41 lines
1.4 KiB
C
41 lines
1.4 KiB
C
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/* kern/i386/tsc.c - x86 TSC time source implementation
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* Requires Pentium or better x86 CPU that supports the RDTSC instruction.
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* This module uses the PIT to calibrate the TSC to
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* real time.
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*
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* GRUB -- GRand Unified Bootloader
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* Copyright (C) 2008 Free Software Foundation, Inc.
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*
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* GRUB is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* GRUB 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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* You should have received a copy of the GNU General Public License
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* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <grub/types.h>
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#include <grub/time.h>
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#include <grub/misc.h>
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#include <grub/i386/tsc.h>
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#include <grub/efi/efi.h>
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#include <grub/efi/api.h>
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int
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grub_tsc_calibrate_from_efi (void)
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{
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grub_uint64_t start_tsc, end_tsc;
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/* Use EFI Time Service to calibrate TSC */
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start_tsc = grub_get_tsc ();
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efi_call_1 (grub_efi_system_table->boot_services->stall, 1000);
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end_tsc = grub_get_tsc ();
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grub_tsc_rate = grub_divmod64 ((1ULL << 32), end_tsc - start_tsc, 0);
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return 1;
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}
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