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/*
* Copyright (C) 2009 Juergen Beisert, Pengutronix
*
* 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 2 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, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*
*/
/**
* @file
* @brief Clocksource based on the 'Programmable Interval Timer' PIT (8253)
*
* This timer should be available on almost all PCs. It also should be run
* at a fixed frequency (1193181.8181 Hz) and not modified to use another
* reload value than 0xFFFF. So, it always counts from 0xffff down to 0.
*
* @note: We can't reprogram the PIT, it will be still used by the BIOS. This
* clocksource driver does not touch any PIT settings.
*/
#include <init.h>
#include <clock.h>
#include <asm/io.h>
/** base address of the PIT in a standard PC */
#define PIT 0x40
static uint64_t pit_clocksource_read(void)
{
uint16_t val1, val2;
outb(0x00, PIT + 3); /* latch counter 0 */
outb(0x00, 0x80);
val1 = inb(PIT);
outb(0x00, 0x80);
val2 = inb(PIT);
val2 <<= 8;
/* note: its a down counter */
return 0xFFFFU - (val1 | val2);
}
static struct clocksource cs = {
.read = pit_clocksource_read,
.mask = CLOCKSOURCE_MASK(16),
.shift = 10,
};
static int clocksource_init (void)
{
cs.mult = clocksource_hz2mult(1193182, cs.shift);
init_clock(&cs);
return 0;
}
core_initcall(clocksource_init);