xref: /src/sys/arch/x86/isa/clock.c

/*	$NetBSD: clock.c,v 1.2 2006/09/04 03:07:52 perry Exp $	*/

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz and Don Ahn.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)clock.c	7.2 (Berkeley) 5/12/91
 */
/*-
 * Copyright (c) 1993, 1994 Charles M. Hannum.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz and Don Ahn.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)clock.c	7.2 (Berkeley) 5/12/91
 */
/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989 Carnegie Mellon University
 * All Rights Reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution (at) CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
  Copyright 1988, 1989 by Intel Corporation, Santa Clara, California.

		All Rights Reserved

Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appears in all
copies and that both the copyright notice and this permission notice
appear in supporting documentation, and that the name of Intel
not be used in advertising or publicity pertaining to distribution
of the software without specific, written prior permission.

INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

/*
 * Primitive clock interrupt routines.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: clock.c,v 1.2 2006/09/04 03:07:52 perry Exp $");

/* #define CLOCKDEBUG */
/* #define CLOCK_PARANOIA */

#include "opt_multiprocessor.h"
#include "opt_ntp.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/timetc.h>
#include <sys/kernel.h>
#include <sys/device.h>

#include <machine/cpu.h>
#include <machine/intr.h>
#include <machine/pio.h>
#include <machine/cpufunc.h>

#include <dev/isa/isareg.h>
#include <dev/isa/isavar.h>
#include <dev/ic/mc146818reg.h>
#include <dev/ic/i8253reg.h>
#include <i386/isa/nvram.h>
#include <x86/x86/tsc.h>
#include <dev/clock_subr.h>
#include <machine/specialreg.h>

#include "config_time.h"		/* for CONFIG_TIME */

#ifndef __x86_64__
#include "mca.h"
#endif
#if NMCA > 0
#include <machine/mca_machdep.h>	/* for MCA_system */
#endif

#include "pcppi.h"
#if (NPCPPI > 0)
#include <dev/isa/pcppivar.h>

int sysbeepmatch(struct device *, struct cfdata *, void *);
void sysbeepattach(struct device *, struct device *, void *);

CFATTACH_DECL(sysbeep, sizeof(struct device),
    sysbeepmatch, sysbeepattach, NULL, NULL);

static int ppi_attached;
static pcppi_tag_t ppicookie;
#endif /* PCPPI */

#ifdef __x86_64__
#define READ_FLAGS()	read_rflags()
#define WRITE_FLAGS(x)	write_rflags(x)
#else /* i386 architecture processor */
#define READ_FLAGS()	read_eflags()
#define WRITE_FLAGS(x)	write_eflags(x)
#endif

#ifdef CLOCKDEBUG
int clock_debug = 0;
#define DPRINTF(arg) if (clock_debug) printf arg
#else
#define DPRINTF(arg)
#endif

int		gettick(void);
void		sysbeep(int, int);
static void     tickle_tc(void);

static int	clockintr(void *, struct intrframe);
static void	rtcinit(void);
static int	rtcget(mc_todregs *);
static void	rtcput(mc_todregs *);

static int	cmoscheck(void);

static int	clock_expandyear(int);

static inline int gettick_broken_latch(void);

static volatile uint32_t i8254_lastcount;
static volatile uint32_t i8254_offset;
static volatile int i8254_ticked;

static struct simplelock tmr_lock = SIMPLELOCK_INITIALIZER;  /* protect TC timer variables */

inline u_int mc146818_read(void *, u_int);
inline void mc146818_write(void *, u_int, u_int);

u_int i8254_get_timecount(struct timecounter *);
static void rtc_register(void);

static struct timecounter i8254_timecounter = {
	i8254_get_timecount,	/* get_timecount */
	0,			/* no poll_pps */
	~0u,			/* counter_mask */
	TIMER_FREQ,		/* frequency */
	"i8254",		/* name */
	100,			/* quality */
	NULL,			/* prev */
	NULL,			/* next */
};

/* XXX use sc? */
inline u_int
mc146818_read(void *sc, u_int reg)
{

	outb(IO_RTC, reg);
	return (inb(IO_RTC+1));
}

/* XXX use sc? */
inline void
mc146818_write(void *sc, u_int reg, u_int datum)
{

	outb(IO_RTC, reg);
	outb(IO_RTC+1, datum);
}

u_long rtclock_tval;		/* i8254 reload value for countdown */
int    rtclock_init = 0;

int clock_broken_latch = 0;

