arch/common/boot/grub2/kern/generic/rtc_get_time_ms.c

   1 /* rtc_get_time_ms.c - get_time_ms implementation using platform RTC.
   2  * The generic implementation of these functions can be used for architectures
   3  * or platforms that do not have a more specialized implementation. */
   4 /*
   5  *  GRUB  --  GRand Unified Bootloader
   6  *  Copyright (C) 2008  Free Software Foundation, Inc.
   7  *
   8  *  GRUB is free software: you can redistribute it and/or modify
   9  *  it under the terms of the GNU General Public License as published by
  10  *  the Free Software Foundation, either version 3 of the License, or
  11  *  (at your option) any later version.
  12  *
  13  *  GRUB is distributed in the hope that it will be useful,
  14  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  *  GNU General Public License for more details.
  17  *
  18  *  You should have received a copy of the GNU General Public License
  19  *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
  20  */
  21
  22 #include <grub/time.h>
  23 #include <grub/misc.h>
  24
  25 /* Calculate the time in milliseconds since the epoch based on the RTC. */
  26 grub_uint64_t
  27 grub_rtc_get_time_ms (void)
  28 {
  29   /* By dimensional analysis:
  30
  31       1000 ms   N rtc ticks       1 s
  32       ------- * ----------- * ----------- = 1000*N/T ms
  33         1 s          1        T rtc ticks
  34    */
  35   grub_uint64_t ticks_ms_per_sec = ((grub_uint64_t) 1000) * grub_get_rtc ();
  36   return grub_divmod64 (ticks_ms_per_sec, GRUB_TICKS_PER_SECOND, 0);
  37 }