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*/
1 /*
2 * linux/arch/i386/kernel/time.c
3 *
4 * Copyright (C) 1991, 1992, 1995 Linus Torvalds
5 *
6 * This file contains the PC-specific time handling details:
7 * reading the RTC at bootup, etc..
8 * 1994-07-02 Alan Modra
9 * fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
10 * 1995-03-26 Markus Kuhn
11 * fixed 500 ms bug at call to set_rtc_mmss, fixed DS12887
12 * precision CMOS clock update
13 */
14 #include <linux/errno.h>
15 #include <linux/sched.h>
16 #include <linux/kernel.h>
17 #include <linux/param.h>
18 #include <linux/string.h>
19 #include <linux/mm.h>
20
21 #include <asm/segment.h>
22 #include <asm/io.h>
23
24 #include <linux/mc146818rtc.h>
25 #include <linux/timex.h>
26
27 #define TIMER_IRQ 0
28
29 static int set_rtc_mmss(unsigned long);
30
31 /*
32 * timer_interrupt() needs to keep up the real-time clock,
33 * as well as call the "do_timer()" routine every clocktick
34 */
35 static void timer_interrupt(int irq, struct pt_regs * regs)
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*/
36 {
37 /* last time the cmos clock got updated */
38 static long last_rtc_update=0;
39
40 do_timer(regs);
41
42 /*
43 * If we have an externally synchronized Linux clock, then update
44 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
45 * called as close as possible to 500 ms before the new second starts.
46 */
47 if (time_state != TIME_BAD && xtime.tv_sec > last_rtc_update + 660 &&
48 xtime.tv_usec > 500000 - (tick >> 1) &&
49 xtime.tv_usec < 500000 + (tick >> 1))
50 if (set_rtc_mmss(xtime.tv_sec) == 0)
51 last_rtc_update = xtime.tv_sec;
52 else
53 last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
54 }
55
56 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
57 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
58 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
59 *
60 * [For the Julian calendar (which was used in Russia before 1917,
61 * Britain & colonies before 1752, anywhere else before 1582,
62 * and is still in use by some communities) leave out the
63 * -year/100+year/400 terms, and add 10.]
64 *
65 * This algorithm was first published by Gauss (I think).
66 *
67 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
68 * machines were long is 32-bit! (However, as time_t is signed, we
69 * will already get problems at other places on 2038-01-19 03:14:08)
70 */
71 static inline unsigned long mktime(unsigned int year, unsigned int mon,
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*/
72 unsigned int day, unsigned int hour,
73 unsigned int min, unsigned int sec)
74 {
75 if (0 >= (int) (mon -= 2)) { /* 1..12 -> 11,12,1..10 */
76 mon += 12; /* Puts Feb last since it has leap day */
77 year -= 1;
78 }
79 return (((
80 (unsigned long)(year/4 - year/100 + year/400 + 367*mon/12 + day) +
81 year*365 - 719499
82 )*24 + hour /* now have hours */
83 )*60 + min /* now have minutes */
84 )*60 + sec; /* finally seconds */
85 }
86
87 void time_init(void)
/* */
88 {
89 unsigned int year, mon, day, hour, min, sec;
90 int i;
91
92 /* The Linux interpretation of the CMOS clock register contents:
93 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
94 * RTC registers show the second which has precisely just started.
95 * Let's hope other operating systems interpret the RTC the same way.
96 */
97 /* read RTC exactly on falling edge of update flag */
98 for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
99 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
100 break;
101 for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
102 if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
103 break;
104 do { /* Isn't this overkill ? UIP above should guarantee consistency */
105 sec = CMOS_READ(RTC_SECONDS);
106 min = CMOS_READ(RTC_MINUTES);
107 hour = CMOS_READ(RTC_HOURS);
108 day = CMOS_READ(RTC_DAY_OF_MONTH);
109 mon = CMOS_READ(RTC_MONTH);
110 year = CMOS_READ(RTC_YEAR);
111 } while (sec != CMOS_READ(RTC_SECONDS));
112 if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
113 {
114 BCD_TO_BIN(sec);
115 BCD_TO_BIN(min);
116 BCD_TO_BIN(hour);
117 BCD_TO_BIN(day);
118 BCD_TO_BIN(mon);
119 BCD_TO_BIN(year);
120 }
121 if ((year += 1900) < 1970)
122 year += 100;
123 xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
124 xtime.tv_usec = 0;
125 if (request_irq(TIMER_IRQ, timer_interrupt, 0, "timer") != 0)
126 panic("Could not allocate timer IRQ!");
127 }
128
129 /* This function must be called with interrupts disabled
130 * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
131 *
132 * However, the pc-audio speaker driver changes the divisor so that
133 * it gets interrupted rather more often - it loads 64 into the
134 * counter rather than 11932! This has an adverse impact on
135 * do_gettimeoffset() -- it stops working! What is also not
136 * good is that the interval that our timer function gets called
137 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
138 * would require using a different timing source. Maybe someone
139 * could use the RTC - I know that this can interrupt at frequencies
140 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
141 * it so that at startup, the timer code in sched.c would select
142 * using either the RTC or the 8253 timer. The decision would be
143 * based on whether there was any other device around that needed
144 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
145 * and then do some jiggery to have a version of do_timer that
146 * advanced the clock by 1/1024 s. Every time that reached over 1/100
147 * of a second, then do all the old code. If the time was kept correct
148 * then do_gettimeoffset could just return 0 - there is no low order
149 * divider that can be accessed.
