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// SPDX-License-Identifier: GPL-2.0-or-later
// SPDX-FileCopyrightText: 2009 Juergen Beisert, Pengutronix */
/**
* @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 <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);
return init_clock(&cs);
}
core_initcall(clocksource_init);
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