if (pevent != (OS_EVENT *)0) {                         /* Get an event control block               */
            pevent->OSEventType = OS_EVENT_TYPE_SEM;            //OS_EVENT_TYPE_SEM信号量类型
            pevent->OSEventCnt  = cnt;                         /* Set semaphore value                      */
            pevent->OSEventPtr  = (void *)0;                   /* Unlink from ECB free list                */
            //初始化一个信号量 Initialize to 'nobody waiting' on sem.  
            OS_EventWaitListInit(pevent);                      /* Initialize to 'nobody waiting' on sem.   */
        }
        return (pevent);
    }

    /*$PAGE*/
    /*
    *********************************************************************************************************
    *                                         DELETE A SEMAPHORE
    *
    * Description: This function deletes a semaphore and readies all tasks pending on the semaphore.
    *
    * Arguments  : pevent        is a pointer to the event control block associated with the desired
    *                            semaphore.
    *
    *              opt           determines delete options as follows:
    *                            opt == OS_DEL_NO_PEND   Delete semaphore ONLY if no task pending
    *                            opt == OS_DEL_ALWAYS    Deletes the semaphore 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 semaphore was deleted
    *                            OS_ERR_DEL_ISR          If you attempted to delete the semaphore from an ISR
    *                            OS_ERR_INVALID_OPT      An invalid option was specified
    *                            OS_ERR_TASK_WAITING     One or more tasks were waiting on the semaphore
    *                            OS_ERR_EVENT_TYPE       If you didn't pass a pointer to a semaphore
    *                            OS_ERR_PEVENT_NULL      If 'pevent' is a NULL pointer.
    *
    * Returns    : pevent        upon error
    *              (OS_EVENT *)0 if the semaphore was successfully deleted.
    *
    * Note(s)    : 1) This function must be used with care.  Tasks that would normally expect the presence of
    *                 the semaphore MUST check the return code of OSSemPend().
    *              2) OSSemAccept() callers will not know that the intended semaphore 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 semaphore.
    *              4) Because ALL tasks pending on the semaphore will be readied, you MUST be careful in
    *                 applications where the semaphore is used for mutual exclusion because the resource(s)
    *                 will no longer be guarded by the semaphore.
    *********************************************************************************************************
    */
    //This function deletes a semaphore and readies all tasks pending on the semaphore  opt指明信号量的删除条件
    #if OS_SEM_DEL_EN > 0
    OS_EVENT  *OSSemDel (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;
        
        //各种判断
        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 (pevent);
        }
        if (pevent->OSEventType != OS_EVENT_TYPE_SEM) {        /* Validate event block type                */
            *err = OS_ERR_EVENT_TYPE;
            return (pevent);
        }
    #endif
        OS_ENTER_CRITICAL();
        //See if any tasks waiting on semaphore
        if (pevent->OSEventGrp != 0x00) {                      /* See if any tasks waiting on semaphore    */
            tasks_waiting = TRUE;                              /* Yes                                      */
        } else {
            tasks_waiting = FALSE;                             /* No                                       */
        }
        switch (opt) {
            // Delete semaphore only if no task waiting
            case OS_DEL_NO_PEND:                               /* Delete semaphore only if no task waiting */
                 if (tasks_waiting == FALSE) {
                     pevent->OSEventType = OS_EVENT_TYPE_UNUSED;//0
                     pevent->OSEventPtr  = OSEventFreeList;    /* Return Event Control Block to free list  */
                     OSEventFreeList     = pevent;             /* Get next free event control block        */
                     OS_EXIT_CRITICAL();
                     *err = OS_NO_ERR;
                    // Semaphore has been deleted  
                     return ((OS_EVENT *)0);                   /* Semaphore has been deleted               */
                 } else {
                     OS_EXIT_CRITICAL();
                     *err = OS_EpeventRR_TASK_WAITING;
                     return ();
                 }
            //Always delete the semaphore   无论如何都删除
            case OS_DEL_ALWAYS:                                /* Always delete the semaphore              */
                 while (pevent->OSEventGrp != 0x00) {          /* Ready ALL tasks waiting for semaphore    */
                     //若事件就绪不为0  说明有任务等待  --让任务就绪
                     OS_EventTaskRdy(pevent, (void *)0, OS_STAT_SEM);
                 }
                 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  */
                    //若任务是在等待的话
                     OS_Sched();                               /* Find highest priority task ready to run  */
                 }
                 *err = OS_NO_ERR;
                 return ((OS_EVENT *)0);                       /* Semaphore has been deleted               */

