create-mutex.txt

ucos-ii中互斥信号mutex建立源码

*                                  CREATE A MUTUAL EXCLUSION SEMAPHORE
*
* Description: This function creates a mutual exclusion 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.
*

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

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;


    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);                            
    }
    OSTCBPrioTbl[prio] = (OS_TCB *)1;                      /* Reserve the table entry                  */
    pevent             = OSEventFreeList;                  /* Get next free event control block        */
    if (pevent == (OS_EVENT *)0) {                         /* See if an ECB was available              */
        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);
    }
    OSEventFreeList     = (OS_EVENT *)OSEventFreeList->OSEventPtr;   /* Adjust the free list           */
    OS_EXIT_CRITICAL();
    pevent->OSEventType = OS_EVENT_TYPE_MUTEX;
    pevent->OSEventCnt  = (prio << 8) | OS_MUTEX_AVAILABLE;/* Resource is available                    */
    pevent->OSEventPtr  = (void *)0;                       /* No task owning the mutex                 */
    OS_EventWaitListInit(pevent);
    *err                = OS_NO_ERR;
    return (pevent);
}