time.c

这个linux源代码是很全面的~基本完整了~使用c编译的~由于时间问题我没有亲自测试~但就算用来做参考资料也是非常好的

	xtime.tv_usec = new_usec;
	xtime.tv_sec = new_sec;

	/* In case of a large backwards jump in time with NTP, we want the 
	 * clock to be updated as soon as the PLL is again in lock.
	 */
	last_rtc_update = new_sec - 658;

	time_adjust = 0;                /* stop active adjtime() */
	time_status |= STA_UNSYNC;
	time_maxerror = NTP_PHASE_LIMIT;
	time_esterror = NTP_PHASE_LIMIT;

	delta_xsec = mulhdu( (tb_last_stamp-naca->tb_orig_stamp), naca->tb_to_xs );
	new_xsec = (new_usec * XSEC_PER_SEC) / USEC_PER_SEC;
	new_xsec += new_sec * XSEC_PER_SEC;
	if ( new_xsec > delta_xsec ) {
		naca->stamp_xsec = new_xsec - delta_xsec;
	}
	else {
		/* This is only for the case where the user is setting the time
		 * way back to a time such that the boot time would have been
		 * before 1970 ... eg. we booted ten days ago, and we are
		 * setting the time to Jan 5, 1970 */
		naca->stamp_xsec = new_xsec;
		naca->tb_orig_stamp = tb_last_stamp;
	}

	naca->tz_minuteswest = sys_tz.tz_minuteswest;
	naca->tz_dsttime = sys_tz.tz_dsttime;

	write_unlock_irqrestore(&xtime_lock, flags);
}

/*
 * This function is a copy of the architecture independent function
 * but which calls do_settimeofday rather than setting the xtime
 * fields itself.  This way, the fields which are used for 
 * do_settimeofday get updated too.
 */
long ppc64_sys32_stime(int* tptr)
{
	int value;
	struct timeval myTimeval;

	if (!capable(CAP_SYS_TIME))
		return -EPERM;

	if (get_user(value, tptr))
		return -EFAULT;

	myTimeval.tv_sec = value;
	myTimeval.tv_usec = 0;

	do_settimeofday(&myTimeval);

	return 0;
}

/*
 * This function is a copy of the architecture independent function
 * but which calls do_settimeofday rather than setting the xtime
 * fields itself.  This way, the fields which are used for 
 * do_settimeofday get updated too.
 */
long ppc64_sys_stime(long* tptr)
{
	long value;
	struct timeval myTimeval;

	if (!capable(CAP_SYS_TIME))
		return -EPERM;

	if (get_user(value, tptr))
		return -EFAULT;

	myTimeval.tv_sec = value;
	myTimeval.tv_usec = 0;

	do_settimeofday(&myTimeval);

	return 0;
}

void __init time_init(void)
{
	/* This function is only called on the boot processor */
	unsigned long flags;
	struct rtc_time tm;

	ppc_md.calibrate_decr();

	if ( ! piranha_simulator ) {
		ppc_md.get_boot_time(&tm);
	}
	write_lock_irqsave(&xtime_lock, flags);
	xtime.tv_sec = mktime(tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
			      tm.tm_hour, tm.tm_min, tm.tm_sec);
	tb_last_stamp = get_tb();
	naca->tb_orig_stamp = tb_last_stamp;
	naca->tb_update_count = 0;
	naca->tb_ticks_per_sec = tb_ticks_per_sec;
	naca->stamp_xsec = xtime.tv_sec * XSEC_PER_SEC;
	naca->tb_to_xs = tb_to_xs;

	xtime_sync_interval = tb_ticks_per_sec - (tb_ticks_per_sec/8);
	next_xtime_sync_tb = tb_last_stamp + xtime_sync_interval;

	time_freq = 0;

	xtime.tv_usec = 0;
	last_rtc_update = xtime.tv_sec;
	write_unlock_irqrestore(&xtime_lock, flags);

	/* Not exact, but the timer interrupt takes care of this */
	set_dec(tb_ticks_per_jiffy);

	/* This horrible hack gives setup a hook just before console_init */
	setup_before_console_init();
}

/* 
 * After adjtimex is called, adjust the conversion of tb ticks
 * to microseconds to keep do_gettimeofday synchronized 
 * with ntpd.
 *
 * Use the time_adjust, time_freq and time_offset computed by adjtimex to 
 * adjust the frequency.
 */

/* #define DEBUG_PPC_ADJTIMEX 1 */

void ppc_adjtimex(void)
{
	unsigned long den, new_tb_ticks_per_sec, tb_ticks, old_xsec, new_tb_to_xs, new_xsec, new_stamp_xsec;
	unsigned long tb_ticks_per_sec_delta;
	long delta_freq, ltemp;
	struct div_result divres; 
	unsigned long flags;
	long singleshot_ppm = 0;

