2 * linux/arch/i386/kernel/time.c
4 * Copyright (C) 1991, 1992, 1995 Linus Torvalds
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 * 1996-05-03 Ingo Molnar
14 * fixed time warps in do_[slow|fast]_gettimeoffset()
15 * 1997-09-10 Updated NTP code according to technical memorandum Jan '96
16 * "A Kernel Model for Precision Timekeeping" by Dave Mills
17 * 1998-09-05 (Various)
18 * More robust do_fast_gettimeoffset() algorithm implemented
19 * (works with APM, Cyrix 6x86MX and Centaur C6),
20 * monotonic gettimeofday() with fast_get_timeoffset(),
21 * drift-proof precision TSC calibration on boot
22 * (C. Scott Ananian <cananian@alumni.princeton.edu>, Andrew D.
23 * Balsa <andrebalsa@altern.org>, Philip Gladstone <philip@raptor.com>;
24 * ported from 2.0.35 Jumbo-9 by Michael Krause <m.krause@tu-harburg.de>).
25 * 1998-12-16 Andrea Arcangeli
26 * Fixed Jumbo-9 code in 2.1.131: do_gettimeofday was missing 1 jiffy
27 * because was not accounting lost_ticks.
28 * 1998-12-24 Copyright (C) 1998 Andrea Arcangeli
29 * Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
30 * serialize accesses to xtime/lost_ticks).
33 #include <linux/errno.h>
34 #include <linux/module.h>
35 #include <linux/sched.h>
36 #include <linux/kernel.h>
37 #include <linux/param.h>
38 #include <linux/string.h>
40 #include <linux/interrupt.h>
41 #include <linux/time.h>
42 #include <linux/delay.h>
43 #include <linux/init.h>
44 #include <linux/smp.h>
50 #include <asm/delay.h>
51 #include <asm/mpspec.h>
52 #include <asm/uaccess.h>
53 #include <asm/processor.h>
55 #include <linux/mc146818rtc.h>
56 #include <linux/timex.h>
57 #include <linux/config.h>
59 #include <asm/fixmap.h>
60 #include <asm/cobalt.h>
63 * for x86_do_profile()
65 #include <linux/irq.h>
68 unsigned long cpu_khz; /* Detected as we calibrate the TSC */
70 /* Number of usecs that the last interrupt was delayed */
71 static int delay_at_last_interrupt;
73 static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
75 /* Cached *multiplier* to convert TSC counts to microseconds.
76 * (see the equation below).
77 * Equal to 2^32 * (1 / (clocks per usec) ).
78 * Initialized in time_init.
80 unsigned long fast_gettimeoffset_quotient;
82 extern rwlock_t xtime_lock;
83 extern unsigned long wall_jiffies;
85 spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;
87 static inline unsigned long do_fast_gettimeoffset(void)
89 register unsigned long eax, edx;
91 /* Read the Time Stamp Counter */
95 /* .. relative to previous jiffy (32 bits is enough) */
96 eax -= last_tsc_low; /* tsc_low delta */
99 * Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
100 * = (tsc_low delta) * (usecs_per_clock)
101 * = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
103 * Using a mull instead of a divl saves up to 31 clock cycles
104 * in the critical path.
108 :"=a" (eax), "=d" (edx)
109 :"rm" (fast_gettimeoffset_quotient),
112 /* our adjusted time offset in microseconds */
113 return delay_at_last_interrupt + edx;
116 #define TICK_SIZE tick
118 spinlock_t i8253_lock = SPIN_LOCK_UNLOCKED;
120 EXPORT_SYMBOL(i8253_lock);
122 extern spinlock_t i8259A_lock;
124 #ifndef CONFIG_X86_TSC
126 /* This function must be called with interrupts disabled
127 * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
129 * However, the pc-audio speaker driver changes the divisor so that
130 * it gets interrupted rather more often - it loads 64 into the
131 * counter rather than 11932! This has an adverse impact on
132 * do_gettimeoffset() -- it stops working! What is also not
133 * good is that the interval that our timer function gets called
134 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
135 * would require using a different timing source. Maybe someone
136 * could use the RTC - I know that this can interrupt at frequencies
137 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
138 * it so that at startup, the timer code in sched.c would select
139 * using either the RTC or the 8253 timer. The decision would be
140 * based on whether there was any other device around that needed
141 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
142 * and then do some jiggery to have a version of do_timer that
143 * advanced the clock by 1/1024 s. Every time that reached over 1/100
144 * of a second, then do all the old code. If the time was kept correct
145 * then do_gettimeoffset could just return 0 - there is no low order
146 * divider that can be accessed.
