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clock.c revision 1.35.2.1 
      1 /*	$NetBSD: clock.c,v 1.35.2.1 2001/04/09 01:50:35 nathanw Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1988 University of Utah.
      5  * Copyright (c) 1982, 1990 The Regents of the University of California.
      6  * All rights reserved.
      7  *
      8  * This code is derived from software contributed to Berkeley by
      9  * the Systems Programming Group of the University of Utah Computer
     10  * Science Department.
     11  *
     12  * Redistribution and use in source and binary forms, with or without
     13  * modification, are permitted provided that the following conditions
     14  * are met:
     15  * 1. Redistributions of source code must retain the above copyright
     16  *    notice, this list of conditions and the following disclaimer.
     17  * 2. Redistributions in binary form must reproduce the above copyright
     18  *    notice, this list of conditions and the following disclaimer in the
     19  *    documentation and/or other materials provided with the distribution.
     20  * 3. All advertising materials mentioning features or use of this software
     21  *    must display the following acknowledgement:
     22  *	This product includes software developed by the University of
     23  *	California, Berkeley and its contributors.
     24  * 4. Neither the name of the University nor the names of its contributors
     25  *    may be used to endorse or promote products derived from this software
     26  *    without specific prior written permission.
     27  *
     28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     38  * SUCH DAMAGE.
     39  *
     40  * from: Utah $Hdr: clock.c 1.18 91/01/21$
     41  *
     42  *	@(#)clock.c	7.6 (Berkeley) 5/7/91
     43  */
     44 
     45 #include <sys/param.h>
     46 #include <sys/kernel.h>
     47 #include <sys/device.h>
     48 #include <sys/systm.h>
     49 #include <machine/psl.h>
     50 #include <machine/cpu.h>
     51 #include <amiga/amiga/device.h>
     52 #include <amiga/amiga/custom.h>
     53 #include <amiga/amiga/cia.h>
     54 #ifdef DRACO
     55 #include <amiga/amiga/drcustom.h>
     56 #include <m68k/include/asm_single.h>
     57 #endif
     58 #include <amiga/dev/rtc.h>
     59 #include <amiga/dev/zbusvar.h>
     60 
     61 #if defined(PROF) && defined(PROFTIMER)
     62 #include <sys/PROF.h>
     63 #endif
     64 
     65 /* the clocks run at NTSC: 715.909kHz or PAL: 709.379kHz.
     66    We're using a 100 Hz clock. */
     67 
     68 #define CLK_INTERVAL amiga_clk_interval
     69 int amiga_clk_interval;
     70 int eclockfreq;
     71 struct CIA *clockcia;
     72 
     73 /*
     74  * Machine-dependent clock routines.
     75  *
     76  * Startrtclock restarts the real-time clock, which provides
     77  * hardclock interrupts to kern_clock.c.
     78  *
     79  * Inittodr initializes the time of day hardware which provides
     80  * date functions.
     81  *
     82  * Resettodr restores the time of day hardware after a time change.
     83  *
     84  * A note on the real-time clock:
     85  * We actually load the clock with CLK_INTERVAL-1 instead of CLK_INTERVAL.
     86  * This is because the counter decrements to zero after N+1 enabled clock
     87  * periods where N is the value loaded into the counter.
     88  */
     89 
     90 int clockmatch __P((struct device *, struct cfdata *, void *));
     91 void clockattach __P((struct device *, struct device *, void *));
     92 void cpu_initclocks __P((void));
     93 void calibrate_delay __P((struct device *));
     94 
     95 struct cfattach clock_ca = {
     96 	sizeof(struct device), clockmatch, clockattach
     97 };
     98 
     99 int
    100 clockmatch(pdp, cfp, auxp)
    101 	struct device *pdp;
    102 	struct cfdata *cfp;
    103 	void *auxp;
    104 {
    105 	if (matchname("clock", auxp))
    106 		return(1);
    107 	return(0);
    108 }
    109 
    110 /*
    111  * Start the real-time clock.
