/*
 ATtiny25/45/85 Blink 32KHz
 Version: 1.0
 Author: Alex from Inside Gadgets (http://www.insidegadgets.com)
 Created: 2/010/2011
 Last Modified: 2/10/2011

 Blink an LED on the ATtiny25/45/85 using the timer every 1 second with a 32.768 KHz watch crystal then go to IDLE sleep.

 */

#define F_CPU 32768 // 32.768 KHz clock

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>

// ATtiny25/45/85 Pin map
//                        +-\/-+
// Reset/Ain0 (D 5) PB5  1|o   |8  Vcc
//       Ain3 (D 3) PB3  2|    |7  PB2 (D 2) Ain1
//       Ain2 (D 4) PB4  3|    |6  PB1 (D 1) pwm1
//                  GND  4|    |5  PB0 (D 0) pwm0 <-- connect resistor and LED here
//                        +----+

#define ledPin PB0

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

#ifndef boolean
  typedef uint8_t boolean;
#endif

volatile boolean led_state = 0; // LED state on/off variable
volatile int count = 0;
volatile int of_count = 0;

int main(void) {

  setup();

  DDRB = (1<<ledPin); // Set LED as an output
  PORTB |= ((1<<PB2) | (1<<PB1)); // Turn on pull-up resistors on other ports to save power

  while(1) {

    if (led_state==1) {  // wait for timed out watchdog / flag is set when a watchdog timeout occurs
      led_state=0;       // reset flag

      if (count == of_count){
        count = 0;
        digitalWrite(ledPin,HIGH);
        delayMicroseconds(500);
        digitalWrite(ledPin,LOW);
      } else {
       count++;
      }
   }
    set_sleep_mode(SLEEP_MODE_IDLE); // Set sleep mode as idle
    sleep_mode(); // System sleeps here

  }
}

// Timer 1 interrupt
ISR(TIMER1_OVF_vect) {
  led_state = 1; // Change led state to be the opposite of what it is
}

/*
 ATtiny25/45/85 Blink 32KHz
 Version: 1.0
 Author: Alex from Inside Gadgets (http://www.insidegadgets.com)
 Created: 2/010/2011
 Last Modified: 2/10/2011

 Blink an LED on the ATtiny25/45/85 using the timer every 1 second with a 32.768 KHz watch crystal then go to IDLE sleep.

 */


// Used from Arduino wiring.c - to setup the ATtiny
void setup(void) {
  sei(); // Turn on interrupts

  // Set prescaler to 128 to give exactly 1 second before an overflow occurs.
  // 128 prescaler x 256 timer bits / 32768 clock = 1 second
  sbi(TCCR1, CS13);
  sbi(TCCR1, CS11);

  // Enable timer 1 overflow interrupt
  sbi(TIMSK, TOIE1);

}