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/*
* Copyright (c) 2011, 2012 Richard Braun.
*
* This program 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.
*
* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <kern/init.h>
#include <lib/assert.h>
#include <machine/io.h>
#include <machine/pit.h>
/*
* I/O ports.
*/
#define PIT_PORT_COUNTER0 0x40
#define PIT_PORT_MODE 0x43
/*
* Mode control register bits.
*/
#define PIT_MODE_LATCH 0x00
#define PIT_MODE_RATE_GEN 0x04
#define PIT_MODE_RW_LSB 0x10
#define PIT_MODE_RW_MSB 0x20
/*
* Native timer frequency.
*/
#define PIT_FREQ 1193182
/*
* Maximum value of a counter.
*/
#define PIT_MAX_COUNT 0xffff
void __init
pit_setup(void)
{
io_write_byte(PIT_PORT_MODE, PIT_MODE_RATE_GEN | PIT_MODE_RW_LSB
| PIT_MODE_RW_MSB);
io_write_byte(PIT_PORT_COUNTER0, PIT_MAX_COUNT & 0xff);
io_write_byte(PIT_PORT_COUNTER0, PIT_MAX_COUNT >> 8);
}
static unsigned int
pit_read(void)
{
unsigned int low, high;
io_write_byte(PIT_PORT_MODE, PIT_MODE_LATCH);
low = io_read_byte(PIT_PORT_COUNTER0);
high = io_read_byte(PIT_PORT_COUNTER0);
return (high << 8) | low;
}
void
pit_delay(unsigned long usecs)
{
long total, prev, count, diff;
assert(usecs != 0);
/* TODO Avoid 64-bits conversion if result is known not to overflow */
total = (long)(((long long)usecs * PIT_FREQ + 999999) / 1000000);
prev = pit_read();
do {
count = pit_read();
diff = prev - count;
prev = count;
if (diff < 0)
diff += PIT_MAX_COUNT;
total -= diff;
} while (total > 0);
}
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