kern/i386/pit.c

   1 /*
   2  *  GRUB  --  GRand Unified Bootloader
   3  *  Copyright (C) 2008  Free Software Foundation, Inc.
   4  *
   5  *  GRUB is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 3 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  GRUB is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19 #include <grub/types.h>
  20 #include <grub/i386/io.h>
  21 #include <grub/i386/pit.h>
  22
  23 #define TIMER2_REG_CONTROL      0x42
  24 #define TIMER_REG_COMMAND       0x43
  25 #define TIMER2_REG_LATCH        0x61
  26
  27 #define TIMER2_SELECT           0x80
  28 #define TIMER_ENABLE_LSB        0x20
  29 #define TIMER_ENABLE_MSB        0x10
  30 #define TIMER2_LATCH            0x20
  31 #define TIMER2_SPEAKER          0x02
  32 #define TIMER2_GATE             0x01
  33
  34 void
  35 grub_pit_wait (grub_uint16_t tics)
  36 {
  37   /* Disable timer2 gate and speaker.  */
  38   grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE),
  39              TIMER2_REG_LATCH);
  40
  41   /* Set tics.  */
  42   grub_outb (TIMER2_SELECT | TIMER_ENABLE_LSB | TIMER_ENABLE_MSB, TIMER_REG_COMMAND);
  43   grub_outb (tics & 0xff, TIMER2_REG_CONTROL);
  44   grub_outb (tics >> 8, TIMER2_REG_CONTROL);
  45
  46   /* Enable timer2 gate, keep speaker disabled.  */
  47   grub_outb ((grub_inb (TIMER2_REG_LATCH) & ~ TIMER2_SPEAKER) | TIMER2_GATE,
  48              TIMER2_REG_LATCH);
  49
  50   /* Wait.  */
  51   while ((grub_inb (TIMER2_REG_LATCH) & TIMER2_LATCH) == 0x00);
  52
  53   /* Disable timer2 gate and speaker.  */
  54   grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE),
  55              TIMER2_REG_LATCH);
  56 }