2 * RTC related functions
5 #include <linux/mc146818rtc.h>
10 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
11 * called 500 ms after the second nowtime has started, because when
12 * nowtime is written into the registers of the CMOS clock, it will
13 * jump to the next second precisely 500 ms later. Check the Motorola
14 * MC146818A or Dallas DS12887 data sheet for details.
16 * BUG: This routine does not handle hour overflow properly; it just
17 * sets the minutes. Usually you'll only notice that after reboot!
19 int mach_set_rtc_mmss(unsigned long nowtime)
22 int real_seconds, real_minutes, cmos_minutes;
23 unsigned char save_control, save_freq_select;
25 save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
26 CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
28 save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
29 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
31 cmos_minutes = CMOS_READ(RTC_MINUTES);
32 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
33 BCD_TO_BIN(cmos_minutes);
36 * since we're only adjusting minutes and seconds,
37 * don't interfere with hour overflow. This avoids
38 * messing with unknown time zones but requires your
39 * RTC not to be off by more than 15 minutes
41 real_seconds = nowtime % 60;
42 real_minutes = nowtime / 60;
43 if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
44 real_minutes += 30; /* correct for half hour time zone */
47 if (abs(real_minutes - cmos_minutes) < 30) {
48 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
49 BIN_TO_BCD(real_seconds);
50 BIN_TO_BCD(real_minutes);
52 CMOS_WRITE(real_seconds,RTC_SECONDS);
53 CMOS_WRITE(real_minutes,RTC_MINUTES);
56 "set_rtc_mmss: can't update from %d to %d\n",
57 cmos_minutes, real_minutes);
61 /* The following flags have to be released exactly in this order,
62 * otherwise the DS12887 (popular MC146818A clone with integrated
63 * battery and quartz) will not reset the oscillator and will not
64 * update precisely 500 ms later. You won't find this mentioned in
65 * the Dallas Semiconductor data sheets, but who believes data
66 * sheets anyway ... -- Markus Kuhn
68 CMOS_WRITE(save_control, RTC_CONTROL);
69 CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
74 unsigned long mach_get_cmos_time(void)
76 unsigned int year, mon, day, hour, min, sec;
79 sec = CMOS_READ(RTC_SECONDS);
80 min = CMOS_READ(RTC_MINUTES);
81 hour = CMOS_READ(RTC_HOURS);
82 day = CMOS_READ(RTC_DAY_OF_MONTH);
83 mon = CMOS_READ(RTC_MONTH);
84 year = CMOS_READ(RTC_YEAR);
85 } while (sec != CMOS_READ(RTC_SECONDS));
87 if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
100 return mktime(year, mon, day, hour, min, sec);
103 DEFINE_SPINLOCK(rtc_lock);
104 EXPORT_SYMBOL(rtc_lock);
107 * This is a special lock that is owned by the CPU and holds the index
108 * register we are working with. It is required for NMI access to the
109 * CMOS/RTC registers. See include/asm-i386/mc146818rtc.h for details.
111 volatile unsigned long cmos_lock = 0;
112 EXPORT_SYMBOL(cmos_lock);
114 /* Routines for accessing the CMOS RAM/RTC. */
115 unsigned char rtc_cmos_read(unsigned char addr)
119 lock_cmos_prefix(addr);
120 outb_p(addr, RTC_PORT(0));
121 val = inb_p(RTC_PORT(1));
122 lock_cmos_suffix(addr);
125 EXPORT_SYMBOL(rtc_cmos_read);
127 void rtc_cmos_write(unsigned char val, unsigned char addr)
129 lock_cmos_prefix(addr);
130 outb_p(addr, RTC_PORT(0));
131 outb_p(val, RTC_PORT(1));
132 lock_cmos_suffix(addr);
134 EXPORT_SYMBOL(rtc_cmos_write);
136 static int set_rtc_mmss(unsigned long nowtime)
141 /* gets recalled with irq locally disabled */
142 /* XXX - does irqsave resolve this? -johnstul */
143 spin_lock_irqsave(&rtc_lock, flags);
144 retval = set_wallclock(nowtime);
145 spin_unlock_irqrestore(&rtc_lock, flags);
150 /* not static: needed by APM */
151 unsigned long read_persistent_clock(void)
153 unsigned long retval;
156 spin_lock_irqsave(&rtc_lock, flags);
157 retval = get_wallclock();
158 spin_unlock_irqrestore(&rtc_lock, flags);
163 int update_persistent_clock(struct timespec now)
165 return set_rtc_mmss(now.tv_sec);