#ifdef CLOCK_PARANOIA
static int ticks[6];
#endif
/*
 * i8254 latch check routine:
 *     National Geode (formerly Cyrix MediaGX) has a serious bug in
 *     its built-in i8254-compatible clock module.
 *     machdep sets the variable 'clock_broken_latch' to indicate it.
 */

int
gettick_broken_latch(void)
{
	u_long flags;
	int v1, v2, v3;
	int w1, w2, w3;

	/* Don't want someone screwing with the counter while we're here. */
	flags = READ_FLAGS();
	disable_intr();

	v1 = inb(IO_TIMER1+TIMER_CNTR0);
	v1 |= inb(IO_TIMER1+TIMER_CNTR0) << 8;
	v2 = inb(IO_TIMER1+TIMER_CNTR0);
	v2 |= inb(IO_TIMER1+TIMER_CNTR0) << 8;
	v3 = inb(IO_TIMER1+TIMER_CNTR0);
	v3 |= inb(IO_TIMER1+TIMER_CNTR0) << 8;

	WRITE_FLAGS(flags);

#ifdef CLOCK_PARANOIA
	if (clock_debug) {
		ticks[0] = ticks[3];
		ticks[1] = ticks[4];
		ticks[2] = ticks[5];
		ticks[3] = v1;
		ticks[4] = v2;
		ticks[5] = v3;
	}
#endif

	if (v1 >= v2 && v2 >= v3 && v1 - v3 < 0x200)
		return (v2);

#define _swap_val(a, b) do { \
	int c = a; \
	a = b; \
	b = c; \
} while (0)

	/*
	 * sort v1 v2 v3
	 */
	if (v1 < v2)
		_swap_val(v1, v2);
	if (v2 < v3)
		_swap_val(v2, v3);
	if (v1 < v2)
		_swap_val(v1, v2);

	/*
	 * compute the middle value
	 */

	if (v1 - v3 < 0x200)
		return (v2);

	w1 = v2 - v3;
	w2 = v3 - v1 + rtclock_tval;
	w3 = v1 - v2;
	if (w1 >= w2) {
		if (w1 >= w3)
		        return (v1);
	} else {
		if (w2 >= w3)
			return (v2);
	}
	return (v3);
}

/* minimal initialization, enough for delay() */
void
initrtclock(u_long freq)
{
	u_long tval;
	/*
	 * Compute timer_count, the count-down count the timer will be
	 * set to.  Also, correctly round
	 * this by carrying an extra bit through the division.
	 */
	tval = (freq * 2) / (u_long) hz;
	tval = (tval / 2) + (tval & 0x1);

	/* initialize 8254 clock */
	outb(IO_TIMER1+TIMER_MODE, TIMER_SEL0|TIMER_RATEGEN|TIMER_16BIT);

	/* Correct rounding will buy us a better precision in timekeeping */
	outb(IO_TIMER1+TIMER_CNTR0, tval % 256);
	outb(IO_TIMER1+TIMER_CNTR0, tval / 256);

	rtclock_tval = tval ? tval : 0xFFFF;
	rtclock_init = 1;
}

void
startrtclock(void)
{
	int s;

	if (!rtclock_init)
		initrtclock(TIMER_FREQ);

	/* Check diagnostic status */
	if ((s = mc146818_read(NULL, NVRAM_DIAG)) != 0) { /* XXX softc */
		char bits[128];
		printf("RTC BIOS diagnostic error %s\n",
		    bitmask_snprintf(s, NVRAM_DIAG_BITS, bits, sizeof(bits)));
	}

	tc_init(&i8254_timecounter);

#if defined(I586_CPU) || defined(I686_CPU) || defined(__x86_64__)
	init_TSC();
#endif

	rtc_register();
}


static void
tickle_tc(void)
{
#if defined(MULTIPROCESSOR)
	struct cpu_info *ci = curcpu();
	/*
	 * If we are not the primary CPU, we're not allowed to do
	 * any more work.
	 */
	if (CPU_IS_PRIMARY(ci) == 0)
		return;
#endif
	if (rtclock_tval && timecounter->tc_get_timecount == i8254_get_timecount) {
		simple_lock(&tmr_lock);
		if (i8254_ticked)
			i8254_ticked    = 0;
		else {
			i8254_offset   += rtclock_tval;
			i8254_lastcount = 0;
		}
		simple_unlock(&tmr_lock);
	}

}

static int
clockintr(void *arg, struct intrframe frame)
{
	tickle_tc();

	hardclock((struct clockframe *)&frame);

