Chapter 7.2 - 消息队列管理
Created by : Mr Dk.
2019 / 11 / 20 21:16
Nanjing, Jiangsu, China
7.2.1 概述
消息队列是一种以消息链表为方式进行通信的机制。从本质上来说，消息队列是一个邮箱阵列，消息队列可以在编译前被剪裁。
7.2.2 实现消息队列所需要的各种数据结构
ECB 是必须的，需要在编译前定义消息队列中的最大消息数 OS_MAX_QS。需要一个与消息队列最大消息数相同大小的 指针数组，分别指向每一条消息。还需要一个队列控制块 OS_Q，并链接到 ECB 的 OS_EventPtr 域上，其中维护了队列的 metadata。
typedef struct os_q { /* QUEUE CONTROL BLOCK */
struct os_q *OSQPtr; /* Link to next queue control block in list of free blocks */
void **OSQStart; /* Pointer to start of queue data */
void **OSQEnd; /* Pointer to end of queue data */
void **OSQIn; /* Pointer to where next message will be inserted in the Q */
void **OSQOut; /* Pointer to where next message will be extracted from the Q */
INT16U OSQSize; /* Size of queue (maximum number of entries) */
INT16U OSQEntries; /* Current number of entries in the queue */
} OS_Q;
OSQPtr用于链接空闲队列控制块，一旦控制块被取下来，就没用了OSQStart/OSQEnd指向指针数组的起始地址和最后一个地址的下一个地址OSQIn/OSQOut指向队列的头和尾QSQSize队列中总的单元数QSQEntries队列中当前的消息数量
消息队列的核心就是一个循环缓冲区。
7.2.3 建立消息队列 - OSQCreate() 函数
建立一个消息队列，需要将消息队列指针数组的首地址和消息指针队列的长度作为参数。
原理：
- 从空闲 ECB 链表和空闲队列控制块链表中各取一个控制块
- 初始化，将队列控制块链接到 ECB 上
- 返回 ECB 的指针
/*
*********************************************************************************************************
* CREATE A MESSAGE QUEUE
*
* Description: This function creates a message queue if free event control blocks are available.
*
* Arguments : start is a pointer to the base address of the message queue storage area. The
* storage area MUST be declared as an array of pointers to 'void' as follows
*
* void *MessageStorage[size]
*
* size is the number of elements in the storage area
*
* Returns : != (OS_EVENT *)0 is a pointer to the event control clock (OS_EVENT) associated with the
* created queue
* == (OS_EVENT *)0 if no event control blocks were available or an error was detected
*********************************************************************************************************
*/
OS_EVENT *OSQCreate (void **start,
INT16U size)
{
OS_EVENT *pevent;
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL_IEC61508
if (OSSafetyCriticalStartFlag == OS_TRUE) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
if (OSIntNesting > 0u) { /* See if called from ISR ... */
return ((OS_EVENT *)0); /* ... can't CREATE from an ISR */
}
OS_ENTER_CRITICAL();
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) { /* See if we have an event control block */
OS_ENTER_CRITICAL();
pq = OSQFreeList; /* Get a free queue control block */
if (pq != (OS_Q *)0) { /* Were we able to get a queue control block ? */
OSQFreeList = OSQFreeList->OSQPtr; /* Yes, Adjust free list pointer to next free*/
OS_EXIT_CRITICAL();
pq->OSQStart = start; /* Initialize the queue */
pq->OSQEnd = &start[size];
pq->OSQIn = start;
pq->OSQOut = start;
pq->OSQSize = size;
pq->OSQEntries = 0u;
pevent->OSEventType = OS_EVENT_TYPE_Q;
pevent->OSEventCnt = 0u;
pevent->OSEventPtr = pq;
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
OS_EventWaitListInit(pevent); /* Initalize the wait list */
} else {
pevent->OSEventPtr = (void *)OSEventFreeList; /* No, Return event control block on error */
OSEventFreeList = pevent;
OS_EXIT_CRITICAL();
pevent = (OS_EVENT *)0;
}
}
return (pevent);
}
7.2.4 删除消息队列 - OSQDel() 函数
删除消息队列。依旧可以指定删除选项：
OS_DEL_NO_PENDOS_DEL_ALWAYS
原理：将 ECB 和队列控制块设置为初始状态，并归还到空闲链表中。
/*
*********************************************************************************************************
* DELETE A MESSAGE QUEUE
*
* Description: This function deletes a message queue and readies all tasks pending on the queue.
*
* Arguments : pevent is a pointer to the event control block associated with the desired
* queue.