	/* Compute parts per million frequency adjustment to accomplish the time adjustment
	   implied by time_offset to be applied over the elapsed time indicated by time_constant.
	   Use SHIFT_USEC to get it into the same units as time_freq. */
	if ( time_offset < 0 ) {
		ltemp = -time_offset;
		ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
		ltemp >>= SHIFT_KG + time_constant;
		ltemp = -ltemp;
	}
	else {
		ltemp = time_offset;
		ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
		ltemp >>= SHIFT_KG + time_constant;
	}
	
	/* If there is a single shot time adjustment in progress */
	if ( time_adjust ) {
#ifdef DEBUG_PPC_ADJTIMEX
		printk("ppc_adjtimex: ");
		if ( adjusting_time == 0 )
			printk("starting ");
		printk("single shot time_adjust = %ld\n", time_adjust);
#endif	
	
		adjusting_time = 1;
		
		/* Compute parts per million frequency adjustment to match time_adjust */
		singleshot_ppm = tickadj * HZ;	
		/*
		 * The adjustment should be tickadj*HZ to match the code in
		 * linux/kernel/timer.c, but experiments show that this is too
		 * large. 3/4 of tickadj*HZ seems about right
		 */
		singleshot_ppm -= singleshot_ppm / 4;
		/* Use SHIFT_USEC to get it into the same units as time_freq */	
		singleshot_ppm <<= SHIFT_USEC;
		if ( time_adjust < 0 )
			singleshot_ppm = -singleshot_ppm;
	}
	else {
#ifdef DEBUG_PPC_ADJTIMEX
		if ( adjusting_time )
			printk("ppc_adjtimex: ending single shot time_adjust\n");
#endif
		adjusting_time = 0;
	}
	
	/* Add up all of the frequency adjustments */
	delta_freq = time_freq + ltemp + singleshot_ppm;
	
	/* Compute a new value for tb_ticks_per_sec based on the frequency adjustment */
	den = 1000000 * (1 << (SHIFT_USEC - 8));
	if ( delta_freq < 0 ) {
		tb_ticks_per_sec_delta = ( tb_ticks_per_sec * ( (-delta_freq) >> (SHIFT_USEC - 8))) / den;
		new_tb_ticks_per_sec = tb_ticks_per_sec + tb_ticks_per_sec_delta;
	}
	else {
		tb_ticks_per_sec_delta = ( tb_ticks_per_sec * ( delta_freq >> (SHIFT_USEC - 8))) / den;
		new_tb_ticks_per_sec = tb_ticks_per_sec - tb_ticks_per_sec_delta;
	}
	
#ifdef DEBUG_PPC_ADJTIMEX
	printk("ppc_adjtimex: ltemp = %ld, time_freq = %ld, singleshot_ppm = %ld\n", ltemp, time_freq, singleshot_ppm);
	printk("ppc_adjtimex: tb_ticks_per_sec - base = %ld  new = %ld\n", tb_ticks_per_sec, new_tb_ticks_per_sec);
#endif
				
	/*
	 * Compute a new value of tb_to_xs (used to convert tb to microseconds
	 * and a new value of stamp_xsec which is the time (in 1/2^20 second
	 * units) corresponding to tb_orig_stamp.  This new value of stamp_xsec
	 * compensates for the change in frequency (implied by the new
	 * tb_to_xs) and so guarantees that the current time remains the same
	 *
	 */ 
	tb_ticks = get_tb() - naca->tb_orig_stamp;
	div128_by_32( 1024*1024, 0, new_tb_ticks_per_sec, &divres );
	new_tb_to_xs = divres.result_low;
	new_xsec = mulhdu( tb_ticks, new_tb_to_xs );

	write_lock_irqsave( &xtime_lock, flags );
	old_xsec = mulhdu( tb_ticks, naca->tb_to_xs );
	new_stamp_xsec = naca->stamp_xsec + old_xsec - new_xsec;

	/*
	 * tb_update_count is used to allow the problem state gettimeofday code
	 * to assure itself that it sees a consistent view of the tb_to_xs and
	 * stamp_xsec variables.  It reads the tb_update_count, then reads
	 * tb_to_xs and stamp_xsec and then reads tb_update_count again.  If
	 * the two values of tb_update_count match and are even then the
	 * tb_to_xs and stamp_xsec values are consistent.  If not, then it
	 * loops back and reads them again until this criteria is met.
	 */
	++(naca->tb_update_count);
	wmb();
	naca->tb_to_xs = new_tb_to_xs;
	naca->stamp_xsec = new_stamp_xsec;
	wmb();
	++(naca->tb_update_count);

	write_unlock_irqrestore( &xtime_lock, flags );

