106 lines
3.1 KiB
C
106 lines
3.1 KiB
C
/* 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 RTC (via grub_get_rtc()) 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/i386/pit.h>
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#include <grub/cpu/io.h>
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/* This defines the value TSC had at the epoch (that is, when we calibrated it). */
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static grub_uint64_t tsc_boot_time;
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/* Calibrated TSC rate. (In ms per 2^32 ticks) */
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/* We assume that the tick is less than 1 ms and hence this value fits
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in 32-bit. */
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grub_uint32_t grub_tsc_rate;
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static void
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grub_pit_wait (grub_uint16_t tics)
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{
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/* Disable timer2 gate and speaker. */
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grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
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& ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
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GRUB_PIT_SPEAKER_PORT);
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/* Set tics. */
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grub_outb (GRUB_PIT_CTRL_SELECT_2 | GRUB_PIT_CTRL_READLOAD_WORD,
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GRUB_PIT_CTRL);
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grub_outb (tics & 0xff, GRUB_PIT_COUNTER_2);
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grub_outb (tics >> 8, GRUB_PIT_COUNTER_2);
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/* Enable timer2 gate, keep speaker disabled. */
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grub_outb ((grub_inb (GRUB_PIT_SPEAKER_PORT) & ~ GRUB_PIT_SPK_DATA)
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| GRUB_PIT_SPK_TMR2,
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GRUB_PIT_SPEAKER_PORT);
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/* Wait. */
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while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0x00);
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/* Disable timer2 gate and speaker. */
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grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
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& ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
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GRUB_PIT_SPEAKER_PORT);
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}
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grub_uint64_t
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grub_tsc_get_time_ms (void)
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{
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grub_uint64_t a = grub_get_tsc () - tsc_boot_time;
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grub_uint64_t ah = a >> 32;
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grub_uint64_t al = a & 0xffffffff;
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return ((al * grub_tsc_rate) >> 32) + ah * grub_tsc_rate;
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}
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/* Calibrate the TSC based on the RTC. */
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static void
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calibrate_tsc (void)
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{
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/* First calibrate the TSC rate (relative, not absolute time). */
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grub_uint64_t end_tsc;
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tsc_boot_time = grub_get_tsc ();
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grub_pit_wait (0xffff);
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end_tsc = grub_get_tsc ();
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grub_tsc_rate = grub_divmod64 ((55ULL << 32), end_tsc - tsc_boot_time, 0);
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}
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void
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grub_tsc_init (void)
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{
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if (grub_cpu_is_tsc_supported ())
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{
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calibrate_tsc ();
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grub_install_get_time_ms (grub_tsc_get_time_ms);
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}
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else
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{
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#if defined (GRUB_MACHINE_PCBIOS) || defined (GRUB_MACHINE_IEEE1275)
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grub_install_get_time_ms (grub_rtc_get_time_ms);
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#else
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grub_fatal ("no TSC found");
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#endif
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}
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}
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