#if NMCA > 0
	if (MCA_system) {
		/* Reset PS/2 clock interrupt by asserting bit 7 of port 0x61 */
		outb(0x61, inb(0x61) | 0x80);
	}
#endif
	return -1;
}

u_int
i8254_get_timecount(struct timecounter *tc)
{
	u_int count;
	u_char high, low;
	u_long flags;

	/* Don't want someone screwing with the counter while we're here. */
	flags = READ_FLAGS();
	disable_intr();

	simple_lock(&tmr_lock);

	/* Select timer0 and latch counter value. */
	outb(IO_TIMER1 + TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);

	low = inb(IO_TIMER1 + TIMER_CNTR0);
	high = inb(IO_TIMER1 + TIMER_CNTR0);
	count = rtclock_tval - ((high << 8) | low);

	if (rtclock_tval && (count < i8254_lastcount || !i8254_ticked)) {
		i8254_ticked = 1;
		i8254_offset += rtclock_tval;
	}

	i8254_lastcount = count;
	count += i8254_offset;

	simple_unlock(&tmr_lock);

	WRITE_FLAGS(flags);
	return (count);
}

int
gettick(void)
{
	u_long flags;
	u_char lo, hi;

	if (clock_broken_latch)
		return (gettick_broken_latch());

	/* Don't want someone screwing with the counter while we're here. */
	flags = READ_FLAGS();
	disable_intr();
	/* Select counter 0 and latch it. */
	outb(IO_TIMER1+TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);
	lo = inb(IO_TIMER1+TIMER_CNTR0);
	hi = inb(IO_TIMER1+TIMER_CNTR0);
	WRITE_FLAGS(flags);
	return ((hi << 8) | lo);
}

/*
 * Wait approximately `n' microseconds.
 * Relies on timer 1 counting down from (TIMER_FREQ / hz) at TIMER_FREQ Hz.
 * Note: timer had better have been programmed before this is first used!
 * (Note that we use `rate generator' mode, which counts at 1:1; `square
 * wave' mode counts at 2:1).
 * Don't rely on this being particularly accurate.
 */
void
i8254_delay(int n)
{
	int delay_tick, odelay_tick;
	static const int delaytab[26] = {
		 0,  2,  3,  4,  5,  6,  7,  9, 10, 11,
		12, 13, 15, 16, 17, 18, 19, 21, 22, 23,
		24, 25, 27, 28, 29, 30,
	};

	/* allow DELAY() to be used before startrtclock() */
	if (!rtclock_init)
		initrtclock(TIMER_FREQ);

	/*
	 * Read the counter first, so that the rest of the setup overhead is
	 * counted.
	 */
	odelay_tick = gettick();

	if (n <= 25)
		n = delaytab[n];
	else {
#ifdef __GNUC__
		/*
		 * Calculate ((n * TIMER_FREQ) / 1e6) using explicit assembler
		 * code so we can take advantage of the intermediate 64-bit
		 * quantity to prevent loss of significance.
		 */
		int m;
		__asm volatile("mul %3"
				 : "=a" (n), "=d" (m)
				 : "0" (n), "r" (TIMER_FREQ));
		__asm volatile("div %4"
				 : "=a" (n), "=d" (m)
				 : "0" (n), "1" (m), "r" (1000000));
#else
		/*
		 * Calculate ((n * TIMER_FREQ) / 1e6) without using floating
		 * point and without any avoidable overflows.
		 */
		int sec = n / 1000000,
		    usec = n % 1000000;
		n = sec * TIMER_FREQ +
		    usec * (TIMER_FREQ / 1000000) +
		    usec * ((TIMER_FREQ % 1000000) / 1000) / 1000 +
		    usec * (TIMER_FREQ % 1000) / 1000000;
#endif
	}

	while (n > 0) {
#ifdef CLOCK_PARANOIA
		int delta;
		delay_tick = gettick();
		if (delay_tick > odelay_tick)
			delta = rtclock_tval - (delay_tick - odelay_tick);
		else
			delta = odelay_tick - delay_tick;
		if (delta < 0 || delta >= rtclock_tval / 2) {
			DPRINTF(("delay: ignore ticks %.4x-%.4x",
				 odelay_tick, delay_tick));
			if (clock_broken_latch) {
				DPRINTF(("  (%.4x %.4x %.4x %.4x %.4x %.4x)\n",
				         ticks[0], ticks[1], ticks[2],
				         ticks[3], ticks[4], ticks[5]));
			} else {
				DPRINTF(("\n"));
			}
		} else
			n -= delta;
#else
		delay_tick = gettick();
		if (delay_tick > odelay_tick)
			n -= rtclock_tval - (delay_tick - odelay_tick);
		else
			n -= odelay_tick - delay_tick;
#endif
		odelay_tick = delay_tick;
	}
}

