68 lines
1.6 KiB
C
68 lines
1.6 KiB
C
/*
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* Copyright (C) 2009 Juergen Beisert, Pengutronix
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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*
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*/
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/**
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* @file
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* @brief Clocksource based on the 'Programmable Interval Timer' PIT (8253)
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*
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* This timer should be available on almost all PCs. It also should be run
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* at a fixed frequency (1193181.8181 Hz) and not modified to use another
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* reload value than 0xFFFF. So, it always counts from 0xffff down to 0.
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*
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* @note: We can't reprogram the PIT, it will be still used by the BIOS. This
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* clocksource driver does not touch any PIT settings.
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*/
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#include <init.h>
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#include <clock.h>
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#include <io.h>
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/** base address of the PIT in a standard PC */
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#define PIT 0x40
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static uint64_t pit_clocksource_read(void)
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{
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uint16_t val1, val2;
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outb(0x00, PIT + 3); /* latch counter 0 */
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outb(0x00, 0x80);
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val1 = inb(PIT);
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outb(0x00, 0x80);
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val2 = inb(PIT);
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val2 <<= 8;
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/* note: its a down counter */
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return 0xFFFFU - (val1 | val2);
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}
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static struct clocksource cs = {
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.read = pit_clocksource_read,
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.mask = CLOCKSOURCE_MASK(16),
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.shift = 10,
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};
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static int clocksource_init (void)
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{
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cs.mult = clocksource_hz2mult(1193182, cs.shift);
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init_clock(&cs);
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return 0;
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}
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core_initcall(clocksource_init);
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