*
* opt determines delete options as follows:
* opt == OS_DEL_NO_PEND Delete the queue ONLY if no task pending
* opt == OS_DEL_ALWAYS Deletes the queue even if tasks are waiting.
* In this case, all the tasks pending will be readied.
*
* perr is a pointer to an error code that can contain one of the following values:
* OS_ERR_NONE The call was successful and the queue was deleted
* OS_ERR_DEL_ISR If you tried to delete the queue from an ISR
* OS_ERR_INVALID_OPT An invalid option was specified
* OS_ERR_TASK_WAITING One or more tasks were waiting on the queue
* OS_ERR_EVENT_TYPE If you didn't pass a pointer to a queue
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer.
*
* Returns : pevent upon error
* (OS_EVENT *)0 if the queue was successfully deleted.
*
* Note(s) : 1) This function must be used with care. Tasks that would normally expect the presence of
* the queue MUST check the return code of OSQPend().
* 2) OSQAccept() callers will not know that the intended queue 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 queue.
* 4) Because ALL tasks pending on the queue will be readied, you MUST be careful in
* applications where the queue is used for mutual exclusion because the resource(s)
* will no longer be guarded by the queue.
* 5) If the storage for the message queue was allocated dynamically (i.e. using a malloc()
* type call) then your application MUST release the memory storage by call the counterpart
* call of the dynamic allocation scheme used. If the queue storage was created statically
* then, the storage can be reused.
*********************************************************************************************************
*/
#if OS_Q_DEL_EN > 0u
OS_EVENT *OSQDel (OS_EVENT *pevent,
INT8U opt,
INT8U *perr)
{
BOOLEAN tasks_waiting;
OS_EVENT *pevent_return;
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL
if (perr == (INT8U *)0) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*perr = OS_ERR_PEVENT_NULL;
return (pevent);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
*perr = OS_ERR_EVENT_TYPE;
return (pevent);
}
if (OSIntNesting > 0u) { /* See if called from ISR ... */
*perr = OS_ERR_DEL_ISR; /* ... can't DELETE from an ISR */
return (pevent);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any tasks waiting on queue */
tasks_waiting = OS_TRUE; /* Yes */
} else {
tasks_waiting = OS_FALSE; /* No */
}
switch (opt) {
case OS_DEL_NO_PEND: /* Delete queue only if no task waiting */
if (tasks_waiting == OS_FALSE) {
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
pq = (OS_Q *)pevent->OSEventPtr; /* Return OS_Q to free list */
pq->OSQPtr = OSQFreeList;
OSQFreeList = pq;
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
pevent->OSEventCnt = 0u;
OSEventFreeList = pevent; /* Get next free event control block */
OS_EXIT_CRITICAL();
*perr = OS_ERR_NONE;
pevent_return = (OS_EVENT *)0; /* Queue has been deleted */
} else {
OS_EXIT_CRITICAL();
*perr = OS_ERR_TASK_WAITING;
pevent_return = pevent;
}
break;
case OS_DEL_ALWAYS: /* Always delete the queue */
while (pevent->OSEventGrp != 0u) { /* Ready ALL tasks waiting for queue */
(void)OS_EventTaskRdy(pevent, (void *)0, OS_STAT_Q, OS_STAT_PEND_OK);
}
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
pq = (OS_Q *)pevent->OSEventPtr; /* Return OS_Q to free list */
pq->OSQPtr = OSQFreeList;
OSQFreeList = pq;
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
pevent->OSEventCnt = 0u;
OSEventFreeList = pevent; /* Get next free event control block */
OS_EXIT_CRITICAL();
if (tasks_waiting == OS_TRUE) { /* Reschedule only if task(s) were waiting */
OS_Sched(); /* Find highest priority task ready to run */
}
*perr = OS_ERR_NONE;
pevent_return = (OS_EVENT *)0; /* Queue has been deleted */
break;
default:
OS_EXIT_CRITICAL();
*perr = OS_ERR_INVALID_OPT;
pevent_return = pevent;
break;
}
return (pevent_return);
}
#endif
7.2.5 等待消息队列中的一则消息 - OSQPend() 函数
等待队列中的消息：
