arch/sh/boards/mach-dreamcast/rtc.c

   1 /*
   2  * arch/sh/boards/dreamcast/rtc.c
   3  *
   4  * Dreamcast AICA RTC routines.
   5  *
   6  * Copyright (c) 2001, 2002 M. R. Brown <mrbrown@0xd6.org>
   7  * Copyright (c) 2002 Paul Mundt <lethal@chaoticdreams.org>
   8  *
   9  * Released under the terms of the GNU GPL v2.0.
  10  *
  11  */
  12
  13 #include <linux/time.h>
  14 #include <asm/rtc.h>
  15 #include <asm/io.h>
  16
  17 /* The AICA RTC has an Epoch of 1/1/1950, so we must subtract 20 years (in
  18    seconds) to get the standard Unix Epoch when getting the time, and add
  19    20 years when setting the time. */
  20 #define TWENTY_YEARS ((20 * 365LU + 5) * 86400)
  21
  22 /* The AICA RTC is represented by a 32-bit seconds counter stored in 2 16-bit
  23    registers.*/
  24 #define AICA_RTC_SECS_H         0xa0710000
  25 #define AICA_RTC_SECS_L         0xa0710004
  26
  27 /**
  28  * aica_rtc_gettimeofday - Get the time from the AICA RTC
  29  * @ts: pointer to resulting timespec
  30  *
  31  * Grabs the current RTC seconds counter and adjusts it to the Unix Epoch.
  32  */
  33 static void aica_rtc_gettimeofday(struct timespec *ts)
  34 {
  35         unsigned long val1, val2;
  36
  37         do {
  38                 val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  39                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  40
  41                 val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  42                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  43         } while (val1 != val2);
  44
  45         ts->tv_sec = val1 - TWENTY_YEARS;
  46
  47         /* Can't get nanoseconds with just a seconds counter. */
  48         ts->tv_nsec = 0;
  49 }
  50
  51 /**
  52  * aica_rtc_settimeofday - Set the AICA RTC to the current time
  53  * @secs: contains the time_t to set
  54  *
  55  * Adjusts the given @tv to the AICA Epoch and sets the RTC seconds counter.
  56  */
  57 static int aica_rtc_settimeofday(const time_t secs)
  58 {
  59         unsigned long val1, val2;
  60         unsigned long adj = secs + TWENTY_YEARS;
  61
  62         do {
  63                 __raw_writel((adj & 0xffff0000) >> 16, AICA_RTC_SECS_H);
  64                 __raw_writel((adj & 0xffff), AICA_RTC_SECS_L);
  65
  66                 val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  67                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  68
  69                 val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
  70                         (__raw_readl(AICA_RTC_SECS_L) & 0xffff);
  71         } while (val1 != val2);
  72
  73         return 0;
  74 }
  75
  76 void aica_time_init(void)
  77 {
  78         rtc_sh_get_time = aica_rtc_gettimeofday;
  79         rtc_sh_set_time = aica_rtc_settimeofday;
  80 }
  81