include/asm-mips/mc146818-time.h

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Machine dependent access functions for RTC registers.
   7  */
   8 #ifndef __ASM_MC146818_TIME_H
   9 #define __ASM_MC146818_TIME_H
  10
  11 #include <linux/bcd.h>
  12 #include <linux/mc146818rtc.h>
  13 #include <linux/time.h>
  14
  15 /*
  16  * For check timing call set_rtc_mmss() 500ms; used in timer interrupt.
  17  */
  18 #define USEC_AFTER      500000
  19 #define USEC_BEFORE     500000
  20
  21 /*
  22  * In order to set the CMOS clock precisely, set_rtc_mmss has to be
  23  * called 500 ms after the second nowtime has started, because when
  24  * nowtime is written into the registers of the CMOS clock, it will
  25  * jump to the next second precisely 500 ms later. Check the Motorola
  26  * MC146818A or Dallas DS12887 data sheet for details.
  27  *
  28  * BUG: This routine does not handle hour overflow properly; it just
  29  *      sets the minutes. Usually you'll only notice that after reboot!
  30  */
  31 static inline int mc146818_set_rtc_mmss(unsigned long nowtime)
  32 {
  33         int real_seconds, real_minutes, cmos_minutes;
  34         unsigned char save_control, save_freq_select;
  35         int retval = 0;
  36         unsigned long flags;
  37
  38         spin_lock_irqsave(&rtc_lock, flags);
  39         save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
  40         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
  41
  42         save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
  43         CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
  44
  45         cmos_minutes = CMOS_READ(RTC_MINUTES);
  46         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  47                 BCD_TO_BIN(cmos_minutes);
  48
  49         /*
  50          * since we're only adjusting minutes and seconds,
  51          * don't interfere with hour overflow. This avoids
  52          * messing with unknown time zones but requires your
  53          * RTC not to be off by more than 15 minutes
  54          */
  55         real_seconds = nowtime % 60;
  56         real_minutes = nowtime / 60;
  57         if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
  58                 real_minutes += 30;             /* correct for half hour time zone */
  59         real_minutes %= 60;
  60
  61         if (abs(real_minutes - cmos_minutes) < 30) {
  62                 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  63                         BIN_TO_BCD(real_seconds);
  64                         BIN_TO_BCD(real_minutes);
  65                 }
  66                 CMOS_WRITE(real_seconds,RTC_SECONDS);
  67                 CMOS_WRITE(real_minutes,RTC_MINUTES);
  68         } else {
  69                 printk(KERN_WARNING
  70                        "set_rtc_mmss: can't update from %d to %d\n",
  71                        cmos_minutes, real_minutes);
  72                 retval = -1;
  73         }
  74
  75         /* The following flags have to be released exactly in this order,
  76          * otherwise the DS12887 (popular MC146818A clone with integrated
  77          * battery and quartz) will not reset the oscillator and will not
  78          * update precisely 500 ms later. You won't find this mentioned in
  79          * the Dallas Semiconductor data sheets, but who believes data
  80          * sheets anyway ...                           -- Markus Kuhn
  81          */
  82         CMOS_WRITE(save_control, RTC_CONTROL);
  83         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
  84         spin_unlock_irqrestore(&rtc_lock, flags);
  85
  86         return retval;
  87 }
  88
  89 /*
  90  * Returns true if a clock update is in progress
  91  */
  92 static inline unsigned char rtc_is_updating(void)
  93 {
  94         unsigned char uip;
  95         unsigned long flags;
  96
  97         spin_lock_irqsave(&rtc_lock, flags);
  98         uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
  99         spin_unlock_irqrestore(&rtc_lock, flags);
 100         return uip;
 101 }
 102
 103 static inline unsigned long mc146818_get_cmos_time(void)
 104 {
 105         unsigned int year, mon, day, hour, min, sec;
 106         int i;
 107         unsigned long flags;
 108
 109         /*
 110          * The Linux interpretation of the CMOS clock register contents:
 111          * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
 112          * RTC registers show the second which has precisely just started.
 113          * Let's hope other operating systems interpret the RTC the same way.
 114          */
 115
 116         /* read RTC exactly on falling edge of update flag */
 117         for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
 118                 if (rtc_is_updating())
 119                         break;
 120         for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
 121                 if (!rtc_is_updating())
 122                         break;
 123
 124         spin_lock_irqsave(&rtc_lock, flags);
 125         do { /* Isn't this overkill ? UIP above should guarantee consistency */
 126                 sec = CMOS_READ(RTC_SECONDS);
 127                 min = CMOS_READ(RTC_MINUTES);
 128                 hour = CMOS_READ(RTC_HOURS);
 129                 day = CMOS_READ(RTC_DAY_OF_MONTH);
 130                 mon = CMOS_READ(RTC_MONTH);
 131                 year = CMOS_READ(RTC_YEAR);
 132         } while (sec != CMOS_READ(RTC_SECONDS));
 133
 134         if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 135                 BCD_TO_BIN(sec);
 136                 BCD_TO_BIN(min);
 137                 BCD_TO_BIN(hour);
 138                 BCD_TO_BIN(day);
 139                 BCD_TO_BIN(mon);
 140                 BCD_TO_BIN(year);
 141         }
 142         spin_unlock_irqrestore(&rtc_lock, flags);
 143         year = mc146818_decode_year(year);
 144
 145         return mktime(year, mon, day, hour, min, sec);
 146 }
 147
 148 #endif /* __ASM_MC146818_TIME_H */