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
  37         save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
  38         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
  39
  40         save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
  41         CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
  42
  43         cmos_minutes = CMOS_READ(RTC_MINUTES);
  44         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  45                 BCD_TO_BIN(cmos_minutes);
  46
  47         /*
  48          * since we're only adjusting minutes and seconds,
  49          * don't interfere with hour overflow. This avoids
  50          * messing with unknown time zones but requires your
  51          * RTC not to be off by more than 15 minutes
  52          */
  53         real_seconds = nowtime % 60;
  54         real_minutes = nowtime / 60;
  55         if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
  56                 real_minutes += 30;             /* correct for half hour time zone */
  57         real_minutes %= 60;
  58
  59         if (abs(real_minutes - cmos_minutes) < 30) {
  60                 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  61                         BIN_TO_BCD(real_seconds);
  62                         BIN_TO_BCD(real_minutes);
  63                 }
  64                 CMOS_WRITE(real_seconds,RTC_SECONDS);
  65                 CMOS_WRITE(real_minutes,RTC_MINUTES);
  66         } else {
  67                 printk(KERN_WARNING
  68                        "set_rtc_mmss: can't update from %d to %d\n",
  69                        cmos_minutes, real_minutes);
  70                 retval = -1;
  71         }
  72
  73         /* The following flags have to be released exactly in this order,
  74          * otherwise the DS12887 (popular MC146818A clone with integrated
  75          * battery and quartz) will not reset the oscillator and will not
  76          * update precisely 500 ms later. You won't find this mentioned in
  77          * the Dallas Semiconductor data sheets, but who believes data
  78          * sheets anyway ...                           -- Markus Kuhn
  79          */
  80         CMOS_WRITE(save_control, RTC_CONTROL);
  81         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
  82
  83         return retval;
  84 }
  85
  86 static inline unsigned long mc146818_get_cmos_time(void)
  87 {
  88         unsigned int year, mon, day, hour, min, sec;
  89         int i;
  90
  91         /*
  92          * The Linux interpretation of the CMOS clock register contents:
  93          * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
  94          * RTC registers show the second which has precisely just started.
  95          * Let's hope other operating systems interpret the RTC the same way.
  96          */
  97
  98         /* read RTC exactly on falling edge of update flag */
  99         for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
 100                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
 101                         break;
 102         for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
 103                 if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
 104                         break;
 105
 106         do { /* Isn't this overkill ? UIP above should guarantee consistency */
 107                 sec = CMOS_READ(RTC_SECONDS);
 108                 min = CMOS_READ(RTC_MINUTES);
 109                 hour = CMOS_READ(RTC_HOURS);
 110                 day = CMOS_READ(RTC_DAY_OF_MONTH);
 111                 mon = CMOS_READ(RTC_MONTH);
 112                 year = CMOS_READ(RTC_YEAR);
 113         } while (sec != CMOS_READ(RTC_SECONDS));
 114
 115         if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 116                 BCD_TO_BIN(sec);
 117                 BCD_TO_BIN(min);
 118                 BCD_TO_BIN(hour);
 119                 BCD_TO_BIN(day);
 120                 BCD_TO_BIN(mon);
 121                 BCD_TO_BIN(year);
 122         }
 123         year = mc146818_decode_year(year);
 124
 125         return mktime(year, mon, day, hour, min, sec);
 126 }
 127
 128 #endif /* __ASM_MC146818_TIME_H */