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/*
wiring_serial.c - serial functions.
Part of Arduino - http://www.arduino.cc/
Copyright (c) 2005-2006 David A. Mellis
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General
Public License along with this library; if not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330,
Boston, MA 02111-1307 USA
$Id: wiring.c 248 2007-02-03 15:36:30Z mellis $
*/
#include "wiring_private.h"
// Define constants and variables for buffering incoming serial data. We're
// using a ring buffer (I think), in which rx_buffer_head is the index of the
// location to which to write the next incoming character and rx_buffer_tail
// is the index of the location from which to read.
#define RX_BUFFER_SIZE 128
unsigned char rx_buffer[RX_BUFFER_SIZE];
int rx_buffer_head = 0;
int rx_buffer_tail = 0;
void beginSerial(long baud)
{
#if defined(__AVR_ATmega168__)
UBRR0H = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
UBRR0L = ((F_CPU / 16 + baud / 2) / baud - 1);
// enable rx and tx
sbi(UCSR0B, RXEN0);
sbi(UCSR0B, TXEN0);
// enable interrupt on complete reception of a byte
sbi(UCSR0B, RXCIE0);
#else
UBRRH = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
UBRRL = ((F_CPU / 16 + baud / 2) / baud - 1);
// enable rx and tx
sbi(UCSRB, RXEN);
sbi(UCSRB, TXEN);
// enable interrupt on complete reception of a byte
sbi(UCSRB, RXCIE);
#endif
// defaults to 8-bit, no parity, 1 stop bit
}
void serialWrite(unsigned char c)
{
#if defined(__AVR_ATmega168__)
while (!(UCSR0A & (1 << UDRE0)))
;
UDR0 = c;
#else
while (!(UCSRA & (1 << UDRE)))
;
UDR = c;
#endif
}
int serialAvailable()
{
return (RX_BUFFER_SIZE + rx_buffer_head - rx_buffer_tail) % RX_BUFFER_SIZE;
}
int serialRead()
{
// if the head isn't ahead of the tail, we don't have any characters
if (rx_buffer_head == rx_buffer_tail) {
return -1;
} else {
unsigned char c = rx_buffer[rx_buffer_tail];
rx_buffer_tail = (rx_buffer_tail + 1) % RX_BUFFER_SIZE;
return c;
}
}
void serialFlush()
{
// don't reverse this or there may be problems if the RX interrupt
// occurs after reading the value of rx_buffer_head but before writing
// the value to rx_buffer_tail; the previous value of rx_buffer_head
// may be written to rx_buffer_tail, making it appear as if the buffer
// were full, not empty.
rx_buffer_head = rx_buffer_tail;
}
#if defined(__AVR_ATmega168__)
SIGNAL(SIG_USART_RECV)
#else
SIGNAL(SIG_UART_RECV)
#endif
{
#if defined(__AVR_ATmega168__)
unsigned char c = UDR0;
#else
unsigned char c = UDR;
#endif
int i = (rx_buffer_head + 1) % RX_BUFFER_SIZE;
// if we should be storing the received character into the location
// just before the tail (meaning that the head would advance to the
// current location of the tail), we're about to overflow the buffer
// and so we don't write the character or advance the head.
if (i != rx_buffer_tail) {
rx_buffer[rx_buffer_head] = c;
rx_buffer_head = i;
}
}
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