include/asm-arm/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 extern void __delay(int loops);
  10
  11 /*
  12  * This function intentionally does not exist; if you see references to
  13  * it, it means that you're calling udelay() with an out of range value.
  14  *
  15  * With currently imposed limits, this means that we support a max delay
  16  * of 2000us and 671 bogomips
  17  */
  18 extern void __bad_udelay(void);
  19
  20 /*
  21  * division by multiplication: you don't have to worry about
  22  * loss of precision.
  23  *
  24  * Use only for very small delays ( < 1 msec).  Should probably use a
  25  * lookup table, really, as the multiplications take much too long with
  26  * short delays.  This is a "reasonable" implementation, though (and the
  27  * first constant multiplications gets optimized away if the delay is
  28  * a constant)
  29  */
  30 extern void __udelay(unsigned long usecs);
  31 extern void __const_udelay(unsigned long);
  32
  33 #define MAX_UDELAY_MS 2
  34
  35 #define udelay(n)                                               \
  36         (__builtin_constant_p(n) ?                              \
  37           ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :      \
  38                         __const_udelay((n) * 0x68dbul)) :       \
  39           __udelay(n))
  40
  41 #endif /* defined(_ARM_DELAY_H) */
  42