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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
47typedef unsigned int cycles_t;
48
49static inline cycles_t get_cycles (void)
50{
51 return read_c0_count();
52}
53
54#endif /* _ASM_TIMEX_H */