148 * Ideally, you would be able to use the RTC for the speaker driver,
149 * but it appears that the speaker driver really needs interrupt more
150 * often than every 120 us or so.
152 * Anyway, this needs more thought.... pjsg (1993-08-28)
154 * If you are really that interested, you should be reading
155 * comp.protocols.time.ntp!
158 static unsigned long do_slow_gettimeoffset(void)
162 static int count_p = LATCH; /* for the first call after boot */
163 static unsigned long jiffies_p = 0;
166 * cache volatile jiffies temporarily; we have IRQs turned off.
168 unsigned long jiffies_t;
170 /* gets recalled with irq locally disabled */
171 spin_lock(&i8253_lock);
172 /* timer count may underflow right here */
173 outb_p(0x00, 0x43); /* latch the count ASAP */
175 count = inb_p(0x40); /* read the latched count */
178 * We do this guaranteed double memory access instead of a _p
179 * postfix in the previous port access. Wheee, hackady hack
183 count |= inb_p(0x40) << 8;
185 /* VIA686a test code... reset the latch if count > max + 1 */
188 outb_p(LATCH & 0xff, 0x40);
189 outb(LATCH >> 8, 0x40);
193 spin_unlock(&i8253_lock);
196 * avoiding timer inconsistencies (they are rare, but they happen)...
197 * there are two kinds of problems that must be avoided here:
198 * 1. the timer counter underflows
199 * 2. hardware problem with the timer, not giving us continuous time,
200 * the counter does small "jumps" upwards on some Pentium systems,
201 * (see c't 95/10 page 335 for Neptun bug.)
204 /* you can safely undefine this if you don't have the Neptune chipset */
206 #define BUGGY_NEPTUN_TIMER
208 if( jiffies_t == jiffies_p ) {
209 if( count > count_p ) {
214 spin_lock(&i8259A_lock);
216 * This is tricky when I/O APICs are used;
217 * see do_timer_interrupt().
220 spin_unlock(&i8259A_lock);
222 /* assumption about timer being IRQ0 */
225 * We cannot detect lost timer interrupts ...
226 * well, that's why we call them lost, don't we? :)
227 * [hmm, on the Pentium and Alpha we can ... sort of]
231 #ifdef BUGGY_NEPTUN_TIMER
233 * for the Neptun bug we know that the 'latch'
234 * command doesnt latch the high and low value
235 * of the counter atomically. Thus we have to
236 * substract 256 from the counter
237 * ... funny, isnt it? :)
242 printk("do_slow_gettimeoffset(): hardware timer problem?\n");
247 jiffies_p = jiffies_t;
251 count = ((LATCH-1) - count) * TICK_SIZE;
252 count = (count + LATCH/2) / LATCH;
257 static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;
260 /* IBM Summit (EXA) Cyclone Timer code*/
261 #ifdef CONFIG_X86_SUMMIT
263 #define CYCLONE_CBAR_ADDR 0xFEB00CD0
264 #define CYCLONE_PMCC_OFFSET 0x51A0
265 #define CYCLONE_MPMC_OFFSET 0x51D0
266 #define CYCLONE_MPCS_OFFSET 0x51A8
267 #define CYCLONE_TIMER_FREQ 100000000
270 int __init cyclone_setup(char *str)
276 static u32* volatile cyclone_timer; /* Cyclone MPMC0 register */
277 static u32 last_cyclone_timer;
279 static inline void mark_timeoffset_cyclone(void)
283 unsigned long delta = last_cyclone_timer;
284 spin_lock(&i8253_lock);
285 /* quickly read the cyclone timer */
287 last_cyclone_timer = cyclone_timer[0];
289 /* calculate delay_at_last_interrupt */
290 outb_p(0x00, 0x43); /* latch the count ASAP */
292 count = inb_p(0x40); /* read the latched count */
293 count |= inb(0x40) << 8;
294 spin_unlock(&i8253_lock);
296 /*lost tick compensation*/
297 delta = last_cyclone_timer - delta;
298 delta /= (CYCLONE_TIMER_FREQ/1000000);
299 delta += delay_at_last_interrupt;
300 lost = delta/(1000000/HZ);
304 count = ((LATCH-1) - count) * TICK_SIZE;
305 delay_at_last_interrupt = (count + LATCH/2) / LATCH;
308 static unsigned long do_gettimeoffset_cyclone(void)
313 return delay_at_last_interrupt;
315 /* Read the cyclone timer */
316 offset = cyclone_timer[0];
