linux/include/asm-i386/delay.h

#ifndef _I386_DELAY_H
#define _I386_DELAY_H

/*
 * Copyright (C) 1993 Linus Torvalds
 *
 * Delay routines calling functions in arch/i386/lib/delay.c
 */
 
extern void __bad_udelay(void);
extern void __bad_ndelay(void);

extern void __udelay(unsigned long usecs);
extern void __ndelay(unsigned long nsecs);
extern void __const_udelay(unsigned long usecs);
extern void __delay(unsigned long loops);

#define udelay(n) (__builtin_constant_p(n) ? \
	((n) > 20000 ? __bad_udelay() : __const_udelay((n) * 0x10c7ul)) : \
	__udelay(n))
	
#define ndelay(n) (__builtin_constant_p(n) ? \
	((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \
	__ndelay(n))

void use_tsc_delay(void);

#endif /* defined(_I386_DELAY_H) */