系统时钟不准确，久了会死机的疑问？

static DWORD dwPartialCurMSec = 0;		// Keep CPU-specific sub-millisecond leftover.

void

OEMIdle( DWORD dwIdleParam )

{

	DWORD dwIdleMSec;

	DWORD dwPrevMSec = *pCurMSec;

	

	// Use for 64-bit math

	ULARGE_INTEGER currIdle = { curridlelow, curridlehigh };



	if ((int) (dwIdleMSec = dwReschedTime - dwPrevMSec) <= 0) 

	{

		return;				// already time to wakeup

	}



	// just idle till tick if profiling or running iltiming

	if (bProfileTimerRunning || fIntrTime)	// fIntrTime : Interrupt Latency timeing.

	{

		// idle till end of 'tick'

		CPUEnterIdle(dwIdleParam);



		// Update global idle time and return

		currIdle.QuadPart += RESCHED_PERIOD;

		curridlelow = currIdle.LowPart;

		curridlehigh = currIdle.HighPart;

        

		return;

	}

	RETAILMSG(1,(TEXT("OEMIdle ->RESCHED_PERIOD=%d \r\n"),RESCHED_PERIOD));  

	//

	// Since OEMIdle( ) is being called in the middle of a normal reschedule

	// period, CurMSec, dwPartialCurMSec, and CurTicks need to be updated accordingly.

	// Once we reach this point, we must re-program the timer (if we ever did) 

	// because dwPartialCurMSec will be modified in the next function call.

	//

	CPUGetSysTimerCountElapsed(RESCHED_PERIOD, pCurMSec, &dwPartialCurMSec, pCurTicks);



	if ((int) (dwIdleMSec -= *pCurMSec - dwPrevMSec) > 0)

	{

		dwPrevMSec = *pCurMSec;



		//

		// The system timer may not be capable of arbitrary timeouts. Get the

		// CPU-specific highest possible timeout available.

		//

		dwIdleMSec = CPUGetSysTimerCountMax(dwIdleMSec);



		//

		// Set the timer to wake up much later than usual, if needed.

		//

		CPUSetSysTimerCount(dwIdleMSec);

		CPUClearSysTimerIRQ( );



		//

		// Enable wakeup on any interrupt, then go to sleep.

		//

//		DEBUGMSG(1, (TEXT("OEMIDle  \r\n")));

		CPUEnterIdle(dwIdleParam);

		INTERRUPTS_OFF( );

        

		//

		// We're awake! The wake-up ISR (or any other ISR) has already run.

		//

		if (dwPrevMSec != *pCurMSec)

		{

			//

			// We completed the full period we asked to sleep.  Update the counters.

			//

			*pCurMSec  += (dwIdleMSec - RESCHED_PERIOD); // Subtract resched period, because ISR also incremented.

			CurTicks.QuadPart += (dwIdleMSec - RESCHED_PERIOD) * dwReschedIncrement;



			currIdle.QuadPart += dwIdleMSec;

		} else {

			//

			// Some other interrupt woke us up before the full idle period was

			// complete.  Determine how much time has elapsed.

			//

			currIdle.QuadPart += CPUGetSysTimerCountElapsed(dwIdleMSec, pCurMSec, &dwPartialCurMSec, pCurTicks);

		}

	}



	// Re-arm counters

	CPUSetSysTimerCount(RESCHED_PERIOD);

	CPUClearSysTimerIRQ( );



	// Update global idle time

	curridlelow = currIdle.LowPart;

	curridlehigh = currIdle.HighPart;



	return;

}



------------------------------------------------------------------------------------------------------

void 

InitClock(void) 

{

    volatile PWMreg *s2440PWM =(PWMreg *)PWM_BASE;

    volatile INTreg *s2440INT = (INTreg *)INT_BASE;  

    DWORD ttmp;  





	// Timer4 as OS tick and disable it first.

    s2440INT->rINTMSK |= BIT_TIMER4;		// Mask timer4 interrupt.

    s2440INT->rSRCPND = BIT_TIMER4;			// Clear pending bit

    s2440INT->rINTPND = BIT_TIMER4;



	// Operating clock : PCLK=101500000 (101.5 Mhz)    

	// IMPORTANT : MUST CHECK S2440.H DEFINITIONS !!!!

	s2440PWM->rTCFG1  = 0x8080;	//;;; SHL

	s2440PWM->rTCFG0 &= ~(0xff << 8);		/* Prescaler 1's Value			*/

	s2440PWM->rTCFG0 |= (PRESCALER << 8);	// prescaler value=15	



	RETAILMSG(1, (_T("InitClock_PRESCALER=%d\r\n"),PRESCALER));

	/* Timer4 Divider field clear */

	s2440PWM->rTCFG1 = 0x11111;	// ;;; SHL

	s2440PWM->rTCFG1 &= ~(0xf << 16);

	

#if( SYS_TIMER_DIVIDER == D2 )

	  	s2440PWM->rTCFG1  |=  (D1_2   << 16);		/* 1/2							*/

#elif ( SYS_TIMER_DIVIDER == D4 )

		s2440PWM->rTCFG1  |=  (D1_4   << 16);		/* 1/4							*/

#elif ( SYS_TIMER_DIVIDER == D8 )

	  	s2440PWM->rTCFG1  |=  (D1_8   << 16);		/* 1/8							*/

#elif ( SYS_TIMER_DIVIDER == D16 )

	  	s2440PWM->rTCFG1  |=  (D1_16   << 16);		/* 1/16							*/

#endif

	s2440PWM->rTCNTB4 = RESCHED_INCREMENT;	//((RESCHED_PERIOD * OEM_CLOCK_FREQ) / 1000)  	

	ttmp = s2440PWM->rTCON & (~(0xf << 20));



	s2440PWM->rTCON = ttmp | (2 << 20);		/* update TCVNTB4, stop					*/

	s2440PWM->rTCON = ttmp | (1 << 20);		/* one-shot mode,  start				*/



    // Number of timer counts for reschedule interval

    dwReschedIncrement = RESCHED_INCREMENT;



	// Set OEM timer count for 1 ms

    OEMCount1ms = OEM_COUNT_1MS;

    

    // Set OEM clock frequency

    OEMClockFreq = OEM_CLOCK_FREQ;



    s2440INT->rINTMSK &= ~BIT_TIMER4;		



    return;

}