128 lines
3.4 KiB
C
128 lines
3.4 KiB
C
/*
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serial.c - serial functions.
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Part of Arduino - http://www.arduino.cc/
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Copyright (c) 2005-2006 David A. Mellis
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General
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Public License along with this library; if not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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Boston, MA 02111-1307 USA
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*/
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#include <avr/interrupt.h>
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#include <avr/sleep.h>
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// Define constants and variables for buffering incoming serial data. We're
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// using a ring buffer (I think), in which rx_buffer_head is the index of the
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// location to which to write the next incoming character and rx_buffer_tail
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// is the index of the location from which to read.
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#ifdef __AVR_ATmega328P__
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#define RX_BUFFER_SIZE 256
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#else
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#define RX_BUFFER_SIZE 64
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#endif
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#define TX_BUFFER_SIZE 16
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uint8_t rx_buffer[RX_BUFFER_SIZE];
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uint8_t rx_buffer_head = 0;
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uint8_t rx_buffer_tail = 0;
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uint8_t tx_buffer[TX_BUFFER_SIZE];
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uint8_t tx_buffer_head = 0;
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volatile uint8_t tx_buffer_tail = 0;
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void serial_init(long baud)
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{
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UBRR0H = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
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UBRR0L = ((F_CPU / 16 + baud / 2) / baud - 1);
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/* baud doubler off - Only needed on Uno XXX */
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UCSR0A &= ~(1 << U2X0);
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// enable rx and tx
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UCSR0B |= 1<<RXEN0;
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UCSR0B |= 1<<TXEN0;
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// enable interrupt on complete reception of a byte
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UCSR0B |= 1<<RXCIE0;
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// defaults to 8-bit, no parity, 1 stop bit
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}
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void serial_write(uint8_t data) {
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// Calculate next head
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uint8_t next_head = (tx_buffer_head + 1) % TX_BUFFER_SIZE;
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// Wait until there's a space in the buffer
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while (next_head == tx_buffer_tail) { sleep_mode(); };
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// Store data and advance head
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tx_buffer[tx_buffer_head] = data;
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tx_buffer_head = next_head;
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// Enable Data Register Empty Interrupt
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UCSR0B |= (1 << UDRIE0);
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}
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// Data Register Empty Interrupt handler
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SIGNAL(USART_UDRE_vect) {
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// temporary tx_buffer_tail (to optimize for volatile)
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uint8_t tail = tx_buffer_tail;
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// Send a byte from the buffer
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UDR0 = tx_buffer[tail];
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// Update tail position
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tail ++;
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tail %= TX_BUFFER_SIZE;
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tx_buffer_tail = tail;
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// Turn off Data Register Empty Interrupt if this concludes the transfer
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if (tail == tx_buffer_head) {
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UCSR0B &= ~(1 << UDRIE0);
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}
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}
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uint8_t serial_read()
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{
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if (rx_buffer_head != rx_buffer_tail) {
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return 0xff;
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} else {
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uint8_t data = rx_buffer[rx_buffer_tail];
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rx_buffer_tail = (rx_buffer_tail + 1) % RX_BUFFER_SIZE;
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return data;
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}
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}
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SIGNAL(USART_RX_vect)
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{
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uint8_t data = UDR0;
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uint8_t next_head = (rx_buffer_head + 1) % RX_BUFFER_SIZE;
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// if we should be storing the received character into the location
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// just before the tail (meaning that the head would advance to the
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// current location of the tail), we're about to overflow the buffer
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// and so we don't write the character or advance the head.
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if (next_head != rx_buffer_tail) {
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rx_buffer[rx_buffer_head] = data;
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rx_buffer_head = next_head;
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}
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}
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