    112  */
    113 void
    114 clockattach(pdp, dp, auxp)
    115 	struct device *pdp, *dp;
    116 	void *auxp;
    117 {
    118 	char *clockchip;
    119 	unsigned short interval;
    120 #ifdef DRACO
    121 	u_char dracorev;
    122 #endif
    123 
    124 	if (eclockfreq == 0)
    125 		eclockfreq = 715909;	/* guess NTSC */
    126 
    127 	CLK_INTERVAL = (eclockfreq / 100);
    128 
    129 #ifdef DRACO
    130 	dracorev = is_draco();
    131 	if (dracorev >= 4) {
    132 		CLK_INTERVAL = (eclockfreq / 700);
    133 		clockchip = "QuickLogic";
    134 	} else if (dracorev) {
    135 		clockcia = (struct CIA *)CIAAbase;
    136 		clockchip = "CIA A";
    137 	} else
    138 #endif
    139 	{
    140 		clockcia = (struct CIA *)CIABbase;
    141 		clockchip = "CIA B";
    142 	}
    143 
    144 	if (dp)
    145 		printf(": %s system hz %d hardware hz %d\n", clockchip, hz,
    146 #ifdef DRACO
    147 		dracorev >= 4 ? eclockfreq / 7 : eclockfreq);
    148 #else
    149 		eclockfreq);
    150 #endif
    151 
    152 #ifdef DRACO
    153 	if (dracorev >= 4) {
    154 		/*
    155 		 * can't preload anything beforehand, timer is free_running;
    156 		 * but need this for delay calibration.
    157 		 */
    158 
    159 		draco_ioct->io_timerlo = CLK_INTERVAL & 0xff;
    160 		draco_ioct->io_timerhi = CLK_INTERVAL >> 8;
    161 
    162 		calibrate_delay(dp);
    163 
    164 		return;
    165 	}
    166 #endif
    167 	/*
    168 	 * stop timer A
    169 	 */
    170 	clockcia->cra = clockcia->cra & 0xc0;
    171 	clockcia->icr = 1 << 0;		/* disable timer A interrupt */
    172 	interval = clockcia->icr;		/* and make sure it's clear */
    173 
    174 	/*
    175 	 * load interval into registers.
    176          * the clocks run at NTSC: 715.909kHz or PAL: 709.379kHz
    177 	 * supprort for PAL WHEN?!?! XXX
    178 	 */
    179 	interval = CLK_INTERVAL - 1;
    180 
    181 	/*
    182 	 * order of setting is important !
    183 	 */
    184 	clockcia->talo = interval & 0xff;
    185 	clockcia->tahi = interval >> 8;
    186 	/*
    187 	 * start timer A in continuous mode
    188 	 */
    189 	clockcia->cra = (clockcia->cra & 0xc0) | 1;
    190 
    191 	calibrate_delay(dp);
    192 }
    193 
    194 /*
    195  * Calibrate delay loop.
    196  * We use two iterations because we don't have enough bits to do a factor of
    197  * 8 with better than 1%.
    198  *
    199  * XXX Note that we MUST stay below 1 tick if using clkread(), even for
    200  * underestimated values of delaydivisor.
