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 9 #include <asm/memory.h> 10 #include <asm/param.h> /* HZ */ 11 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 */ 39 #define MAX_UDELAY_MS 2 40 #define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000) 41 #define UDELAY_SHIFT 31 42 43 #ifndef __ASSEMBLY__ 44 45 struct delay_timer { 46 unsigned long (*read_current_timer)(void); 47 unsigned long freq; 48 }; 49 50 extern struct arm_delay_ops { 51 void (*delay)(unsigned long); 52 void (*const_udelay)(unsigned long); 53 void (*udelay)(unsigned long); 54 unsigned long ticks_per_jiffy; 55 } arm_delay_ops; 56 57 #define __delay(n) arm_delay_ops.delay(n) 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 64 * of 2000us. Further limits: HZ<=1000 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 * 72 * Use only for very small delays ( < 2 msec). Should probably use a 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 */ 78 #define __udelay(n) arm_delay_ops.udelay(n) 79 #define __const_udelay(n) arm_delay_ops.const_udelay(n) 80 81 #define udelay(n) \ 82 (__builtin_constant_p(n) ? \ 83 ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \ 84 __const_udelay((n) * UDELAY_MULT)) : \ 85 __udelay(n)) 86 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 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 96 #endif /* __ASSEMBLY__ */ 97 98 #endif /* defined(_ARM_DELAY_H) */ 99 100