#include <stdlib.h>
#include <stdio.h>
#include <avr/io.h>
#include <avr/interrupt.h>

#define F_CPU 11059200UL

#define UART_BAUD_RATE      9600      
#define BAUD_PRESCALE (((F_CPU / (UART_BAUD_RATE * 16UL))) - 1)


#include <avr/sleep.h> //Needed for sleep_mode
#include <avr/wdt.h>


void InitWatchdog(); //initialize watchdog
void GoToSleep();
void SendByte1(char byte);
void SendByte2(char byte);

int main()
{

UBRR0H = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value into the hig
UBRR0L = BAUD_PRESCALE; // Load lower 8-bits of the baud rate value into the low byte o

UCSR0B= (1 << RXEN0) | (1 << TXEN0); // Turn on the transmission and reception
UCSR0C = (1 << USBS0) | (1 << UCSZ00) | (1 << UCSZ01); // Use 2 stop bits,  8-bit character size,
//UCSR0C = (1 << UCSZ00) | (1 << UCSZ01); // Use 1 stop bit,  8-bit character size,
//UCSR0C |= (1 << UMSEL01) ; // Synchronous USART

  
SendByte1('A') ;

   
 InitWatchdog();
     set_sleep_mode(SLEEP_MODE_PWR_DOWN);  // define sleep as 'deep sleep mode' 
   
 while(1)
 {
     
   SendByte1('B');
   GoToSleep();
   
 }
  
 return 1;  
}


//===========================================================================


void GoToSleep()
{

    
  WDTCSR |= (1<<WDIE); // |(1<<WDE); //    To stay in Interrupt and System Reset Mode, WDIE must be set after each interrupt
   
 //   sleep_enable();  
        
     SendByte1('C');   
     SendByte1('D');   
    sleep_mode();
   
//==============  Sleeping ==============================================
    
    sleep_disable();
    
    WDTCSR |= (1<<WDIE); // |(1<<WDE); //    To stay in Interrupt and System Reset Mode, WDIE must be set after each interrupt

    SendByte1('E');
   
        
}

//===========================================================================


//Watchdog timeout ISR

ISR(WDT_vect) 
{   
         SendByte2('X');       
         SendByte2('Y');       
         SendByte2('Z');       

   
}

//===========================================================================



// http://web.csulb.edu/~hill/ee346/Lectures/22%20C++%20Watchdog%20Timer.pdf
// https://studfile.net/preview/2297025/page:14/

void InitWatchdog() //initialize watchdog
{
   
       SendByte1('H');
    
    cli(); //disable interrupts
    
     WDTCSR = (1<<WDCE); // | (1<<WDE); // WDCE (allow these changes),  WDE: choose IR -> system reset mode
     WDTCSR |= (1<<WDE) | (1 << WDIE); //  | (1<<WDP3); // (0111 1000) WDIE (WD-IR enable), WDP3 (4s),  
     wdt_enable(WDTO_4S);
//     wdt_enable(WDTO_500MS);,  

    sei(); //Enable global interrupts
}

void SendByte1(char byte)
{
    UDR0 = byte ;
   while (( UCSR0A & (1<<UDRE0))  == 0){};  
 //  while(UDR0 != 0) {}
}

void SendByte2(char byte)
{
    UDR0 = byte ;
    while (( UCSR0A & (1<<UDRE0) && ((UCSR0A)|(1<<TXC0)))  == 0){}; 
   UCSR0A &=  ~(1<<TXC0); 
 //  while(UDR0 != 0) {}
}