    201  *
    202  * XXX the "ns" below is only correct for a shift of 10 bits, and even then
    203  * off by 2.4%
    204  */
    205 
    206 void calibrate_delay(dp)
    207 	struct device *dp;
    208 {
    209 	unsigned long t1, t2;
    210 	extern u_int32_t delaydivisor;
    211 		/* XXX this should be defined elsewhere */
    212 
    213 	if (dp)
    214 		printf("Calibrating delay loop... ");
    215 
    216 	do {
    217 		t1 = clkread();
    218 		delay(1024);
    219 		t2 = clkread();
    220 	} while (t2 <= t1);
    221 	t2 -= t1;
    222 	delaydivisor = (delaydivisor * t2 + 1023) >> 10;
    223 #ifdef DEBUG
    224 	if (dp)
    225 		printf("\ndiff %ld us, new divisor %u/1024 us\n", t2,
    226 		    delaydivisor);
    227 	do {
    228 		t1 = clkread();
    229 		delay(1024);
    230 		t2 = clkread();
    231 	} while (t2 <= t1);
    232 	t2 -= t1;
    233 	delaydivisor = (delaydivisor * t2 + 1023) >> 10;
    234 	if (dp)
    235 		printf("diff %ld us, new divisor %u/1024 us\n", t2,
    236 		    delaydivisor);
    237 #endif
    238 	do {
    239 		t1 = clkread();
    240 		delay(1024);
    241 		t2 = clkread();
    242 	} while (t2 <= t1);
    243 	t2 -= t1;
    244 	delaydivisor = (delaydivisor * t2 + 1023) >> 10;
    245 #ifdef DEBUG
    246 	if (dp)
    247 		printf("diff %ld us, new divisor ", t2);
    248 #endif
    249 	if (dp)
    250 		printf("%u/1024 us\n", delaydivisor);
    251 }
    252 
    253 void
    254 cpu_initclocks()
    255 {
    256 #ifdef DRACO
    257 	unsigned char dracorev;
    258 	dracorev = is_draco();
    259 	if (dracorev >= 4) {
    260 		draco_ioct->io_timerlo = CLK_INTERVAL & 0xFF;
    261 		draco_ioct->io_timerhi = CLK_INTERVAL >> 8;
    262 		draco_ioct->io_timerrst = 0;	/* any value resets */
    263 		single_inst_bset_b(draco_ioct->io_status2, DRSTAT2_TMRINTENA);
    264 
    265 		return;
    266 	}
    267 #endif
    268 	/*
    269 	 * enable interrupts for timer A
    270 	 */
    271 	clockcia->icr = (1<<7) | (1<<0);
    272 
    273 	/*
    274 	 * start timer A in continuous shot mode
    275 	 */
    276 	clockcia->cra = (clockcia->cra & 0xc0) | 1;
    277 
    278 	/*
    279 	 * and globally enable interrupts for ciab
    280 	 */
    281 #ifdef DRACO
    282 	if (dracorev)		/* we use cia a on DraCo */
    283 		single_inst_bset_b(*draco_intena, DRIRQ_INT2);
    284 	else
    285 #endif
    286 		custom.intena = INTF_SETCLR | INTF_EXTER;
    287 
    288 }
    289 
    290 void
    291 setstatclockrate(hz)
    292 	int hz;
    293 {
    294 }
    295 
    296 /*
    297  * Returns number of usec since last recorded clock "tick"
    298  * (i.e. clock interrupt).
    299  */
    300 u_long
    301 clkread()
    302 {
    303 	u_int interval;
    304 	u_char hi, hi2, lo;
    305 
    306 #ifdef DRACO
    307 	if (is_draco() >= 4) {
    308 		hi2 = draco_ioct->io_chiprev;	/* latch timer */
    309 		hi = draco_ioct->io_timerhi;
    310 		lo = draco_ioct->io_timerlo;
    311 		interval = ((hi<<8) | lo);
    312 		if (interval > CLK_INTERVAL)	/* timer underflow */
    313 			interval = 65536 + CLK_INTERVAL - interval;
    314 		else
    315 			interval = CLK_INTERVAL - interval;
    316 
    317 	} else
    318 #endif
    319 	{
    320 		hi  = clockcia->tahi;
    321 		lo  = clockcia->talo;
    322 		hi2 = clockcia->tahi;
    323 		if (hi != hi2) {
    324 			lo = clockcia->talo;
    325 			hi = hi2;
    326 		}
    327 
    328 		interval = (CLK_INTERVAL - 1) - ((hi<<8) | lo);
    329 
    330 		/*
    331 		 * should read ICR and if there's an int pending, adjust
    332 		 * interval. However, since reading ICR clears the interrupt,
    333 		 * we'd lose a hardclock int, and this is not tolerable.
    334 		 */
    335 	}
    336 
    337 	return((interval * tick) / CLK_INTERVAL);
    338 }
    339 
    340 #if notyet
    341 
    342 /* implement this later. I'd suggest using both timers in CIA-A, they're
    343    not yet used. */
    344 
    345 #include "clock.h"
    346 #if NCLOCK > 0
    347 /*
    348  * /dev/clock: mappable high resolution timer.
