/*
 *  linux/arch/i386/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 <cananian@alumni.princeton.edu>, Andrew D.
 *      Balsa <andrebalsa@altern.org>, Philip Gladstone <philip@raptor.com>;
 *      ported from 2.0.35 Jumbo-9 by Michael Krause <m.krause@tu-harburg.de>).
 * 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/module.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>
#include <asm/cobalt.h>

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


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

/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;

static unsigned long 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 long fast_gettimeoffset_quotient;

extern rwlock_t xtime_lock;
extern unsigned long wall_jiffies;

spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;

static inline unsigned long do_fast_gettimeoffset(void)
{
        register unsigned long 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;

EXPORT_SYMBOL(i8253_lock);

extern spinlock_t i8259A_lock;

#ifndef CONFIG_X86_TSC

/* 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!
 */

static unsigned long do_slow_gettimeoffset(void)
{
        int count;

        static int count_p = LATCH;    /* for the first call after boot */
        static unsigned long jiffies_p = 0;

        /*
         * cache volatile jiffies temporarily; we have IRQs turned off. 
         */
        unsigned long jiffies_t;

        /* gets recalled with irq locally disabled */
        spin_lock(&i8253_lock);
        /* timer count may underflow right here */
        outb_p(0x00, 0x43);     /* latch the count ASAP */

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

        /*
         * We do this guaranteed double memory access instead of a _p 
         * postfix in the previous port access. Wheee, hackady hack
         */
        jiffies_t = jiffies;

        count |= inb_p(0x40) << 8;
        
        /* VIA686a test code... reset the latch if count > max + 1 */
        if (count > LATCH) {
                outb_p(0x34, 0x43);
                outb_p(LATCH & 0xff, 0x40);
                outb(LATCH >> 8, 0x40);
                count = LATCH - 1;
        }
        
        spin_unlock(&i8253_lock);

        /*
         * avoiding timer inconsistencies (they are rare, but they happen)...
         * there are two kinds of problems that must be avoided here:
         *  1. the timer counter underflows
         *  2. hardware problem with the timer, not giving us continuous time,
         *     the counter does small "jumps" upwards on some Pentium systems,
         *     (see c't 95/10 page 335 for Neptun bug.)
         */

/* you can safely undefine this if you don't have the Neptune chipset */

#define BUGGY_NEPTUN_TIMER

        if( jiffies_t == jiffies_p ) {
                if( count > count_p ) {
                        /* the nutcase */

                        int i;

                        spin_lock(&i8259A_lock);
                        /*
                         * This is tricky when I/O APICs are used;
                         * see do_timer_interrupt().
                         */
                        i = inb(0x20);
                        spin_unlock(&i8259A_lock);

                        /* assumption about timer being IRQ0 */
                        if (i & 0x01) {
                                /*
                                 * We cannot detect lost timer interrupts ... 
                                 * well, that's why we call them lost, don't we? :)
                                 * [hmm, on the Pentium and Alpha we can ... sort of]
                                 */
                                count -= LATCH;
                        } else {
#ifdef BUGGY_NEPTUN_TIMER
                                /*
                                 * for the Neptun bug we know that the 'latch'
                                 * command doesnt latch the high and low value
                                 * of the counter atomically. Thus we have to 
                                 * substract 256 from the counter 
                                 * ... funny, isnt it? :)
                                 */

                                count -= 256;
#else
                                printk("do_slow_gettimeoffset(): hardware timer problem?\n");
#endif
                        }
                }
        } else
                jiffies_p = jiffies_t;

        count_p = count;

        count = ((LATCH-1) - count) * TICK_SIZE;
        count = (count + LATCH/2) / LATCH;

        return count;
}

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


/* IBM Summit (EXA) Cyclone Timer code*/
#ifdef CONFIG_X86_SUMMIT

#define CYCLONE_CBAR_ADDR 0xFEB00CD0
#define CYCLONE_PMCC_OFFSET 0x51A0
#define CYCLONE_MPMC_OFFSET 0x51D0
#define CYCLONE_MPCS_OFFSET 0x51A8
#define CYCLONE_TIMER_FREQ 100000000

