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1da177e4 LT |
1 | /* |
2 | * Copyright (C) 1995-2004 Russell King | |
3 | * | |
4 | * Delay routines, using a pre-computed "loops_per_second" value. | |
5 | */ | |
6 | #ifndef __ASM_ARM_DELAY_H | |
7 | #define __ASM_ARM_DELAY_H | |
8 | ||
d0a533b1 | 9 | #include <asm/memory.h> |
6d4518d7 PT |
10 | #include <asm/param.h> /* HZ */ |
11 | ||
207b1150 NP |
12 | /* |
13 | * Loop (or tick) based delay: | |
14 | * | |
15 | * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec | |
16 | * | |
17 | * where: | |
18 | * | |
19 | * jiffies_per_sec = HZ | |
20 | * us_per_sec = 1000000 | |
21 | * | |
22 | * Therefore the constant part is HZ / 1000000 which is a small | |
23 | * fractional number. To make this usable with integer math, we | |
24 | * scale up this constant by 2^31, perform the actual multiplication, | |
25 | * and scale the result back down by 2^31 with a simple shift: | |
26 | * | |
27 | * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31 | |
28 | * | |
29 | * where: | |
30 | * | |
31 | * UDELAY_MULT = 2^31 * HZ / 1000000 | |
32 | * = (2^31 / 1000000) * HZ | |
33 | * = 2147.483648 * HZ | |
34 | * = 2147 * HZ + 483648 * HZ / 1000000 | |
35 | * | |
36 | * 31 is the biggest scale shift value that won't overflow 32 bits for | |
37 | * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000. | |
38 | */ | |
d0a533b1 | 39 | #define MAX_UDELAY_MS 2 |
fb833b1f | 40 | #define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000) |
215e362d | 41 | #define UDELAY_SHIFT 31 |
d0a533b1 WD |
42 | |
43 | #ifndef __ASSEMBLY__ | |
44 | ||
56942fec JA |
45 | struct delay_timer { |
46 | unsigned long (*read_current_timer)(void); | |
47 | unsigned long freq; | |
48 | }; | |
49 | ||
d0a533b1 WD |
50 | extern struct arm_delay_ops { |
51 | void (*delay)(unsigned long); | |
52 | void (*const_udelay)(unsigned long); | |
53 | void (*udelay)(unsigned long); | |
6f3d90e5 | 54 | unsigned long ticks_per_jiffy; |
d0a533b1 WD |
55 | } arm_delay_ops; |
56 | ||
57 | #define __delay(n) arm_delay_ops.delay(n) | |
1da177e4 LT |
58 | |
59 | /* | |
60 | * This function intentionally does not exist; if you see references to | |
61 | * it, it means that you're calling udelay() with an out of range value. | |
62 | * | |
63 | * With currently imposed limits, this means that we support a max delay | |
215e362d | 64 | * of 2000us. Further limits: HZ<=1000 |
1da177e4 LT |
65 | */ |
66 | extern void __bad_udelay(void); | |
67 | ||
68 | /* | |
69 | * division by multiplication: you don't have to worry about | |
70 | * loss of precision. | |
71 | * | |
d0a533b1 | 72 | * Use only for very small delays ( < 2 msec). Should probably use a |
1da177e4 LT |
73 | * lookup table, really, as the multiplications take much too long with |
74 | * short delays. This is a "reasonable" implementation, though (and the | |
75 | * first constant multiplications gets optimized away if the delay is | |
76 | * a constant) | |
77 | */ | |
d0a533b1 WD |
78 | #define __udelay(n) arm_delay_ops.udelay(n) |
79 | #define __const_udelay(n) arm_delay_ops.const_udelay(n) | |
1da177e4 | 80 | |
6d4518d7 PT |
81 | #define udelay(n) \ |
82 | (__builtin_constant_p(n) ? \ | |
83 | ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \ | |
d0a533b1 | 84 | __const_udelay((n) * UDELAY_MULT)) : \ |
1da177e4 LT |
85 | __udelay(n)) |
86 | ||
d0a533b1 WD |
87 | /* Loop-based definitions for assembly code. */ |
88 | extern void __loop_delay(unsigned long loops); | |
89 | extern void __loop_udelay(unsigned long usecs); | |
90 | extern void __loop_const_udelay(unsigned long); | |
91 | ||
56942fec JA |
92 | /* Delay-loop timer registration. */ |
93 | #define ARCH_HAS_READ_CURRENT_TIMER | |
94 | extern void register_current_timer_delay(const struct delay_timer *timer); | |
95 | ||
d0a533b1 WD |
96 | #endif /* __ASSEMBLY__ */ |
97 | ||
1da177e4 LT |
98 | #endif /* defined(_ARM_DELAY_H) */ |
99 |