/*
*********************************************************************************************************
* 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接受信号量
*
* 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
建立一个信号量
描述：建立一个信号量
参数：cnt：信号量的初始化值，如果为零，则没有信号量可用（或者没有事件发生）
用非零值初始化信号量则显示它有多少可用资源，如果你有十个
资源，则初始化信号量为10
返回：!= (void *)0 指向事件控制块结合建立的信号量的指针
* == (void *)0 如果没有可用事件控制块
*********************************************************************************************************
*/
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 */
}//中断服务子程序不能调用此函数，所有建立信号弹量的工作必须在任务级
//代码中或者多任务启动前完成
OS_ENTER_CRITICAL();
pevent = OSEventFreeList; /* Get next free event control block */
//从空余事件控制块链表中获得一个事件控制块ECB
if (OSEventFreeList != (OS_EVENT *)0) { /* See if pool of free ECB pool was empty */
//如果成功获得，则调整空余事件控制块链表。使之指向下一个空余的事件控制块
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
}
OS_EXIT_CRITICAL();
if (pevent != (OS_EVENT *)0) { /* Get an event control block */
//如果得到的事件控制块可用，就将其的事件类型设置成信号量，
pevent->OSEventType = OS_EVENT_TYPE_SEM;
pevent->OSEventCnt = cnt; /* Set semaphore value */
//将信号量的初始值存入事件控制块ECB中。
pevent->OSEventPtr = (void *)0; /* Unlink from ECB free list */
//将.OSEventPtr初始化为NULL，因为它不于属于空余事件控制块链表了。
OS_EventWaitListInit(pevent); /* Initialize to 'nobody waiting' on sem. */
//对等待任务列表进行初始化，因为信号量正在初始化，这时没有任何
//任务等待该信号量，所以函数将.OSEventGrp()和.OSEventTbl[]清零
}
return (pevent);//返回调用函数一个指向事件控制块ECB的指针
}
/*$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.
删除一个信号量
描述：删除一个信号量
参数：pevent：指向事件控制块结合目标信号量的指针
opt:决定删除选项：
* opt == OS_DEL_NO_PEND 没有任务挂起的时候才删除。
* opt == OS_DEL_ALWAYS 即使有任务等待也删除信号量，这种情况下，
所有挂起的任务将就绪
* err 可能包含指下信息的错误代码的指针
* OS_NO_ERR 调用成功，信号量删除
* OS_ERR_DEL_ISR 如果想从中断服务子程序中删除信号量
* OS_ERR_INVALID_OPT 指定了不合理的选项
* OS_ERR_TASK_WAITING 一个或者多个任务在信号量中等待
* OS_ERR_EVENT_TYPE 没有传递指针到信号量
* OS_ERR_PEVENT_NULL 如果 'pevent'是一个空指针************
备注：删除信号量之前，必须首先删除操作该信号量的所有任务
*/
#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);
}//是不是在ISR中调用
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*err = OS_ERR_PEVENT_NULL;
return (pevent);//非法的pevent
}
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
*err = OS_ERR_EVENT_TYPE;
return (pevent);//不是事件块类型
}
#endif
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0x00) { /* See if any tasks waiting on semaphore */
//如果有任务在等待
tasks_waiting = TRUE; /* Yes */
} else {
tasks_waiting = FALSE; /* No */
}
switch (opt) {//删除选项
case OS_DEL_NO_PEND: /* Delete semaphore only if no task waiting */
//如果只有没有任务等待的时候才删除
if (tasks_waiting == FALSE) {//真没有任务等待
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;//将事件控制块标记为未用，并退回到
//空余ECB中，此操作允许该事件控制块用于建立另一信号量
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
//原空闲表头变成老二了。
OSEventFreeList = pevent; /* Get next free event control block */
//pevent指向新的空闲表头
OS_EXIT_CRITICAL();
*err = OS_NO_ERR;//返回无错
return ((OS_EVENT *)0); /* Semaphore has been deleted */
} else {//如果有任务等待
OS_EXIT_CRITICAL();
*err = OS_ERR_TASK_WAITING;
return (pevent);
}
case OS_DEL_ALWAYS: /* Always delete the semaphore */
//无论如何都要删除
while (pevent->OSEventGrp != 0x00) { /* Ready ALL tasks waiting for semaphore */
OS_EventTaskRdy(pevent, (void *)0, OS_STAT_SEM);
}//使所有等待的任务就绪
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;//标记为未用
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
//原空闲表头变成老二了。
OSEventFreeList = pevent; /* Get next free event control block */
//pevent指向新的空闲表头
OS_EXIT_CRITICAL();
if (tasks_waiting == TRUE) { /* Reschedule only if task(s) were waiting */
OS_Sched(); /* Find highest priority task ready to run */
//有任务等待的话，因为有任务就绪，所以要任务调度
}
*err = OS_NO_ERR;
return ((OS_EVENT *)0); /* Semaphore has been deleted */
default://其它非法选项
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
等待一个信号量
描述：等待一个信号量
参数：pevent：指向事件控制块结合目标信号量的指针
timeout：定时超时选项（以时钟节拍为单位），如果非零，你的任务将等待
//资源的时间值就是这个参数，如果为零，将永远等待直到资源变成可用（或者其它事件发生）
err 指向错误代码的消息指针
* 消息为：
*
* OS_NO_ERR 调用成功，任务拥有资源或者目标事件发生
* OS_TIMEOUT 规定时间内信号量没有发生
* OS_ERR_EVENT_TYPE 如果没有传递指针到信号量
