/*
 * UART-LF.c
 *
 * Created: 29.01.2017 23:43:39
 * Author : Petter
 */ 

#define F_CPU 3333333UL
#define BAUD_9600 ((4UL*F_CPU)/9600)

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

/*
In this exercise we will set up and use UART communication.
The embedded debugger has a virtual com port that we will use to communicate with the computer.

*/


void uart_init(unsigned long baud){
	
	//From chapter 24.3 in datasheet
	PORTB.DIRSET = (1 << PIN2_bp); 	//Setting up TX pin as output
	PORTB.OUTSET = (1 << PIN2_bp); 	//Setting the TX pin high
	
	USART0.BAUDH = (baud >> 8); 	//Shift register right by 8 bits to get the 8 high bits
	USART0.BAUDL = baud; 			//Set baud rate without shifting to get the 8 low bits
	
	//It turns out the compiler can handle this automatically, meaning this works just as well:
	//USART0.BAUD = baud;
	
	
	//USART.CTRLC CMODE bits default to async, 1 stop bit, 8 bit character size
	
	USART0.CTRLB |= (1 << USART_RXEN_bp) | (1 << USART_TXEN_bp);	//Enable RX and TX

	USART0.CTRLA |= (1 << USART_RXCIE_bp); //Enable interrupts on incoming data
}

// function to transmit data
void uart_transmit(unsigned char data){
	
	//In this function we will be send data.
	
	//First we should check that there isn't already data being sent
	//	if there is, we should probably wait for it to finish first
	while (!(USART0.STATUS & (1 << USART_DREIF_bp))){
		//wait for previous transmit to finish
	};
	
	//Put our new data into se sending register
	USART0.TXDATAL = data;
}


int main(void)
{
	//Initialize the UART with our function. 
	//We will be using a baudrate of 9600 (defined as BAUD_9600 at the top of the file)
	uart_init(BAUD_9600);
	
	sei(); //Enable inerrupt, important for anything here to work
	
    while (1) 
    {
		//We don't really need to do anything here.
		//the ISR will handle receiving. 
    }
}


//Interrupt service routine for the receiver.
ISR(USART0_RXC_vect){
	
	//Read out the received data to a variable
	uint8_t data = USART0_RXDATAL;
	//Do things with data:
	uart_transmit(data + 1); //Example: Shift all characters by one step A -> B, B -> C etc.

}