![[first]](../icons/first.png){kind=icon}
![[previous]](../icons/n_left.png){kind=icon}
![[next]](../icons/n_right.png){kind=icon}
![[last]](../icons/last.png){kind=icon}
![[top]](../icons/n_top.png){kind=icon}
![[bottom]](../icons/bottom.png){kind=icon}
![[index]](../icons/index.png){kind=icon}
![[help]](../icons/help.png){kind=icon}
*/
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 /* Cycle counter value at the previous timer interrupt.. */
30 static unsigned long long last_timer_cc = 0;
31 static unsigned long long init_timer_cc = 0;
32
33 static unsigned long do_fast_gettimeoffset(void)
/* ![[next]](../icons/right.png)
![[first]](../icons/n_first.png)
![[top]](../icons/top.png)
*/
34 {
35 unsigned long time_low, time_high;
36 unsigned long quotient, remainder;
37
38 /* Get last timer tick in absolute kernel time */
39 __asm__("subl %2,%0\n\t"
40 "sbbl %3,%1"
41 :"=r" (time_low), "=r" (time_high)
42 :"m" (*(0+(long *)&init_timer_cc)),
43 "m" (*(1+(long *)&init_timer_cc)),
44 "0" (*(0+(long *)&last_timer_cc)),
45 "1" (*(1+(long *)&last_timer_cc)));
46 /*
47 * Divide the 64-bit time with the 32-bit jiffy counter,
48 * getting the quotient in clocks.
49 *
50 * Giving quotient = "average internal clocks per jiffy"
51 */
52 __asm__("divl %2"
53 :"=a" (quotient), "=d" (remainder)
54 :"r" (jiffies),
55 "0" (time_low), "1" (time_high));
56
57 /* Read the time counter */
58 __asm__(".byte 0x0f,0x31"
59 :"=a" (time_low), "=d" (time_high));
60
61 /* .. relative to previous jiffy (32 bits is enough) */
62 time_low -= (unsigned long) last_timer_cc;
63
64 /*
65 * Time offset = (1000000/HZ * remainder) / quotient.
66 */
67 __asm__("mull %1\n\t"
68 "divl %2"
69 :"=a" (quotient), "=d" (remainder)
70 :"r" (quotient),
71 "0" (time_low), "1" (1000000/HZ));
72
73 /*
74 * Due to rounding errors (and jiffies inconsistencies),
75 * we need to check the result so that we'll get a timer
76 * that is monotonous.
77 */
78 if (quotient >= 1000000/HZ)
79 quotient = 1000000/HZ-1;
80 return quotient;
81 }
82
83 /* This function must be called with interrupts disabled
84 * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
85 *
86 * However, the pc-audio speaker driver changes the divisor so that
87 * it gets interrupted rather more often - it loads 64 into the
88 * counter rather than 11932! This has an adverse impact on
89 * do_gettimeoffset() -- it stops working! What is also not
90 * good is that the interval that our timer function gets called
91 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
92 * would require using a different timing source. Maybe someone
93 * could use the RTC - I know that this can interrupt at frequencies
94 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
95 * it so that at startup, the timer code in sched.c would select
96 * using either the RTC or the 8253 timer. The decision would be
97 * based on whether there was any other device around that needed
98 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
99 * and then do some jiggery to have a version of do_timer that
100 * advanced the clock by 1/1024 s. Every time that reached over 1/100
101 * of a second, then do all the old code. If the time was kept correct
102 * then do_gettimeoffset could just return 0 - there is no low order
103 * divider that can be accessed.
104 *
105 * Ideally, you would be able to use the RTC for the speaker driver,
106 * but it appears that the speaker driver really needs interrupt more
107 * often than every 120 us or so.
108 *
109 * Anyway, this needs more thought.... pjsg (1993-08-28)
110 *
111 * If you are really that interested, you should be reading
112 * comp.protocols.time.ntp!
113 */
114
115 #define TICK_SIZE tick
116
117 static unsigned long do_slow_gettimeoffset(void)
/* ![[previous]](../icons/left.png)
*/
118 {
119 int count;
120 unsigned long offset = 0;
121
122 /* timer count may underflow right here */
123 outb_p(0x00, 0x43); /* latch the count ASAP */
124 count = inb_p(0x40); /* read the latched count */
125 count |= inb(0x40) << 8;
126 /* we know probability of underflow is always MUCH less than 1% */
127 if (count > (LATCH - LATCH/100)) {
128 /* check for pending timer interrupt */
129 outb_p(0x0a, 0x20);
130 if (inb(0x20) & 1)
131 offset = TICK_SIZE;
132 }
133 count = ((LATCH-1) - count) * TICK_SIZE;
134 count = (count + LATCH/2) / LATCH;
135 return offset + count;
136 }
137
138 static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;
139
140 /*
141 * This version of gettimeofday has near microsecond resolution.
