src/arch/i386/interface/pcbios/bios_timer.c

   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  */
  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 );