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 { 69 printk_once(KERN_NOTICE 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 time64_t 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); 100 day = CMOS_READ(RTC_DAY_OF_MONTH); 101 mon = CMOS_READ(RTC_MONTH); 102 year = CMOS_READ(RTC_YEAR); 103 } while (sec != CMOS_READ(RTC_SECONDS)); 104 105 if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) { 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 mktime64(year, mon, day, hour, min, sec); 117 } 118 119 #endif /* __ASM_MC146818_TIME_H */ 120