/* 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/acpi.h>
#include <grub/cpu/io.h>

int
grub_tsc_calibrate_from_pmtimer (void)
{
  grub_uint32_t start;
  grub_uint32_t last;
  grub_uint32_t cur, end;
  struct grub_acpi_fadt *fadt;
  grub_port_t p;
  grub_uint64_t start_tsc;
  grub_uint64_t end_tsc;
  int num_iter = 0;

  fadt = grub_acpi_find_fadt ();
  if (!fadt)
    return 0;
  p = fadt->pmtimer;
  if (!p)
    return 0;

  start = grub_inl (p) & 0xffffff;
  last = start;
  /* It's 3.579545 MHz clock. Wait 1 ms.  */
  end = start + 3580;
  start_tsc = grub_get_tsc ();
  while (1)
    {
      cur = grub_inl (p) & 0xffffff;
      if (cur < last)
	cur |= 0x1000000;
      num_iter++;
      if (cur >= end)
	{
	  end_tsc = grub_get_tsc ();
	  grub_tsc_rate = grub_divmod64 ((1ULL << 32), end_tsc - start_tsc, 0);
	  return 1;
	}
      /* Check for broken PM timer.
	 50000000 TSCs is between 5 ms (10GHz) and 200 ms (250 MHz)
	 if after this time we still don't have 1 ms on pmtimer, then
	 pmtimer is broken.
       */
      if ((num_iter & 0xffffff) == 0 && grub_get_tsc () - start_tsc > 5000000) {
	return 0;
      }
    }
}