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

    /*$PAGE*/
    /*
    *********************************************************************************************************
    *                                           PEND ON SEMAPHORE
    *
    * Description: This function waits for a semaphore.
    *
    * Arguments  : pevent        is a pointer to the event control block associated with the desired
    *                            semaphore.
    *
    *              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
    *                            semaphore or, until the resource becomes available (or the event occurs).
    *
    *              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 resource
    *                                                or, the event you are waiting for occurred.
    *                            OS_TIMEOUT          The semaphore was not received within the specified
    *                                                timeout.
    *                            OS_ERR_EVENT_TYPE   If you didn't pass a pointer to a semaphore.
    *                            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    : none
    *********************************************************************************************************
    */
    //This function waits for a semaphore. timeout--表示等待时延0也就是说防止
    //得不到信号量而处于长期的等待状态,函数容许用时间延迟来设置一个时间限制---pevent表示被请求信号量的指针
    void  OSSemPend (OS_EVENT *pevent, INT16U timeout, INT8U *err)
    {
    #if OS_CRITICAL_METHOD == 3                           /* Allocate storage for CPU status register      */
        OS_CPU_SR  cpu_sr;
    #endif    

        //各种判断
        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
        if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */
            *err = OS_ERR_PEVENT_NULL;
            return;
        }
        if (pevent->OSEventType != OS_EVENT_TYPE_SEM) {   /* Validate event block type                     */
            *err = OS_ERR_EVENT_TYPE;
            return;
        }
    #endif
        OS_ENTER_CRITICAL();
        //成立  表示资源可用
        if (pevent->OSEventCnt > 0) {                     /* If sem. is positive, resource available ...   */
            //信号量计数器减一
            pevent->OSEventCnt--;                         /* ... decrement semaphore only if positive.     */
            OS_EXIT_CRITICAL();
            *err = OS_NO_ERR;
            return;
        }
        //否则
                                                          /* Otherwise, must wait until event occurs       */
        OSTCBCur->OSTCBStat |= OS_STAT_SEM;               /* Resource not available, pend on semaphore     */
        OSTCBCur->OSTCBDly   = timeout;                   /* Store pend timeout in TCB                     */
        OS_EventTaskWait(pevent);                         /* Suspend task until event or timeout occurs    */
        OS_EXIT_CRITICAL();
        OS_Sched();                                       /* Find next highest priority task ready         */
        