142 */
143 void do_gettimeofday(struct timeval *tv)
/* */
144 {
145 unsigned long flags;
146
147 save_flags(flags);
148 cli();
149 *tv = xtime;
150 tv->tv_usec += do_gettimeoffset();
151 if (tv->tv_usec >= 1000000) {
152 tv->tv_usec -= 1000000;
153 tv->tv_sec++;
154 }
155 restore_flags(flags);
156 }
157
158 void do_settimeofday(struct timeval *tv)
/* */
159 {
160 cli();
161 /* This is revolting. We need to set the xtime.tv_usec
162 * correctly. However, the value in this location is
163 * is value at the last tick.
164 * Discover what correction gettimeofday
165 * would have done, and then undo it!
166 */
167 tv->tv_usec -= do_gettimeoffset();
168
169 if (tv->tv_usec < 0) {
170 tv->tv_usec += 1000000;
171 tv->tv_sec--;
172 }
173
174 xtime = *tv;
175 time_state = TIME_BAD;
176 time_maxerror = 0x70000000;
177 time_esterror = 0x70000000;
178 sti();
179 }
180
181
182 /*
183 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
184 * called 500 ms after the second nowtime has started, because when
185 * nowtime is written into the registers of the CMOS clock, it will
186 * jump to the next second precisely 500 ms later. Check the Motorola
187 * MC146818A or Dallas DS12887 data sheet for details.
188 */
189 static int set_rtc_mmss(unsigned long nowtime)
/* */
190 {
191 int retval = 0;
192 int real_seconds, real_minutes, cmos_minutes;
193 unsigned char save_control, save_freq_select;
194
195 save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
196 CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
197
198 save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
199 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
200
201 cmos_minutes = CMOS_READ(RTC_MINUTES);
202 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
203 BCD_TO_BIN(cmos_minutes);
204
205 /*
206 * since we're only adjusting minutes and seconds,
207 * don't interfere with hour overflow. This avoids
208 * messing with unknown time zones but requires your
209 * RTC not to be off by more than 15 minutes
210 */
211 real_seconds = nowtime % 60;
212 real_minutes = nowtime / 60;
213 if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
214 real_minutes += 30; /* correct for half hour time zone */
215 real_minutes %= 60;
216
217 if (abs(real_minutes - cmos_minutes) < 30) {
218 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
219 BIN_TO_BCD(real_seconds);
220 BIN_TO_BCD(real_minutes);
221 }
222 CMOS_WRITE(real_seconds,RTC_SECONDS);
223 CMOS_WRITE(real_minutes,RTC_MINUTES);
224 } else
225 retval = -1;
226
227 /* The following flags have to be released exactly in this order,
228 * otherwise the DS12887 (popular MC146818A clone with integrated
229 * battery and quartz) will not reset the oscillator and will not
230 * update precisely 500 ms later. You won't find this mentioned in
231 * the Dallas Semiconductor data sheets, but who believes data
232 * sheets anyway ... -- Markus Kuhn
233 */
234 CMOS_WRITE(save_control, RTC_CONTROL);
235 CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
236
237 return retval;
238 }
239
240 /* last time the cmos clock got updated */
241 static long last_rtc_update = 0;
242
243 /*
244 * timer_interrupt() needs to keep up the real-time clock,
245 * as well as call the "do_timer()" routine every clocktick
246 */
247 static inline void timer_interrupt(int irq, struct pt_regs * regs)
/* */
248 {
249 do_timer(regs);
250
251 /*
252 * If we have an externally synchronized Linux clock, then update
253 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
254 * called as close as possible to 500 ms before the new second starts.
