/*************************************************************************** * Atmel AVR USART Library for GCC * Version: 1.0 *  * Works with AVR MCUs equiped with USART hardware (ATmega series).  * Does not work with older UART's or USI of ATtiny series. * Tested with ATmega8. *  * Uses USART Receive Complete Interrupt. Disabling Global Interrupts * after usart initialization disables data receive. * * Jaakko Ala-Paavola 2003/06/28 * http://www.iki.fi/jap email:jap@iki.fi */#include <avr/io.h>#include <avr/signal.h>#include <avr/interrupt.h>#include <string.h>#include "usart.h"char usart_buffer[USART_BUFFER_SIZE];volatile unsigned char usart_buffer_pos_first = 0, usart_buffer_pos_last = 0;volatile unsigned char usart_buffer_overflow = 0;void usart_init(unsigned char baud_divider) {  // Baud rate selection  UBRRH = 0x00;         UBRRL = baud_divider;  // USART setup  UCSRA = 0x02;        // 0000 0010                       // U2X enabled  UCSRC = 0x86;        // 1000 0110                       // Access UCSRC, Asyncronous 8N1  UCSRB = 0x98;        // 1001 1000                       // Receiver enabled, Transmitter enabled                       // RX Complete interrupt enabled  sei();               // Enable interrupts globally}void usart_putc(char data) {    while (!(UCSRA & 0x20)); // Wait untill USART data register is empty    // Transmit data    UDR = data;}void usart_puts(char *data) {  int len, count;    len = strlen(data);  for (count = 0; count < len; count++)     usart_putc(*(data+count));}char usart_getc(void) {  // Wait untill unread data in ring buffer  if (!usart_buffer_overflow)    while(usart_buffer_pos_first == usart_buffer_pos_last);  usart_buffer_overflow = 0;  // Increase first pointer  if (++usart_buffer_pos_first >= USART_BUFFER_SIZE)     usart_buffer_pos_first = 0;  // Get data from the buffer  return usart_buffer[usart_buffer_pos_first];}unsigned char usart_unread_data(void) {  if (usart_buffer_overflow)    return USART_BUFFER_SIZE;  if (usart_buffer_pos_last > usart_buffer_pos_first)    return usart_buffer_pos_last - usart_buffer_pos_first;  if (usart_buffer_pos_last < usart_buffer_pos_first)    return USART_BUFFER_SIZE-usart_buffer_pos_first       + usart_buffer_pos_last;  return 0;}SIGNAL(SIG_UART_RECV) {  // Increase last buffer   if (++usart_buffer_pos_last >= USART_BUFFER_SIZE)    usart_buffer_pos_last = 0;  if (usart_buffer_pos_first == usart_buffer_pos_last)     usart_buffer_overflow++;  // Put data to the buffer  usart_buffer[usart_buffer_pos_last] = UDR;}