Chapter 5 - 事件控制块
Created by : Mr Dk.
2019 / 11 / 19 22:34
Nanjing, Jiangsu, China
5.1 基本概念
事件通信方法的实现方式 - 事件控制块 (Event Control Blocks, ECB)。任务或中断服务子程序可以通过 ECB 向别的任务发送信号：
- 信号量
- 互斥信号量
- 消息邮箱
- 消息队列
- 事件标志组
ECB 是各种事件的基础性数据结构，是这些信号的 metadata：
typedef struct os_event {
INT8U OSEventType; /* Type of event control block (see OS_EVENT_TYPE_xxxx) */
void *OSEventPtr; /* Pointer to message or queue structure */
INT16U OSEventCnt; /* Semaphore Count (not used if other EVENT type) */
OS_PRIO OSEventGrp; /* Group corresponding to tasks waiting for event to occur */
OS_PRIO OSEventTbl[OS_EVENT_TBL_SIZE]; /* List of tasks waiting for event to occur */
#if OS_EVENT_NAME_EN > 0u
INT8U *OSEventName;
#endif
} OS_EVENT;
#endif
OSEventType指明事件的类型OS_EVENT_SEM：信号量OS_EVENT_MUTEX：互斥信号量OS_EVENT_TYPE_MBOX：邮箱OS_EVENT_TYPE_Q：消息队列
OSEventPtr指向对应的邮箱或队列OSEventCnt指明事件是信号量时的个数OSEventGrp和OSEventTbl指明所有等待该事件的任务- 与就绪表的实现方式一致
5.2 将任务置于等待事件的任务列表中
与就绪表中的操作类似
OSEventGrp的每一位代表 8 个任务OSEventTbl指明了 64 个任务哪个处在等待状态
用于快速获得优先级最高的等待任务。
pevent->OSEventGrp |= OSMapTbl[prio >> 3];
pevent->OSEventTbl[prio >> 3] |= OSMapTbl[prio & 0x07];
5.3 从等待事件的任务列表中删除任务
if ((pevent->OSEventTbl[prio >> 3] &= ~OSMapTbl[prio & 0x07]) == 0) {
pevent->OSEventGrp &= ~OSMapTbl[prio >> 3];
}
5.4 在等待事件的任务列表中查找优先级最高的任务
y = OSUnMapTbl[pevent->OSEventGrp];
x = OSUnMapTbl[pevent->OSEventTbl[y]];
prio = (y << 3) + x;
5.5 空闲事件控制块链表
在调用 OSInit() 时，所有的 ECB 被串成一个空闲链表。OSEventFreeList 指针总指向第一个空闲 ECB。建立事件时，就从链表中取下一个空闲 ECB 并进行初始化；删除事件后，ECB 被放回空闲链表中。空闲 ECB 的总数在编译前定义。
5.6 初始化一个 ECB - OS_EventWaitListInit() 函数
当建立任意一种事件时，对应的建立函数都要调该函数，对 ECB 中的等待任务列表进行初始化。
/*
*********************************************************************************************************
* INITIALIZE EVENT CONTROL BLOCK'S WAIT LIST
*
* Description: This function is called by other uC/OS-II services to initialize the event wait list.
*
* Arguments : pevent is a pointer to the event control block allocated to the event.
*
* Returns : none
*
* Note : This function is INTERNAL to uC/OS-II and your application should not call it.
*********************************************************************************************************
*/
#if (OS_EVENT_EN)
void OS_EventWaitListInit (OS_EVENT *pevent)
{
INT8U i;
pevent->OSEventGrp = 0u; /* No task waiting on event */
for (i = 0u; i < OS_EVENT_TBL_SIZE; i++) {
pevent->OSEventTbl[i] = 0u;
}
}
#endif
为避免 for 循环而增加开销，这部分代码也可以由条件编译实现 😂（之后还会有很多这样的方法）。
5.7 使一个任务脱离等待进入就绪 - OS_EventTaskRdy() 函数
事件发生后，等待任务列表中，优先级最高的任务得到这个事件，从而脱离等待进入就绪状态。
原理：
- 从等待任务列表中查找优先级最高的任务，从中清除
- 将 TCB 中的延时变量清零 (等待事件可以设定超时时间)
- 将 TCB 中指向 ECB 的指针置
NULL(任务不再等待该事件发生) - 可能还要将事件中的消息放到 TCB 中 (比如邮箱)
- 用位掩码将 TCB 中的
OSTCBStat位清零 - 判断最高优先级任务的挂起条件
- 如果是因为等待该事件而挂起，则插入就绪表
- (任务可能还因为其它条件挂起，因此也不一定进入就绪状态)
/*
*********************************************************************************************************
* MAKE TASK READY TO RUN BASED ON EVENT OCCURING
*
* Description: This function is called by other uC/OS-II services and is used to ready a task that was
* waiting for an event to occur.
*
* Arguments : pevent is a pointer to the event control block corresponding to the event.
*
* pmsg is a pointer to a message. This pointer is used by message oriented services
* such as MAILBOXEs and QUEUEs. The pointer is not used when called by other
* service functions.
*
* msk is a mask that is used to clear the status byte of the TCB. For example,
* OSSemPost() will pass OS_STAT_SEM, OSMboxPost() will pass OS_STAT_MBOX etc.
*
* pend_stat is used to indicate the readied task's pending status:
*
* OS_STAT_PEND_OK Task ready due to a post (or delete), not a timeout or
* an abort.
* OS_STAT_PEND_ABORT Task ready due to an abort.