318 /* .. relative to previous jiffy */
319 offset = offset - last_cyclone_timer;
321 /* convert cyclone ticks to microseconds */
322 /* XXX slow, can we speed this up? */
323 offset = offset/(CYCLONE_TIMER_FREQ/1000000);
325 /* our adjusted time offset in microseconds */
326 return delay_at_last_interrupt + offset;
329 static void __init init_cyclone_clock(void)
332 u32 base; /* saved cyclone base address */
333 u32 pageaddr; /* page that contains cyclone_timer register */
334 u32 offset; /* offset from pageaddr to cyclone_timer register */
337 printk(KERN_INFO "Summit chipset: Starting Cyclone Counter.\n");
339 /* find base address */
340 pageaddr = (CYCLONE_CBAR_ADDR)&PAGE_MASK;
341 offset = (CYCLONE_CBAR_ADDR)&(~PAGE_MASK);
342 set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
343 reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
345 printk(KERN_ERR "Summit chipset: Could not find valid CBAR register.\n");
351 printk(KERN_ERR "Summit chipset: Could not find valid CBAR value.\n");
357 pageaddr = (base + CYCLONE_PMCC_OFFSET)&PAGE_MASK;
358 offset = (base + CYCLONE_PMCC_OFFSET)&(~PAGE_MASK);
359 set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
360 reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
362 printk(KERN_ERR "Summit chipset: Could not find valid PMCC register.\n");
369 pageaddr = (base + CYCLONE_MPCS_OFFSET)&PAGE_MASK;
370 offset = (base + CYCLONE_MPCS_OFFSET)&(~PAGE_MASK);
371 set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
372 reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
374 printk(KERN_ERR "Summit chipset: Could not find valid MPCS register.\n");
380 /* map in cyclone_timer */
381 pageaddr = (base + CYCLONE_MPMC_OFFSET)&PAGE_MASK;
382 offset = (base + CYCLONE_MPMC_OFFSET)&(~PAGE_MASK);
383 set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
384 cyclone_timer = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
386 printk(KERN_ERR "Summit chipset: Could not find valid MPMC register.\n");
391 /*quick test to make sure its ticking*/
393 u32 old = cyclone_timer[0];
395 while(stall--) barrier();
396 if(cyclone_timer[0] == old){
397 printk(KERN_ERR "Summit chipset: Counter not counting! DISABLED\n");
403 /* Everything looks good, so set do_gettimeoffset */
404 do_gettimeoffset = do_gettimeoffset_cyclone;
406 void __cyclone_delay(unsigned long loops)
408 unsigned long bclock, now;
411 bclock = cyclone_timer[0];
414 now = cyclone_timer[0];
415 } while ((now-bclock) < loops);
417 #endif /* CONFIG_X86_SUMMIT */
421 #define do_gettimeoffset() do_fast_gettimeoffset()
425 /* No-cyclone stubs */
426 #ifndef CONFIG_X86_SUMMIT
427 int __init cyclone_setup(char *str)
429 printk(KERN_ERR "cyclone: Kernel not compiled with CONFIG_X86_SUMMIT, cannot use the cyclone-timer.\n");
433 const int use_cyclone = 0;
434 static void mark_timeoffset_cyclone(void) {}
435 static void init_cyclone_clock(void) {}
436 void __cyclone_delay(unsigned long loops) {}
437 #endif /* CONFIG_X86_SUMMIT */
440 * This version of gettimeofday has microsecond resolution
441 * and better than microsecond precision on fast x86 machines with TSC.
443 void do_gettimeofday(struct timeval *tv)
446 unsigned long usec, sec;
448 read_lock_irqsave(&xtime_lock, flags);
449 usec = do_gettimeoffset();
451 unsigned long lost = jiffies - wall_jiffies;
453 usec += lost * (1000000 / HZ);
456 usec += xtime.tv_usec;
457 read_unlock_irqrestore(&xtime_lock, flags);
459 while (usec >= 1000000) {
468 void do_settimeofday(struct timeval *tv)
470 write_lock_irq(&xtime_lock);
472 * This is revolting. We need to set "xtime" correctly. However, the
473 * value in this location is the value at the most recent update of
474 * wall time. Discover what correction gettimeofday() would have
475 * made, and then undo it!
