include/asm-i386/mach-default/mach_time.h

   1 /*
   2  *  include/asm-i386/mach-default/mach_time.h
   3  *
   4  *  Machine specific set RTC function for generic.
   5  *  Split out from time.c by Osamu Tomita <tomita@cinet.co.jp>
   6  */
   7 #ifndef _MACH_TIME_H
   8 #define _MACH_TIME_H
   9
  10 #include <linux/mc146818rtc.h>
  11
  12 /* for check timing call set_rtc_mmss() 500ms     */
  13 /* used in arch/i386/time.c::do_timer_interrupt() */
  14 #define USEC_AFTER      500000
  15 #define USEC_BEFORE     500000
  16
  17 /*
  18  * In order to set the CMOS clock precisely, set_rtc_mmss has to be
  19  * called 500 ms after the second nowtime has started, because when
  20  * nowtime is written into the registers of the CMOS clock, it will
  21  * jump to the next second precisely 500 ms later. Check the Motorola
  22  * MC146818A or Dallas DS12887 data sheet for details.
  23  *
  24  * BUG: This routine does not handle hour overflow properly; it just
  25  *      sets the minutes. Usually you'll only notice that after reboot!
  26  */
  27 static inline int mach_set_rtc_mmss(unsigned long nowtime)
  28 {
  29         int retval = 0;
  30         int real_seconds, real_minutes, cmos_minutes;
  31         unsigned char save_control, save_freq_select;
  32
  33         save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
  34         CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
  35
  36         save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
  37         CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
  38
  39         cmos_minutes = CMOS_READ(RTC_MINUTES);
  40         if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
  41                 BCD_TO_BIN(cmos_minutes);
  42
  43         /*
  44          * since we're only adjusting minutes and seconds,
  45          * don't interfere with hour overflow. This avoids
  46          * messing with unknown time zones but requires your
  47          * RTC not to be off by more than 15 minutes
  48          */
  49         real_seconds = nowtime % 60;
  50         real_minutes = nowtime / 60;
  51         if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
  52                 real_minutes += 30;             /* correct for half hour time zone */
  53         real_minutes %= 60;
  54
  55         if (abs(real_minutes - cmos_minutes) < 30) {
  56                 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
  57                         BIN_TO_BCD(real_seconds);
  58                         BIN_TO_BCD(real_minutes);
  59                 }
  60                 CMOS_WRITE(real_seconds,RTC_SECONDS);
  61                 CMOS_WRITE(real_minutes,RTC_MINUTES);
  62         } else {
  63                 printk(KERN_WARNING
  64                        "set_rtc_mmss: can't update from %d to %d\n",
  65                        cmos_minutes, real_minutes);
  66                 retval = -1;
  67         }
  68
  69         /* The following flags have to be released exactly in this order,
  70          * otherwise the DS12887 (popular MC146818A clone with integrated
  71          * battery and quartz) will not reset the oscillator and will not
  72          * update precisely 500 ms later. You won't find this mentioned in
  73          * the Dallas Semiconductor data sheets, but who believes data
  74          * sheets anyway ...                           -- Markus Kuhn
  75          */
  76         CMOS_WRITE(save_control, RTC_CONTROL);
  77         CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
  78
  79         return retval;
  80 }
  81
  82 static inline unsigned long mach_get_cmos_time(void)
  83 {
  84         unsigned int year, mon, day, hour, min, sec;
  85         int i;
  86
  87         /* The Linux interpretation of the CMOS clock register contents:
  88          * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
  89          * RTC registers show the second which has precisely just started.
  90          * Let's hope other operating systems interpret the RTC the same way.
  91          */
  92         /* read RTC exactly on falling edge of update flag */
  93         for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
  94                 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
  95                         break;
  96         for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
  97                 if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
  98                         break;
  99         do { /* Isn't this overkill ? UIP above should guarantee consistency */
 100                 sec = CMOS_READ(RTC_SECONDS);
 101                 min = CMOS_READ(RTC_MINUTES);
 102                 hour = CMOS_READ(RTC_HOURS);
 103                 day = CMOS_READ(RTC_DAY_OF_MONTH);
 104                 mon = CMOS_READ(RTC_MONTH);
 105                 year = CMOS_READ(RTC_YEAR);
 106         } while (sec != CMOS_READ(RTC_SECONDS));
 107         if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 108           {
 109             BCD_TO_BIN(sec);
 110             BCD_TO_BIN(min);
 111             BCD_TO_BIN(hour);
 112             BCD_TO_BIN(day);
 113             BCD_TO_BIN(mon);
 114             BCD_TO_BIN(year);
 115           }
 116         if ((year += 1900) < 1970)
 117                 year += 100;
 118
 119         return mktime(year, mon, day, hour, min, sec);
 120 }
 121
 122 #endif /* !_MACH_TIME_H */