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mc146818-time.h

/*
 * 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)
            cmos_minutes = bcd2bin(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) {
                  real_seconds = bin2bcd(real_seconds);
                  real_minutes = bin2bcd(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) {
            sec = bcd2bin(sec);
            min = bcd2bin(min);
            hour = bcd2bin(hour);
            day = bcd2bin(day);
            mon = bcd2bin(mon);
            year = bcd2bin(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 */

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