time.c revision 179825
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 179825 2008-06-16 17:04:04Z olli $"); 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 two 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 try; 75 76 try = 0; 77 check = bios_seconds(); 78 do { 79 now = check; 80 check = bios_seconds(); 81 } while (now != check && ++try < 1000); 82 83 if (now < lasttime) 84 now += 24 * 3600; 85 lasttime = now; 86 87 if (t != NULL) 88 *t = now; 89 return(now); 90} 91 92/* 93 * Use the BIOS Wait function to pause for (period) microseconds. 94 * 95 * Resolution of this function is variable, but typically around 96 * 1ms. 97 */ 98void 99delay(int period) 100{ 101 v86.ctl = 0; 102 v86.addr = 0x15; /* int 0x15, function 0x86 */ 103 v86.eax = 0x8600; 104 v86.ecx = period >> 16; 105 v86.edx = period & 0xffff; 106 v86int(); 107} 108