uCos中的邮箱和消息队列

文章目录

1. 背景
2. 直接通信与间接通信
3. 消息机制
4. 消息队列
5. ucos-ii中实现
- 5.1. 任务创建
- 5.2. 发送消息
- 5.3. 等待消息

1. 背景

前段时间老师上课讲到了uC/OS中的邮箱和消息队列，所以我想要结合《μC/OS-III源码分析笔记》和中国大学MOOC-电子科技大学《嵌入式系统及应用》PPT写一篇笔记对这部分的内容进行总结。

2. 直接通信与间接通信

直接通信：在通信过程中双方必须明确地知道(命名)彼此。
- Send (P，message) – 发送一个消息到任务P
- Receive(Q，message) – 从任务Q接收一个消息
间接通信：通信双方不需要指出消息的来源或去向，而通过中间机制来通信
- send(A，message) – 发送一个消息给邮箱A
- receive(A，message) – 从邮箱A接收一个消息

3. 消息机制

消息队列：属于间接通信方式
- 消息：内存空间中一段长度可变的缓冲区，其长度和内容均可以由用户定义和解释，其内容可以是实际的数据、数据块的指针或空。
- 从操作系统观点看，消息没有定义的格式，所有的消息都是字节流，没有特定的含义。
- 应用可以只把消息当成一个标志，这时消息机制用于实现同步。
消息机制可进一步分为：邮箱和消息队列。邮箱仅能存放单条消息，消息队列可存放若干消息。
消息机制可支持定长与可变长度两种模式的消息。

4. 消息队列

Figure 1. 消息队列机制的主要数据结构\text{Figure 1. 消息队列机制的主要数据结构} Figure 1. 消息队列机制的主要数据结构

消息队列控制块:管理所有创建的消息队列，系统运行时动态分配和回收消息队列控制块。
消息队列缓冲区:存放该队列的消息内容。
如何进行消息的发送或接收?完整的消息内容拷贝 or传递指针(效率高、系统性能好、空间占用小)?

Figure 2. 消息队列的状态图\text{Figure 2. 消息队列的状态图} Figure 2. 消息队列的状态图

Figure 3. 消息队列的主要数据结构\text{Figure 3. 消息队列的主要数据结构} Figure 3. 消息队列的主要数据结构

Figure 4. 消息队列的环形缓冲\text{Figure 4. 消息队列的环形缓冲} Figure 4. 消息队列的环形缓冲

Figure 5. 接收消息流程图\text{Figure 5. 接收消息流程图} Figure 5. 接收消息流程图

Figure 6.消息队列的典型应用\text{Figure 6.消息队列的典型应用} Figure 6.消息队列的典型应用

5. ucos-ii中实现

5.1. 任务创建

OS_EVENT  *OSQCreate (void **start, INT16U size)
{#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */OS_CPU_SR  cpu_sr;
#endifOS_EVENT  *pevent;OS_Q      *pq;if (OSIntNesting > 0) {                      /* 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      = 0;pevent->OSEventType = OS_EVENT_TYPE_Q;pevent->OSEventCnt  = 0;pevent->OSEventPtr  = pq;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);
}

5.2. 发送消息

INT8U  OSQPost (OS_EVENT *pevent, void *msg)
{#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */OS_CPU_SR  cpu_sr;
#endifOS_Q      *pq;#if OS_ARG_CHK_EN > 0if (pevent == (OS_EVENT *)0) {                    /* Validate 'pevent'                             */return (OS_ERR_PEVENT_NULL);}if (msg == (void *)0) {                           /* Make sure we are not posting a NULL pointer   */return (OS_ERR_POST_NULL_PTR);}if (pevent->OSEventType != OS_EVENT_TYPE_Q) {     /* Validate event block type                     */return (OS_ERR_EVENT_TYPE);}
#endifOS_ENTER_CRITICAL();if (pevent->OSEventGrp != 0x00) {                 /* See if any task pending on queue              */OS_EventTaskRdy(pevent, msg, OS_STAT_Q);      /* Ready highest priority task waiting on event  */OS_EXIT_CRITICAL();OS_Sched();                                   /* Find highest priority task ready to run       */return (OS_NO_ERR);}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_Q_FULL);}*pq->OSQIn++ = msg;                               /* 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_NO_ERR);
}

5.3. 等待消息

void  *OSQPend (OS_EVENT *pevent, INT16U timeout, INT8U *err)
{#if OS_CRITICAL_METHOD == 3                      /* Allocate storage for CPU status register           */OS_CPU_SR  cpu_sr;
#endifvoid      *msg;OS_Q      *pq;if (OSIntNesting > 0) {                      /* See if called from ISR ...                         */*err = OS_ERR_PEND_ISR;                  /* ... can't PEND from an ISR                         */return ((void *)0);}
#if OS_ARG_CHK_EN > 0if (pevent == (OS_EVENT *)0) {               /* Validate 'pevent'                                  */*err = OS_ERR_PEVENT_NULL;return ((void *)0);}if (pevent->OSEventType != OS_EVENT_TYPE_Q) {/* Validate event block type                          */*err = OS_ERR_EVENT_TYPE;return ((void *)0);}
#endifOS_ENTER_CRITICAL();pq = (OS_Q *)pevent->OSEventPtr;             /* Point at queue control block                       */if (pq->OSQEntries > 0) {                    /* See if any messages in the queue                   */msg = *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();*err = OS_NO_ERR;return (msg);                            /* Return message received                            */}OSTCBCur->OSTCBStat |= OS_STAT_Q;            /* Task will have to pend for a message to be posted  */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();msg = OSTCBCur->OSTCBMsg;if (msg != (void *)0) {                      /* Did we get a message?                              */OSTCBCur->OSTCBMsg      = (void *)0;     /* Extract message from TCB (Put there by QPost)      */OSTCBCur->OSTCBStat     = OS_STAT_RDY;OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0; /* No longer waiting for event                        */OS_EXIT_CRITICAL();*err                    = OS_NO_ERR;return (msg);                            /* Return message received                            */}OS_EventTO(pevent);                          /* Timed out                                          */OS_EXIT_CRITICAL();*err = OS_TIMEOUT;                           /* Indicate a timeout occured                         */return ((void *)0);                          /* No message received                                */
}

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