    349  *
    350  * This code implements a 32-bit recycling counter (with a 4 usec period)
    351  * using timers 2 & 3 on the 6840 clock chip.  The counter can be mapped
    352  * RO into a user's address space to achieve low overhead (no system calls),
    353  * high-precision timing.
    354  *
    355  * Note that timer 3 is also used for the high precision profiling timer
    356  * (PROFTIMER code above).  Care should be taken when both uses are
    357  * configured as only a token effort is made to avoid conflicting use.
    358  */
    359 #include <sys/proc.h>
    360 #include <sys/resourcevar.h>
    361 #include <sys/ioctl.h>
    362 #include <sys/malloc.h>
    363 #include <uvm/uvm_extern.h>
    364 #include <amiga/amiga/clockioctl.h>
    365 #include <sys/specdev.h>
    366 #include <sys/vnode.h>
    367 #include <sys/mman.h>
    368 
    369 int clockon = 0;		/* non-zero if high-res timer enabled */
    370 #ifdef PROFTIMER
    371 int  profprocs = 0;		/* # of procs using profiling timer */
    372 #endif
    373 #ifdef DEBUG
    374 int clockdebug = 0;
    375 #endif
    376 
    377 /*ARGSUSED*/
    378 clockopen(dev, flags)
    379 	dev_t dev;
    380 {
    381 #ifdef PROFTIMER
    382 #ifdef PROF
    383 	/*
    384 	 * Kernel profiling enabled, give up.
    385 	 */
    386 	if (profiling)
    387 		return(EBUSY);
    388 #endif
    389 	/*
    390 	 * If any user processes are profiling, give up.
    391 	 */
    392 	if (profprocs)
    393 		return(EBUSY);
    394 #endif
    395 	if (!clockon) {
    396 		startclock();
    397 		clockon++;
    398 	}
    399 	return(0);
    400 }
    401 
    402 /*ARGSUSED*/
    403 clockclose(dev, flags)
    404 	dev_t dev;
    405 {
    406 	(void) clockunmmap(dev, (caddr_t)0, curproc);	/* XXX */
    407 	stopclock();
    408 	clockon = 0;
    409 	return(0);
    410 }
    411 
    412 /*ARGSUSED*/
    413 clockioctl(dev, cmd, data, flag, p)
    414 	dev_t dev;
    415 	u_long cmd;
    416 	caddr_t data;
    417 	struct proc *p;
    418 {
    419 	int error = 0;
    420 
    421 	switch (cmd) {
    422 
    423 	case CLOCKMAP:
    424 		error = clockmmap(dev, (caddr_t *)data, p);
    425 		break;
    426 
    427 	case CLOCKUNMAP:
    428 		error = clockunmmap(dev, *(caddr_t *)data, p);
    429 		break;
    430 
    431 	case CLOCKGETRES:
    432 		*(int *)data = CLK_RESOLUTION;
    433 		break;
    434 
    435 	default:
    436 		error = EINVAL;
    437 		break;
    438 	}
    439 	return(error);
    440 }
    441 
    442 /*ARGSUSED*/
    443 clockmap(dev, off, prot)
    444 	dev_t dev;
    445 {
    446 	return((off + (INTIOBASE+CLKBASE+CLKSR-1)) >> PGSHIFT);
    447 }
    448 
    449 clockmmap(dev, addrp, p)
    450 	dev_t dev;
    451 	caddr_t *addrp;
    452 	struct proc *p;
    453 {
    454 	int error;
    455 	struct vnode vn;
    456 	struct specinfo si;
    457 	int flags;
    458 
    459 	flags = MAP_FILE|MAP_SHARED;
    460 	if (*addrp)
    461 		flags |= MAP_FIXED;
    462 	else
    463 		*addrp = (caddr_t)0x1000000;	/* XXX */
    464 	vn.v_type = VCHR;			/* XXX */
    465 	vn.v_specinfo = &si;			/* XXX */
    466 	vn.v_rdev = dev;			/* XXX */
    467 	error = vm_mmap(&p->p_vmspace->vm_map, (vm_offset_t *)addrp,
    468 			PAGE_SIZE, VM_PROT_ALL, flags, (caddr_t)&vn, 0);
    469 	return(error);
    470 }
    471 
    472 clockunmmap(dev, addr, p)
    473 	dev_t dev;
    474 	caddr_t addr;
    475 	struct proc *p;
