μcosii源码试读13- OSTaskCreateExt

 

OS_EXIT_CRITICAL();

        OS_TaskStkClr(pbos, stk_size, opt); /* Clear the task stack (if needed) */

        psp = OSTaskStkInit(task, p_arg, ptos, opt); /* Initialize the task's stack */
        err = OS_TCBInit(prio, psp, pbos, id, stk_size, pext, opt);
        if (err == OS_NO_ERR) {
            if (OSRunning == OS_TRUE) { /* Find HPT if multitasking has started */
                OS_Sched();
            }
        } else {
            OS_ENTER_CRITICAL();
            OSTCBPrioTbl[prio] = (OS_TCB *)0; /* Make this priority avail. to others */
            OS_EXIT_CRITICAL();

今天好奇怪，完整的函数粘贴不上去，那就算了，

这个函数是OSTaskCreate函数的升级版本，增加了5个参数，分别是

id，0-65535的task id

pbos，指向栈底的指针，在arm中这个指向数组的零地址，

stk_size，就是栈的元素个数

pext，指向一个TCB扩展区的指针，例如在上下文切换时保存浮点寄存器的数值，任务已经执行的时间，任务被切换的次数等

opt，* OS_TASK_OPT_STK_CHK      Stack checking to be allowed for the task
* OS_TASK_OPT_STK_CLR      Clear the stack when the task is created
* OS_TASK_OPT_SAVE_FP      If the CPU has floating-point registers, save them during a context switch.

在执行核心代码之前要进行 比如优先级合法的检测，是否有中断嵌套的检测，相应优先级列表中是否被占用的检测。

与之不同的是 OS_TaskStkClr(pbos, stk_size, opt); 执行栈清空的子函数

/*
*********************************************************************************************************
* CLEAR TASK STACK
*
* Description: This function is used to clear the stack of a task (i.e. write all zeros)
*
* Arguments : pbos is a pointer to the task's bottom of stack. If the configuration constant
* OS_STK_GROWTH is set to 1, the stack is assumed to grow downward (i.e. from high
* memory to low memory). 'pbos' will thus point to the lowest (valid) memory
* location of the stack. If OS_STK_GROWTH is set to 0, 'pbos' will point to the
* highest memory location of the stack and the stack will grow with increasing
* memory locations. 'pbos' MUST point to a valid 'free' data item.
*
* size is the number of 'stack elements' to clear.
*
* opt contains additional information (or options) about the behavior of the task. The
* LOWER 8-bits are reserved by uC/OS-II while the upper 8 bits can be application
* specific. See OS_TASK_OPT_??? in uCOS-II.H.
*
* Returns : none
*********************************************************************************************************
*/
#if OS_TASK_CREATE_EXT_EN > 0
void OS_TaskStkClr (OS_STK *pbos, INT32U size, INT16U opt)
{
    if ((opt & OS_TASK_OPT_STK_CHK) != 0x0000) { /* See if stack checking has been enabled */
        if ((opt & OS_TASK_OPT_STK_CLR) != 0x0000) { /* See if stack needs to be cleared */
#if OS_STK_GROWTH == 1
            while (size > 0) { /* Stack grows from HIGH to LOW memory */
                size--;
                *pbos++ = (OS_STK)0; /* Clear from bottom of stack and */
            }
#else
            while (size > 0) { /* Stack grows from LOW to HIGH memory */
                size--;
                *pbos-- = (OS_STK)0; /* Clear from bottom of stack and down */
            }
#endif
        }
    }
}

#endif

清空函数需要栈底指针，栈大小和操作选项三个参数

只有opt中的栈检查和栈清除位使能时，才执行将栈内元素的值清零的代码段

之后执行相同的初始化栈，初始化TCB的指令