1 /*
2 * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19 FILE_LICENCE ( GPL2_OR_LATER );
20
21 /** @file
22 *
23 * BIOS timer
24 *
25 */
26
27 #include <gpxe/timer.h>
28 #include <realmode.h>
29 #include <bios.h>
30
31 /**
32 * Get current system time in ticks
33 *
34 * @ret ticks Current time, in ticks
35 *
36 * Use direct memory access to BIOS variables, longword 0040:006C
37 * (ticks today) and byte 0040:0070 (midnight crossover flag) instead
38 * of calling timeofday BIOS interrupt.
39 */
bios_currticks(void)40 static unsigned long bios_currticks ( void ) {
41 static int days = 0;
42 uint32_t ticks;
43 uint8_t midnight;
44
45 /* Re-enable interrupts so that the timer interrupt can occur */
46 __asm__ __volatile__ ( REAL_CODE ( "sti\n\t"
47 "nop\n\t"
48 "nop\n\t"
49 "cli\n\t" ) : : );
50
51 get_real ( ticks, BDA_SEG, 0x006c );
52 get_real ( midnight, BDA_SEG, 0x0070 );
53
54 if ( midnight ) {
55 midnight = 0;
56 put_real ( midnight, BDA_SEG, 0x0070 );
57 days += 0x1800b0;
58 }
59
60 return ( days + ticks );
61 }
62
63 PROVIDE_TIMER_INLINE ( pcbios, udelay );
64 PROVIDE_TIMER ( pcbios, currticks, bios_currticks );
65 PROVIDE_TIMER_INLINE ( pcbios, ticks_per_sec );
66