#include <avr/interrupt.h>
#include <avr/io.h>
//from https://github.com/Devilbinder/ATMEGA328P_C/blob/master/examples/uart/uart/main.c

#include <util/delay.h>
#include <stdio.h>
#include <stdint.h>


#define RX_BUFFER_SIZE 128

volatile static uint8_t rx_buffer[RX_BUFFER_SIZE] = {0};
volatile static uint16_t rx_count = 0;	
volatile static uint8_t uart_tx_busy = 1;

ISR(USART_RX_vect){
	
	volatile static uint16_t rx_write_pos = 0;
	
	rx_buffer[rx_write_pos] = UDR0;
	rx_count++;
	rx_write_pos++;
	if(rx_write_pos >= RX_BUFFER_SIZE){
		rx_write_pos = 0;
	}
	
}


ISR(USART_TX_vect){
	uart_tx_busy = 1;
}

int sputc(unsigned char c, FILE *file) //stderr and stdout are same
{
  while(uart_tx_busy == 0);
	uart_tx_busy = 0;
	UDR0 = c;
  return c;
}

void init_serial(uint32_t baud, uint8_t high_speed)
{
  uint8_t speed = 16;
	
	if(high_speed != 0){
		speed = 8;
		UCSR0A |= 1 << U2X0;
	}
	
	baud = (F_CPU/(speed*baud)) - 1;
	
	UBRR0H = (baud & 0x0F00) >> 8;
	UBRR0L = (baud & 0x00FF);
	
	UCSR0B |= (1 << TXEN0) | (1 << RXEN0) | (1 << TXCIE0) | (1 << RXCIE0);

  fdevopen(&sputc, 0); //for print only
  sei();
}

int main()
{
  init_serial(9600, 0);

	DDRD |= _BV(6);
  printf("%s","Hello, World!\n\0");

	while(1)
	{
		PORTD |= _BV(6);
		printf("%s","LED ON!\n\0");
		_delay_ms(1000);
		PORTD &= ~_BV(6);
		printf("%s","LED OFF!\n\0");
		_delay_ms(1000);
	}
}