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// Example of sleeping and saving power, and reading a clock
// 
// Author: Nick Gammon
// Date:   25 May 2011

#include <Wire.h>
#include "RTClib.h"

#include <avr/sleep.h>
#include <avr/wdt.h>

RTC_DS1307 RTC;

#define CLOCK_POWER 5

#define LED 13

// watchdog interrupt
ISR(WDT_vect) {
  wdt_disable();  // disable watchdog
}

void myWatchdogEnable(const byte interval) {  // turn on watchdog timer; interrupt mode every 2.0s
  MCUSR = 0;                          // reset various flags
  WDTCSR |= 0b00011000;               // see docs, set WDCE, WDE
  WDTCSR =  0b01000000 | interval;    // set WDIE, and appropriate delay

  wdt_reset();
  
  byte adcsra_save = ADCSRA;
  byte prr_save = PRR;

  // disable ADC
  ADCSRA = 0;  
  
  // power reduction register
  // Bit 7 - PRTWI: Power Reduction TWI
  // Bit 6 - PRTIM2: Power Reduction Timer/Counter2
  // Bit 5 - PRTIM0: Power Reduction Timer/Counter0
  // Bit 4 - Res: Reserved bit
  // Bit 3 - PRTIM1: Power Reduction Timer/Counter1
  // Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
  // Bit 1 - PRUSART0: Power Reduction USART0
  // Bit 0 - PRADC: Power Reduction ADC
  
  // turn off various modules
  PRR = 0b11101111;
    
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);   // sleep mode is set here
  sleep_mode();            // now goes to Sleep and waits for the interrupt
  
  // stop power reduction
  ADCSRA = adcsra_save;
  PRR = prr_save;
} 

void setup()
{
  pinMode (CLOCK_POWER, OUTPUT);
  digitalWrite (CLOCK_POWER, HIGH);  // power up clock
  delay (1);

  Wire.begin();
  RTC.begin();

  // set time in clock chip if not set before
  if (! RTC.isrunning()) {
    // following line sets the RTC to the date & time this sketch was compiled
    RTC.adjust(DateTime(__DATE__, __TIME__));
  }

  digitalWrite (CLOCK_POWER, LOW);  // power down clock
  
}  // end of setup

void loop()
{

  // power up clock
  digitalWrite (CLOCK_POWER, HIGH);  // power up clock
  delay (1);  // give it time to stabilize

  // activate I2C and clock
  Wire.begin();
  RTC.begin();

  // find the time  
  DateTime now = RTC.now();

  // time now available in now.hour(), now.minute() etc.

  // finished with clock
  digitalWrite (CLOCK_POWER, LOW); 
  
  // turn off I2C pull-ups
  digitalWrite (A4, LOW);
  digitalWrite (A5, LOW);
  
  // turn off I2C
  TWCR &= ~(_BV(TWEN) | _BV(TWIE) | _BV(TWEA));

  // -------- do something here if required by the time of day

  // in my case flash an LED for 5 seconds
  pinMode (LED, OUTPUT);
  digitalWrite (LED, HIGH);
  delay (5000);
  digitalWrite (LED, LOW);
  
  // sleep bit patterns:
  //  1 second:  0b000110
  //  2 seconds: 0b000111
  //  4 seconds: 0b100000
  //  8 seconds: 0b100001

  // sleep for a total of 20 seconds
  myWatchdogEnable (0b100001);  // 8 seconds
  myWatchdogEnable (0b100001);  // 8 seconds
  myWatchdogEnable (0b100000);  // 4 seconds

}  // end of loop