255 */
256 if (time_state != TIME_BAD && xtime.tv_sec > last_rtc_update + 660 &&
257 xtime.tv_usec > 500000 - (tick >> 1) &&
258 xtime.tv_usec < 500000 + (tick >> 1))
259 if (set_rtc_mmss(xtime.tv_sec) == 0)
260 last_rtc_update = xtime.tv_sec;
261 else
262 last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
263 /* As we return to user mode fire off the other CPU schedulers.. this is
264 basically because we don't yet share IRQ's around. This message is
265 rigged to be safe on the 386 - basically its a hack, so don't look
266 closely for now.. */
267 smp_message_pass(MSG_ALL_BUT_SELF, MSG_RESCHEDULE, 0L, 0);
268
269 }
270
271 /*
272 * This is the same as the above, except we _also_ save the current
273 * cycle counter value at the time of the timer interrupt, so that
274 * we later on can estimate the time of day more exactly.
275 */
276 static void pentium_timer_interrupt(int irq, struct pt_regs * regs)
/* */
277 {
278 /* read Pentium cycle counter */
279 __asm__(".byte 0x0f,0x31"
280 :"=a" (((unsigned long *) &last_timer_cc)[0]),
281 "=d" (((unsigned long *) &last_timer_cc)[1]));
282 timer_interrupt(irq, regs);
283 }
284
285 /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
286 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
287 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
288 *
289 * [For the Julian calendar (which was used in Russia before 1917,
290 * Britain & colonies before 1752, anywhere else before 1582,
291 * and is still in use by some communities) leave out the
292 * -year/100+year/400 terms, and add 10.]
293 *
294 * This algorithm was first published by Gauss (I think).
295 *
296 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
297 * machines were long is 32-bit! (However, as time_t is signed, we
298 * will already get problems at other places on 2038-01-19 03:14:08)
299 */
300 static inline unsigned long mktime(unsigned int year, unsigned int mon,
/* */
301 unsigned int day, unsigned int hour,
302 unsigned int min, unsigned int sec)
303 {
304 if (0 >= (int) (mon -= 2)) { /* 1..12 -> 11,12,1..10 */
305 mon += 12; /* Puts Feb last since it has leap day */
306 year -= 1;
307 }
308 return (((
309 (unsigned long)(year/4 - year/100 + year/400 + 367*mon/12 + day) +
310 year*365 - 719499
311 )*24 + hour /* now have hours */
312 )*60 + min /* now have minutes */
313 )*60 + sec; /* finally seconds */
314 }
315
316 void time_init(void)
/* ![[last]](../icons/n_last.png)
*/
317 {
318 void (*irq_handler)(int, struct pt_regs *);
319 unsigned int year, mon, day, hour, min, sec;
320 int i;
321
322 /* The Linux interpretation of the CMOS clock register contents:
323 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
324 * RTC registers show the second which has precisely just started.
325 * Let's hope other operating systems interpret the RTC the same way.
326 */
327 /* read RTC exactly on falling edge of update flag */
328 for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
329 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
330 break;
331 for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
332 if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
333 break;
334 do { /* Isn't this overkill ? UIP above should guarantee consistency */
335 sec = CMOS_READ(RTC_SECONDS);
336 min = CMOS_READ(RTC_MINUTES);
337 hour = CMOS_READ(RTC_HOURS);
338 day = CMOS_READ(RTC_DAY_OF_MONTH);
339 mon = CMOS_READ(RTC_MONTH);
340 year = CMOS_READ(RTC_YEAR);
341 } while (sec != CMOS_READ(RTC_SECONDS));
342 if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
343 {
344 BCD_TO_BIN(sec);
345 BCD_TO_BIN(min);
346 BCD_TO_BIN(hour);
347 BCD_TO_BIN(day);
348 BCD_TO_BIN(mon);
349 BCD_TO_BIN(year);
350 }
351 if ((year += 1900) < 1970)
352 year += 100;
353 xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
354 xtime.tv_usec = 0;
355
356 /* If we have the CPU hardware time counters, use them */
357 irq_handler = timer_interrupt;
358 if (x86_capability & 16) {
359 irq_handler = pentium_timer_interrupt;
360 do_gettimeoffset = do_fast_gettimeoffset;
361 /* read Pentium cycle counter */
362 __asm__(".byte 0x0f,0x31"
363 :"=a" (((unsigned long *) &init_timer_cc)[0]),
364 "=d" (((unsigned long *) &init_timer_cc)[1]));
365 }
366 if (request_irq(TIMER_IRQ, irq_handler, 0, "timer") != 0)
367 panic("Could not allocate timer IRQ!");
368 }
![[bottom]](../icons/n_bottom.png){kind=icon}
*/