- 如果队列中已存在消息，那么返回该消息，并将消息从队列中删除
- 如果队列中没有消息，则挂起当前任务，直到消息到来或超时时间满
- 如果有多个任务等待消息，则默认最高优先级的任务取得消息
调用者只能是任务。
原理：
- 从 ECB 中取得队列控制块
- 如果队列中的消息大于 0，则取出消息并递减消息数量
- 否则挂起任务
/*
*********************************************************************************************************
* 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,
INT32U timeout,
INT8U *perr)
{
void *pmsg;
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL
if (perr == (INT8U *)0) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
#if OS_ARG_CHK_EN > 0u
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 > 0u) { /* See if called from ISR ... */
*perr = OS_ERR_PEND_ISR; /* ... can't PEND from an ISR */
return ((void *)0);
}
if (OSLockNesting > 0u) { /* 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 */
if (pq->OSQEntries > 0u) { /* See if any messages in the queue */
pmsg = *pq->OSQOut++; /* Yes, extract oldest message from the queue */
pq->OSQEntries--; /* Update the number of entries in the queue */
if (pq->OSQOut == pq->OSQEnd) { /* Wrap OUT pointer if we are at the end of the queue */
pq->OSQOut = pq->OSQStart;
}
OS_EXIT_CRITICAL();
*perr = OS_ERR_NONE;
return (pmsg); /* Return message received */
}
OSTCBCur->OSTCBStat |= OS_STAT_Q; /* Task will have to pend for a message to be posted */
OSTCBCur->OSTCBStatPend = OS_STAT_PEND_OK;
OSTCBCur->OSTCBDly = timeout; /* Load timeout into TCB */
OS_EventTaskWait(pevent); /* Suspend task until event or timeout occurs */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next highest priority task ready to run */
OS_ENTER_CRITICAL();
switch (OSTCBCur->OSTCBStatPend) { /* See if we timed-out or aborted */
case OS_STAT_PEND_OK: /* Extract message from TCB (Put there by QPost) */
pmsg = OSTCBCur->OSTCBMsg;
*perr = OS_ERR_NONE;
break;
case OS_STAT_PEND_ABORT:
pmsg = (void *)0;
*perr = OS_ERR_PEND_ABORT; /* Indicate that we aborted */
break;
case OS_STAT_PEND_TO:
default:
OS_EventTaskRemove(OSTCBCur, pevent);
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 > 0u)
OSTCBCur->OSTCBEventMultiPtr = (OS_EVENT **)0;
#endif
OSTCBCur->OSTCBMsg = (void *)0; /* Clear received message */
OS_EXIT_CRITICAL();
return (pmsg); /* Return received message */
}
7.2.6 向消息队列发送一则 FIFO 消息 - OSQPost() 函数
向消息队列中加入消息：
- 若队列已满，则丢弃新消息
- 若队列不满，则将消息放入队列中
- 如果有任务在等待消息，则最高优先级任务得到这个消息；如果等待消息的任务的优先级高于当前任务，则发生任务切换
原理：
- 逻辑上，应该先检查 ECB 的等待任务列表中是否有任务在等待消息
- 如果没有，再判断队列是否已满
/*
*********************************************************************************************************
* 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 > 0u
INT8U OSQPost (OS_EVENT *pevent,
void *pmsg)
{
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any task pending on queue */
/* Ready highest priority task waiting on event */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_Q, OS_STAT_PEND_OK);
OS_EXIT_CRITICAL();
OS_Sched(); /* Find highest priority task ready to run */
return (OS_ERR_NONE);
}
pq = (OS_Q *)pevent->OSEventPtr; /* Point to queue control block */
if (pq->OSQEntries >= pq->OSQSize) { /* Make sure queue is not full */
OS_EXIT_CRITICAL();
return (OS_ERR_Q_FULL);
}
*pq->OSQIn++ = pmsg; /* Insert message into queue */
pq->OSQEntries++; /* Update the nbr of entries in the queue */
if (pq->OSQIn == pq->OSQEnd) { /* Wrap IN ptr if we are at end of queue */
pq->OSQIn = pq->OSQStart;
}
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.2.7 向消息队列发送一则 LIFO 消息 - OSQPostFront() 函数
与上一个函数基本类似，差别是将消息插入到队列的最前端而不是最后端。
原理：
- 同样，应该先检查是否有任务在等待消息 (这种情况不需要对队列进行操作)
- 如果没有，再检查队列是否已满
- 若队列未满，则将消息插入队列的最前端 (下一个出队的就是这条消息)
/*
*********************************************************************************************************
* POST MESSAGE TO THE FRONT OF A QUEUE
*
* Description: This function sends a message to a queue but unlike OSQPost(), the message is posted at
* the front instead of the end of the queue. Using OSQPostFront() allows you to send
* 'priority' messages.
