My atmega328 and attiny85 avr-gcc snippet collection

atmega328 low power sleep.c

// prescaler timings:
// 0=16ms, 1=32ms,2=64ms,3=128ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec
void watchdog_init(uint8_t prescaler) {
  MCUSR &= ~(1<<WDRF); // <-- reset wdt
  WDTCSR |= (1<<WDCE) | (1<<WDE);  // <-- start timed sequence
  WDTCSR  = (1<<WDCE) | (1<<WDIE) |
    ((prescaler>>3) & 1)<<WDP3 |
    ((prescaler>>2) & 1)<<WDP2 |
    ((prescaler>>1) & 1)<<WDP1 |
    ((prescaler>>0) & 1)<<WDP0;
}

// system wakes up when watchdog is timed out
// obs: make sure you setup the watchdog before calling this!
void watchdog_sleep() {
  ADCSRA = 0; // switch Analog to Digitalconverter OFF
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  cli();           // timed sequence follows
  sleep_enable();
  // turn off brown-out enable in software
  // MCUCR = 1<<(BODS) | 1<<(BODSE);  // turn on brown-out enable select
  // MCUCR = 1<<(BODS);        // this must be done within 4 clock cycles of above
  sei();             // guarantees next instruction executed
  sleep_cpu ();              // sleep within 3 clock cycles of above
  sleep_disable(); // System continues execution here when watchdog timed out
  ADCSRA = 1; // switch Analog to Digitalconverter ON
}

void watchdog_powerdown(uint8_t prescaler) {
  watchdog_init(prescaler);
  watchdog_sleep();
}