include/asm-mips/timex.h

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 1998, 1999, 2003 by Ralf Baechle
   7  */
   8 #ifndef _ASM_TIMEX_H
   9 #define _ASM_TIMEX_H
  10
  11 #include <asm/mipsregs.h>
  12
  13 /*
  14  * This is the frequency of the timer used for Linux's timer interrupt.
  15  * The value should be defined as accurate as possible or under certain
  16  * circumstances Linux timekeeping might become inaccurate or fail.
  17  *
  18  * For many system the exact clockrate of the timer isn't known but due to
  19  * the way this value is used we can get away with a wrong value as long
  20  * as this value is:
  21  *
  22  *  - a multiple of HZ
  23  *  - a divisor of the actual rate
  24  *
  25  * 500000 is a good such cheat value.
  26  *
  27  * The obscure number 1193182 is the same as used by the original i8254
  28  * time in legacy PC hardware; the chip unfortunately also found in a
  29  * bunch of MIPS systems.  The last remaining user of the i8254 for the
  30  * timer interrupt is the RM200; it's a very standard system so there is
  31  * no reason to make this a separate architecture.
  32  */
  33
  34 #include <timex.h>
  35
  36 /*
  37  * Standard way to access the cycle counter.
  38  * Currently only used on SMP for scheduling.
  39  *
  40  * Only the low 32 bits are available as a continuously counting entity.
  41  * But this only means we'll force a reschedule every 8 seconds or so,
  42  * which isn't an evil thing.
  43  *
  44  * We know that all SMP capable CPUs have cycle counters.
  45  */
  46
  47 typedef unsigned int cycles_t;
  48
  49 static inline cycles_t get_cycles (void)
  50 {
  51         return read_c0_count();
  52 }
  53
  54 #endif /*  _ASM_TIMEX_H */