src/lib/rtc.c

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2
   3 /*
   4  * From U-Boot 2016.05
   5  */
   6
   7 #include <console/console.h>
   8 #include <rtc.h>
   9
  10 #define FEBRUARY                2
  11 #define STARTOFTIME             1970
  12 #define SECDAY                  86400L
  13 #define SECYR                   (SECDAY * 365)
  14 #define LEAP_YEAR(year)         ((year) % 4 == 0)
  15 #define DAYS_IN_YEAR(a)         (LEAP_YEAR(a) ? 366 : 365)
  16 #define DAYS_IN_MONTH(a)        (month_days[(a) - 1])
  17
  18 static const char *const weekdays[] = {
  19         "Sun", "Mon", "Tues", "Wednes", "Thurs", "Fri", "Satur"
  20 };
  21
  22 /* Zeller's rule */
  23 static int rtc_calc_weekday(struct rtc_time *tm)
  24 {
  25         if (tm->year < 1971)
  26                 return -1;
  27
  28         /* In Zeller's rule, January and February are treated as if they
  29            are months 13 and 14 of the previous year (March is still month 3) */
  30         const int zyear = ((tm->mon < 3) ? tm->year - 1 : tm->year);
  31         const int q = tm->mday;
  32         const int m = (tm->mon < 3) ? tm->mon + 12 : tm->mon;
  33         const int K = zyear % 100;
  34         const int J = zyear / 100;
  35
  36         /*
  37          * Because of the way the modulo operator works with negative numbers,
  38          * the traditional formulation of Zeller's rule must be modified
  39          * slightly to make the numerator positive (i.e., add 5J instead of
  40          * subtracting 2J).  Also subtract 1 so that Sunday is day 0.
  41          */
  42         const int h = (q + (13 * (m + 1)) / 5
  43                        + K + (K / 4) + (J / 4) + (5 * J) - 1) % 7;
  44
  45         tm->wday = h;
  46         return 0;
  47 }
  48
  49 int rtc_to_tm(int tim, struct rtc_time *tm)
  50 {
  51         int month_days[12] = {
  52                 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
  53         };
  54         register int i;
  55         register long hms, day;
  56
  57         day = tim / SECDAY;
  58         hms = tim % SECDAY;
  59
  60         /* Hours, minutes, seconds are easy */
  61         tm->hour = hms / 3600;
  62         tm->min = (hms % 3600) / 60;
  63         tm->sec = (hms % 3600) % 60;
  64
  65         /* Number of years in days */
  66         for (i = STARTOFTIME; day >= DAYS_IN_YEAR(i); i++)
  67                 day -= DAYS_IN_YEAR(i);
  68         tm->year = i;
  69
  70         /* Number of months in days left */
  71         if (LEAP_YEAR(tm->year))
  72                 DAYS_IN_MONTH(FEBRUARY) = 29;
  73         for (i = 1; day >= DAYS_IN_MONTH(i); i++)
  74                 day -= DAYS_IN_MONTH(i);
  75         DAYS_IN_MONTH(FEBRUARY) = 28;
  76         tm->mon = i;
  77
  78         /* Days are what is left over (+1) from all that */
  79         tm->mday = day + 1;
  80
  81         /* Determine the day of week */
  82         return rtc_calc_weekday(tm);
  83 }
  84
  85 /*
  86  * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
  87  * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
  88  * => year=1980,  mon=12,  day=31,  hour=23,  min=59,  sec=59.
  89  *
  90  * [For the Julian calendar (which was used in Russia before 1917,
  91  * Britain & colonies before 1752,  anywhere else before 1582,
  92  * and is still in use by some communities) leave out the
  93  * -year / 100 + year / 400 terms,  and add 10.]
  94  *
  95  * This algorithm was first published by Gauss (I think).
  96  *
  97  * WARNING: this function will overflow on 2106-02-07 06:28:16 on
  98  * machines where long is 32-bit! (However, as time_t is signed, we
  99  * will already get problems at other places on 2038-01-19 03:14:08)
 100  */
 101 unsigned long rtc_mktime(const struct rtc_time *tm)
 102 {
 103         int mon = tm->mon;
 104         int year = tm->year;
 105         int days, hours;
 106
 107         mon -= 2;
 108         if (0 >= (int)mon) {    /* 1..12 -> 11, 12, 1..10 */
 109                 mon += 12;      /* Puts Feb last since it has leap day */
 110                 year -= 1;
 111         }
 112
 113         days = (unsigned long)(year / 4 - year / 100 + year / 400 +
 114                                367 * mon / 12 + tm->mday) +
 115                                year * 365 - 719499;
 116         hours = days * 24 + tm->hour;
 117         return (hours * 60 + tm->min) * 60 + tm->sec;
 118 }
 119
 120 void rtc_display(const struct rtc_time *tm)
 121 {
 122         printk(BIOS_INFO, "Date: %5d-%02d-%02d (%sday)  Time: %2d:%02d:%02d\n",
 123                tm->year,  tm->mon,  tm->mday,
 124                (tm->wday < 0 || tm->wday > 6) ? "unknown " : weekdays[tm->wday],
 125                tm->hour,  tm->min,  tm->sec);
 126 }