arch/arm/include/asm/delay.h

   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 #define MAX_UDELAY_MS   2
  13 #define UDELAY_MULT     ((UL(2199023) * HZ) >> 11)
  14 #define UDELAY_SHIFT    30
  15
  16 #ifndef __ASSEMBLY__
  17
  18 extern struct arm_delay_ops {
  19         void (*delay)(unsigned long);
  20         void (*const_udelay)(unsigned long);
  21         void (*udelay)(unsigned long);
  22 } arm_delay_ops;
  23
  24 #define __delay(n)              arm_delay_ops.delay(n)
  25
  26 /*
  27  * This function intentionally does not exist; if you see references to
  28  * it, it means that you're calling udelay() with an out of range value.
  29  *
  30  * With currently imposed limits, this means that we support a max delay
  31  * of 2000us. Further limits: HZ<=1000 and bogomips<=3355
  32  */
  33 extern void __bad_udelay(void);
  34
  35 /*
  36  * division by multiplication: you don't have to worry about
  37  * loss of precision.
  38  *
  39  * Use only for very small delays ( < 2 msec).  Should probably use a
  40  * lookup table, really, as the multiplications take much too long with
  41  * short delays.  This is a "reasonable" implementation, though (and the
  42  * first constant multiplications gets optimized away if the delay is
  43  * a constant)
  44  */
  45 #define __udelay(n)             arm_delay_ops.udelay(n)
  46 #define __const_udelay(n)       arm_delay_ops.const_udelay(n)
  47
  48 #define udelay(n)                                                       \
  49         (__builtin_constant_p(n) ?                                      \
  50           ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
  51                         __const_udelay((n) * UDELAY_MULT)) :            \
  52           __udelay(n))
  53
  54 /* Loop-based definitions for assembly code. */
  55 extern void __loop_delay(unsigned long loops);
  56 extern void __loop_udelay(unsigned long usecs);
  57 extern void __loop_const_udelay(unsigned long);
  58
  59 #endif /* __ASSEMBLY__ */
  60
  61 #endif /* defined(_ARM_DELAY_H) */
  62