text: /*
   * This file is subject to the terms and conditions of the GNU General Public
   * License.  See the file "COPYING" in the main directory of this archive
   * for more details.
   *
   * Machine dependent access functions for RTC registers.
   */
  #ifndef __ASM_MC146818_TIME_H
  #define __ASM_MC146818_TIME_H
  
  #include <linux/bcd.h>
  #include <linux/mc146818rtc.h>
  #include <linux/time.h>
  
  /*
   * For check timing call set_rtc_mmss() 500ms; used in timer interrupt.
   */
  #define USEC_AFTER	500000
  #define USEC_BEFORE	500000
  
  /*
   * In order to set the CMOS clock precisely, set_rtc_mmss has to be
   * called 500 ms after the second nowtime has started, because when
   * nowtime is written into the registers of the CMOS clock, it will
   * jump to the next second precisely 500 ms later. Check the Motorola
   * MC146818A or Dallas DS12887 data sheet for details.
   *
   * BUG: This routine does not handle hour overflow properly; it just
   *      sets the minutes. Usually you'll only notice that after reboot!
   */
  static inline int mc146818_set_rtc_mmss(unsigned long nowtime)
  {
  	int real_seconds, real_minutes, cmos_minutes;
  	unsigned char save_control, save_freq_select;
  	int retval = 0;
  	unsigned long flags;
  
  	spin_lock_irqsave(&rtc_lock, flags);
  	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
  	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
  
  	save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
  	CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
  
  	cmos_minutes = CMOS_READ(RTC_MINUTES);
  	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  		BCD_TO_BIN(cmos_minutes);
  
  	/*
  	 * since we're only adjusting minutes and seconds,
  	 * don't interfere with hour overflow. This avoids
  	 * messing with unknown time zones but requires your
  	 * RTC not to be off by more than 15 minutes
  	 */
  	real_seconds = nowtime % 60;
  	real_minutes = nowtime / 60;
  	if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
  		real_minutes += 30;		/* correct for half hour time zone */
  	real_minutes %= 60;
  
  	if (abs(real_minutes - cmos_minutes) < 30) {
  		if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  			BIN_TO_BCD(real_seconds);
  			BIN_TO_BCD(real_minutes);
  		}
  		CMOS_WRITE(real_seconds, RTC_SECONDS);
  		CMOS_WRITE(real_minutes, RTC_MINUTES);
  	} else {
  		printk(KERN_WARNING
  		       "set_rtc_mmss: can't update from %d to %d\n",
  		       cmos_minutes, real_minutes);
  		retval = -1;
  	}
  
  	/* The following flags have to be released exactly in this order,
  	 * otherwise the DS12887 (popular MC146818A clone with integrated
  	 * battery and quartz) will not reset the oscillator and will not
  	 * update precisely 500 ms later. You won't find this mentioned in
  	 * the Dallas Semiconductor data sheets, but who believes data
  	 * sheets anyway ...                           -- Markus Kuhn
  	 */
  	CMOS_WRITE(save_control, RTC_CONTROL);
  	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
  	spin_unlock_irqrestore(&rtc_lock, flags);
  
  	return retval;
  }
  
  static inline unsigned long mc146818_get_cmos_time(void)
  {
  	unsigned int year, mon, day, hour, min, sec;
  	unsigned long flags;
  
  	spin_lock_irqsave(&rtc_lock, flags);
  
  	do {
  		sec = CMOS_READ(RTC_SECONDS);
  		min = CMOS_READ(RTC_MINUTES);
  		hour = CMOS_READ(RTC_HOURS);
  		day = CMOS_READ(RTC_DAY_OF_MONTH);
  		mon = CMOS_READ(RTC_MONTH);
  		year = CMOS_READ(RTC_YEAR);
  	} while (sec != CMOS_READ(RTC_SECONDS));
  
  	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  		BCD_TO_BIN(sec);
  		BCD_TO_BIN(min);
  		BCD_TO_BIN(hour);
  		BCD_TO_BIN(day);
  		BCD_TO_BIN(mon);
  		BCD_TO_BIN(year);
  	}
  	spin_unlock_irqrestore(&rtc_lock, flags);
  	year = mc146818_decode_year(year);
  
  	return mktime(year, mon, day, hour, min, sec);
  }
  
  #endif /* __ASM_MC146818_TIME_H */
  