time.c revision 228782 
1139825Simp/*-
21541Srgrimes * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
31541Srgrimes * All rights reserved.
41541Srgrimes *
51541Srgrimes * Redistribution and use in source and binary forms, with or without
61541Srgrimes * modification, are permitted provided that the following conditions
71541Srgrimes * are met:
81541Srgrimes * 1. Redistributions of source code must retain the above copyright
91541Srgrimes *    notice, this list of conditions and the following disclaimer.
101541Srgrimes * 2. Redistributions in binary form must reproduce the above copyright
111541Srgrimes *    notice, this list of conditions and the following disclaimer in the
121541Srgrimes *    documentation and/or other materials provided with the distribution.
131541Srgrimes *
141541Srgrimes * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
151541Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
161541Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
171541Srgrimes * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
181541Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
191541Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
201541Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
211541Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
221541Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
231541Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
241541Srgrimes * SUCH DAMAGE.
251541Srgrimes */
261541Srgrimes
271541Srgrimes#include <sys/cdefs.h>
281541Srgrimes__FBSDID("$FreeBSD: head/sys/boot/i386/libi386/time.c 228782 2011-12-21 16:47:01Z ed $");
291541Srgrimes
3050477Speter#include <stand.h>
311541Srgrimes#include <btxv86.h>
321541Srgrimes#include "bootstrap.h"
331541Srgrimes#include "libi386.h"
341541Srgrimes
351541Srgrimesstatic int	bios_seconds(void);
36143063Sjoerg
37143063Sjoerg/*
38143063Sjoerg * Return the BIOS time-of-day value.
3924778Sbde *
4024778Sbde * XXX uses undocumented BCD support from libstand.
4124778Sbde */
4224778Sbdestatic int
431541Srgrimesbios_seconds(void)
441541Srgrimes{
451541Srgrimes    int			hr, minute, sec;
461541Srgrimes
471541Srgrimes    v86.ctl = 0;
4824778Sbde    v86.addr = 0x1a;		/* int 0x1a, function 2 */
4924778Sbde    v86.eax = 0x0200;
501541Srgrimes    v86int();
511541Srgrimes
52    hr = bcd2bin((v86.ecx & 0xff00) >> 8);	/* hour in %ch */
53    minute = bcd2bin(v86.ecx & 0xff);		/* minute in %cl */
54    sec = bcd2bin((v86.edx & 0xff00) >> 8);	/* second in %dh */
55
56    return (hr * 3600 + minute * 60 + sec);
57}
58
59/*
60 * Return the time in seconds since the beginning of the day.
61 *
62 * Some BIOSes (notably qemu) don't correctly read the RTC
63 * registers in an atomic way, sometimes returning bogus values.
64 * Therefore we "debounce" the reading by accepting it only when
65 * we got 8 identical values in succession.
66 *
67 * If we pass midnight, don't wrap back to 0.
68 */
69time_t
70time(time_t *t)
71{
72    static time_t lasttime;
73    time_t now, check;
74    int same, try;
75
76    same = try = 0;
77    check = bios_seconds();
78    do {
79	now = check;
80	check = bios_seconds();
81	if (check != now)
82	    same = 0;
83    } while (++same < 8 && ++try < 1000);
84
85    if (now < lasttime)
86	now += 24 * 3600;
87    lasttime = now;
88
89    if (t != NULL)
90	*t = now;
91    return(now);
92}
93
94/*
95 * Use the BIOS Wait function to pause for (period) microseconds.
96 *
97 * Resolution of this function is variable, but typically around
98 * 1ms.
99 */
100void
101delay(int period)
102{
103    v86.ctl = 0;
104    v86.addr = 0x15;		/* int 0x15, function 0x86 */
105    v86.eax = 0x8600;
106    v86.ecx = period >> 16;
107    v86.edx = period & 0xffff;
108    v86int();
109}
110