*
* 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_FRONT_EN > 0u
INT8U OSQPostFront (OS_EVENT *pevent,
void *pmsg)
{
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any task pending on queue */
/* Ready highest priority task waiting on event */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_Q, OS_STAT_PEND_OK);
OS_EXIT_CRITICAL();
OS_Sched(); /* Find highest priority task ready to run */
return (OS_ERR_NONE);
}
pq = (OS_Q *)pevent->OSEventPtr; /* Point to queue control block */
if (pq->OSQEntries >= pq->OSQSize) { /* Make sure queue is not full */
OS_EXIT_CRITICAL();
return (OS_ERR_Q_FULL);
}
if (pq->OSQOut == pq->OSQStart) { /* Wrap OUT ptr if we are at the 1st queue entry */
pq->OSQOut = pq->OSQEnd;
}
pq->OSQOut--;
*pq->OSQOut = pmsg; /* Insert message into queue */
pq->OSQEntries++; /* Update the nbr of entries in the queue */
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.2.8 以可选方式 (FIFO 或 LIFO) 向消息队列发一则消息 - OSQPostOpt()
- 选项可以指定 LIFO 或 FIFO
- 还可以指定最高优先级的任务得到消息，还是所有等待的任务都得到消息
/*
*********************************************************************************************************
* POST MESSAGE TO A QUEUE
*
* Description: This function sends a message to a queue. This call has been added to reduce code size
* since it can replace both OSQPost() and OSQPostFront(). Also, this function adds the
* capability to broadcast a message to ALL tasks waiting on the message 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.
*
* opt determines the type of POST performed:
* OS_POST_OPT_NONE POST to a single waiting task
* (Identical to OSQPost())
* OS_POST_OPT_BROADCAST POST to ALL tasks that are waiting on the queue
* OS_POST_OPT_FRONT POST as LIFO (Simulates OSQPostFront())
* OS_POST_OPT_NO_SCHED Indicates that the scheduler will NOT be invoked
*
* 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
*
* Warning : Interrupts can be disabled for a long time if you do a 'broadcast'. In fact, the
* interrupt disable time is proportional to the number of tasks waiting on the queue.
*********************************************************************************************************
*/
#if OS_Q_POST_OPT_EN > 0u
INT8U OSQPostOpt (OS_EVENT *pevent,
void *pmsg,
INT8U opt)
{
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0x00u) { /* See if any task pending on queue */
if ((opt & OS_POST_OPT_BROADCAST) != 0x00u) { /* Do we need to post msg to ALL waiting tasks ? */
while (pevent->OSEventGrp != 0u) { /* Yes, Post to ALL tasks waiting on queue */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_Q, OS_STAT_PEND_OK);
}
} else { /* No, Post to HPT waiting on queue */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_Q, OS_STAT_PEND_OK);
}
OS_EXIT_CRITICAL();
if ((opt & OS_POST_OPT_NO_SCHED) == 0u) { /* See if scheduler needs to be invoked */
OS_Sched(); /* Find highest priority task ready to run */
}
return (OS_ERR_NONE);
}
pq = (OS_Q *)pevent->OSEventPtr; /* Point to queue control block */
if (pq->OSQEntries >= pq->OSQSize) { /* Make sure queue is not full */
OS_EXIT_CRITICAL();
return (OS_ERR_Q_FULL);
}
if ((opt & OS_POST_OPT_FRONT) != 0x00u) { /* Do we post to the FRONT of the queue? */
if (pq->OSQOut == pq->OSQStart) { /* Yes, Post as LIFO, Wrap OUT pointer if we ... */
pq->OSQOut = pq->OSQEnd; /* ... are at the 1st queue entry */
}
pq->OSQOut--;
*pq->OSQOut = pmsg; /* Insert message into queue */
} else { /* No, Post as FIFO */
*pq->OSQIn++ = pmsg; /* Insert message into queue */
if (pq->OSQIn == pq->OSQEnd) { /* Wrap IN ptr if we are at end of queue */
pq->OSQIn = pq->OSQStart;
}
}
pq->OSQEntries++; /* Update the nbr of entries in the queue */
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.2.9 无等待地从消息队列中获取一则消息 - OSQAccept() 函数
检查消息队列中是否已经有消息，不挂起任务，立刻返回。调用者可以是任务，也可以是中断。
原理：查询 ECB 对应的消息控制块的 OSQEntries 是否大于 0
- 大于 0，递减该变量，返回消息指针
- 等于 0，则返回空指针
/*
*********************************************************************************************************
* ACCEPT MESSAGE FROM QUEUE
*
* Description: This function checks the queue to see if a message is available. Unlike OSQPend(),
* OSQAccept() does not suspend the calling task if a message is not available.
*
* Arguments : pevent is a pointer to the event control block
*
* 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_EVENT_TYPE You didn't pass a pointer to a queue
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_Q_EMPTY The queue did not contain any messages
*
* Returns : != (void *)0 is the message in the queue if one is available. The message is removed
* from the so the next time OSQAccept() is called, the queue will contain
* one less entry.
