/* kern/i386/tsc.c - x86 TSC time source implementation
 * Requires Pentium or better x86 CPU that supports the RDTSC instruction.
 * This module calibrates 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/cpuid.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 ms per 2^32 ticks) */
/* We assume that the tick is less than 1 ms and hence this value fits
   in 32-bit.  */
grub_uint32_t grub_tsc_rate;

static grub_uint64_t
grub_tsc_get_time_ms (void)
{
  grub_uint64_t a = grub_get_tsc () - tsc_boot_time;
  grub_uint64_t ah = a >> 32;
  grub_uint64_t al = a & 0xffffffff;

  return ((al * grub_tsc_rate) >> 32) + ah * grub_tsc_rate;
}

static int
calibrate_tsc_hardcode (void)
{
  grub_tsc_rate = 5368;/* 800 MHz */
  return 1;
}

void
grub_tsc_init (void)
{
  if (!grub_cpu_is_tsc_supported ())
    {
#if defined (GRUB_MACHINE_PCBIOS) || defined (GRUB_MACHINE_IEEE1275)
      grub_install_get_time_ms (grub_rtc_get_time_ms);
#else
      grub_fatal ("no TSC found");
#endif
      return;
    }

  tsc_boot_time = grub_get_tsc ();

#if defined (GRUB_MACHINE_XEN) || defined (GRUB_MACHINE_XEN_PVH)
  (void) (grub_tsc_calibrate_from_xen () || calibrate_tsc_hardcode());
#elif defined (GRUB_MACHINE_EFI)
  (void) (grub_tsc_calibrate_from_pmtimer () || grub_tsc_calibrate_from_pit () || grub_tsc_calibrate_from_efi() || calibrate_tsc_hardcode());
#elif defined (GRUB_MACHINE_COREBOOT)
  (void) (grub_tsc_calibrate_from_pmtimer () || grub_tsc_calibrate_from_pit () || calibrate_tsc_hardcode());
#else
  (void) (grub_tsc_calibrate_from_pit () || calibrate_tsc_hardcode());
#endif
  grub_install_get_time_ms (grub_tsc_get_time_ms);
}