/**
* MetkuMods - /
* How to get started with AVR microcontrollers, part 2
* Example 2.5 - Interfacing with a computer
*
* Author: Aki Korhonen
* Date: 2009-04-29
*/

// If clock speed isn't set in the project settings then it is set here
#ifndef F_CPU
	#define F_CPU 1000000UL // 1 MHz
#endif

// Wanted baud rate, 2400 bps is ok with the 1 MHz internal clock
#define BAUD 2400

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

#include <inttypes.h>
#include <util/delay.h>
#include <util/setbaud.h>

// General stuff
#define LED1_PIN 0

// Function prototypes
void Init_USART(void);
void USART_SendByte(uint8_t data);
uint8_t USART_ReceiveByte(void);

// Main program
int main(void)
{
	// PB0 out
	DDRB = _BV(LED1_PIN);

	// Set all pins on port B low
	PORTB = 0x00;

	// Initialize UART
	Init_USART();
	
	// Lets flash the led couple times to show that everything is set
	PORTB |= _BV(LED1_PIN); // Turn LED on
	_delay_ms(100); // Wait 100 ms
	PORTB &= ~(_BV(LED1_PIN)); // Turn LED off
	_delay_ms(100);
	PORTB |= _BV(LED1_PIN);
	_delay_ms(100);
	PORTB &= ~(_BV(LED1_PIN));
	_delay_ms(100);

	// Send a short message to the computer to test out the transmitting
	// You should see "Hello" on the terminal program
	USART_SendByte('H');
	USART_SendByte('e');
	USART_SendByte('l');
	USART_SendByte('l');
	USART_SendByte('o');
	USART_SendByte('\n');

	// Enable global interrupts
	sei();
	
	while(1)
	{
		// Nothing is done here, all the work is done on interrupts.
		// The loop has to be here anyway to keep the controller running.
	}

	return 0;
}

// RX interrupt, this gets executed when data is coming from the RX line
ISR(USART_RXC_vect)
{
	uint8_t c;
	
	// Get the byte that is coming
	c = USART_ReceiveByte();
	
	if(c == 'A')
	{
		// If received byte is same as ascii character A, turn led on
		PORTB |= _BV(LED1_PIN);

		USART_SendByte('O');
		USART_SendByte('N');
		USART_SendByte('\n');
	}
	else if(c == 'B')
	{
		// If received byte is same as ascii character B, turn led off
		PORTB &= ~(_BV(LED1_PIN));

		USART_SendByte('O');
		USART_SendByte('F');
		USART_SendByte('F');
		USART_SendByte('\n');
	}
}

// UART initialization
void Init_USART(void)
{
	UBRRH = UBRRH_VALUE;
	UBRRL = UBRRL_VALUE;
	
	UCSRA = 0x00;
	UCSRB |= (1 << RXEN); // RXEN, Enable RX
	UCSRB |= (1 << RXCIE); // RXCIE, Enable RX interrupt
	UCSRB |= (1 << TXEN); // TXEN, Enable TX
	UCSRC = 0x86; // 8 Data, 1 Stop, No Parity
}

// SendByte sends the wanted byte to the TX line
void USART_SendByte(uint8_t data)
{
	// Wait if a byte is being transmitted
	loop_until_bit_is_set(UCSRA, UDRE);

	// Send the given data
	UDR = data;
}

// ReceiveByte reads a byte from RX line
uint8_t USART_ReceiveByte(void)
{
	// Wait until a byte has been received
	loop_until_bit_is_set(UCSRA, RXC);

	// Return received data
	return UDR;
}