time.c

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/*
 *  linux/arch/alpha/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995, 1999, 2000  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
 * 1997-09-10	Updated NTP code according to technical memorandum Jan '96
 *		"A Kernel Model for Precision Timekeeping" by Dave Mills
 * 1997-01-09    Adrian Sun
 *      use interval timer if CONFIG_RTC=y
 * 1997-10-29    John Bowman ([e-mail])
 *      fixed tick loss calculation in timer_interrupt
 *      (round system clock to nearest tick instead of truncating)
 *      fixed algorithm in time_init for getting time from CMOS clock
 * 1999-04-16	Thorsten Kranzkowski ([e-mail])
 *	fixed algorithm in do_gettimeofday() for calculating the precise time
 *	from processor cycle counter (now taking lost_ticks into account)
 * 2000-08-13	Jan-Benedict Glaw <[e-mail]>
 * 	Fixed time_init to be aware of epoches != 1900. This prevents
 * 	booting up in 2048 for me;) Code is stolen from rtc.c.
 */
#include <linux/config.h>
#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/delay.h>
#include <linux/ioport.h>
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/init.h>

#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/hwrpb.h>

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

#include "proto.h"
#include "irq_impl.h"

extern rwlock_t xtime_lock;
extern unsigned long wall_jiffies;	/* kernel/timer.c */

static int set_rtc_mmss(unsigned long);

spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;

/*
 * Shift amount by which scaled_ticks_per_cycle is scaled.  Shifting
 * by 48 gives us 16 bits for HZ while keeping the accuracy good even
 * for large CPU clock rates.
 */
#define FIX_SHIFT	48

/* lump static variables together for more efficient access: */
static struct {
	/* cycle counter last time it got invoked */
	__u32 last_time;
	/* ticks/cycle * 2^48 */
	unsigned long scaled_ticks_per_cycle;
	/* last time the CMOS clock got updated */
	time_t last_rtc_update;
	/* partial unused tick */
	unsigned long partial_tick;
} state;

unsigned long est_cycle_freq;


static inline __u32 rpcc(void)
{
    __u32 result;
    asm volatile ("rpcc %0" : "=r"(result));
    return result;
}


/*
 * timer_interrupt() needs to keep up the real-time clock,
 * as well as call the "do_timer()" routine every clocktick
 */
void timer_interrupt(int irq, void *dev, struct pt_regs * regs)
{
	unsigned long delta;
	__u32 now;
	long nticks;

#ifndef CONFIG_SMP
	/* Not SMP, do kernel PC profiling here.  */
	if (!user_mode(regs))
		alpha_do_profile(regs->pc);
#endif

	write_lock(&xtime_lock);

	/*
	 * Calculate how many ticks have passed since the last update,
	 * including any previous partial leftover.  Save any resulting
	 * fraction for the next pass.
	 */
	now = rpcc();
	delta = now - state.last_time;
	state.last_time = now;
	delta = delta * state.scaled_ticks_per_cycle + state.partial_tick;
	state.partial_tick = delta & ((1UL << FIX_SHIFT) - 1); 
	nticks = delta >> FIX_SHIFT;

	while (nticks > 0) {
		do_timer(regs);
		nticks--;
	}

	/*
	 * If we have an externally synchronized Linux clock, then update
	 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
	 * called as close as possible to 500 ms before the new second starts.
	 */
	if ((time_status & STA_UNSYNC) == 0
	    && xtime.tv_sec > state.last_rtc_update + 660
	    && xtime.tv_usec >= 500000 - ((unsigned) tick) / 2
	    && xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
		int tmp = set_rtc_mmss(xtime.tv_sec);
		state.last_rtc_update = xtime.tv_sec - (tmp ? 600 : 0);
	}

	write_unlock(&xtime_lock);
}

void
common_init_rtc(void)
{
	unsigned char x;

	/* Reset periodic interrupt frequency.  */
	x = CMOS_READ(RTC_FREQ_SELECT) & 0x3f;
	if (x != 0x26 && x != 0x19 && x != 0x06) {
		printk("Setting RTC_FREQ to 1024 Hz (%x)\n", x);
		CMOS_WRITE(0x26, RTC_FREQ_SELECT);
	}

	/* Turn on periodic interrupts.  */
	x = CMOS_READ(RTC_CONTROL);
	if (!(x & RTC_PIE)) {
		printk("Turning on RTC interrupts.\n");
		x |= RTC_PIE;
		x &= ~(RTC_AIE | RTC_UIE);
		CMOS_WRITE(x, RTC_CONTROL);
	}
	(void) CMOS_READ(RTC_INTR_FLAGS);

	outb(0x36, 0x43);	/* pit counter 0: system timer */
	outb(0x00, 0x40);
	outb(0x00, 0x40);

	outb(0xb6, 0x43);	/* pit counter 2: speaker */
	outb(0x31, 0x42);
	outb(0x13, 0x42);

	init_rtc_irq();
}

void __init
time_init(void)
{
	unsigned int year, mon, day, hour, min, sec, cc1, cc2, epoch;
	unsigned long cycle_freq, one_percent;
	long diff;

	/*
	 * The Linux interpretation of the CMOS clock register contents:
	 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
	 * RTC registers show the second which has precisely just started.
	 * Let's hope other operating systems interpret the RTC the same way.
	 */
	do { } while (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP));
	do { } while (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);

	/* Read cycle counter exactly on falling edge of update flag */
	cc1 = rpcc();

	if (!est_cycle_freq) {
		/* Sometimes the hwrpb->cycle_freq value is bogus. 
		   Go another round to check up on it and see.  */
		do { } while (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP));
		do { } while (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
		cc2 = rpcc();
		est_cycle_freq = cc2 - cc1;
		cc1 = cc2;
	}