#if (NPCPPI > 0)
int
sysbeepmatch(struct device *parent, struct cfdata *match, void *aux)
{
	return (!ppi_attached);
}

void
sysbeepattach(struct device *parent, struct device *self, void *aux)
{
	aprint_naive("\n");
	aprint_normal("\n");

	ppicookie = ((struct pcppi_attach_args *)aux)->pa_cookie;
	ppi_attached = 1;
}
#endif

void
sysbeep(int pitch, int period)
{
#if (NPCPPI > 0)
	if (ppi_attached)
		pcppi_bell(ppicookie, pitch, period, 0);
#endif
}

void
i8254_initclocks(void)
{

	/*
	 * XXX If you're doing strange things with multiple clocks, you might
	 * want to keep track of clock handlers.
	 */
	(void)isa_intr_establish(NULL, 0, IST_PULSE, IPL_CLOCK,
	    (int (*)(void *))clockintr, 0);
}

static void
rtcinit(void)
{
	static int first_rtcopen_ever = 1;

	if (!first_rtcopen_ever)
		return;
	first_rtcopen_ever = 0;

	mc146818_write(NULL, MC_REGA,			/* XXX softc */
	    MC_BASE_32_KHz | MC_RATE_1024_Hz);
	mc146818_write(NULL, MC_REGB, MC_REGB_24HR);	/* XXX softc */
}

static int
rtcget(mc_todregs *regs)
{

	rtcinit();
	if ((mc146818_read(NULL, MC_REGD) & MC_REGD_VRT) == 0) /* XXX softc */
		return (-1);
	MC146818_GETTOD(NULL, regs);			/* XXX softc */
	return (0);
}

static void
rtcput(mc_todregs *regs)
{

	rtcinit();
	MC146818_PUTTOD(NULL, regs);			/* XXX softc */
}

static int timeset;

/*
 * check whether the CMOS layout is "standard"-like (ie, not PS/2-like),
 * to be called at splclock()
 */
static int
cmoscheck(void)
{
	int i;
	unsigned short cksum = 0;

	for (i = 0x10; i <= 0x2d; i++)
		cksum += mc146818_read(NULL, i); /* XXX softc */

	return (cksum == (mc146818_read(NULL, 0x2e) << 8)
			  + mc146818_read(NULL, 0x2f));
}

#if NMCA > 0
/*
 * Check whether the CMOS layout is PS/2 like, to be called at splclock().
 */
static int cmoscheckps2(void);
static int
cmoscheckps2(void)
{
#if 0
	/* Disabled until I find out the CRC checksum algorithm IBM uses */
	int i;
	unsigned short cksum = 0;

	for (i = 0x10; i <= 0x31; i++)
		cksum += mc146818_read(NULL, i); /* XXX softc */

	return (cksum == (mc146818_read(NULL, 0x32) << 8)
			  + mc146818_read(NULL, 0x33));
#else
	/* Check 'incorrect checksum' bit of IBM PS/2 Diagnostic Status Byte */
	return ((mc146818_read(NULL, NVRAM_DIAG) & (1<<6)) == 0);
#endif
}
#endif /* NMCA > 0 */

/*
 * patchable to control century byte handling:
 * 1: always update
 * -1: never touch
 * 0: try to figure out itself
 */
int rtc_update_century = 0;

/*
 * Expand a two-digit year as read from the clock chip
 * into full width.
 * Being here, deal with the CMOS century byte.
 */
static int centb = NVRAM_CENTURY;
static int
clock_expandyear(int clockyear)
{
	int s, clockcentury, cmoscentury;

	clockcentury = (clockyear < 70) ? 20 : 19;
	clockyear += 100 * clockcentury;

	if (rtc_update_century < 0)
		return (clockyear);

	s = splclock();
	if (cmoscheck())
		cmoscentury = mc146818_read(NULL, NVRAM_CENTURY);
#if NMCA > 0
	else if (MCA_system && cmoscheckps2())
		cmoscentury = mc146818_read(NULL, (centb = 0x37));
#endif
	else
		cmoscentury = 0;
	splx(s);
	if (!cmoscentury) {
#ifdef DIAGNOSTIC
		printf("clock: unknown CMOS layout\n");
#endif
		return (clockyear);
	}
	cmoscentury = bcdtobin(cmoscentury);

	if (cmoscentury != clockcentury) {
		/* XXX note: saying "century is 20" might confuse the naive. */
		printf("WARNING: NVRAM century is %d but RTC year is %d\n",
		       cmoscentury, clockyear);