    476 {
    477 	int rv;
    478 
    479 	if (addr == 0)
    480 		return(EINVAL);		/* XXX: how do we deal with this? */
    481 	uvm_deallocate(p->p_vmspace->vm_map, (vm_offset_t)addr, PAGE_SIZE);
    482 	return 0;
    483 }
    484 
    485 startclock()
    486 {
    487 	register struct clkreg *clk = (struct clkreg *)clkstd[0];
    488 
    489 	clk->clk_msb2 = -1; clk->clk_lsb2 = -1;
    490 	clk->clk_msb3 = -1; clk->clk_lsb3 = -1;
    491 
    492 	clk->clk_cr2 = CLK_CR3;
    493 	clk->clk_cr3 = CLK_OENAB|CLK_8BIT;
    494 	clk->clk_cr2 = CLK_CR1;
    495 	clk->clk_cr1 = CLK_IENAB;
    496 }
    497 
    498 stopclock()
    499 {
    500 	register struct clkreg *clk = (struct clkreg *)clkstd[0];
    501 
    502 	clk->clk_cr2 = CLK_CR3;
    503 	clk->clk_cr3 = 0;
    504 	clk->clk_cr2 = CLK_CR1;
    505 	clk->clk_cr1 = CLK_IENAB;
    506 }
    507 #endif
    508 
    509 #endif
    510 
    511 
    512 #ifdef PROFTIMER
    513 /*
    514  * This code allows the amiga kernel to use one of the extra timers on
    515  * the clock chip for profiling, instead of the regular system timer.
    516  * The advantage of this is that the profiling timer can be turned up to
    517  * a higher interrupt rate, giving finer resolution timing. The profclock
    518  * routine is called from the lev6intr in locore, and is a specialized
    519  * routine that calls addupc. The overhead then is far less than if
    520  * hardclock/softclock was called. Further, the context switch code in
    521  * locore has been changed to turn the profile clock on/off when switching
    522  * into/out of a process that is profiling (startprofclock/stopprofclock).
    523  * This reduces the impact of the profiling clock on other users, and might
    524  * possibly increase the accuracy of the profiling.
    525  */
    526 int  profint   = PRF_INTERVAL;	/* Clock ticks between interrupts */
    527 int  profscale = 0;		/* Scale factor from sys clock to prof clock */
    528 char profon    = 0;		/* Is profiling clock on? */
    529 
    530 /* profon values - do not change, locore.s assumes these values */
    531 #define PRF_NONE	0x00
    532 #define	PRF_USER	0x01
    533 #define	PRF_KERNEL	0x80
    534 
    535 initprofclock()
    536 {
    537 #if NCLOCK > 0
    538 	struct proc *p = curproc;		/* XXX */
    539 
    540 	/*
    541 	 * If the high-res timer is running, force profiling off.
    542 	 * Unfortunately, this gets reflected back to the user not as
    543 	 * an error but as a lack of results.
    544 	 */
    545 	if (clockon) {
    546 		p->p_stats->p_prof.pr_scale = 0;
    547 		return;
    548 	}
    549 	/*
    550 	 * Keep track of the number of user processes that are profiling
    551 	 * by checking the scale value.
    552 	 *
    553 	 * XXX: this all assumes that the profiling code is well behaved;
    554 	 * i.e. profil() is called once per process with pcscale non-zero
    555 	 * to turn it on, and once with pcscale zero to turn it off.
    556 	 * Also assumes you don't do any forks or execs.  Oh well, there
    557 	 * is always adb...
    558 	 */
    559 	if (p->p_stats->p_prof.pr_scale)
    560 		profprocs++;
    561 	else
    562 		profprocs--;
    563 #endif
    564 	/*
    565 	 * The profile interrupt interval must be an even divisor
    566 	 * of the CLK_INTERVAL so that scaling from a system clock
    567 	 * tick to a profile clock tick is possible using integer math.