}


#define TICK_SIZE tick
#define FEBRUARY	2
#define	STARTOFTIME	1970
#define SECDAY		86400L
#define SECYR		(SECDAY * 365)
#define	leapyear(year)		((year) % 4 == 0)
#define	days_in_year(a) 	(leapyear(a) ? 366 : 365)
#define	days_in_month(a) 	(month_days[(a) - 1])

static int month_days[12] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

/*
 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
 */
void GregorianDay(struct rtc_time * tm)
{
	int leapsToDate;
	int lastYear;
	int day;
	int MonthOffset[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

	lastYear=tm->tm_year-1;

	/*
	 * Number of leap corrections to apply up to end of last year
	 */
	leapsToDate = lastYear/4 - lastYear/100 + lastYear/400;

	/*
	 * This year is a leap year if it is divisible by 4 except when it is
	 * divisible by 100 unless it is divisible by 400
	 *
	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 will be
	 */
	if((tm->tm_year%4==0) &&
	   ((tm->tm_year%100!=0) || (tm->tm_year%400==0)) &&
	   (tm->tm_mon>2))
	{
		/*
		 * We are past Feb. 29 in a leap year
		 */
		day=1;
	}
	else
	{
		day=0;
	}

	day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] +
		   tm->tm_mday;

	tm->tm_wday=day%7;
}

void to_tm(int tim, struct rtc_time * tm)
{
	register int    i;
	register long   hms, day;

	day = tim / SECDAY;
	hms = tim % SECDAY;

	/* Hours, minutes, seconds are easy */
	tm->tm_hour = hms / 3600;
	tm->tm_min = (hms % 3600) / 60;
	tm->tm_sec = (hms % 3600) % 60;

	/* Number of years in days */
	for (i = STARTOFTIME; day >= days_in_year(i); i++)
		day -= days_in_year(i);
	tm->tm_year = i;

	/* Number of months in days left */
	if (leapyear(tm->tm_year))
		days_in_month(FEBRUARY) = 29;
	for (i = 1; day >= days_in_month(i); i++)
		day -= days_in_month(i);
	days_in_month(FEBRUARY) = 28;
	tm->tm_mon = i;

	/* Days are what is left over (+1) from all that. */
	tm->tm_mday = day + 1;

	/*
	 * Determine the day of week
	 */
	GregorianDay(tm);
}

#if 0
/* Auxiliary function to compute scaling factors */
/* Actually the choice of a timebase running at 1/4 the of the bus
 * frequency giving resolution of a few tens of nanoseconds is quite nice.
 * It makes this computation very precise (27-28 bits typically) which
 * is optimistic considering the stability of most processor clock
 * oscillators and the precision with which the timebase frequency
 * is measured but does not harm.
 */
unsigned mulhwu_scale_factor(unsigned inscale, unsigned outscale) {
        unsigned mlt=0, tmp, err;
        /* No concern for performance, it's done once: use a stupid
         * but safe and compact method to find the multiplier.
         */
  
        for (tmp = 1U<<31; tmp != 0; tmp >>= 1) {
                if (mulhwu(inscale, mlt|tmp) < outscale) mlt|=tmp;
        }
  
        /* We might still be off by 1 for the best approximation.
         * A side effect of this is that if outscale is too large
         * the returned value will be zero.
         * Many corner cases have been checked and seem to work,
         * some might have been forgotten in the test however.
         */
  
        err = inscale*(mlt+1);
        if (err <= inscale/2) mlt++;
        return mlt;
  }
#endif

/*
 * Divide a 128-bit dividend by a 32-bit divisor, leaving a 128 bit
 * result.
 */

void div128_by_32( unsigned long dividend_high, unsigned long dividend_low,
		   unsigned divisor, struct div_result *dr )
{
	unsigned long a,b,c,d, w,x,y,z, ra,rb,rc;

	a = dividend_high >> 32;
	b = dividend_high & 0xffffffff;
	c = dividend_low >> 32;
	d = dividend_low & 0xffffffff;

	w = a/divisor;
	ra = (a - (w * divisor)) << 32;

	x = (ra + b)/divisor;
	rb = ((ra + b) - (x * divisor)) << 32;

	y = (rb + c)/divisor;
	rc = ((rb + b) - (y * divisor)) << 32;

	z = (rc + d)/divisor;

	dr->result_high = (w << 32) + x;
	dr->result_low  = (y << 32) + z;

}