119 lines
3.0 KiB
C
119 lines
3.0 KiB
C
/*
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serial.c - Low level functions for sending and recieving bytes via the serial port
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Part of Grbl
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Copyright (c) 2009-2011 Simen Svale Skogsrud
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Grbl is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Grbl 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Grbl. If not, see <http://www.gnu.org/licenses/>.
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*/
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/* This code was initially inspired by the wiring_serial module by David A. Mellis which
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used to be a part of the Arduino project. */
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#include <avr/interrupt.h>
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#include <avr/sleep.h>
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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 to make sure tx-streaming is running
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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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// Turn off Data Register Empty Interrupt to stop tx-streaming if this concludes the transfer
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if (tail == tx_buffer_head) { UCSR0B &= ~(1 << UDRIE0); }
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tx_buffer_tail = tail;
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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 magic number if no data pending
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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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// Write data to buffer unless it is full.
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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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