477 tv->tv_usec -= do_gettimeoffset();
478 tv->tv_usec -= (jiffies - wall_jiffies) * (1000000 / HZ);
480 while (tv->tv_usec < 0) {
481 tv->tv_usec += 1000000;
486 time_adjust = 0; /* stop active adjtime() */
487 time_status |= STA_UNSYNC;
488 time_maxerror = NTP_PHASE_LIMIT;
489 time_esterror = NTP_PHASE_LIMIT;
490 write_unlock_irq(&xtime_lock);
494 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
495 * called 500 ms after the second nowtime has started, because when
496 * nowtime is written into the registers of the CMOS clock, it will
497 * jump to the next second precisely 500 ms later. Check the Motorola
498 * MC146818A or Dallas DS12887 data sheet for details.
500 * BUG: This routine does not handle hour overflow properly; it just
501 * sets the minutes. Usually you'll only notice that after reboot!
503 static int set_rtc_mmss(unsigned long nowtime)
506 int real_seconds, real_minutes, cmos_minutes;
507 unsigned char save_control, save_freq_select;
509 /* gets recalled with irq locally disabled */
510 spin_lock(&rtc_lock);
511 save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
512 CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
514 save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
515 CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
517 cmos_minutes = CMOS_READ(RTC_MINUTES);
518 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
519 BCD_TO_BIN(cmos_minutes);
522 * since we're only adjusting minutes and seconds,
523 * don't interfere with hour overflow. This avoids
524 * messing with unknown time zones but requires your
525 * RTC not to be off by more than 15 minutes
527 real_seconds = nowtime % 60;
528 real_minutes = nowtime / 60;
529 if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
530 real_minutes += 30; /* correct for half hour time zone */
533 if (abs(real_minutes - cmos_minutes) < 30) {
534 if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
535 BIN_TO_BCD(real_seconds);
536 BIN_TO_BCD(real_minutes);
538 CMOS_WRITE(real_seconds,RTC_SECONDS);
539 CMOS_WRITE(real_minutes,RTC_MINUTES);
542 "set_rtc_mmss: can't update from %d to %d\n",
543 cmos_minutes, real_minutes);
547 /* The following flags have to be released exactly in this order,
548 * otherwise the DS12887 (popular MC146818A clone with integrated
549 * battery and quartz) will not reset the oscillator and will not
550 * update precisely 500 ms later. You won't find this mentioned in
551 * the Dallas Semiconductor data sheets, but who believes data
552 * sheets anyway ... -- Markus Kuhn
554 CMOS_WRITE(save_control, RTC_CONTROL);
555 CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
556 spin_unlock(&rtc_lock);
561 /* last time the cmos clock got updated */
562 static long last_rtc_update;
567 * timer_interrupt() needs to keep up the real-time clock,
568 * as well as call the "do_timer()" routine every clocktick
570 static inline void do_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
572 #ifdef CONFIG_X86_IO_APIC
575 * Subtle, when I/O APICs are used we have to ack timer IRQ
576 * manually to reset the IRR bit for do_slow_gettimeoffset().
577 * This will also deassert NMI lines for the watchdog if run
578 * on an 82489DX-based system.
580 spin_lock(&i8259A_lock);
582 /* Ack the IRQ; AEOI will end it automatically. */
584 spin_unlock(&i8259A_lock);
589 /* Clear the interrupt */
590 co_cpu_write(CO_CPU_STAT,co_cpu_read(CO_CPU_STAT) & ~CO_STAT_TIMEINTR);
594 * In the SMP case we use the local APIC timer interrupt to do the
595 * profiling, except when we simulate SMP mode on a uniprocessor
596 * system, in that case we have to call the local interrupt handler.
598 #ifndef CONFIG_X86_LOCAL_APIC
599 if (!user_mode(regs))
600 x86_do_profile(regs->eip);
602 if (!using_apic_timer)
603 smp_local_timer_interrupt(regs);
607 * If we have an externally synchronized Linux clock, then update
608 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
609 * called as close as possible to 500 ms before the new second starts.