* OS_ERR_PEND_ISR 如果ISR调用此函数，结果将异常
* OS_ERR_PEVENT_NULL 如果 'pevent' 是一个空指针
*********************************************************************************************************
*/
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
if (OSIntNesting > 0) { /* See if called from ISR ... */
*err = OS_ERR_PEND_ISR; /* ... can't PEND from an ISR */
return;
}//是不是在ISR中调用
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*err = OS_ERR_PEVENT_NULL;
return;
}//非法的pevent
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
*err = OS_ERR_EVENT_TYPE;
return;
}//不是事件块类型
#endif
OS_ENTER_CRITICAL();
if (pevent->OSEventCnt > 0) { /* If sem. is positive, resource available ... */
pevent->OSEventCnt--; /* ... decrement semaphore only if positive. */
OS_EXIT_CRITICAL();
*err = OS_NO_ERR;
return;
}
//如果信号量有效，则信号量计数值递减，返回无错给调用它的函数，如果此
//函数用于等待一共享资源的信号量，那么通过返回此值，知道代码是否正确运行。
//如果信号量的计数值为0，则调用此函数的任务将进入睡眠状态，等待另一个任务
//或者ISR发出信号量。
/* Otherwise, must wait until event occurs */
OSTCBCur->OSTCBStat |= OS_STAT_SEM; /* Resource not available, pend on semaphore */
//资源不可用，挂起任务
OSTCBCur->OSTCBDly = timeout; /* Store pend timeout in TCB */
//保存挂起定时到TCB
OS_EventTaskWait(pevent); /* Suspend task until event or timeout occurs */
//使任务等待事件发生（将任务挂起）
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next highest priority task ready */
//由于得不到信号量，当前任务不再处于就绪状态，任务调度，让下一个
//优先级最高的任务运行。这样，调用此函数的任务被挂起，直到信号量出现，
//才能继续运行。
OS_ENTER_CRITICAL();
if (OSTCBCur->OSTCBStat & OS_STAT_SEM) { /* Must have timed out if still waiting for event*/
//再次检查任务控制块中的状态标志，是否仍处于等待信号量的状态，如果是，
//则说明该任务并没有被此函数发出的信号量唤醒；而实际上该任务是因为等待
//超时，而被TimeTick()函数置为就绪态。
OS_EventTO(pevent);//等待事件超时，将任务从等待列表中删除，让任务继续运行。
OS_EXIT_CRITICAL();
*err = OS_TIMEOUT; /* Indicate that didn't get event within TO *///返回超时错误代码
return;//超时了
}
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;//将指向信号量ECB的指针从该任务的任务控制块中删除
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.
发出一个信号量
描述：发出一个信号量
参数：pevent ：指向事件控制块结合目标信号量的指针
返回：OS_NO_ERR 调用成功，信号量发出
* OS_SEM_OVF 信号量数目超出范围. 也就是说你发送的信号量多于在either
* OSSemAccept() or OSSemPend()中等待的
* OS_ERR_EVENT_TYPE 没有传递指针给信号量
* OS_ERR_PEVENT_NULL 如果 'pevent' 是空指针
*********************************************************************************************************
*/
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);
}//非法的pevent
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}//不是事件块类型
#endif
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0x00) { /* See if any task waiting for semaphore */
//是不是有任务等待
OS_EventTaskRdy(pevent, (void *)0, OS_STAT_SEM); /* Ready highest prio task waiting on event */
//就绪最高优先级的等待任务
OS_EXIT_CRITICAL();
OS_Sched(); /* Find highest priority task ready to run *///任务调度，找最高优先级的任务运行
return (OS_NO_ERR);
}
if (pevent->OSEventCnt < 65535) { /* Make sure semaphore will not overflow */
//保证信号量没有溢出
pevent->OSEventCnt++; /* Increment semaphore count to register event */
//更新信号量数目
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
}
OS_EXIT_CRITICAL(); /* Semaphore value has reached its maximum *///信号量满了。
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.
查询一个信号量的当前状态
描述：获得一个信号量的信息
参数：pevent：指向事件控制块结合目标信号量的指针
pdata：指向包含信号量信息的结构指针
返回：OS_NO_ERR 调用成功，消息发送
* OS_ERR_EVENT_TYPE 如果想从非信号量获得数据
* OS_ERR_PEVENT_NULL 如果 'pevent' 是空指针
*********************************************************************************************************
*/
#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;
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}//非法的pevent
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}//不是事件块类型
#endif
OS_ENTER_CRITICAL();
pdata->OSEventGrp = pevent->OSEventGrp; /* Copy message mailbox wait list */
//将OS_EVENT结构中的等待任务列表复制到OS_SEM_DATA数据结构中，
//此处使用条件编译不不用循环语句，目的是使程序运行得更愉
psrc = &pevent->OSEventTbl[0];
pdest = &pdata->OSEventTbl[0];//指向表头
#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 */
//获得信号量数。
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
}
#endif /* OS_SEM_QUERY_EN */
#endif /* OS_SEM_EN */