* == (void *)0 if you received a NULL pointer message
* if the queue is empty or,
* if 'pevent' is a NULL pointer or,
* if you passed an invalid event type
*
* Note(s) : As of V2.60, you can now pass NULL pointers through queues. Because of this, the argument
* 'perr' has been added to the API to tell you about the outcome of the call.
*********************************************************************************************************
*/
#if OS_Q_ACCEPT_EN > 0u
void *OSQAccept (OS_EVENT *pevent,
INT8U *perr)
{
void *pmsg;
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL
if (perr == (INT8U *)0) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
#if OS_ARG_CHK_EN > 0u
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);
}
OS_ENTER_CRITICAL();
pq = (OS_Q *)pevent->OSEventPtr; /* Point at queue control block */
if (pq->OSQEntries > 0u) { /* See if any messages in the queue */
pmsg = *pq->OSQOut++; /* Yes, extract oldest message from the queue */
pq->OSQEntries--; /* Update the number of entries in the queue */
if (pq->OSQOut == pq->OSQEnd) { /* Wrap OUT pointer if we are at the end of the queue */
pq->OSQOut = pq->OSQStart;
}
*perr = OS_ERR_NONE;
} else {
*perr = OS_ERR_Q_EMPTY;
pmsg = (void *)0; /* Queue is empty */
}
OS_EXIT_CRITICAL();
return (pmsg); /* Return message received (or NULL) */
}
#endif
7.2.10 清空消息队列 - OSQFlush() 函数
清空消息队列。
原理：
- 将头指针和尾指针都调整到缓冲区起始单元
- 清空消息数量计数器
/*
*********************************************************************************************************
* FLUSH QUEUE
*
* Description : This function is used to flush the contents of the message queue.
*
* Arguments : none
*
* Returns : OS_ERR_NONE upon success
* OS_ERR_EVENT_TYPE If you didn't pass a pointer to a queue
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
*
* WARNING : You should use this function with great care because, when to flush the queue, you LOOSE
* the references to what the queue entries are pointing to and thus, you could cause
* 'memory leaks'. In other words, the data you are pointing to that's being referenced
* by the queue entries should, most likely, need to be de-allocated (i.e. freed).
*********************************************************************************************************
*/
#if OS_Q_FLUSH_EN > 0u
INT8U OSQFlush (OS_EVENT *pevent)
{
OS_Q *pq;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
#endif
OS_ENTER_CRITICAL();
pq = (OS_Q *)pevent->OSEventPtr; /* Point to queue storage structure */
pq->OSQIn = pq->OSQStart;
pq->OSQOut = pq->OSQStart;
pq->OSQEntries = 0u;
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.2.11 查询一个消息队列的状态 - OSQQuery() 函数
查询一个消息队列的当前状态。将 ECB 和队列控制块中的变量复制到 OS_Q_DATA 数据结构中。
/*
*********************************************************************************************************
* QUERY A MESSAGE QUEUE
*
* Description: This function obtains information about a message queue.
*
* Arguments : pevent is a pointer to the event control block associated with the desired queue
*
* p_q_data is a pointer to a structure that will contain information about the message
* queue.
*
* Returns : OS_ERR_NONE The call was successful and the message was sent
* OS_ERR_EVENT_TYPE If you are attempting to obtain data from a non queue.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_PDATA_NULL If 'p_q_data' is a NULL pointer
*********************************************************************************************************
*/
#if OS_Q_QUERY_EN > 0u
INT8U OSQQuery (OS_EVENT *pevent,
OS_Q_DATA *p_q_data)
{
OS_Q *pq;
INT8U i;
OS_PRIO *psrc;
OS_PRIO *pdest;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (p_q_data == (OS_Q_DATA *)0) { /* Validate 'p_q_data' */
return (OS_ERR_PDATA_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_Q) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
p_q_data->OSEventGrp = pevent->OSEventGrp; /* Copy message queue wait list */
psrc = &pevent->OSEventTbl[0];
pdest = &p_q_data->OSEventTbl[0];
for (i = 0u; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++;
}
pq = (OS_Q *)pevent->OSEventPtr;
if (pq->OSQEntries > 0u) {
p_q_data->OSMsg = *pq->OSQOut; /* Get next message to return if available */
} else {
p_q_data->OSMsg = (void *)0;
}
p_q_data->OSNMsgs = pq->OSQEntries;
p_q_data->OSQSize = pq->OSQSize;
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif /* OS_Q_QUERY_EN */
Summary
核心多出来的一个数据结构 - 队列控制块，用于维护一个消息的循环队列。还需要注意发送消息时，可以单播，也可以广播。