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/* kern/i386/tsc.c - x86 TSC time source implementation
* Requires Pentium or better x86 CPU that supports the RDTSC instruction.
* This module uses the PIT to calibrate the TSC to
* real time.
*
* 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/time.h>
#include <grub/misc.h>
#include <grub/i386/tsc.h>
#include <grub/i386/pit.h>
#include <grub/cpu/io.h>
static int
grub_pit_wait (void)
{
int ret = 0;
/* Disable timer2 gate and speaker. */
grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
& ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
GRUB_PIT_SPEAKER_PORT);
/* Set tics. */
grub_outb (GRUB_PIT_CTRL_SELECT_2 | GRUB_PIT_CTRL_READLOAD_WORD,
GRUB_PIT_CTRL);
/* 0xffff ticks: 55ms. */
grub_outb (0xff, GRUB_PIT_COUNTER_2);
grub_outb (0xff, GRUB_PIT_COUNTER_2);
/* Enable timer2 gate, keep speaker disabled. */
grub_outb ((grub_inb (GRUB_PIT_SPEAKER_PORT) & ~ GRUB_PIT_SPK_DATA)
| GRUB_PIT_SPK_TMR2,
GRUB_PIT_SPEAKER_PORT);
if ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0x00) {
ret = 1;
/* Wait. */
while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0x00);
}
/* Disable timer2 gate and speaker. */
grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
& ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
GRUB_PIT_SPEAKER_PORT);
return ret;
}
/* Calibrate the TSC based on the RTC. */
int
grub_tsc_calibrate_from_pit (void)
{
/* First calibrate the TSC rate (relative, not absolute time). */
grub_uint64_t start_tsc, end_tsc;
start_tsc = grub_get_tsc ();
if (!grub_pit_wait ())
return 0;
end_tsc = grub_get_tsc ();
grub_tsc_rate = 0;
if (end_tsc > start_tsc)
grub_tsc_rate = grub_divmod64 ((55ULL << 32), end_tsc - start_tsc, 0);
if (grub_tsc_rate == 0)
return 0;
return 1;
}
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