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- UID
- 1029342
- 性别
- 男
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1：ucos时钟在ucos中使用硬件定时器产生一个周期为毫秒级的周期性中断来实现系统时钟，最小的时钟单位就是俩次时间中断之间的间隔，
这个最小时间叫做：tick。
硬件定时器以时钟节拍为周期定时地产生中断，该中断的中断服务程序为：
在context-M3中为： OS_CPU_SysTickHandler()
DCD OS_CPU_SysTickHandler ; SysTick Handler
__Vectors DCD __initial_sp ; Top of Stack
DCD Reset_Handler ; Reset Handler
DCD NMI_Handler ; NMI Handler
DCD HardFault_Handler ; Hard Fault Handler
DCD MemManage_Handler ; MPU Fault Handler
DCD BusFault_Handler ; Bus Fault Handler
DCD UsageFault_Handler ; Usage Fault Handler
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD SVC_Handler ; SVCall Handler
DCD DebugMon_Handler ; Debug Monitor Handler
DCD 0 ; Reserved
DCD OS_CPU_PendSVHandler ; PendSV Handler
DCD OS_CPU_SysTickHandler ; SysTick Handler
/*
*********************************************************************************************************
* OS_CPU_SysTickHandler()
*
* Description: Handle the system tick (SysTick) interrupt, which is used to generate the uC/OS-II tick
* interrupt.
* Arguments : none.
*
* Note(s) : 1) This function MUST be placed on entry 15 of the Cortex-M3 vector table.
*********************************************************************************************************
*/
void OS_CPU_SysTickHandler (void)
{
OS_CPU_SR cpu_sr;
OS_ENTER_CRITICAL(); /* Tell uC/OS-II that we are starting an ISR */
OSIntNesting++;
OS_EXIT_CRITICAL();
OSTimeTick(); /* Call uC/OS-II's OSTimeTick() */
OSIntExit(); /* Tell uC/OS-II that we are leaving the ISR */
}
在函数OSTimeTick()中
void OSTimeTick (void)
{
OS_TCB *ptcb;
#if OS_TICK_STEP_EN > 0
BOOLEAN step;
#endif
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0;
#endif
#if OS_TIME_TICK_HOOK_EN > 0
OSTimeTickHook(); /* Call user definable hook */
#endif
#if OS_TIME_GET_SET_EN > 0
OS_ENTER_CRITICAL(); /* Update the 32-bit tick counter */
OSTime++;
OS_EXIT_CRITICAL();
#endif
if (OSRunning == OS_TRUE) {
ptcb = OSTCBList; /* Point at first TCB in TCB list */
while (ptcb->OSTCBPrio != OS_TASK_IDLE_PRIO) { /* Go through all TCBs in TCB list */
OS_ENTER_CRITICAL();
if (ptcb->OSTCBDly != 0) { /* No, Delayed or waiting for event with TO */
if (--ptcb->OSTCBDly == 0) { /* Decrement nbr of ticks to end of delay */
/* Check for timeout */
if ((ptcb->OSTCBStat & OS_STAT_PEND_ANY) != OS_STAT_RDY) {
ptcb->OSTCBStat &= ~(INT8U)OS_STAT_PEND_ANY; /* Yes, Clear status flag */
ptcb->OSTCBStatPend = OS_STAT_PEND_TO; /* Indicate PEND timeout */
} else {
ptcb->OSTCBStatPend = OS_STAT_PEND_OK;
}
if ((ptcb->OSTCBStat & OS_STAT_SUSPEND) == OS_STAT_RDY) { /* Is task suspended? */
OSRdyGrp |= ptcb->OSTCBBitY; /* No, Make ready */
OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
}
}
}
ptcb = ptcb->OSTCBNext; /* Point at next TCB in TCB list */
OS_EXIT_CRITICAL();
}
}
}
上面的函数中主要做了俩件事情：
1：给计数器OSTime加1操作。
2：遍历任务TCB链表中的所有TCB，在任务的OSTCBDly不为0时，对OSTCBDly减1操作，当OSTCBDly为0并且此TCB没有挂起，
则使此任务进入就绪状态。 |
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