μcosii源码试读7- OS_QInit；消息队列初始化函数

 

在内存管理初始化函数之后是消息队列初始化函数；这个函数也有一个开关叫做

OS_Q_EN

能够控制当前的操作系统是否使用消息队列功能

/*
*********************************************************************************************************
* QUEUE MODULE INITIALIZATION
*
* Description : This function is called by uC/OS-II to initialize the message queue module. Your
* application MUST NOT call this function.
*
* Arguments : none
*
* Returns : none
*
* Note(s) : This function is INTERNAL to uC/OS-II and your application should not call it.
*********************************************************************************************************
*/

void OS_QInit (void)
{
#if OS_MAX_QS == 1
    OSQFreeList = &OSQTbl[0]; /* Only ONE */
    OSQFreeList->OSQPtr = (OS_Q *)0;
#endif

#if OS_MAX_QS >= 2
    INT16U i;
    OS_Q *pq1;
    OS_Q *pq2;



    OS_MemClr((INT8U *)&OSQTbl[0], sizeof(OSQTbl)); /* Clear the queue table */
    pq1 = &OSQTbl[0];
    pq2 = &OSQTbl[1];
    for (i = 0; i < (OS_MAX_QS - 1); i++) { /* Init. list of free QUEUE control blocks */
        pq1->OSQPtr = pq2;
        pq1++;
        pq2++;
    }
    pq1->OSQPtr = (OS_Q *)0;
    OSQFreeList = &OSQTbl[0];
#endif
}

其结构与前面的双链表结构初始化相同，核心数据结构为

OS_Q和OS_Q_DATA

/*
*********************************************************************************************************
* MESSAGE QUEUE DATA
*********************************************************************************************************
*/

#if OS_Q_EN > 0
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;


typedef struct os_q_data {
    void *OSMsg; /* Pointer to next message to be extracted from queue */
    INT16U OSNMsgs; /* Number of messages in message queue */
    INT16U OSQSize; /* Size of message queue */
#if OS_LOWEST_PRIO <= 63
    INT8U OSEventTbl[OS_EVENT_TBL_SIZE]; /* List of tasks waiting for event to occur */
    INT8U OSEventGrp; /* Group corresponding to tasks waiting for event to occur */
#else
    INT16U OSEventTbl[OS_EVENT_TBL_SIZE]; /* List of tasks waiting for event to occur */
    INT16U OSEventGrp; /* Group corresponding to tasks waiting for event to occur */
#endif
} OS_Q_DATA;
#endif

这个数据结构有如下的内容：

struct os_q   *OSQPtr;指向下一个OS_Q的指针

void         **OSQStart;指向消息队列数据链表开始的指针

void         **OSQEnd;指向消息队列数据链表结束的指针

void         **OSQIn; 指向消息队列放入消息数据的入口

void         **OSQOut;指向消息队列取出消息数据的出口

OSQSize;最多可以放进多少个消息

OSQEntries;现在有多少个数据存放在当前消息队列里面

 

将所有的空消息队列串联起来构成一个单链表，然后将表头返回给OSQFreeList

将表尾节点指向NULL就行了

 

建立一个消息队列的函数为

/*
*********************************************************************************************************
* 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 == 3 /* Allocate storage for CPU status register */
    OS_CPU_SR cpu_sr = 0;
#endif



    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;
#if OS_EVENT_NAME_SIZE > 1
            pevent->OSEventName[0] = '?'; /* Unknown name */
            pevent->OSEventName[1] = OS_ASCII_NUL;
#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);
}

关中断，取得一个事件控制块ECB，将空事件控制链表的表头后移一个数据结构

取得一个空消息队列块，向消息队列块和事件控制块中写入如下的信息

           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;

然后初始化事件控制块

 OS_EventWaitListInit(pevent); 

如果成功，返回事件控制块的指针pevent

消息队列是一个循环链表，元素中的核心数据是指向msg类型的指针，每当OSQIn/OSQOut到达数组结尾OSQEnd

就会自动跳转到OSQStart，在创建一个消息队列之前，要创建一个size大小跟消息队列大小一样的指针数组，这个数组是消息队列存放指向msg的指针的实体