OS_SEM.rar_sem.c

/* ********************************************************************************************************* * 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 */ retu