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mc146818-time.h
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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  cmos_minutes = bcd2bin(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  real_seconds = bin2bcd(real_seconds);
64  real_minutes = bin2bcd(real_minutes);
65  }
66  CMOS_WRITE(real_seconds, RTC_SECONDS);
67  CMOS_WRITE(real_minutes, RTC_MINUTES);
68  } else {
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 static inline unsigned long mc146818_get_cmos_time(void)
90 {
91  unsigned int year, mon, day, hour, min, sec;
92  unsigned long flags;
93 
94  spin_lock_irqsave(&rtc_lock, flags);
95 
96  do {
97  sec = CMOS_READ(RTC_SECONDS);
98  min = CMOS_READ(RTC_MINUTES);
99  hour = CMOS_READ(RTC_HOURS);
101  mon = CMOS_READ(RTC_MONTH);
102  year = CMOS_READ(RTC_YEAR);
103  } while (sec != CMOS_READ(RTC_SECONDS));
104 
106  sec = bcd2bin(sec);
107  min = bcd2bin(min);
108  hour = bcd2bin(hour);
109  day = bcd2bin(day);
110  mon = bcd2bin(mon);
111  year = bcd2bin(year);
112  }
113  spin_unlock_irqrestore(&rtc_lock, flags);
114  year = mc146818_decode_year(year);
115 
116  return mktime(year, mon, day, hour, min, sec);
117 }
118 
119 #endif /* __ASM_MC146818_TIME_H */