150 *
151 * Ideally, you would be able to use the RTC for the speaker driver,
152 * but it appears that the speaker driver really needs interrupt more
153 * often than every 120 us or so.
154 *
155 * Anyway, this needs more thought.... pjsg (1993-08-28)
156 *
157 * If you are really that interested, you should be reading
158 * comp.protocols.time.ntp!
159 */
160
161 #define TICK_SIZE tick
162
163 static inline unsigned long do_gettimeoffset(void)
/* */
164 {
165 int count;
166 unsigned long offset = 0;
167
168 /* timer count may underflow right here */
169 outb_p(0x00, 0x43); /* latch the count ASAP */
170 count = inb_p(0x40); /* read the latched count */
171 count |= inb(0x40) << 8;
172 /* we know probability of underflow is always MUCH less than 1% */
173 if (count > (LATCH - LATCH/100)) {
174 /* check for pending timer interrupt */
175 outb_p(0x0a, 0x20);
176 if (inb(0x20) & 1)
177 offset = TICK_SIZE;
178 }
179 count = ((LATCH-1) - count) * TICK_SIZE;
180 count = (count + LATCH/2) / LATCH;
181 return offset + count;
182 }
183
184 /*
185 * This version of gettimeofday has near microsecond resolution.
186 */
187 void do_gettimeofday(struct timeval *tv)
/* */
188 {
189 unsigned long flags;
190
191 save_flags(flags);
192 cli();
193 *tv = xtime;
194 tv->tv_usec += do_gettimeoffset();
195 if (tv->tv_usec >= 1000000) {
196 tv->tv_usec -= 1000000;
197 tv->tv_sec++;
198 }
199 restore_flags(flags);
200 }
201
202 void do_settimeofday(struct timeval *tv)
/* */
203 {
204 cli();
205 /* This is revolting. We need to set the xtime.tv_usec
206 * correctly. However, the value in this location is
207 * is value at the last tick.
208 * Discover what correction gettimeofday
209 * would have done, and then undo it!
210 */
211 tv->tv_usec -= do_gettimeoffset();
212
213 if (tv->tv_usec < 0) {
214 tv->tv_usec += 1000000;
215 tv->tv_sec--;
216 }
217
218 xtime = *tv;
219 time_state = TIME_BAD;
220 time_maxerror = 0x70000000;
221 time_esterror = 0x70000000;
222 sti();
223 }
224
225
226 /*
227 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
228 * called 500 ms after the second nowtime has started, because when
229 * nowtime is written into the registers of the CMOS clock, it will
230 * jump to the next second precisely 500 ms later. Check the Motorola
231 * MC146818A or Dallas DS12887 data sheet for details.
232 */
233 static int set_rtc_mmss(unsigned long nowtime)
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234 {
235 int retval = 0;
236 int real_seconds, real_minutes, cmos_minutes;
237 unsigned char save_control, save_freq_select;
238
239 save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
240 CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
241
242 save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
243 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
244
245 cmos_minutes = CMOS_READ(RTC_MINUTES);
246 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
247 BCD_TO_BIN(cmos_minutes);
248
249 /*
250 * since we're only adjusting minutes and seconds,
251 * don't interfere with hour overflow. This avoids
252 * messing with unknown time zones but requires your
253 * RTC not to be off by more than 15 minutes
254 */
255 real_seconds = nowtime % 60;
256 real_minutes = nowtime / 60;
257 if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
258 real_minutes += 30; /* correct for half hour time zone */
259 real_minutes %= 60;
260
261 if (abs(real_minutes - cmos_minutes) < 30) {
262 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
263 BIN_TO_BCD(real_seconds);
264 BIN_TO_BCD(real_minutes);
265 }
266 CMOS_WRITE(real_seconds,RTC_SECONDS);
267 CMOS_WRITE(real_minutes,RTC_MINUTES);
268 } else
269 retval = -1;
270
271 /* The following flags have to be released exactly in this order,
272 * otherwise the DS12887 (popular MC146818A clone with integrated
273 * battery and quartz) will not reset the oscillator and will not
274 * update precisely 500 ms later. You won't find this mentioned in
275 * the Dallas Semiconductor data sheets, but who believes data
276 * sheets anyway ... -- Markus Kuhn
277 */
278 CMOS_WRITE(save_control, RTC_CONTROL);
279 CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
280
281 return retval;
282 }
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*/