int use_cyclone = 0;
int __init cyclone_setup(char *str) 
{
        use_cyclone = 1;
        return 1;
}

static u32* volatile cyclone_timer;     /* Cyclone MPMC0 register */
static u32 last_cyclone_timer;

static inline void mark_timeoffset_cyclone(void)
{
        int count;
        unsigned long delta = last_cyclone_timer;
        spin_lock(&i8253_lock);
        /* quickly read the cyclone timer */
        if(cyclone_timer)
                last_cyclone_timer = cyclone_timer[0];

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

        count = inb_p(0x40);    /* read the latched count */
        count |= inb(0x40) << 8;
        spin_unlock(&i8253_lock);

        /*lost tick compensation*/
        delta = last_cyclone_timer - delta;
        if(delta > loops_per_jiffy+2000){
                delta = (delta/loops_per_jiffy)-1;
                jiffies += delta;
        }
               
        count = ((LATCH-1) - count) * TICK_SIZE;
        delay_at_last_interrupt = (count + LATCH/2) / LATCH;
}

static unsigned long do_gettimeoffset_cyclone(void)
{
        u32 offset;

        if(!cyclone_timer)
                return delay_at_last_interrupt;

        /* Read the cyclone timer */
        offset = cyclone_timer[0];

        /* .. relative to previous jiffy */
        offset = offset - last_cyclone_timer;

        /* convert cyclone ticks to microseconds */     
        /* XXX slow, can we speed this up? */
        offset = offset/(CYCLONE_TIMER_FREQ/1000000);

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

static void __init init_cyclone_clock(void)
{
        u32* reg;       
        u32 base;               /* saved cyclone base address */
        u32 pageaddr;   /* page that contains cyclone_timer register */
        u32 offset;             /* offset from pageaddr to cyclone_timer register */
        int i;
        
        printk(KERN_INFO "Summit chipset: Starting Cyclone Counter.\n");

        /* find base address */
        pageaddr = (CYCLONE_CBAR_ADDR)&PAGE_MASK;
        offset = (CYCLONE_CBAR_ADDR)&(~PAGE_MASK);
        set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
        reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
        if(!reg){
                printk(KERN_ERR "Summit chipset: Could not find valid CBAR register.\n");
                use_cyclone = 0;
                return;
        }
        base = *reg;    
        if(!base){
                printk(KERN_ERR "Summit chipset: Could not find valid CBAR value.\n");
                use_cyclone = 0;
                return;
        }
        
        /* setup PMCC */
        pageaddr = (base + CYCLONE_PMCC_OFFSET)&PAGE_MASK;
        offset = (base + CYCLONE_PMCC_OFFSET)&(~PAGE_MASK);
        set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
        reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
        if(!reg){
                printk(KERN_ERR "Summit chipset: Could not find valid PMCC register.\n");
                use_cyclone = 0;
                return;
        }
        reg[0] = 0x00000001;

        /* setup MPCS */
        pageaddr = (base + CYCLONE_MPCS_OFFSET)&PAGE_MASK;
        offset = (base + CYCLONE_MPCS_OFFSET)&(~PAGE_MASK);
        set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
        reg = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
        if(!reg){
                printk(KERN_ERR "Summit chipset: Could not find valid MPCS register.\n");
                use_cyclone = 0;
                return;
        }
        reg[0] = 0x00000001;

        /* map in cyclone_timer */
        pageaddr = (base + CYCLONE_MPMC_OFFSET)&PAGE_MASK;
        offset = (base + CYCLONE_MPMC_OFFSET)&(~PAGE_MASK);
        set_fixmap_nocache(FIX_CYCLONE_TIMER, pageaddr);
        cyclone_timer = (u32*)(fix_to_virt(FIX_CYCLONE_TIMER) + offset);
        if(!cyclone_timer){
                printk(KERN_ERR "Summit chipset: Could not find valid MPMC register.\n");
                use_cyclone = 0;
                return;
        }

