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2012-11-14 11:20:25
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/*
*********************************************************************************************************
* CREATE A TASK (Extended Version)
*
* Description: This function is used to have uC/OS-II manage the execution of a task. Tasks can either
* be created prior to the start of multitasking or by a running task. A task cannot be
* created by an ISR. This function is similar to OSTaskCreate() except that it allows
* additional information about a task to be specified.
*
* Arguments : task is a pointer to the task's code
*
* p_arg is a pointer to an optional data area which can be used to pass parameters to
* the task when the task first executes. Where the task is concerned it thinks
* it was invoked and passed the argument 'p_arg' as follows:
*
* void Task (void *p_arg)
* {
* for (;;) {
* Task code;
* }
* }
*
* ptos is a pointer to the task's top 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). 'ptos' will thus point to the highest (valid) memory
* location of the stack. If OS_STK_GROWTH is set to 0, 'ptos' will point to the
* lowest memory location of the stack and the stack will grow with increasing
* memory locations. 'ptos' MUST point to a valid 'free' data item.
*
* prio is the task's priority. A unique priority MUST be assigned to each task and the
* lower the number, the higher the priority.
*
* id is the task's ID (0..65535)
*
* 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.
*
* stk_size is the size of the stack in number of elements. If OS_STK is set to INT8U,
* 'stk_size' corresponds to the number of bytes available. If OS_STK is set to
* INT16U, 'stk_size' contains the number of 16-bit entries available. Finally, if
* OS_STK is set to INT32U, 'stk_size' contains the number of 32-bit entries
* available on the stack.
*
* pext is a pointer to a user supplied memory location which is used as a TCB extension.
* For example, this user memory can hold the contents of floating-point registers
* during a context switch, the time each task takes to execute, the number of times
* the task has been switched-in, etc.
*
* 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. Current choices are:
*
* 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.
*
* Returns : OS_NO_ERR if the function was successful.
* OS_PRIO_EXIT if the task priority already exist
* (each task MUST have a unique priority).
* OS_PRIO_INVALID if the priority you specify is higher that the maximum allowed
* (i.e. > OS_LOWEST_PRIO)
* OS_ERR_TASK_CREATE_ISR if you tried to create a task from an ISR.
*********************************************************************************************************
*/
/*$PAGE*/
#if OS_TASK_CREATE_EXT_EN > 0
INT8U OSTaskCreateExt (void (*task)(void *p_arg),
void *p_arg,
OS_STK *ptos,
INT8U prio,
INT16U id,
OS_STK *pbos,
INT32U stk_size,
void *pext,
INT16U opt)
{
OS_STK *psp;
INT8U err;
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
#if OS_ARG_CHK_EN > 0
if (prio > OS_LOWEST_PRIO) { /* Make sure priority is within allowable range */
return (OS_PRIO_INVALID);
}
#endif
OS_ENTER_CRITICAL();
if (OSIntNesting > 0) { /* Make sure we don't create the task from within an ISR */
OS_EXIT_CRITICAL();
return (OS_ERR_TASK_CREATE_ISR);
}
if (OSTCBPrioTbl[prio] == (OS_TCB *)0) { /* Make sure task doesn't already exist at this priority */
OSTCBPrioTbl[prio] = (OS_TCB *)1; /* Reserve the priority to prevent others from doing ... */
/* ... the same thing until task is created. */
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();
}
return (err);
}
OS_EXIT_CRITICAL();
return (OS_PRIO_EXIST);
}
#endif
