//BY 简单的元清
//部分内容引用了其他博主的文章，对这些博主表示感谢，时间关系就不一一指出了。
//如有转载，请说明，谢谢
/*
*********************************************************************************************************
* uC/OS-II
* The Real-Time Kernel
* SEMAPHORE MANAGEMENT
*
* (c) Copyright 1992-1998, Jean J. Labrosse, Plantation, FL
* All Rights Reserved
*
* V2.00
*
* File : OS_SEM.C
* By : Jean J. Labrosse
*********************************************************************************************************
*/
#ifndef OS_MASTER_FILE
#include "software\includes.h"
#endif
#if OS_SEM_EN
/*
*********************************************************************************************************
* 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,
* you didn't pass a pointer to a semaphore
*********************************************************************************************************
*/
#if OS_SEM_ACCEPT_EN > 0
//无等待地请求一个信号量
INT16U OSSemAccept (OS_EVENT *pevent) reentrant
{
INT16U cnt;
OS_ENTER_CRITICAL();
//进入临界区
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
OS_EXIT_CRITICAL();
return (0);
//如果类型不是信号量，退出临界区返回错误码
}
cnt = pevent->OSEventCnt;
//读取信号量
if (cnt > 0) { /* See if resource is available */
pevent->OSEventCnt--; /* Yes, decrement semaphore and notify caller */
//如果信号量不是0，计数器减一
}
OS_EXIT_CRITICAL();
//退出临界区
return (cnt);
//返回信号量
// /* Return semaphore count */
}
#endif
/*$PAGE*/
/*
*********************************************************************************************************
* CREATE A SEMAPHORE
*
* Description: This function creates a semaphore.
*
* Arguments : cnt is the initial value for the semaphore. If the value is 0, no resource is
* available (or no event has occurred). You initialize the semaphore to a
* non-zero value to specify how many resources are available (e.g. if you have
* 10 resources, you would initialize the semaphore to 10).
*
* Returns : != (void *)0 is a pointer to the event control clock (OS_EVENT) associated with the
* created semaphore
* == (void *)0 if no event control blocks were available
*********************************************************************************************************
*/
//创建一个信号量
OS_EVENT *OSSemCreate (INT16U cnt) reentrant
{
OS_EVENT *pevent;
OS_ENTER_CRITICAL();
//进入临界区
pevent = OSEventFreeList; /* Get next free event control block */
//从空的列表中取出一块
if (OSEventFreeList != (OS_EVENT *)0) { /* See if pool of free ECB pool was empty */
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
//判断ECB块是不是空
}
OS_EXIT_CRITICAL();
//退出临界区
if (pevent != (OS_EVENT *)0) { /* Get an event control block */
pevent->OSEventType = OS_EVENT_TYPE_SEM;
pevent->OSEventCnt = cnt;
//如果有事件发生，把类型设置为SEM，赋值 /* Set semaphore value */
OSEventWaitListInit(pevent);
//添加进等待列表
}
return (pevent);
}
/*$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.
*
* Returns : none
*********************************************************************************************************
*/
//等待一个信号量
void OSSemPend (OS_EVENT *pevent, INT16U timeout, INT8U *err) reentrant
{
OS_ENTER_CRITICAL();
//进入临界区
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
OS_EXIT_CRITICAL();
*err = OS_ERR_EVENT_TYPE;
//如果事件的类型不是信号量，退出临界区然后返回错误码
}
if (pevent->OSEventCnt > 0) { /* If sem. is positive, resource available ... */
//如果有信号发生
pevent->OSEventCnt--; /* ... decrement semaphore only if positive. */
//数目减一
OS_EXIT_CRITICAL();
//退出临界区
*err = OS_NO_ERR;
//返回错误码
} else if (OSIntNesting > 0) { /* See if called from ISR ... */
//如果有中断发生
OS_EXIT_CRITICAL(); /* ... can't PEND from an ISR */
//退出临界区
*err = OS_ERR_PEND_ISR;
//返回错误码
} else { /* 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 */
OSEventTaskWait(pevent); /* Suspend task until event or timeout occurs */
//赋值信号量参数给给OSTCBCur并加入等待列表
OS_EXIT_CRITICAL();
//退出临界区
OSSched(); /* Find next highest priority task ready */
//退出临界区
OS_ENTER_CRITICAL();
//进入临界区
if (OSTCBCur->OSTCBStat & OS_STAT_SEM) { /* Must have timed out if still waiting for event*/
//如果超时并存在等待任务
OSEventTO(pevent);
//直接运行不再等待
OS_EXIT_CRITICAL();
//退出临界区
*err = OS_TIMEOUT; /* Indicate that didn't get event within TO */
//返回错误码
} else {
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
//OSTCBCur->OSTCBEventPtr指向空指针
OS_EXIT_CRITICAL();
*err = OS_NO_ERR;
//退出临界区然后返回错误码
}
}
}
/*$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
*********************************************************************************************************
*/
//发送信号量
INT8U OSSemPost (OS_EVENT *pevent) reentrant
{
OS_ENTER_CRITICAL();
//进入临界区
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
OS_EXIT_CRITICAL();
return (OS_ERR_EVENT_TYPE);
//如果事件的类型不是信号量，退出临界区然后返回错误码
}
if (pevent->OSEventGrp) { /* See if any task waiting for semaphore */
//如果有事件发生
OSEventTaskRdy(pevent, (void *)0, OS_STAT_SEM); /* Ready highest prio task waiting on event */
//把任务就绪
OS_EXIT_CRITICAL();
//退出临界区
OSSched(); /* Find highest priority task ready to run */
//进行调度
return (OS_NO_ERR);
//返回错误码
} else {
if (pevent->OSEventCnt < 65535) { /* Make sure semaphore will not overflow */
pevent->OSEventCnt++; /* Increment semaphore count to register event */
//如果信号量满足小于65535，pevent->OSEventCnt加加
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
//退出临界区然后返回错误码
} else { /* Semaphore value has reached its maximum */
OS_EXIT_CRITICAL();
//退出临界区
return (OS_SEM_OVF);
}
}
}
/*
*********************************************************************************************************
* 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.
*********************************************************************************************************
*/
#if OS_SEM_QUERY_EN > 0
INT8U OSSemQuery (OS_EVENT *pevent, OS_SEM_DATA *ppdata) reentrant
{
INT8U i;
INT8U *psrc;
INT8U *pdest;
OS_ENTER_CRITICAL();
//进入临界区
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
OS_EXIT_CRITICAL();
return (OS_ERR_EVENT_TYPE);
//如果事件的类型不是信号量，退出临界区然后返回错误码
}
ppdata->OSEventGrp = pevent->OSEventGrp; /* Copy message mailbox wait list */
psrc = &pevent->OSEventTbl[0];
pdest = &ppdata->OSEventTbl[0];
for (i = 0; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++;
}
ppdata->OSCnt = pevent->OSEventCnt; /* Get semaphore count */
//复制信号量的参数给ppdata
OS_EXIT_CRITICAL();
//退出临界区
return (OS_NO_ERR);
//返回错误码
}
#endif
//*************************
#endif
逐字逐句解析ucos ii 源代码-》OS_SEM.C
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