time.c

是关于linux2.5.1的完全源码

/*
 *  linux/arch/x86-64/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
 *
 * This file contains the PC-specific time handling details:
 * reading the RTC at bootup, etc..
 * 1994-07-02    Alan Modra
 *	fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
 * 1995-03-26    Markus Kuhn
 *      fixed 500 ms bug at call to set_rtc_mmss, fixed DS12887
 *      precision CMOS clock update
 * 1996-05-03    Ingo Molnar
 *      fixed time warps in do_[slow|fast]_gettimeoffset()
 * 1997-09-10	Updated NTP code according to technical memorandum Jan '96
 *		"A Kernel Model for Precision Timekeeping" by Dave Mills
 * 1998-09-05    (Various)
 *	More robust do_fast_gettimeoffset() algorithm implemented
 *	(works with APM, Cyrix 6x86MX and Centaur C6),
 *	monotonic gettimeofday() with fast_get_timeoffset(),
 *	drift-proof precision TSC calibration on boot
 *	(C. Scott Ananian <[e-mail]>, Andrew D.
 *	Balsa <[e-mail]>, Philip Gladstone <[e-mail]>;
 *	ported from 2.0.35 Jumbo-9 by Michael Krause <[e-mail]>).
 * 1998-12-16    Andrea Arcangeli
 *	Fixed Jumbo-9 code in 2.1.131: do_gettimeofday was missing 1 jiffy
 *	because was not accounting lost_ticks.
 * 1998-12-24 Copyright (C) 1998  Andrea Arcangeli
 *	Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
 *	serialize accesses to xtime/lost_ticks).
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/smp.h>

#include <asm/io.h>
#include <asm/smp.h>
#include <asm/irq.h>
#include <asm/msr.h>
#include <asm/delay.h>
#include <asm/mpspec.h>
#include <asm/uaccess.h>
#include <asm/processor.h>

#include <linux/mc146818rtc.h>
#include <linux/timex.h>
#include <linux/config.h>

#include <asm/fixmap.h>

/*
 * for x86_do_profile()
 */
#include <linux/irq.h>


unsigned int cpu_khz;	/* Detected as we calibrate the TSC */

/* Number of usecs that the last interrupt was delayed */
int __delay_at_last_interrupt __section_delay_at_last_interrupt;

unsigned int __last_tsc_low __section_last_tsc_low; /* lsb 32 bits of Time Stamp Counter */

/* Cached *multiplier* to convert TSC counts to microseconds.
 * (see the equation below).
 * Equal to 2^32 * (1 / (clocks per usec) ).
 * Initialized in time_init.
 */
unsigned int __fast_gettimeoffset_quotient __section_fast_gettimeoffset_quotient;

extern rwlock_t xtime_lock;
struct timeval __xtime __section_xtime;
volatile unsigned long __jiffies __section_jiffies;
unsigned long __wall_jiffies __section_wall_jiffies;
struct timezone __sys_tz __section_sys_tz;
 
spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;

inline unsigned long do_gettimeoffset(void)
{
	register unsigned int eax, edx;

	/* Read the Time Stamp Counter */

	rdtsc(eax,edx);

	/* .. relative to previous jiffy (32 bits is enough) */
	eax -= last_tsc_low;	/* tsc_low delta */

	/*
         * Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
         *             = (tsc_low delta) * (usecs_per_clock)
         *             = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
	 *
	 * Using a mull instead of a divl saves up to 31 clock cycles
	 * in the critical path.
         */

	__asm__("mull %2"
		:"=a" (eax), "=d" (edx)
		:"rm" (fast_gettimeoffset_quotient),
		 "0" (eax));

	/* our adjusted time offset in microseconds */
	return delay_at_last_interrupt + edx;
}

#define TICK_SIZE tick

spinlock_t i8253_lock = SPIN_LOCK_UNLOCKED;

extern spinlock_t i8259A_lock;