		/* Kludge to roll over century. */
		if ((rtc_update_century > 0) ||
		    ((cmoscentury == 19) && (clockcentury == 20) &&
		     (clockyear == 2000))) {
			printf("WARNING: Setting NVRAM century to %d\n",
			       clockcentury);
			s = splclock();
			mc146818_write(NULL, centb, bintobcd(clockcentury));
			splx(s);
		}
	} else if (cmoscentury == 19 && rtc_update_century == 0)
		rtc_update_century = 1; /* will update later in resettodr() */

	return (clockyear);
}

static int
rtc_gettime(todr_chip_handle_t tch, volatile struct timeval *tv)
{
	int s;
	mc_todregs rtclk;
	struct clock_ymdhms dt;

	s = splclock();
	if (rtcget(&rtclk)) {
		splx(s);
		return -1;
	}
	splx(s);

	dt.dt_sec = bcdtobin(rtclk[MC_SEC]);
	dt.dt_min = bcdtobin(rtclk[MC_MIN]);
	dt.dt_hour = bcdtobin(rtclk[MC_HOUR]);
	dt.dt_day = bcdtobin(rtclk[MC_DOM]);
	dt.dt_mon = bcdtobin(rtclk[MC_MONTH]);
	dt.dt_year = clock_expandyear(bcdtobin(rtclk[MC_YEAR]));

	/*
	 * If time_t is 32 bits, then the "End of Time" is
	 * Mon Jan 18 22:14:07 2038 (US/Eastern)
	 * This code copes with RTC's past the end of time if time_t
	 * is an int32 or less. Needed because sometimes RTCs screw
	 * up or are badly set, and that would cause the time to go
	 * negative in the calculation below, which causes Very Bad
	 * Mojo. This at least lets the user boot and fix the problem.
	 * Note the code is self eliminating once time_t goes to 64 bits.
	 */
	if (sizeof(time_t) <= sizeof(int32_t)) {
		if (dt.dt_year >= 2038) {
			return -1;
		}
	}

	tv->tv_sec = clock_ymdhms_to_secs(&dt) + rtc_offset * 60;
	tv->tv_usec = 0;
	return 0;
}

static int
rtc_settime(todr_chip_handle_t tch, volatile struct timeval *tvp)
{
	mc_todregs rtclk;
	struct clock_ymdhms dt;
	int century;
	int s;

	/*
	 * We might have been called by boot() due to a crash early
	 * on.  Don't reset the clock chip in this case.
	 */
	if (!timeset)
		return 0;

	s = splclock();
	if (rtcget(&rtclk))
		memset(&rtclk, 0, sizeof(rtclk));
	splx(s);

	clock_secs_to_ymdhms(time_second - rtc_offset * 60, &dt);

	rtclk[MC_SEC] = bintobcd(dt.dt_sec);
	rtclk[MC_MIN] = bintobcd(dt.dt_min);
	rtclk[MC_HOUR] = bintobcd(dt.dt_hour);
	rtclk[MC_DOW] = dt.dt_wday + 1;
	rtclk[MC_YEAR] = bintobcd(dt.dt_year % 100);
	rtclk[MC_MONTH] = bintobcd(dt.dt_mon);
	rtclk[MC_DOM] = bintobcd(dt.dt_day);

#ifdef DEBUG_CLOCK
	printf("setclock: %x/%x/%x %x:%x:%x\n", rtclk[MC_YEAR], rtclk[MC_MONTH],
	   rtclk[MC_DOM], rtclk[MC_HOUR], rtclk[MC_MIN], rtclk[MC_SEC]);
#endif
	s = splclock();
	rtcput(&rtclk);
	if (rtc_update_century > 0) {
		century = bintobcd(dt.dt_year / 100);
		mc146818_write(NULL, centb, century); /* XXX softc */
	}
	splx(s);
	return 0;

}

static int
rtc_getcal(todr_chip_handle_t tch, int *vp)
{
	return EOPNOTSUPP;
}

static int
rtc_setcal(todr_chip_handle_t tch, int v)
{
	return EOPNOTSUPP;
}

static void
rtc_register(void)
{
	static struct todr_chip_handle	tch;
	tch.todr_gettime = rtc_gettime;
	tch.todr_settime = rtc_settime;
	tch.todr_getcal = rtc_getcal;
	tch.todr_setcal = rtc_setcal;
	tch.todr_setwen = NULL;

	todr_attach(&tch);
}

void
setstatclockrate(int arg)
{
}