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1da177e4 LT |
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 */ |