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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/efi/efi.h>
#include <grub/efi/api.h>
int
grub_tsc_calibrate_from_efi (void)
{
grub_uint64_t start_tsc, end_tsc;
/* Use EFI Time Service to calibrate TSC */
start_tsc = grub_get_tsc ();
grub_efi_system_table->boot_services->stall (1000);
end_tsc = grub_get_tsc ();
grub_tsc_rate = grub_divmod64 ((1ULL << 32), end_tsc - start_tsc, 0);
return 1;
}
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