课程笔记|uCos中的邮箱和消息队列嵌入式系统|嵌入式|队列|邮箱

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

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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)?

【课程笔记|uCos中的邮箱和消息队列】

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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

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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

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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

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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

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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_SRcpu_sr; #endif OS_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

INT8UOSQPost (OS_EVENT *pevent, void *msg) { #if OS_CRITICAL_METHOD == 3/* Allocate storage for CPU status register*/ OS_CPU_SRcpu_sr; #endif OS_Q*pq; #if OS_ARG_CHK_EN > 0 if (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); } #endif OS_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_SRcpu_sr; #endif void*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 > 0 if (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); } #endif OS_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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