μcosii源码试读3- OS_InitTCBList();任务控制块链表初始化及其功能

上次是就绪表，这次是任务控制块，初始化程序如下

/*
*********************************************************************************************************
* INITIALIZATION
* INITIALIZE THE FREE LIST OF TASK CONTROL BLOCKS
*
* Description: This function is called by OSInit() to initialize the free list of OS_TCBs.
*
* Arguments : none
*
* Returns : none
*********************************************************************************************************
*/

static void OS_InitTCBList (void)
{
    INT8U i;
    OS_TCB *ptcb1;
    OS_TCB *ptcb2;


    OS_MemClr((INT8U *)&OSTCBTbl[0], sizeof(OSTCBTbl)); /* Clear all the TCBs */
    OS_MemClr((INT8U *)&OSTCBPrioTbl[0], sizeof(OSTCBPrioTbl)); /* Clear the priority table */
    ptcb1 = &OSTCBTbl[0];
    ptcb2 = &OSTCBTbl[1];
    for (i = 0; i < (OS_MAX_TASKS + OS_N_SYS_TASKS - 1); i++) { /* Init. list of free TCBs */
        ptcb1->OSTCBNext = ptcb2;
#if OS_TASK_NAME_SIZE > 1
        ptcb1->OSTCBTaskName[0] = '?'; /* Unknown name */
        ptcb1->OSTCBTaskName[1] = OS_ASCII_NUL;
#endif
        ptcb1++;
        ptcb2++;
    }
    ptcb1->OSTCBNext = (OS_TCB *)0; /* Last OS_TCB */
#if OS_TASK_NAME_SIZE > 1
    ptcb1->OSTCBTaskName[0] = '?'; /* Unknown name */
    ptcb1->OSTCBTaskName[1] = OS_ASCII_NUL;
#endif
    OSTCBList = (OS_TCB *)0; /* TCB lists initializations */
    OSTCBFreeList = &OSTCBTbl[0];
}

任务控制块是一个数据结构，其内容如下，这个结构在我理解相当于进程描述符的作用

/*
*********************************************************************************************************
* TASK CONTROL BLOCK
*********************************************************************************************************
*/

typedef struct os_tcb {
    OS_STK *OSTCBStkPtr; /* Pointer to current top of stack */

#if OS_TASK_CREATE_EXT_EN > 0
    void *OSTCBExtPtr; /* Pointer to user definable data for TCB extension */
    OS_STK *OSTCBStkBottom; /* Pointer to bottom of stack */
    INT32U OSTCBStkSize; /* Size of task stack (in number of stack elements) */
    INT16U OSTCBOpt; /* Task options as passed by OSTaskCreateExt() */
    INT16U OSTCBId; /* Task ID (0..65535) */
#endif

    struct os_tcb *OSTCBNext; /* Pointer to next TCB in the TCB list */
    struct os_tcb *OSTCBPrev; /* Pointer to previous TCB in the TCB list */

#if OS_EVENT_EN
    OS_EVENT *OSTCBEventPtr; /* Pointer to event control block */
#endif

#if ((OS_Q_EN > 0) && (OS_MAX_QS > 0)) || (OS_MBOX_EN > 0)
    void *OSTCBMsg; /* Message received from OSMboxPost() or OSQPost() */
#endif

#if (OS_VERSION >= 251) && (OS_FLAG_EN > 0) && (OS_MAX_FLAGS > 0)
#if OS_TASK_DEL_EN > 0
    OS_FLAG_NODE *OSTCBFlagNode; /* Pointer to event flag node */
#endif
    OS_FLAGS OSTCBFlagsRdy; /* Event flags that made task ready to run */
#endif

    INT16U OSTCBDly; /* Nbr ticks to delay task or, timeout waiting for event */
    INT8U OSTCBStat; /* Task status */
    BOOLEAN OSTCBPendTO; /* Flag indicating PEND timed out (OS_TRUE == timed out) */
    INT8U OSTCBPrio; /* Task priority (0 == highest) */

    INT8U OSTCBX; /* Bit position in group corresponding to task priority */
    INT8U OSTCBY; /* Index into ready table corresponding to task priority */
#if OS_LOWEST_PRIO <= 63
    INT8U OSTCBBitX; /* Bit mask to access bit position in ready table */
    INT8U OSTCBBitY; /* Bit mask to access bit position in ready group */
#else
    INT16U OSTCBBitX; /* Bit mask to access bit position in ready table */
    INT16U OSTCBBitY; /* Bit mask to access bit position in ready group */
#endif

#if OS_TASK_DEL_EN > 0
    INT8U OSTCBDelReq; /* Indicates whether a task needs to delete itself */
#endif

#if OS_TASK_PROFILE_EN > 0
    INT32U OSTCBCtxSwCtr; /* Number of time the task was switched in */
    INT32U OSTCBCyclesTot; /* Total number of clock cycles the task has been running */
    INT32U OSTCBCyclesStart; /* Snapshot of cycle counter at start of task resumption */
    OS_STK *OSTCBStkBase; /* Pointer to the beginning of the task stack */
    INT32U OSTCBStkUsed; /* Number of bytes used from the stack */
#endif

#if OS_TASK_NAME_SIZE > 1
    INT8U OSTCBTaskName[OS_TASK_NAME_SIZE];
#endif
} OS_TCB;

OSTCBStkPtr 指向任务堆栈顶端的指针 栈的元素大小为32位宽

 

当允许使用OSTaskCreatExt（）时即OS_TASK_CREATE_EXT_EN被置为1时可用：

void * OSTCBExtPtr 使用系统调用OSTaskCreatExt（）创建的用户自定义数据段

OSTCBStkBottom 指向栈底的指针，系统调用OSTaskStkChk（）来检测运行中堆栈的情况

OSTCBStkSize 存储栈所能容纳的指针元素，如果一个指针是32位，则有栈的大小为本数*4个字节

OSTCBOpt选择项用来告诉TaskCreatExt（）在任务建立的时候任务栈检验功能得到了允许，

OSTCBNext OSTCBPrev 构成双链表的双向指针，指向上一个或者下一个TCB数据结构，构成了一个双向非循环链表

 

OSTCBEventPtr 指向事件控制数据块 用于任务间的通信和同步

OSTCBTaskName存任务名的数组，其中第一个数据[0]存入'？'

OSTCBList是一个指向TCB双链表表头的指针，初始化中赋值为NULL指针，之后创建task时加入TCB双链表

OSTCBFreeList空任务控制块指针，指向由空任务组成的链表，当一个任务建立时，将头指针指向的任务块交给该任务使用，当任务删除时，任务把任务块交还给空任务链表。

OSTCBTbl[]存放所有任务块的数组，不论是空任务块还是非空任务块，都在这个数组中，在不同的链表中组织结构不同

OSTCBPrioTbl[]指针数组 每一个元素都指向TCB

 

 

总结：这个初始化函数初始化了TCB数组和链表，TCB结构的初始化在建立新task时才会用到