/* -*- mode: c++; c-basic-offset: 8; indent-tabs-mode: t -*- */

#include "utils.h"

void delayMicrosecondsInterruptible(unsigned int us)
{
#if F_CPU >= 16000000L
	// for the 16 MHz clock on most Arduino boards
  
	// for a one-microsecond delay, simply return.  the overhead
	// of the function call yields a delay of approximately 1 1/8 us.
	if (--us == 0) return;
  
	// the following loop takes a quarter of a microsecond (4 cycles)
	// per iteration, so execute it four times for each microsecond of
	// delay requested.
	us <<= 2;
  
	// account for the time taken in the preceeding commands.
	us -= 2;
#else
	// for the 8 MHz internal clock on the ATmega168
  
	// for a one- or two-microsecond delay, simply return.  the overhead of
	// the function calls takes more than two microseconds.  can't just
	// subtract two, since us is unsigned; we'd overflow.
	if (--us == 0) return;
	if (--us == 0) return;
  
	// the following loop takes half of a microsecond (4 cycles)
	// per iteration, so execute it twice for each microsecond of
	// delay requested.
	us <<= 1;
  
	// partially compensate for the time taken by the preceeding commands.
	// we can't subtract any more than this or we'd overflow w/ small delays.
	us--;
#endif
  
	// busy wait
	__asm__ __volatile__ (
			      "1: sbiw %0,1" "\n\t" // 2 cycles
			      "brne 1b" : "=w" (us) : "0" (us) // 2 cycles
			      );
}