        /*quick test to make sure its ticking*/
        for(i=0; i<3; i++){
                u32 old = cyclone_timer[0];
                int stall = 100;
                while(stall--) barrier();
                if(cyclone_timer[0] == old){
                        printk(KERN_ERR "Summit chipset: Counter not counting! DISABLED\n");
                        cyclone_timer = 0;
                        use_cyclone = 0;
                        return;
                }
        }
        /* Everything looks good, so set do_gettimeoffset */
        do_gettimeoffset = do_gettimeoffset_cyclone;    
}
void __cyclone_delay(unsigned long loops)
{
        unsigned long bclock, now;
        if(!cyclone_timer)
                return;
        bclock = cyclone_timer[0];
        do {
                rep_nop();
                now = cyclone_timer[0];
        } while ((now-bclock) < loops);
}
#endif /* CONFIG_X86_SUMMIT */

#else

#define do_gettimeoffset()      do_fast_gettimeoffset()

#endif

/* No-cyclone stubs */
#ifndef CONFIG_X86_SUMMIT
int __init cyclone_setup(char *str) 
{
        printk(KERN_ERR "cyclone: Kernel not compiled with CONFIG_X86_SUMMIT, cannot use the cyclone-timer.\n");
        return 1;
}

const int use_cyclone = 0;
static void mark_timeoffset_cyclone(void) {}
static unsigned long do_gettimeoffset_cyclone(void) {return 0;}
static void init_cyclone_clock(void) {}
void __cyclone_delay(unsigned long loops) {}
#endif /* CONFIG_X86_SUMMIT */

/*
 * 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);
        /*
         * 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;
        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.
                 */
                spin_lock(&i8259A_lock);
                outb(0x0c, 0x20);
                /* Ack the IRQ; AEOI will end it automatically. */
                inb(0x20);
                spin_unlock(&i8259A_lock);
        }
#endif

#ifdef CONFIG_VISWS
        /* Clear the interrupt */
        co_cpu_write(CO_CPU_STAT,co_cpu_read(CO_CPU_STAT) & ~CO_STAT_TIMEINTR);
#endif
        do_timer(regs);
/*
 * In the SMP case we use the local APIC timer interrupt to do the
 * profiling, except when we simulate SMP mode on a uniprocessor
 * system, in that case we have to call the local interrupt handler.
 */
#ifndef CONFIG_X86_LOCAL_APIC
        if (!user_mode(regs))
                x86_do_profile(regs->eip);
#else
        if (!using_apic_timer)
                smp_local_timer_interrupt(regs);
#endif

        /*
         * 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 > last_rtc_update + 660 &&
            xtime.tv_usec >= 500000 - ((unsigned) tick) / 2 &&
            xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
                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 */
        }
            
#ifdef CONFIG_MCA
        if( MCA_bus ) {
                /* The PS/2 uses level-triggered interrupts.  You can't
                turn them off, nor would you want to (any attempt to
                enable edge-triggered interrupts usually gets intercepted by a
                special hardware circuit).  Hence we have to acknowledge
                the timer interrupt.  Through some incredibly stupid
                design idea, the reset for IRQ 0 is done by setting the
                high bit of the PPI port B (0x61).  Note that some PS/2s,
                notably the 55SX, work fine if this is removed.  */

                irq = inb_p( 0x61 );    /* read the current state */
                outb_p( irq|0x80, 0x61 );       /* reset the IRQ */
        }
#endif
}

static int use_tsc;

/*
 * This is the same as the above, except we _also_ save the current
 * Time Stamp Counter value at the time of the timer interrupt, so that
 * we later on can estimate the time of day more exactly.
 */
static void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
        int count;