	/* If the given value is within 1% of what we calculated, 
	   accept it.  Otherwise, use what we found.  */
	cycle_freq = hwrpb->cycle_freq;
	one_percent = cycle_freq / 100;
	diff = cycle_freq - est_cycle_freq;
	if (diff < 0)
		diff = -diff;
	if (diff > one_percent) {
		cycle_freq = est_cycle_freq;
		printk("HWRPB cycle frequency bogus.  Estimated %lu Hz\n",
		       cycle_freq);
	}
	else {
		est_cycle_freq = 0;
	}

	/* From John Bowman <[e-mail]>: allow the values
	   to settle, as the Update-In-Progress bit going low isn't good
	   enough on some hardware.  2ms is our guess; we havn't found 
	   bogomips yet, but this is close on a 500Mhz box.  */
	__delay(1000000);

	sec = CMOS_READ(RTC_SECONDS);
	min = CMOS_READ(RTC_MINUTES);
	hour = CMOS_READ(RTC_HOURS);
	day = CMOS_READ(RTC_DAY_OF_MONTH);
	mon = CMOS_READ(RTC_MONTH);
	year = CMOS_READ(RTC_YEAR);

	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
		BCD_TO_BIN(sec);
		BCD_TO_BIN(min);
		BCD_TO_BIN(hour);
		BCD_TO_BIN(day);
		BCD_TO_BIN(mon);
		BCD_TO_BIN(year);
	}

	/* PC-like is standard; used for year < 20 || year >= 70 */
	epoch = 1900;
	if (year >= 20 && year < 48)
		/* NT epoch */
		epoch = 1980;
	else if (year >= 48 && year < 70)
		/* Digital UNIX epoch */
		epoch = 1952;

	printk(KERN_INFO "Using epoch = %d\n", epoch);

	if ((year += epoch) < 1970)
		year += 100;

	xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
	xtime.tv_usec = 0;

	if (HZ > (1<<16)) {
		extern void __you_loose (void);
		__you_loose();
	}

	state.last_time = cc1;
	state.scaled_ticks_per_cycle
		= ((unsigned long) HZ << FIX_SHIFT) / cycle_freq;
	state.last_rtc_update = 0;
	state.partial_tick = 0L;

	/* Startup the timer source. */
	alpha_mv.init_rtc();

	do_get_fast_time = do_gettimeofday;
}

/*
 * Use the cycle counter to estimate an displacement from the last time
 * tick.  Unfortunately the Alpha designers made only the low 32-bits of
 * the cycle counter active, so we overflow on 8.2 seconds on a 500MHz
 * part.  So we can't do the "find absolute time in terms of cycles" thing
 * that the other ports do.
 */
void
do_gettimeofday(struct timeval *tv)
{
	unsigned long sec, usec, lost, flags;
	unsigned long delta_cycles, delta_usec, partial_tick;

	read_lock_irqsave(&xtime_lock, flags);

	delta_cycles = rpcc() - state.last_time;
	sec = xtime.tv_sec;
	usec = xtime.tv_usec;
	partial_tick = state.partial_tick;
	lost = jiffies - wall_jiffies;

	read_unlock_irqrestore(&xtime_lock, flags);

#ifdef CONFIG_SMP
	/* Until and unless we figure out how to get cpu cycle counters
	   in sync and keep them there, we can't use the rpcc tricks.  */
	delta_usec = lost * (1000000 / HZ);
#else
	/*
	 * usec = cycles * ticks_per_cycle * 2**48 * 1e6 / (2**48 * ticks)
	 *	= cycles * (s_t_p_c) * 1e6 / (2**48 * ticks)
	 *	= cycles * (s_t_p_c) * 15625 / (2**42 * ticks)
	 *
	 * which, given a 600MHz cycle and a 1024Hz tick, has a
	 * dynamic range of about 1.7e17, which is less than the
	 * 1.8e19 in an unsigned long, so we are safe from overflow.
	 *
	 * Round, but with .5 up always, since .5 to even is harder
	 * with no clear gain.
	 */

	delta_usec = (delta_cycles * state.scaled_ticks_per_cycle 
		      + partial_tick
		      + (lost << FIX_SHIFT)) * 15625;
	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
#endif

	usec += delta_usec;
	if (usec >= 1000000) {
		sec += 1;
		usec -= 1000000;
	}

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

void
do_settimeofday(struct timeval *tv)
{
	unsigned long delta_usec;
	long sec, usec;
	
	write_lock_irq(&xtime_lock);

	/* The offset that is added into time in do_gettimeofday above
	   must be subtracted out here to keep a coherent view of the
	   time.  Without this, a full-tick error is possible.  */

#ifdef CONFIG_SMP
	delta_usec = (jiffies - wall_jiffies) * (1000000 / HZ);
#else
	delta_usec = rpcc() - state.last_time;
	delta_usec = (delta_usec * state.scaled_ticks_per_cycle 
		      + state.partial_tick
		      + ((jiffies - wall_jiffies) << FIX_SHIFT)) * 15625;
	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
#endif

	sec = tv->tv_sec;
	usec = tv->tv_usec;
	usec -= delta_usec;
	if (usec < 0) {
		usec += 1000000;
		sec -= 1;
	}

	xtime.tv_sec = sec;
	xtime.tv_usec = usec;
	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 won't notice until after reboot!
 */

extern int abs(int);

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;

	/* irq are locally disabled here */
	spin_lock(&rtc_lock);
	/* Tell the clock it's being set */
	save_control = CMOS_READ(RTC_CONTROL);
	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);

	/* Stop and reset prescaler */
	save_freq_select = CMOS_READ(RTC_FREQ_SELECT);
	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) {
		/* correct for half hour time zone */
		real_minutes += 30;
	}
	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;
}