os_sem.c

完整的ucos实例

/* 
********************************************************************************************************* 
*                                                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 
********************************************************************************************************* 
*/ 
 
#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; 
    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 
********************************************************************************************************* 
*/ 
 
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(); 
    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; 
        pevent->OSEventCnt  = cnt;                         /* Set semaphore value                      */ 
        pevent->OSEventPtr  = (void *)0;                   /* Unlink from ECB free list                */ 
        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. 
********************************************************************************************************* 
*/ 
 
#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; 
 
 
    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(); 
    if (pevent->OSEventGrp != 0x00) {                      /* See if any tasks waiting on semaphore    */ 
        tasks_waiting = TRUE;                              /* Yes                                      */ 
    } else { 
        tasks_waiting = FALSE;                             /* No                                       */ 
    } 
    switch (opt) { 
        case OS_DEL_NO_PEND:                               /* Delete semaphore only if no task waiting */ 
             if (tasks_waiting == FALSE) { 
                 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(); 
                 *err = OS_NO_ERR; 
                 return ((OS_EVENT *)0);                   /* Semaphore has been deleted               */ 
             } else { 
                 OS_EXIT_CRITICAL(); 
                 *err = OS_ERR_TASK_WAITING; 
                 return (pevent); 
             } 
 
        case OS_DEL_ALWAYS:                                /* Always delete the semaphore              */ 
             while (pevent->OSEventGrp != 0x00) {          /* Ready ALL tasks waiting for semaphore    */ 
                 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  */ 
                 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);