grub-core/kern/i386/pit.c

/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2008  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <grub/types.h>
#include <grub/i386/io.h>
#include <grub/i386/pit.h>

#define TIMER2_REG_CONTROL	0x42
#define TIMER_REG_COMMAND	0x43
#define TIMER2_REG_LATCH	0x61

#define TIMER2_SELECT		0x80
#define TIMER_ENABLE_LSB	0x20
#define TIMER_ENABLE_MSB	0x10
#define TIMER2_LATCH		0x20
#define TIMER2_SPEAKER		0x02
#define TIMER2_GATE		0x01

void
grub_pit_wait (grub_uint16_t tics)
{
  /* Disable timer2 gate and speaker.  */
  grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE),
             TIMER2_REG_LATCH);

  /* Set tics.  */
  grub_outb (TIMER2_SELECT | TIMER_ENABLE_LSB | TIMER_ENABLE_MSB, TIMER_REG_COMMAND);
  grub_outb (tics & 0xff, TIMER2_REG_CONTROL);
  grub_outb (tics >> 8, TIMER2_REG_CONTROL);

  /* Enable timer2 gate, keep speaker disabled.  */
  grub_outb ((grub_inb (TIMER2_REG_LATCH) & ~ TIMER2_SPEAKER) | TIMER2_GATE,
             TIMER2_REG_LATCH);

  /* Wait.  */
  while ((grub_inb (TIMER2_REG_LATCH) & TIMER2_LATCH) == 0x00);

  /* Disable timer2 gate and speaker.  */
  grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE),
             TIMER2_REG_LATCH);
}