        /*
         * Here we are in the timer irq handler. We just have irqs locally
         * disabled but we don't know if the timer_bh is running on the other
         * CPU. We need to avoid to SMP race with it. NOTE: we don' t need
         * the irq version of write_lock because as just said we have irq
         * locally disabled. -arca
         */
        write_lock(&xtime_lock);

        if(use_cyclone)
                mark_timeoffset_cyclone();
        else if (use_tsc) {
                /*
                 * It is important that these two operations happen almost at
                 * the same time. We do the RDTSC stuff first, since it's
                 * faster. To avoid any inconsistencies, we need interrupts
                 * disabled locally.
                 */

                /*
                 * Interrupts are just disabled locally since the timer irq
                 * has the SA_INTERRUPT flag set. -arca
                 */
        
                /* read Pentium cycle counter */

                rdtscl(last_tsc_low);

                spin_lock(&i8253_lock);
                outb_p(0x00, 0x43);     /* latch the count ASAP */

                count = inb_p(0x40);    /* read the latched count */
                count |= inb(0x40) << 8;

                /* Any unpaired read will cause the above to swap MSB/LSB
                   forever.  Try to detect this and reset the counter. 
                   
                   This happens very occasionally with buggy SMM bios
                   code at least */
                   
                if (count > LATCH) {
                        printk(KERN_WARNING 
                               "i8253 count too high! resetting..\n");
                        outb_p(0x34, 0x43);
                        outb_p(LATCH & 0xff, 0x40);
                        outb(LATCH >> 8, 0x40);
                        count = LATCH - 1;
                }

                spin_unlock(&i8253_lock);

                /* Some i8253 clones hold the LATCH value visible
                   momentarily as they flip back to zero */
                if (count == LATCH) {
                        count--;
                }

                count = ((LATCH-1) - count) * TICK_SIZE;
                delay_at_last_interrupt = (count + LATCH/2) / LATCH;
        }

        do_timer_interrupt(irq, NULL, regs);

        write_unlock(&xtime_lock);

}

/* not static: needed by APM */
unsigned long get_cmos_time(void)
{
        unsigned int year, mon, day, hour, min, sec;
        int i;

        spin_lock(&rtc_lock);
        /* 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);
          }
        spin_unlock(&rtc_lock);
        if ((year += 1900) < 1970)
                year += 100;
        return mktime(year, mon, day, hour, min, sec);
}

static struct irqaction irq0  = { timer_interrupt, SA_INTERRUPT, 0, "timer", NULL, NULL};

/* ------ Calibrate the TSC ------- 
 * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
 * Too much 64-bit arithmetic here to do this cleanly in C, and for
 * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
 * output busy loop as low as possible. We avoid reading the CTC registers
 * directly because of the awkward 8-bit access mechanism of the 82C54
 * device.
 */

#define CALIBRATE_LATCH (5 * LATCH)
#define CALIBRATE_TIME  (5 * 1000020/HZ)

static unsigned long __init calibrate_tsc(void)
{
       /* Set the Gate high, disable speaker */
        outb((inb(0x61) & ~0x02) | 0x01, 0x61);

        /*
         * Now let's take care of CTC channel 2
         *
         * Set the Gate high, program CTC channel 2 for mode 0,
         * (interrupt on terminal count mode), binary count,
         * load 5 * LATCH count, (LSB and MSB) to begin countdown.
         */
        outb(0xb0, 0x43);                       /* binary, mode 0, LSB/MSB, Ch 2 */
        outb(CALIBRATE_LATCH & 0xff, 0x42);     /* LSB of count */
        outb(CALIBRATE_LATCH >> 8, 0x42);       /* MSB of count */

        {
                unsigned long startlow, starthigh;
                unsigned long endlow, endhigh;
                unsigned long count;

                rdtsc(startlow,starthigh);
                count = 0;
                do {
                        count++;
                } while ((inb(0x61) & 0x20) == 0);
                rdtsc(endlow,endhigh);

                last_tsc_low = endlow;

                /* Error: ECTCNEVERSET */
                if (count <= 1)
                        goto bad_ctc;