    568 	 */
    569 	if (profint > CLK_INTERVAL || (CLK_INTERVAL % profint) != 0)
    570 		profint = CLK_INTERVAL;
    571 	profscale = CLK_INTERVAL / profint;
    572 }
    573 
    574 startprofclock()
    575 {
    576   unsigned short interval;
    577 
    578   /* stop timer B */
    579   clockcia->crb = clockcia->crb & 0xc0;
    580 
    581   /* load interval into registers.
    582      the clocks run at NTSC: 715.909kHz or PAL: 709.379kHz */
    583 
    584   interval = profint - 1;
    585 
    586   /* order of setting is important ! */
    587   clockcia->tblo = interval & 0xff;
    588   clockcia->tbhi = interval >> 8;
    589 
    590   /* enable interrupts for timer B */
    591   clockcia->icr = (1<<7) | (1<<1);
    592 
    593   /* start timer B in continuous shot mode */
    594   clockcia->crb = (clockcia->crb & 0xc0) | 1;
    595 }
    596 
    597 stopprofclock()
    598 {
    599   /* stop timer B */
    600   clockcia->crb = clockcia->crb & 0xc0;
    601 }
    602 
    603 #ifdef PROF
    604 /*
    605  * profclock() is expanded in line in lev6intr() unless profiling kernel.
    606  * Assumes it is called with clock interrupts blocked.
    607  */
    608 profclock(pc, ps)
    609 	caddr_t pc;
    610 	int ps;
    611 {
    612 	/*
    613 	 * Came from user mode.
    614 	 * If this process is being profiled record the tick.
    615 	 */
    616 	if (USERMODE(ps)) {
    617 		if (p->p_stats.p_prof.pr_scale)
    618 			addupc(pc, &curproc->p_stats.p_prof, 1);
    619 	}
    620 	/*
    621 	 * Came from kernel (supervisor) mode.
    622 	 * If we are profiling the kernel, record the tick.
    623 	 */
    624 	else if (profiling < 2) {
    625 		register int s = pc - s_lowpc;
    626 
    627 		if (s < s_textsize)
    628 			kcount[s / (HISTFRACTION * sizeof (*kcount))]++;
    629 	}
    630 	/*
    631 	 * Kernel profiling was on but has been disabled.
    632 	 * Mark as no longer profiling kernel and if all profiling done,
    633 	 * disable the clock.
    634 	 */
    635 	if (profiling && (profon & PRF_KERNEL)) {
    636 		profon &= ~PRF_KERNEL;
    637 		if (profon == PRF_NONE)
    638 			stopprofclock();
    639 	}
    640 }
    641 #endif
    642 #endif
    643 
    644 /*
    645  * Initialize the time of day register, based on the time base which is, e.g.
    646  * from a filesystem.
    647  */
    648 void
    649 inittodr(base)
    650 	time_t base;
    651 {
    652 	struct timeval tvbuf;
    653 
    654 	tvbuf.tv_usec = 0;
    655 	tvbuf.tv_sec = base;	/* assume no battery clock exists */
    656 
    657 	if (ugettod == NULL)
    658 		printf("WARNING: no battery clock\n");
    659 	else {
    660 		ugettod(&tvbuf);
    661 		tvbuf.tv_sec +=  rtc_offset * 60;
    662 	}
    663 
    664 	if (tvbuf.tv_sec < base) {
    665 		printf("WARNING: bad date in battery clock\n");
    666 		tvbuf.tv_sec = base;
    667 	}
    668 
    669 	time = tvbuf;
    670 }
    671 
    672 void
    673 resettodr()
    674 {
    675 	struct timeval tvbuf;
    676 
    677 	if (!usettod)
    678 		return;
    679 
    680 	tvbuf = time;
    681 
    682 	tvbuf.tv_sec -= rtc_offset * 60;
    683 
    684 	if (!usettod(&tvbuf))
    685 		printf("Cannot set battery backed clock\n");
    686 }
    687