arduino_nano/lib/usart.c

/* This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/* Copyright (c) 2015 King Kévin <kingkevin@cuvoodoo.info> */
/* this library handles the USART
 * it uses the TX and RX pins
 * it can be used with or without interrupts
 */

#include <stdint.h> // Standard Integer Types
#include <stdio.h> // Standard IO facilities
#include <stdlib.h> // General utilities

#include <avr/io.h> // AVR device-specific IO definitions
#include <avr/interrupt.h> // Interrupts
#include <avr/sleep.h> // Power Management and Sleep Modes

#include "usart.h" // USART header
#include <util/setbaud.h> // Helper macros for baud rate calculations

/* assign input and output streams */
FILE usart_input = FDEV_SETUP_STREAM(NULL, (int (*)(struct __file *)) usart_getchar, _FDEV_SETUP_READ);
#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
FILE usart_output = FDEV_SETUP_STREAM((int (*)(char, struct __file *)) usart_putchar_nonblocking, NULL, _FDEV_SETUP_WRITE);
FILE usart_io = FDEV_SETUP_STREAM((int (*)(char, struct __file *)) usart_putchar_nonblocking, (int (*)(struct __file *)) usart_getchar, _FDEV_SETUP_RW);
#else
FILE usart_output = FDEV_SETUP_STREAM((int (*)(char, struct __file *)) usart_putchar_blocking, NULL, _FDEV_SETUP_WRITE);
FILE usart_io = FDEV_SETUP_STREAM((int (*)(char, struct __file *)) usart_putchar_blocking, (int (*)(struct __file *)) usart_getchar, _FDEV_SETUP_RW);
#endif

#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
/* input and output ring buffer, indexes, and available memory */
uint8_t rx_buffer[32] = {0};
volatile uint8_t rx_i = 0;
volatile uint8_t rx_used = 0;
uint8_t tx_buffer[32] = {0};
volatile uint8_t tx_i = 0;
volatile uint8_t tx_used = 0;
/* show the user how much received data is ready */
volatile uint8_t usart_incoming = 0; // same as rx_used, but since the user can write this variable we don't rely on it
#endif

/* configure USART serial port */
void usart_init(void)
{
	UBRR0H = UBRRH_VALUE; // set baurate (calculated from BAUD)
	UBRR0L = UBRRL_VALUE; // set baurate (calculated from BAUD)
#if USE_2X
	UCSR0A |= (1<<U2X0); // use double speed (set depending on BAUD)
#else
	UCSR0A &= ~(1<<U2X0); // do not use double speed (set depending on BAUD)
#endif
	UCSR0C = (0<<UMSEL00)|(0<<UMSEL01)|(0<<UCSZ02)|(1<<UCSZ01)|(1<<UCSZ00)|(0<<UPM01)|(0<<UPM00)|(0<<USBS0); // async 8N1 bit data
	UCSR0B = (1<<RXEN0)|(1<<TXEN0); // enable RX and TX
#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
	UCSR0B |= (1<<RXCIE0)|(1<<UDRIE0); // enable RX complete and TX data register empty interrupt
	// reset buffer states
	rx_i = 0;
	rx_used = 0;
	tx_i = 0;
	tx_used = 0;
#else
	UCSR0B &= ~((1<<RXCIE0)|(1<<UDRIE0)); // disable RX complete and TX data register empty interrupt
#endif
}

/* put character on USART stream (blocking) */
void usart_putchar_blocking(char c, FILE *stream)
{
	if (c == '\n') { // add carrier return before line feed. this is recommended for most UART terminals
		usart_putchar_blocking('\r', stream);
	}
#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
	// idle until buffer is empty
	while (tx_used) {
		set_sleep_mode(SLEEP_MODE_IDLE);
		sleep_mode();
	}
#endif
	while (!(UCSR0A&(1<<UDRE0))); // wait for transmit register to empty
	UDR0 = c; // put data in transmit register
}

/* ensure all data has been transmitted */
void usart_flush()
{
#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
	while (tx_used) { // idle until buffer is empty
		set_sleep_mode(SLEEP_MODE_IDLE);
		sleep_mode();
	}
#endif
	while (!(UCSR0A&(1<<TXC0))); // wait for transmission to complete
	UCSR0A |= (1<<TXC0); // clear transmit flag
}

/* get character from USART stream (blocking) */
char usart_getchar(FILE *stream)
{
#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
	// idle until data is available
	while (!rx_used) {
		set_sleep_mode(SLEEP_MODE_IDLE);
		sleep_mode();
	}
	char to_return = rx_buffer[rx_i];
	rx_i = (rx_i+1)%sizeof(rx_buffer); // update used buffer
	rx_used--; // update used buffer
	usart_incoming = rx_used; // update available data
	return to_return;
#else
	while (!(UCSR0A&(1<<RXC0))); // wait until data exists
	return UDR0;
#endif
}

#if defined(USART_INTERRUPT) && (USART_INTERRUPT==1)
ISR(USART_RX_vect) { // USART receive interrupt
	// only save data if there is space in the buffer
	if (rx_used>=sizeof(rx_buffer)) {
		return;
	}
	cli();
	rx_buffer[(rx_i+rx_used)%sizeof(rx_buffer)] = UDR0; // put character in buffer
	rx_used++; // update used buffer
	usart_incoming = rx_used; // update available data
	sei();
}

/* put character on USART stream (non-blocking using a buffer) */
void usart_putchar_nonblocking(char c, FILE *stream)
{
	if (c == '\n') { // add carrier return before line feed. this is recommended for most UART terminals
		usart_putchar_nonblocking('\r', stream);
	}
	if (UCSR0A&(1<<UDRE0)) { // if transmit register is empty immediatly send the data
		UDR0 = c; // put data in transmit register
	} else { // save into buffer
		// idle until buffer has some space
		while (tx_used>=sizeof(tx_buffer)) {
			set_sleep_mode(SLEEP_MODE_IDLE);
			sleep_mode();
		}
		cli();
		tx_buffer[(tx_i+tx_used)%sizeof(tx_buffer)] = c; // put character in buffer
		tx_used++; // update used buffer
		sei();
	}
}

ISR(USART_UDRE_vect) { // USART transmit register interrupt
	if (!tx_used) { // no data in the buffer to transmit
		return;
	}
	UDR0 = tx_buffer[tx_i]; // put data in transmit register
	tx_i = (tx_i+1)%sizeof(rx_buffer); // update location on buffer
	tx_used--; // update used size
}
#endif