time.c revision 228782 
1/*-
2 * Copyright (c) 1998 Michael Smith <msmith@freebsd.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: head/sys/boot/i386/libi386/time.c 228782 2011-12-21 16:47:01Z ed $");
29
30#include <stand.h>
31#include <btxv86.h>
32#include "bootstrap.h"
33#include "libi386.h"
34
35static int	bios_seconds(void);
36
37/*
38 * Return the BIOS time-of-day value.
39 *
40 * XXX uses undocumented BCD support from libstand.
41 */
42static int
43bios_seconds(void)
44{
45    int			hr, minute, sec;
46
47    v86.ctl = 0;
48    v86.addr = 0x1a;		/* int 0x1a, function 2 */
49    v86.eax = 0x0200;
50    v86int();
51
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