/*
 * This version of gettimeofday has microsecond resolution
 * and better than microsecond precision on fast x86 machines with TSC.
 */
void do_gettimeofday(struct timeval *tv)
{
	unsigned long flags;
	unsigned long usec, sec;

	read_lock_irqsave(&xtime_lock, flags);
	usec = do_gettimeoffset();
	{
		unsigned long lost = jiffies - wall_jiffies;
		if (lost)
			usec += lost * (1000000 / HZ);
	}
	sec = xtime.tv_sec;
	usec += xtime.tv_usec;
	read_unlock_irqrestore(&xtime_lock, flags);

	while (usec >= 1000000) {
		usec -= 1000000;
		sec++;
	}

	tv->tv_sec = sec;
	tv->tv_usec = usec;
}

void do_settimeofday(struct timeval *tv)
{
	write_lock_irq(&xtime_lock);
	vxtime_lock();
	/*
	 * This is revolting. We need to set "xtime" correctly. However, the
	 * value in this location is the value at the most recent update of
	 * wall time.  Discover what correction gettimeofday() would have
	 * made, and then undo it!
	 */
	tv->tv_usec -= do_gettimeoffset();
	tv->tv_usec -= (jiffies - wall_jiffies) * (1000000 / HZ);

	while (tv->tv_usec < 0) {
		tv->tv_usec += 1000000;
		tv->tv_sec--;
	}

	xtime = *tv;
	vxtime_unlock();

	time_adjust = 0;		/* stop active adjtime() */
	time_status |= STA_UNSYNC;
	time_maxerror = NTP_PHASE_LIMIT;
	time_esterror = NTP_PHASE_LIMIT;
	write_unlock_irq(&xtime_lock);
}

/*
 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
 * called 500 ms after the second nowtime has started, because when
 * nowtime is written into the registers of the CMOS clock, it will
 * jump to the next second precisely 500 ms later. Check the Motorola
 * MC146818A or Dallas DS12887 data sheet for details.
 *
 * BUG: This routine does not handle hour overflow properly; it just
 *      sets the minutes. Usually you'll only notice that after reboot!
 */
static int set_rtc_mmss(unsigned long nowtime)
{
	int retval = 0;
	int real_seconds, real_minutes, cmos_minutes;
	unsigned char save_control, save_freq_select;

	/* gets recalled with irq locally disabled */
	spin_lock(&rtc_lock);
	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);

	save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
	CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);

	cmos_minutes = CMOS_READ(RTC_MINUTES);
	if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
		BCD_TO_BIN(cmos_minutes);

	/*
	 * since we're only adjusting minutes and seconds,
	 * don't interfere with hour overflow. This avoids
	 * messing with unknown time zones but requires your
	 * RTC not to be off by more than 15 minutes
	 */
	real_seconds = nowtime % 60;
	real_minutes = nowtime / 60;
	if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
		real_minutes += 30;		/* correct for half hour time zone */
	real_minutes %= 60;

	if (abs(real_minutes - cmos_minutes) < 30) {
		if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
			BIN_TO_BCD(real_seconds);
			BIN_TO_BCD(real_minutes);
		}
		CMOS_WRITE(real_seconds,RTC_SECONDS);
		CMOS_WRITE(real_minutes,RTC_MINUTES);
	} else {
		printk(KERN_WARNING
		       "set_rtc_mmss: can't update from %d to %d\n",
		       cmos_minutes, real_minutes);
		retval = -1;
	}

	/* The following flags have to be released exactly in this order,
	 * otherwise the DS12887 (popular MC146818A clone with integrated
	 * battery and quartz) will not reset the oscillator and will not
	 * update precisely 500 ms later. You won't find this mentioned in
	 * the Dallas Semiconductor data sheets, but who believes data
	 * sheets anyway ...                           -- Markus Kuhn
	 */
	CMOS_WRITE(save_control, RTC_CONTROL);
	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
	spin_unlock(&rtc_lock);

	return retval;
}

/* last time the cmos clock got updated */
static long last_rtc_update;

int timer_ack;

/*
 * timer_interrupt() needs to keep up the real-time clock,
 * as well as call the "do_timer()" routine every clocktick
 */
static inline void do_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
#ifdef CONFIG_X86_IO_APIC
	if (timer_ack) {
		/*
		 * Subtle, when I/O APICs are used we have to ack timer IRQ
		 * manually to reset the IRR bit for do_slow_gettimeoffset().
		 * This will also deassert NMI lines for the watchdog if run
		 * on an 82489DX-based system.