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rtc.c
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1 /*
2  * arch/sh/boards/dreamcast/rtc.c
3  *
4  * Dreamcast AICA RTC routines.
5  *
6  * Copyright (c) 2001, 2002 M. R. Brown <[email protected]>
7  * Copyright (c) 2002 Paul Mundt <[email protected]>
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 
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 
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