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 #include <asm/param.h>  /* HZ */
  10
  11 extern void __delay(int loops);
  12
  13 /*
  14  * This function intentionally does not exist; if you see references to
  15  * it, it means that you're calling udelay() with an out of range value.
  16  *
  17  * With currently imposed limits, this means that we support a max delay
  18  * of 2000us. Further limits: HZ<=1000 and bogomips<=3355
  19  */
  20 extern void __bad_udelay(void);
  21
  22 /*
  23  * division by multiplication: you don't have to worry about
  24  * loss of precision.
  25  *
  26  * Use only for very small delays ( < 1 msec).  Should probably use a
  27  * lookup table, really, as the multiplications take much too long with
  28  * short delays.  This is a "reasonable" implementation, though (and the
  29  * first constant multiplications gets optimized away if the delay is
  30  * a constant)
  31  */
  32 extern void __udelay(unsigned long usecs);
  33 extern void __const_udelay(unsigned long);
  34
  35 #define MAX_UDELAY_MS 2
  36
  37 #define udelay(n)                                                       \
  38         (__builtin_constant_p(n) ?                                      \
  39           ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
  40                         __const_udelay((n) * ((2199023U*HZ)>>11))) :    \
  41           __udelay(n))
  42
  43 #endif /* defined(_ARM_DELAY_H) */
  44