一、向消息队列发送一则消息（FIFO OSQPost()）
/*
*********************************************************************************************************
* POST MESSAGE TO A QUEUE
*
* Description: This function sends a message to a queue
*
* Arguments : pevent is a pointer to the event control block associated with the desired queue
*
* pmsg is a pointer to the message to send.
*
* Returns : OS_ERR_NONE The call was successful and the message was sent
* OS_ERR_Q_FULL If the queue cannot accept any more messages because it is full.
* OS_ERR_EVENT_TYPE If you didn't pass a pointer to a queue.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
*
* Note(s) : As of V2.60, this function allows you to send NULL pointer messages.
*********************************************************************************************************
*/
#if OS_Q_POST_EN > 0
INT8U OSQPost (OS_EVENT *pevent, void *pmsg) /* 实际上是：进行消息入队操作 */
{
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
#if OS_ARG_CHK_EN > 0
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' 空指针？ */
return (OS_ERR_PEVENT_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type 发送的消息为空指针？ */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0) { /* See if any task pending on queue 是否有任务在等待该队列中的消息？ */
/* Ready highest priority task waiting on event */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_Q, OS_STAT_PEND_OK);
/* 从等待列表中取出最高优先级的任务，并将它置于就绪态 */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find highest priority task ready to run
任务调度，若上面进入就绪态的任务是就绪态任务中优先级最高的任务，而且OSPost()函数是被
任务级调用的，就执行任务切换，运行最高优先级任务，否则， OS_Sched()函数返回，
让调用本函数的任务继续执行 */
return (OS_ERR_NONE);
}
pq = (OS_Q *)pevent->OSEventPt /* Point to queue control block 从事件控制块的数据成员 OSEventPtr 中取得队列控制块的地址 */
if (pq->OSQEntries >= pq->OSQSize) { /* Make sure queue is not full 若队列控制块中当前消息个数OSQEntries 已达队列容OSQSize /* 量，表明队列已满，新的消息无法入队，操作失败 */
OS_EXIT_CRITICAL();
return (OS_ERR_Q_FULL);
}
*pq->OSQIn++ = pmsg; /* Insert message into queue 否则（队列未满） 将消息插入队列，然后调整入队指针OSQIn */
pq->OSQEntries++; /* Update the nbr of entries in the queue 调整当前有效消息个数计数器 */
if (pq->OSQIn == pq->OSQEnd) { /* Wrap IN ptr if we are at end of queue 调整环形队列的指针，避免超出指针数组的范围 */
pq->OSQIn = pq->OSQStart;
}
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
二、等待消息队列中的消息（OSQPend()）
/*
*********************************************************************************************************
* PEND ON A QUEUE FOR A MESSAGE
*
* Description: This function waits for a message to be sent to a queue
*
* Arguments : pevent is a pointer to the event control block associated with the desired queue
*
* timeout is an optional timeout period (in clock ticks). If non-zero, your task will
* wait for a message to arrive at the queue up to the amount of time
* specified by this argument. If you specify 0, however, your task will wait
* forever at the specified queue or, until a message arrives.
*
* perr is a pointer to where an error message will be deposited. Possible error
* messages are:
*
* OS_ERR_NONE The call was successful and your task received a
* message.
* OS_ERR_TIMEOUT A message was not received within the specified 'timeout'.
* OS_ERR_PEND_ABORT The wait on the queue was aborted.
* OS_ERR_EVENT_TYPE You didn't pass a pointer to a queue
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_PEND_ISR If you called this function from an ISR and the result
* would lead to a suspension.
* OS_ERR_PEND_LOCKED If you called this function with the scheduler is locked
*
* Returns : != (void *)0 is a pointer to the message received
* == (void *)0 if you received a NULL pointer message or,
* if no message was received or,
* if 'pevent' is a NULL pointer or,
* if you didn't pass a pointer to a queue.
*
* Note(s) : As of V2.60, this function allows you to receive NULL pointer messages.
