#include <avr/io.h>

//  Comment below back into the code if using 16MHz crystal
//#define CLK16MHZ


#ifdef CLK16MHZ
#define F_CPU 16000000UL // 1 MHz  
#define MS_SHIFT 4
#define MS_GATE 0x0f
#else
#define F_CPU 1000000UL // 1 MHz  
#define MS_SHIFT 8
#define MS_GATE 0xff
#endif

#include <avr/delay.h>

// convert from loop cycles to msecs
#define _delay_ms(x) _delay_loop_2((x)*(F_CPU/4000))

/*
  void delay_ms(unsigned int t) 

  _delay_loop_2() can only take a 16-bit argument.  This routine 
  repeatedly calls _delay_loop_2() in order to get the desired busy
  wait length.  Note that there is some overhead in the loop that is
  not counted in the delay (so the delay is actually just a little longer)

  This code is also specific to the 1 MHz clock

*/

void delay_ms(unsigned int t) {
  unsigned int nloops = (unsigned short) (t >> MS_SHIFT);
  unsigned int i;

  for(i = 0; i < nloops; ++i) {
    _delay_ms(256);
  };
  i = t & MS_GATE;
  if(i > 0) {
    _delay_ms(i);
  };
  
};

/*
  void delay_us(unsigned int t)

  Busy wait for a specified number of microseconds.

  Assumptions:
  - F_CPU is a multiple of 1,000,000

  Note:
  - Maximum delay will vary with F_CPU

  For a 1MHz clock:
  - You can delay up to 65536 us
  - Your resolution is 4 us

*/
void delay_us(unsigned int t) {
  _delay_loop_2((t*(F_CPU/1000000)) >> 2);
};

//////////////////////////////////////////////////////////////////////////////////////////

int main (void)
{
  unsigned int counter = 0;

  /* Set PORTB (LEDs) to all outputs */
  DDRB = 0xFF;

  while(1) {
    // Total delay: 500 ms
    for(counter = 0; counter < 50; ++counter) {
      // Delay for 10 ms
      delay_us(10000);
    };
	  
    PORTB ^= 1;
  }
};