Tooltron

#include <stdint.h>

#include <avr/io.h>

#include <avr/interrupt.h>

#include "serial.h"

static int rx_start = 0, rx_end = 0;

static uint8_t rx_buffer[RX_BUFFER_SIZE];

ISR(USART1_RX_vect) {

  uint8_t data = UDR1;

  int new_end = rx_end+1;

  if (new_end == RX_BUFFER_SIZE) {

    new_end = 0;

  }

  if (new_end == rx_start) {

    // TODO warn of buffer overflow?

  } else {

    rx_buffer[rx_end] = data;

    rx_end = new_end;

  }

}

void serial_init() {

  // baud = F_CPU / (div (UBRR + 1))

  // where div = 16 if U2X = 0, or 8 otherwise

  uint16_t ubrr = F_CPU / 8 / BAUD_RATE - 1;

  UBRR1H = ubrr >> 8;

  UBRR1L = ubrr;

  // UMSEL = 0, asynchronous usart

  // UPM = 0, parity check disabled

  // USBS = 0, 1 stop bit

  // UCSZ = 3, 8-bit

  // U2X = 1, use 8 prescale instead of 16 for a more accurate baud rate

  UCSR1A = _BV(U2X1);

  UCSR1B = _BV(RXCIE1) | _BV(RXEN1) | _BV(TXEN1);

  UCSR1C = _BV(UCSZ11) | _BV(UCSZ10);

}

int serial_read() {

  int ret;

  cli();

  if (rx_start == rx_end) {

    ret = -1;

  } else {

    ret = rx_buffer[rx_start];

    rx_start++;

    if (rx_start == RX_BUFFER_SIZE) {

      rx_start = 0;

    }

  }

  sei();

  return ret;

}

void serial_flush() {

  cli();

  rx_start = 0;

  rx_end = 0;

  sei();

}

uint8_t serial_read_blocking() {

  int c;

  do {

    c = serial_read();

  } while (c < 0);

  return c;

}

void serial_write(uint8_t* data, int length) {

  int i;

  for (i = 0; i < length; i++) {

    while (!(UCSR1A & _BV(UDRE1)));

    UDR1 = data[i];

  }

}