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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 RTC (via grub_get_rtc()) 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>
/* This defines the value TSC had at the epoch (that is, when we calibrated it). */
static grub_uint64_t tsc_boot_time;
/* Calibrated TSC rate. (In TSC ticks per millisecond.) */
static grub_uint64_t tsc_ticks_per_ms;
grub_uint64_t
grub_tsc_get_time_ms (void)
{
return tsc_boot_time + grub_divmod64 (grub_get_tsc (), tsc_ticks_per_ms, 0);
}
/* How many RTC ticks to use for calibration loop. (>= 1) */
#define CALIBRATION_TICKS 2
/* Calibrate the TSC based on the RTC. */
static void
calibrate_tsc (void)
{
/* First calibrate the TSC rate (relative, not absolute time). */
grub_uint64_t start_tsc;
grub_uint64_t end_tsc;
start_tsc = grub_get_tsc ();
grub_pit_wait (0xffff);
end_tsc = grub_get_tsc ();
tsc_ticks_per_ms = grub_divmod64 (end_tsc - start_tsc, 55, 0);
}
void
grub_tsc_init (void)
{
if (grub_cpu_is_tsc_supported ())
{
tsc_boot_time = grub_get_tsc ();
calibrate_tsc ();
grub_install_get_time_ms (grub_tsc_get_time_ms);
}
else
{
grub_install_get_time_ms (grub_rtc_get_time_ms);
}
}
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