/*
*********************************************************************************************************
* 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
*********************************************************************************************************
*/
//无等待请求信号量--这函数function:当一个任务请求信号量时，如果希望在信
//量无效时准许任务不进入等待状态而继续运行，则不调用函数OSSPend 而是调用本函数OSSemAccept
#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;
//See if resource is available
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
/*$PAGE*/
/*
*********************************************************************************************************
* CREATE A SEMAPHORE
*
* Description: This function creates a semaphore.
*
* Arguments : cnt is the initial value for the semaphore. If the value is 0, no resource is
* available (or no event has occurred). You initialize the semaphore to a
* non-zero value to specify how many resources are available (e.g. if you have
* 10 resources, you would initialize the semaphore to 10).
*
* Returns : != (void *)0 is a pointer to the event control clock (OS_EVENT) associated with the
* created semaphore
* == (void *)0 if no event control blocks were available
*********************************************************************************************************
*/
//This function creates a semaphore.
OS_EVENT *OSSemCreate (INT16U cnt)
{
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr;
#endif
OS_EVENT *pevent;
if (OSIntNesting > 0) { /* See if called from ISR ... */
return ((OS_EVENT *)0); /* ... can't CREATE from an ISR */
}
OS_ENTER_CRITICAL();
/* Get next free event control block */
pevent = OSEventFreeList; /* Get next free event control block */
if (OSEventFreeList != (OS_EVENT *)0) { /* See if pool of free ECB pool was empty */
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
}
OS_EXIT_CRITICAL();
if (pevent != (OS_EVENT *)0) { /* Get an event control block */
pevent->OSEventType = OS_EVENT_TYPE_SEM; //OS_EVENT_TYPE_SEM信号量类型
pevent->OSEventCnt = cnt; /* Set semaphore value */
pevent->OSEventPtr = (void *)0; /* Unlink from ECB free list */
//初始化一个信号量 Initialize to 'nobody waiting' on sem.
OS_EventWaitListInit(pevent); /* Initialize to 'nobody waiting' on sem. */
}
return (pevent);
}
/*$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.
*********************************************************************************************************
*/
//This function deletes a semaphore and readies all tasks pending on the semaphore opt指明信号量的删除条件
#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;
//各种判断
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();
//See if any tasks waiting on semaphore
if (pevent->OSEventGrp != 0x00) { /* See if any tasks waiting on semaphore */
tasks_waiting = TRUE; /* Yes */
} else {
tasks_waiting = FALSE; /* No */
}
switch (opt) {
// Delete semaphore only if no task waiting
case OS_DEL_NO_PEND: /* Delete semaphore only if no task waiting */
if (tasks_waiting == FALSE) {
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;//0
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;
// Semaphore has been deleted
return ((OS_EVENT *)0); /* Semaphore has been deleted */
} else {
OS_EXIT_CRITICAL();
*err = OS_EpeventRR_TASK_WAITING;
return ();
}
//Always delete the semaphore 无论如何都删除
case OS_DEL_ALWAYS: /* Always delete the semaphore */
while (pevent->OSEventGrp != 0x00) { /* Ready ALL tasks waiting for semaphore */
//若事件就绪不为0 说明有任务等待 --让任务就绪
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 */
//若任务是在等待的话
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);
}
}
#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
*********************************************************************************************************
*/
//This function waits for a semaphore. timeout--表示等待时延0也就是说防止
//得不到信号量而处于长期的等待状态，函数容许用时间延迟来设置一个时间限制---pevent表示被请求信号量的指针
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
//各种判断
if (OSIntNesting > 0) { /* See if called from ISR ... */
*err = OS_ERR_PEND_ISR; /* ... can't PEND from an ISR */
return;
}
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*err = OS_ERR_PEVENT_NULL;
return;
}
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
*err = OS_ERR_EVENT_TYPE;
return;
}
#endif
OS_ENTER_CRITICAL();
//成立 表示资源可用
if (pevent->OSEventCnt > 0) { /* If sem. is positive, resource available ... */
//信号量计数器减一
pevent->OSEventCnt--; /* ... decrement semaphore only if positive. */
OS_EXIT_CRITICAL();
*err = OS_NO_ERR;
return;
}
//否则
/* 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 */
OS_EventTaskWait(pevent); /* Suspend task until event or timeout occurs */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next highest priority task ready */
OS_ENTER_CRITICAL();
if (OSTCBCur->OSTCBStat & OS_STAT_SEM) { /* Must have timed out if still waiting for event*/
// to make a task ready to run because a timeout occurred.
OS_EventTO(pevent);
OS_EXIT_CRITICAL();
*err = OS_TIMEOUT; /* Indicate that didn't get event within TO */
return;
}
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0;
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.
*********************************************************************************************************
*/
//发送信号量--也就是释放一个信号量
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);
}
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
#endif
OS_ENTER_CRITICAL();
//See if any task waiting for semaphore
if (pevent->OSEventGrp != 0x00) { /* See if any task waiting for semaphore */
//Ready highest prio task waiting on event
OS_EventTaskRdy(pevent, (void *)0, OS_STAT_SEM); /* Ready highest prio task waiting on event */
OS_EXIT_CRITICAL();
//任务调度
OS_Sched(); /* Find highest priority task ready to run */
return (OS_NO_ERR);
}
//Make sure semaphore will not overflow
if (pevent->OSEventCnt < 65535) { /* Make sure semaphore will not overflow */
//信号计数器加1
pevent->OSEventCnt++; /* Increment semaphore count to register event */
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
}
OS_EXIT_CRITICAL(); /* Semaphore value has reached its maximum */
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.
*********************************************************************************************************
*/
//This function obtains/获取 information about a semaphore pdata存储信号量状态的结构OS_SEM_DATA---结构体指针
#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;
//判断
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (pevent->OSEventType != OS_EVENT_TYPE_SEM) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
#endif
OS_ENTER_CRITICAL();
pdata->OSEventGrp = pevent->OSEventGrp; /* Copy message mailbox wait list */
psrc = &pevent->OSEventTbl[0];
pdest = &pdata->OSEventTbl[0];
#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 */
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
}
#endif /* OS_SEM_QUERY_EN */
#endif /* OS_SEM_EN */