1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
|
#include "devices/rtc.h"
#include <stdio.h>
#include "threads/io.h"
/* This code is an interface to the MC146818A-compatible real
time clock found on PC motherboards. See [MC146818A] for
hardware details. */
/* I/O register addresses. */
#define CMOS_REG_SET 0x70 /* Selects CMOS register exposed by REG_IO. */
#define CMOS_REG_IO 0x71 /* Contains the selected data byte. */
/* Indexes of CMOS registers with real-time clock functions.
Note that all of these registers are in BCD format,
so that 0x59 means 59, not 89. */
#define RTC_REG_SEC 0 /* Second: 0x00...0x59. */
#define RTC_REG_MIN 2 /* Minute: 0x00...0x59. */
#define RTC_REG_HOUR 4 /* Hour: 0x00...0x23. */
#define RTC_REG_MDAY 7 /* Day of the month: 0x01...0x31. */
#define RTC_REG_MON 8 /* Month: 0x01...0x12. */
#define RTC_REG_YEAR 9 /* Year: 0x00...0x99. */
/* Indexes of CMOS control registers. */
#define RTC_REG_A 0x0a /* Register A: update-in-progress. */
#define RTC_REG_B 0x0b /* Register B: 24/12 hour time, irq enables. */
#define RTC_REG_C 0x0c /* Register C: pending interrupts. */
#define RTC_REG_D 0x0d /* Register D: valid time? */
/* Register A. */
#define RTCSA_UIP 0x80 /* Set while time update in progress. */
/* Register B. */
#define RTCSB_SET 0x80 /* Disables update to let time be set. */
#define RTCSB_DM 0x04 /* 0 = BCD time format, 1 = binary format. */
#define RTCSB_24HR 0x02 /* 0 = 12-hour format, 1 = 24-hour format. */
static int bcd_to_bin (uint8_t);
static uint8_t cmos_read (uint8_t index);
/* Returns number of seconds since Unix epoch of January 1,
1970. */
time_t
rtc_get_time (void)
{
static const int days_per_month[12] =
{
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};
int sec, min, hour, mday, mon, year;
time_t time;
int i;
/* Get time components.
We repeatedly read the time until it is stable from one read
to another, in case we start our initial read in the middle
of an update. This strategy is not recommended by the
MC146818A datasheet, but it is simpler than any of their
suggestions and, furthermore, it is also used by Linux.
The MC146818A can be configured for BCD or binary format,
but for historical reasons everyone always uses BCD format
except on obscure non-PC platforms, so we don't bother
trying to detect the format in use. */
do
{
sec = bcd_to_bin (cmos_read (RTC_REG_SEC));
min = bcd_to_bin (cmos_read (RTC_REG_MIN));
hour = bcd_to_bin (cmos_read (RTC_REG_HOUR));
mday = bcd_to_bin (cmos_read (RTC_REG_MDAY));
mon = bcd_to_bin (cmos_read (RTC_REG_MON));
year = bcd_to_bin (cmos_read (RTC_REG_YEAR));
}
while (sec != bcd_to_bin (cmos_read (RTC_REG_SEC)));
/* Translate years-since-1900 into years-since-1970.
If it's before the epoch, assume that it has passed 2000.
This will break at 2070, but that's long after our 31-bit
time_t breaks in 2038. */
if (year < 70)
year += 100;
year -= 70;
/* Break down all components into seconds. */
time = (year * 365 + (year - 1) / 4) * 24 * 60 * 60;
for (i = 1; i <= mon; i++)
time += days_per_month[i - 1] * 24 * 60 * 60;
if (mon > 2 && year % 4 == 0)
time += 24 * 60 * 60;
time += (mday - 1) * 24 * 60 * 60;
time += hour * 60 * 60;
time += min * 60;
time += sec;
return time;
}
/* Returns the integer value of the given BCD byte. */
static int
bcd_to_bin (uint8_t x)
{
return (x & 0x0f) + ((x >> 4) * 10);
}
/* Reads a byte from the CMOS register with the given INDEX and
returns the byte read. */
static uint8_t
cmos_read (uint8_t index)
{
outb (CMOS_REG_SET, index);
return inb (CMOS_REG_IO);
}
|
