xref: /illumos-gate/usr/src/boot/i386/libi386/time.c (revision 22028508)
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 
29 #include <stand.h>
30 #include <btxv86.h>
31 #include "bootstrap.h"
32 #include "libi386.h"
33 
34 time_t		getsecs(void);
35 static int	bios_seconds(void);
36 
37 /*
38  * Return the BIOS time-of-day value.
39  *
40  * XXX uses undocumented BCD support from libstand.
41  */
42 static int
bios_seconds(void)43 bios_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  */
69 time_t
time(time_t * t)70 time(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 time_t
getsecs(void)95 getsecs(void)
96 {
97 	time_t n = 0;
98 	time(&n);
99 	return n;
100 }
101 
102 /*
103  * Use the BIOS Wait function to pause for (period) microseconds.
104  *
105  * Resolution of this function is variable, but typically around
106  * 1ms.
107  */
108 void
delay(int period)109 delay(int period)
110 {
111     v86.ctl = 0;
112     v86.addr = 0x15;		/* int 0x15, function 0x86 */
113     v86.eax = 0x8600;
114     v86.ecx = period >> 16;
115     v86.edx = period & 0xffff;
116     v86int();
117 }
118