611 if ((time_status & STA_UNSYNC) == 0 &&
612 xtime.tv_sec > last_rtc_update + 660 &&
613 xtime.tv_usec >= 500000 - ((unsigned) tick) / 2 &&
614 xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
615 if (set_rtc_mmss(xtime.tv_sec) == 0)
616 last_rtc_update = xtime.tv_sec;
618 last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
623 /* The PS/2 uses level-triggered interrupts. You can't
624 turn them off, nor would you want to (any attempt to
625 enable edge-triggered interrupts usually gets intercepted by a
626 special hardware circuit). Hence we have to acknowledge
627 the timer interrupt. Through some incredibly stupid
628 design idea, the reset for IRQ 0 is done by setting the
629 high bit of the PPI port B (0x61). Note that some PS/2s,
630 notably the 55SX, work fine if this is removed. */
632 irq = inb_p( 0x61 ); /* read the current state */
633 outb_p( irq|0x80, 0x61 ); /* reset the IRQ */
641 * This is the same as the above, except we _also_ save the current
642 * Time Stamp Counter value at the time of the timer interrupt, so that
643 * we later on can estimate the time of day more exactly.
645 static void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
650 * Here we are in the timer irq handler. We just have irqs locally
651 * disabled but we don't know if the timer_bh is running on the other
652 * CPU. We need to avoid to SMP race with it. NOTE: we don' t need
653 * the irq version of write_lock because as just said we have irq
654 * locally disabled. -arca
656 write_lock(&xtime_lock);
659 mark_timeoffset_cyclone();
662 * It is important that these two operations happen almost at
663 * the same time. We do the RDTSC stuff first, since it's
664 * faster. To avoid any inconsistencies, we need interrupts
669 * Interrupts are just disabled locally since the timer irq
670 * has the SA_INTERRUPT flag set. -arca
673 /* read Pentium cycle counter */
675 rdtscl(last_tsc_low);
677 spin_lock(&i8253_lock);
678 outb_p(0x00, 0x43); /* latch the count ASAP */
680 count = inb_p(0x40); /* read the latched count */
681 count |= inb(0x40) << 8;
683 /* Any unpaired read will cause the above to swap MSB/LSB
684 forever. Try to detect this and reset the counter.
686 This happens very occasionally with buggy SMM bios
691 "i8253 count too high! resetting..\n");
693 outb_p(LATCH & 0xff, 0x40);
694 outb(LATCH >> 8, 0x40);
698 spin_unlock(&i8253_lock);
700 /* Some i8253 clones hold the LATCH value visible
701 momentarily as they flip back to zero */
702 if (count == LATCH) {
706 count = ((LATCH-1) - count) * TICK_SIZE;
707 delay_at_last_interrupt = (count + LATCH/2) / LATCH;
710 do_timer_interrupt(irq, NULL, regs);
712 write_unlock(&xtime_lock);
716 /* not static: needed by APM */
717 unsigned long get_cmos_time(void)
719 unsigned int year, mon, day, hour, min, sec;
722 spin_lock(&rtc_lock);
723 /* The Linux interpretation of the CMOS clock register contents:
724 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
725 * RTC registers show the second which has precisely just started.
726 * Let's hope other operating systems interpret the RTC the same way.