                /* 64-bit subtract - gcc just messes up with long longs */
                __asm__("subl %2,%0\n\t"
                        "sbbl %3,%1"
                        :"=a" (endlow), "=d" (endhigh)
                        :"g" (startlow), "g" (starthigh),
                         "0" (endlow), "1" (endhigh));

                /* Error: ECPUTOOFAST */
                if (endhigh)
                        goto bad_ctc;

                /* Error: ECPUTOOSLOW */
                if (endlow <= CALIBRATE_TIME)
                        goto bad_ctc;

                __asm__("divl %2"
                        :"=a" (endlow), "=d" (endhigh)
                        :"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));

                return endlow;
        }

        /*
         * The CTC wasn't reliable: we got a hit on the very first read,
         * or the CPU was so fast/slow that the quotient wouldn't fit in
         * 32 bits..
         */
bad_ctc:
        return 0;
}

void __init time_init(void)
{
        extern int x86_udelay_tsc;
        
        xtime.tv_sec = get_cmos_time();
        xtime.tv_usec = 0;

/*
 * If we have APM enabled or the CPU clock speed is variable
 * (CPU stops clock on HLT or slows clock to save power)
 * then the TSC timestamps may diverge by up to 1 jiffy from
 * 'real time' but nothing will break.
 * The most frequent case is that the CPU is "woken" from a halt
 * state by the timer interrupt itself, so we get 0 error. In the
 * rare cases where a driver would "wake" the CPU and request a
 * timestamp, the maximum error is < 1 jiffy. But timestamps are
 * still perfectly ordered.
 * Note that the TSC counter will be reset if APM suspends
 * to disk; this won't break the kernel, though, 'cuz we're
 * smart.  See arch/i386/kernel/apm.c.
 */
        /*
         *      Firstly we have to do a CPU check for chips with
         *      a potentially buggy TSC. At this point we haven't run
         *      the ident/bugs checks so we must run this hook as it
         *      may turn off the TSC flag.
         *
         *      NOTE: this doesnt yet handle SMP 486 machines where only
         *      some CPU's have a TSC. Thats never worked and nobody has
         *      moaned if you have the only one in the world - you fix it!
         */
 
        dodgy_tsc();

        if(use_cyclone)
                init_cyclone_clock();
                
        if (cpu_has_tsc) {
                unsigned long tsc_quotient = calibrate_tsc();
                if (tsc_quotient) {
                        fast_gettimeoffset_quotient = tsc_quotient;
                        /* XXX: This is messy
                         * However, we want to allow for the cyclone timer 
                         * to work w/ or w/o the TSCs being avaliable
                         *      -johnstul@us.ibm.com
                         */
                        if(!use_cyclone){
                                /*
                                 *      We could be more selective here I suspect
                                 *      and just enable this for the next intel chips ?
                                 */
                                use_tsc = 1;
                                x86_udelay_tsc = 1;
#ifndef do_gettimeoffset
                                do_gettimeoffset = do_fast_gettimeoffset;
#endif
                        }
                        /* report CPU clock rate in Hz.
                         * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
                         * clock/second. Our precision is about 100 ppm.
                         */
                        {       unsigned long eax=0, edx=1000;
                                __asm__("divl %2"
                                :"=a" (cpu_khz), "=d" (edx)
                                :"r" (tsc_quotient),
                                "0" (eax), "1" (edx));
                                printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz % 1000);
                        }
                }
        }


#ifdef CONFIG_VISWS
        printk("Starting Cobalt Timer system clock\n");

        /* Set the countdown value */
        co_cpu_write(CO_CPU_TIMEVAL, CO_TIME_HZ/HZ);

        /* Start the timer */
        co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) | CO_CTRL_TIMERUN);

        /* Enable (unmask) the timer interrupt */
        co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) & ~CO_CTRL_TIMEMASK);

        /* Wire cpu IDT entry to s/w handler (and Cobalt APIC to IDT) */
        setup_irq(CO_IRQ_TIMER, &irq0);
#else
        setup_irq(0, &irq0);
#endif
}