*
* Returns : none
*
* Note : This function is INTERNAL to uC/OS-II and your application should not call it.
*********************************************************************************************************
*/
#if (OS_EVENT_EN)
INT8U OS_EventTaskRdy (OS_EVENT *pevent,
void *pmsg,
INT8U msk,
INT8U pend_stat)
{
OS_TCB *ptcb;
INT8U y;
INT8U x;
INT8U prio;
#if OS_LOWEST_PRIO > 63u
OS_PRIO *ptbl;
#endif
#if OS_LOWEST_PRIO <= 63u
y = OSUnMapTbl[pevent->OSEventGrp]; /* Find HPT waiting for message */
x = OSUnMapTbl[pevent->OSEventTbl[y]];
prio = (INT8U)((y << 3u) + x); /* Find priority of task getting the msg */
#else
if ((pevent->OSEventGrp & 0xFFu) != 0u) { /* Find HPT waiting for message */
y = OSUnMapTbl[ pevent->OSEventGrp & 0xFFu];
} else {
y = OSUnMapTbl[(OS_PRIO)(pevent->OSEventGrp >> 8u) & 0xFFu] + 8u;
}
ptbl = &pevent->OSEventTbl[y];
if ((*ptbl & 0xFFu) != 0u) {
x = OSUnMapTbl[*ptbl & 0xFFu];
} else {
x = OSUnMapTbl[(OS_PRIO)(*ptbl >> 8u) & 0xFFu] + 8u;
}
prio = (INT8U)((y << 4u) + x); /* Find priority of task getting the msg */
#endif
ptcb = OSTCBPrioTbl[prio]; /* Point to this task's OS_TCB */
ptcb->OSTCBDly = 0u; /* Prevent OSTimeTick() from readying task */
#if ((OS_Q_EN > 0u) && (OS_MAX_QS > 0u)) || (OS_MBOX_EN > 0u)
ptcb->OSTCBMsg = pmsg; /* Send message directly to waiting task */
#else
pmsg = pmsg; /* Prevent compiler warning if not used */
#endif
ptcb->OSTCBStat &= (INT8U)~msk; /* Clear bit associated with event type */
ptcb->OSTCBStatPend = pend_stat; /* Set pend status of post or abort */
/* See if task is ready (could be susp'd) */
if ((ptcb->OSTCBStat & OS_STAT_SUSPEND) == OS_STAT_RDY) {
OSRdyGrp |= ptcb->OSTCBBitY; /* Put task in the ready to run list */
OSRdyTbl[y] |= ptcb->OSTCBBitX;
}
OS_EventTaskRemove(ptcb, pevent); /* Remove this task from event wait list */
#if (OS_EVENT_MULTI_EN > 0u)
if (ptcb->OSTCBEventMultiPtr != (OS_EVENT **)0) { /* Remove this task from events' wait lists */
OS_EventTaskRemoveMulti(ptcb, ptcb->OSTCBEventMultiPtr);
ptcb->OSTCBEventPtr = (OS_EVENT *)pevent;/* Return event as first multi-pend event ready*/
}
#endif
return (prio);
}
#endif
5.8 使一个任务进入等待事件发生状态 - OS_EventTaskWait() 函数
某个任务要等待某个事件发生时被调用
- 将任务从就绪表中删除
- 放到对应 ECB 的等待任务列表中
/*
*********************************************************************************************************
* MAKE TASK WAIT FOR EVENT TO OCCUR
*
* Description: This function is called by other uC/OS-II services to suspend a task because an event has
* not occurred.
*
* Arguments : pevent is a pointer to the event control block for which the task will be waiting for.
*
* Returns : none
*
* Note : This function is INTERNAL to uC/OS-II and your application should not call it.
*********************************************************************************************************
*/
#if (OS_EVENT_EN)
void OS_EventTaskWait (OS_EVENT *pevent)
{
INT8U y;
OSTCBCur->OSTCBEventPtr = pevent; /* Store ptr to ECB in TCB */
pevent->OSEventTbl[OSTCBCur->OSTCBY] |= OSTCBCur->OSTCBBitX; /* Put task in waiting list */
pevent->OSEventGrp |= OSTCBCur->OSTCBBitY;
y = OSTCBCur->OSTCBY; /* Task no longer ready */
OSRdyTbl[y] &= (OS_PRIO)~OSTCBCur->OSTCBBitX;
if (OSRdyTbl[y] == 0u) { /* Clear event grp bit if this was only task pending */
OSRdyGrp &= (OS_PRIO)~OSTCBCur->OSTCBBitY;
}
}
#endif
5.9 由于等待超时而将任务置为就绪态 - OS_EventTO() 函数
在预先设定的时间内，事件没有发生，任务的状态会被重新设置为就绪。
- 将任务从等待列表中删除
- 将任务设置为就绪状态
- 从 TCB 中删除指向 ECB 的指针
/* no source code ??? */
#if OS_EVENT_EN > 0
void OS_EventTO (OS_EVENT *pevent) reentrant
{
if((pevent->OSEventTbl[OSTCBCur->OSTCBY] &= ~OSTCBCur->OSTCBBitX) == 0) {
pevent->OSEventGrp &= ~OSTCBCur->OSTCBBitY;
}
OSTCBCur->OSTCBStat = OS_STAT_RDY;
OSTCBCur->OSTCBEventPtr = (OS_EVENT *) 0;
}
#endif
Summary
这一章中的函数会被接下来几章中不同事件的具体实现所调用。