728 /* read RTC exactly on falling edge of update flag */
729 for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
730 if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
732 for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
733 if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
735 do { /* Isn't this overkill ? UIP above should guarantee consistency */
736 sec = CMOS_READ(RTC_SECONDS);
737 min = CMOS_READ(RTC_MINUTES);
738 hour = CMOS_READ(RTC_HOURS);
739 day = CMOS_READ(RTC_DAY_OF_MONTH);
740 mon = CMOS_READ(RTC_MONTH);
741 year = CMOS_READ(RTC_YEAR);
742 } while (sec != CMOS_READ(RTC_SECONDS));
743 if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
752 spin_unlock(&rtc_lock);
753 if ((year += 1900) < 1970)
755 return mktime(year, mon, day, hour, min, sec);
758 static struct irqaction irq0 = { timer_interrupt, SA_INTERRUPT, 0, "timer", NULL, NULL};
760 /* ------ Calibrate the TSC -------
761 * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
762 * Too much 64-bit arithmetic here to do this cleanly in C, and for
763 * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
764 * output busy loop as low as possible. We avoid reading the CTC registers
765 * directly because of the awkward 8-bit access mechanism of the 82C54
769 #define CALIBRATE_LATCH (5 * LATCH)
770 #define CALIBRATE_TIME (5 * 1000020/HZ)
772 static unsigned long __init calibrate_tsc(void)
774 /* Set the Gate high, disable speaker */
775 outb((inb(0x61) & ~0x02) | 0x01, 0x61);
778 * Now let's take care of CTC channel 2
780 * Set the Gate high, program CTC channel 2 for mode 0,
781 * (interrupt on terminal count mode), binary count,
782 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
784 outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */
785 outb(CALIBRATE_LATCH & 0xff, 0x42); /* LSB of count */
786 outb(CALIBRATE_LATCH >> 8, 0x42); /* MSB of count */
789 unsigned long startlow, starthigh;
790 unsigned long endlow, endhigh;
793 rdtsc(startlow,starthigh);
797 } while ((inb(0x61) & 0x20) == 0);
798 rdtsc(endlow,endhigh);
800 last_tsc_low = endlow;
802 /* Error: ECTCNEVERSET */
806 /* 64-bit subtract - gcc just messes up with long longs */
807 __asm__("subl %2,%0\n\t"
809 :"=a" (endlow), "=d" (endhigh)
810 :"g" (startlow), "g" (starthigh),
811 "0" (endlow), "1" (endhigh));
813 /* Error: ECPUTOOFAST */
817 /* Error: ECPUTOOSLOW */
818 if (endlow <= CALIBRATE_TIME)
822 :"=a" (endlow), "=d" (endhigh)
823 :"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));
829 * The CTC wasn't reliable: we got a hit on the very first read,
830 * or the CPU was so fast/slow that the quotient wouldn't fit in
837 void __init time_init(void)
839 extern int x86_udelay_tsc;
841 xtime.tv_sec = get_cmos_time();
845 * If we have APM enabled or the CPU clock speed is variable
846 * (CPU stops clock on HLT or slows clock to save power)
847 * then the TSC timestamps may diverge by up to 1 jiffy from
848 * 'real time' but nothing will break.
849 * The most frequent case is that the CPU is "woken" from a halt
850 * state by the timer interrupt itself, so we get 0 error. In the
851 * rare cases where a driver would "wake" the CPU and request a
852 * timestamp, the maximum error is < 1 jiffy. But timestamps are
853 * still perfectly ordered.
854 * Note that the TSC counter will be reset if APM suspends
855 * to disk; this won't break the kernel, though, 'cuz we're
856 * smart. See arch/i386/kernel/apm.c.
859 * Firstly we have to do a CPU check for chips with
860 * a potentially buggy TSC. At this point we haven't run
861 * the ident/bugs checks so we must run this hook as it
862 * may turn off the TSC flag.
864 * NOTE: this doesnt yet handle SMP 486 machines where only
865 * some CPU's have a TSC. Thats never worked and nobody has
866 * moaned if you have the only one in the world - you fix it!
872 init_cyclone_clock();
875 unsigned long tsc_quotient = calibrate_tsc();
877 fast_gettimeoffset_quotient = tsc_quotient;
878 /* XXX: This is messy
879 * However, we want to allow for the cyclone timer
880 * to work w/ or w/o the TSCs being avaliable
881 * -johnstul@us.ibm.com
885 * We could be more selective here I suspect
886 * and just enable this for the next intel chips ?
890 #ifndef do_gettimeoffset
891 do_gettimeoffset = do_fast_gettimeoffset;
894 /* report CPU clock rate in Hz.
895 * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
896 * clock/second. Our precision is about 100 ppm.
898 { unsigned long eax=0, edx=1000;
900 :"=a" (cpu_khz), "=d" (edx)
902 "0" (eax), "1" (edx));
903 printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz % 1000);
910 printk("Starting Cobalt Timer system clock\n");
912 /* Set the countdown value */
913 co_cpu_write(CO_CPU_TIMEVAL, CO_TIME_HZ/HZ);
915 /* Start the timer */
916 co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) | CO_CTRL_TIMERUN);
918 /* Enable (unmask) the timer interrupt */
919 co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) & ~CO_CTRL_TIMEMASK);
921 /* Wire cpu IDT entry to s/w handler (and Cobalt APIC to IDT) */
922 setup_irq(CO_IRQ_TIMER, &irq0);