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/*

 *  linux/arch/mips/kernel/time.c

 *

 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds

 *

 * This file contains the time handling details for PC-style clocks as

 * found in some MIPS systems.

 */

#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 <asm/segment.h>

#include <asm/io.h>

#include <linux/mc146818rtc.h>

#include <linux/timex.h>

#define TIMER_IRQ 0

/* This function must be called with interrupts disabled

 * It was inspired by Steve McCanne's microtime-i386 for BSD.  -- jrs

 *

 * However, the pc-audio speaker driver changes the divisor so that

 * it gets interrupted rather more often - it loads 64 into the

 * counter rather than 11932! This has an adverse impact on

 * do_gettimeoffset() -- it stops working! What is also not

 * good is that the interval that our timer function gets called

 * is no longer 10.0002 ms, but 9.9767 ms. To get around this

 * would require using a different timing source. Maybe someone

 * could use the RTC - I know that this can interrupt at frequencies

 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix

 * it so that at startup, the timer code in sched.c would select

 * using either the RTC or the 8253 timer. The decision would be

 * based on whether there was any other device around that needed

 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,

 * and then do some jiggery to have a version of do_timer that

 * advanced the clock by 1/1024 s. Every time that reached over 1/100

 * of a second, then do all the old code. If the time was kept correct

 * then do_gettimeoffset could just return 0 - there is no low order

 * divider that can be accessed.

 *

 * Ideally, you would be able to use the RTC for the speaker driver,

 * but it appears that the speaker driver really needs interrupt more

 * often than every 120 us or so.

 *

 * Anyway, this needs more thought....          pjsg (1993-08-28)

 *

 * If you are really that interested, you should be reading

 * comp.protocols.time.ntp!

 */

#define TICK_SIZE tick

static unsigned long do_slow_gettimeoffset(void)

{

        int count;

        unsigned long offset = 0;

        /* timer count may underflow right here */

        outb_p(0x00, 0x43);     /* latch the count ASAP */

        count = inb_p(0x40);    /* read the latched count */

        count |= inb(0x40) << 8;

        /* we know probability of underflow is always MUCH less than 1% */

        if (count > (LATCH - LATCH/100)) {

                /* check for pending timer interrupt */

                outb_p(0x0a, 0x20);

                if (inb(0x20) & 1)

                        offset = TICK_SIZE;

        }

        count = ((LATCH-1) - count) * TICK_SIZE;

        count = (count + LATCH/2) / LATCH;

        return offset + count;

}

static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;

/*

 * This version of gettimeofday has near microsecond resolution.

 */

void do_gettimeofday(struct timeval *tv)

{

        unsigned long flags;

        save_flags(flags);

        cli();

        *tv = xtime;

        tv->tv_usec += do_gettimeoffset();

        if (tv->tv_usec >= 1000000) {

                tv->tv_usec -= 1000000;

                tv->tv_sec++;

        }

        restore_flags(flags);

}

void do_settimeofday(struct timeval *tv)

{

        cli();

        /* This is revolting. We need to set the xtime.tv_usec

         * correctly. However, the value in this location is

         * is value at the last tick.

         * Discover what correction gettimeofday

         * would have done, and then undo it!

         */

        tv->tv_usec -= do_gettimeoffset();

        if (tv->tv_usec < 0) {

                tv->tv_usec += 1000000;

                tv->tv_sec--;

        }

        xtime = *tv;

        time_state = TIME_BAD;

        time_maxerror = 0x70000000;

        time_esterror = 0x70000000;

        sti();

}

/*

 * 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.

 */

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;

        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

                retval = -1;

        /* The following flags have to be released exactly in this order,

         * otherwise the DS12887 (popular MC146818A clone with integrated

         * battery and crystal) 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);

        return retval;

}

/* last time the cmos clock got updated */

static long last_rtc_update = 0;

/*

 * timer_interrupt() needs to keep up the real-time clock,

 * as well as call the "do_timer()" routine every clocktick

 */

static void timer_interrupt(int irq, struct pt_regs * regs)

{

        do_timer(regs);

        /*

         * 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_state != TIME_BAD && xtime.tv_sec > last_rtc_update + 660 &&

            xtime.tv_usec > 500000 - (tick >> 1) &&

            xtime.tv_usec < 500000 + (tick >> 1))

          if (set_rtc_mmss(xtime.tv_sec) == 0)

            last_rtc_update = xtime.tv_sec;

          else

            last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */

        /* As we return to user mode fire off the other CPU schedulers.. this is

           basically because we don't yet share IRQ's around. This message is

           rigged to be safe on the 386 - basically it's a hack, so don't look

           closely for now.. */

        smp_message_pass(MSG_ALL_BUT_SELF, MSG_RESCHEDULE, 0L, 0);

}

/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.

 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59

 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.

 *

 * [For the Julian calendar (which was used in Russia before 1917,

 * Britain & colonies before 1752, anywhere else before 1582,

 * and is still in use by some communities) leave out the

 * -year/100+year/400 terms, and add 10.]

 *

 * This algorithm was first published by Gauss (I think).

 *

 * WARNING: this function will overflow on 2106-02-07 06:28:16 on

 * machines were long is 32-bit! (However, as time_t is signed, we

 * will already get problems at other places on 2038-01-19 03:14:08)

 */

static inline unsigned long mktime(unsigned int year, unsigned int mon,

        unsigned int day, unsigned int hour,

        unsigned int min, unsigned int sec)

{

        if (0 >= (int) (mon -= 2)) {     /* 1..12 -> 11,12,1..10 */

                mon += 12;      /* Puts Feb last since it has leap day */

                year -= 1;

        }

        return (((

            (unsigned long)(year/4 - year/100 + year/400 + 367*mon/12 + day) +

              year*365 - 719499

            )*24 + hour /* now have hours */

           )*60 + min /* now have minutes */

          )*60 + sec; /* finally seconds */

}

void time_init(void)

{

        void (*irq_handler)(int, struct pt_regs *);

        unsigned int year, mon, day, hour, min, sec;

        int i;

        /* 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.

         */

        /* read RTC exactly on falling edge of update flag */

        for (i = 0 ; i < 1000000 ; i++)  /* may take up to 1 second... */

                if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)

                        break;

        for (i = 0 ; i < 1000000 ; i++)  /* must try at least 2.228 ms */

                if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))

                        break;

        do { /* Isn't this overkill ? UIP above should guarantee consistency */

                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);

        } while (sec != CMOS_READ(RTC_SECONDS));

        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);

          }

        if ((year += 1900) < 1970)

                year += 100;

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

        xtime.tv_usec = 0;

        /* FIXME: If we have the CPU hardware time counters, use them */

        irq_handler = timer_interrupt;

        if (request_irq(TIMER_IRQ, irq_handler, 0, "timer") != 0)

                panic("Could not allocate timer IRQ!");

}