        OS_ENTER_CRITICAL();
        if (OSTCBCur->OSTCBStat & OS_STAT_SEM) {          /* Must have timed out if still waiting for event*/
            // to make a task ready to run because a timeout occurred.
            OS_EventTO(pevent);
            OS_EXIT_CRITICAL();
            *err = OS_TIMEOUT;                            /* Indicate that didn't get event within TO      */
            return;
        }
        OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
        OS_EXIT_CRITICAL();
        *err = OS_NO_ERR;
    }
    /*$PAGE*/
    /*
    *********************************************************************************************************
    *                                         POST TO A SEMAPHORE
    *
    * Description: This function signals a semaphore
    *
    * Arguments  : pevent        is a pointer to the event control block associated with the desired
    *                            semaphore.
    *
    * Returns    : OS_NO_ERR           The call was successful and the semaphore was signaled.
    *              OS_SEM_OVF          If the semaphore count exceeded its limit.  In other words, you have
    *                                  signalled the semaphore more often than you waited on it with either
    *                                  OSSemAccept() or OSSemPend().
    *              OS_ERR_EVENT_TYPE   If you didn't pass a pointer to a semaphore
    *              OS_ERR_PEVENT_NULL  If 'pevent' is a NULL pointer.
    *********************************************************************************************************
    */
    //发送信号量--也就是释放一个信号量
    INT8U  OSSemPost (OS_EVENT *pevent)
    {
    #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);
        }
        if (pevent->OSEventType != OS_EVENT_TYPE_SEM) {        /* Validate event block type                */
            return (OS_ERR_EVENT_TYPE);
        }
    #endif
        OS_ENTER_CRITICAL();
        //See if any task waiting for semaphore
        if (pevent->OSEventGrp != 0x00) {                      /* See if any task waiting for semaphore    */
            //Ready highest prio task waiting on event
            OS_EventTaskRdy(pevent, (void *)0, OS_STAT_SEM);   /* Ready highest prio task waiting on event */
            OS_EXIT_CRITICAL();
            //任务调度
            OS_Sched();                                        /* Find highest priority task ready to run  */
            return (OS_NO_ERR);
        }
        //Make sure semaphore will not overflow  
        if (pevent->OSEventCnt < 65535) {                 /* Make sure semaphore will not overflow         */
        //信号计数器加1
            pevent->OSEventCnt++;                         /* Increment semaphore count to register event   */
            OS_EXIT_CRITICAL();
            return (OS_NO_ERR);
        }
        OS_EXIT_CRITICAL();                               /* Semaphore value has reached its maximum       */
        return (OS_SEM_OVF);
    }
    /*$PAGE*/
    /*
    *********************************************************************************************************
    *                                          QUERY A SEMAPHORE
    *
    * Description: This function obtains information about a semaphore
    *
    * Arguments  : pevent        is a pointer to the event control block associated with the desired
    *                            semaphore
    *
    *              pdata         is a pointer to a structure that will contain information about the
    *                            semaphore.
    *
    * Returns    : OS_NO_ERR           The call was successful and the message was sent
    *              OS_ERR_EVENT_TYPE   If you are attempting to obtain data from a non semaphore.
    *              OS_ERR_PEVENT_NULL  If 'pevent' is a NULL pointer.
    *********************************************************************************************************
    */
    //This function obtains/获取 information about a semaphore  pdata存储信号量状态的结构OS_SEM_DATA---结构体指针
    #if OS_SEM_QUERY_EN > 0
    INT8U  OSSemQuery (OS_EVENT *pevent, OS_SEM_DATA *pdata)
    {
    #if OS_CRITICAL_METHOD == 3                                /* Allocate storage for CPU status register */
        OS_CPU_SR  cpu_sr;
    #endif    
        INT8U     *psrc;
        INT8U     *pdest;

    //判断
    #if OS_ARG_CHK_EN > 0
        if (pevent == (OS_EVENT *)0) {                         /* Validate 'pevent'                        */
            return (OS_ERR_PEVENT_NULL);
        }
        if (pevent->OSEventType != OS_EVENT_TYPE_SEM) {        /* Validate event block type                */
            return (OS_ERR_EVENT_TYPE);
        }
    #endif
        OS_ENTER_CRITICAL();
        pdata->OSEventGrp = pevent->OSEventGrp;                /* Copy message mailbox 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
        pdata->OSCnt      = pevent->OSEventCnt;                /* Get semaphore count                      */
        OS_EXIT_CRITICAL();
        return (OS_NO_ERR);
    }
    #endif                                                     /* OS_SEM_QUERY_EN                          */
    #endif                                                     /* OS_SEM_EN                                */

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  • 原文地址:https://www.cnblogs.com/wxb20/p/6230846.html
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