#include <avr/io.h>
#include <stdlib.h>
#include "usart.h"
#include "conf.h"
#include "ringbuffer.h"
#include <avr/interrupt.h>

volatile ringbuffer_t usart_buffer;


void
usart_init(void)
{
	usart_buffer = ringbuffer_new(USART_BUFFER_SIZE);
	UBRR0H = (unsigned char)(UBRR_VALUE >> 8);
	UBRR0L = (unsigned char)UBRR_VALUE;
	UCSR0B = _BV(TXEN0) | _BV(TXCIE0);
	UCSR0C = _BV(UCSZ00) | _BV(UCSZ01);
	sei();
}

int
usart_putc(char c)
{
	int result = ringbuffer_put_char(usart_buffer, c);
	// If the buffer is already emtpy there is no
	// need to wait for the interrupt.
	// Also it is likely that the interrupt will never happen.
	// (For instance because this is the first byte sent)
	if(UCSR0A & _BV(UDRE0))
	{
		UDR0 = ringbuffer_get_char(usart_buffer);
	}
	return result;
}
	


ISR(USART_TX_vect)
{
	if(ringbuffer_nonempty(usart_buffer))
	{
		UDR0 = ringbuffer_get_char(usart_buffer);
		UCSR0A |= _BV(TXC0);
	}
}