*********************************************************************************************************
*/
void *OSQPend (OS_EVENT *pevent, INT16U timeout, INT8U *perr) /* 实际上是：进行消息出队操作 */
{
void *pmsg;
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
#if OS_ARG_CHK_EN > 0
if (perr == (INT8U *)0) { /* Validate 'perr' */
return ((void *)0);
}
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*perr = OS_ERR_PEVENT_NULL;
return ((void *)0);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) {/* Validate event block type */
*perr = OS_ERR_EVENT_TYPE;
return ((void *)0);
}
if (OSIntNesting > 0) { /* See if called from ISR ... */
*perr = OS_ERR_PEND_ISR; /* ... can't PEND from an ISR */
return ((void *)0);
}
if (OSLockNesting > 0) { /* See if called with scheduler locked ... */
*perr = OS_ERR_PEND_LOCKED; /* ... can't PEND when locked */
return ((void *)0);
}
OS_ENTER_CRITICAL();
pq = (OS_Q *)pevent->OSEventPtr; /* Point at queue control block 从事件控制块的数据成员 OSEventPtr 中取得队列控制块的地址 */
if (pq->OSQEntries > 0) { /* See if any messages in the queue 有消息可用？ */
pmsg = *pq->OSQOut++; /* Yes, extract oldest message from the queue 取出消息，然后调整入队指针OSQout */
pq->OSQEntries--; /* Update the number of entries in the queue 调整当前有效消息个数计数器 */
if (pq->OSQOut == pq->OSQEnd) { /* Wrap OUT pointer if we are at the end of the queue 是否越界？ */
pq->OSQOut = pq->OSQStart;
}
OS_EXIT_CRITICAL();
*perr = OS_ERR_NONE;
return (pmsg); /* Return message received 返回消息指针，该指针指向消息的存放地址 */
}
/* 队列中无消息时的处理 */
OSTCBCur->OSTCBStat |= OS_STAT_Q; /* Task will have to pend for a message to be posted */
OSTCBCur->OSTCBStatPend = OS_STAT_PEND_OK;
/* 以此表明等待队列消息的任务被挂起 */
OSTCBCur->OSTCBDly = timeout; /* Load timeout into TCB 将超时值置入当前任务控制块 */
OS_EventTaskWait(pevent); /* Suspend task until event or timeout occurs 真正将等待队列消息的任务进入睡眠状态 */
OS_Sched(); /* Find next highest priority task ready to run
由于调用本函数的任务不再在就绪态，调度器会安排下一个进入就绪态的优先级最高的任务执行
在用户程序中，调用本函数的任务并不知道在消息没有来到之前，自己已经被挂起，
当队列接收到一则消息（或等待超时）后，本函数就会在调用 OS_Sched() 之后恢复执行 */
OS_ENTER_CRITICAL();
/* 当OS_Sched() 返回后，本函数会检查OSPost()是否已经将消息放在任务的任务控制块TCB中 */
switch (OSTCBCur->OSTCBStatPend) { /* See if we timed-out or aborted */
case OS_STAT_PEND_OK: /* Extract message from TCB (Put there by QPost) 等到消息 */
pmsg = OSTCBCur->OSTCBMsg; /* 取出消息 */
*perr = OS_ERR_NONE;
break;
case OS_STAT_PEND_ABORT: /* 主动放弃等待 */
pmsg = (void *)0;
*perr = OS_ERR_PEND_ABORT; /* Indicate that we aborted */
break;
case OS_STAT_PEND_TO: /* 等待超时 */
default:
OS_EventTaskRemove(OSTCBCur, pevent); /* 把调用本函数的任务从等待列表中除去 */
pmsg = (void *)0;
*perr = OS_ERR_TIMEOUT; /* Indicate that we didn't get event within TO */
break;
}
OSTCBCur->OSTCBStat = OS_STAT_RDY; /* Set task status to ready */
OSTCBCur->OSTCBStatPend = OS_STAT_PEND_OK; /* Clear pend status */
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0; /* Clear event pointers */
#if (OS_EVENT_MULTI_EN > 0)
OSTCBCur->OSTCBEventMultiPtr = (OS_EVENT **)0;
#endif
OSTCBCur->OSTCBMsg = (void *)0; /* Clear received message */
OS_EXIT_CRITICAL();
return (pmsg); /* Return received message */
}