Tooltron

/********

 * This file is part of Tooltron.

 *

 * Tooltron is free software: you can redistribute it and/or modify

 * it under the terms of the Lesser GNU General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * Tooltron 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

 * Lesser GNU General Public License for more details.

 * You should have received a copy of the Lesser GNU General Public License

 * along with Tooltron.  If not, see <http://www.gnu.org/licenses/>.

 *

 * Copyright 2009 Kevin Woo <kwoo@2ndt.com>

 *

 ********/

/** 

 * @file rs485_poll.h

 * @brief Implements rs485 using the uart hardware module.

 *

 * See rs485_sw.c for more information

 *

 * @author Kevin Woo (kwoo)

 */

#ifndef _RS485_SW_H

#define _RS485_SW_H

#include <avr/io.h>

#include <avr/interrupt.h>

#include <stdint.h>

#define RS485_TX_OFF 0

#define RS485_TX_ON 1

/** @brief RX Pin for the RS485 */

#define RX		_BV(PORTD0)

/** @brief TX Pin for the RS485 */

#define TX		_BV(PORTD1)

/** @brief TX Enable Pin for the RS485 */

#define TX_EN	_BV(PORTD5)

void rs485_init(uint16_t baud);

int8_t rs485_get_byte(uint8_t *output_byte);

void rs485_send_byte(uint8_t data);

static void rs485_toggle_transmit(uint8_t state);

#endif

/**

 * @file rs485_poll.c

 * @brief RS485 implementation using UART hardware module and polling

 *

 * This uses the AVR's UART hardware module but does polling rather than

 * interrupts to handle transmission and receiving. It assumes the use

 * of an external UART<->RS485 converter with the RXEN and TXEN pins tied

 * together.

 *

 * @author Kevin Woo <kwoo@2ndt.com>

 **/

/**

 * @brief Initializes the uart

 * @param baud The baudrate. Use the definitions in rs485_sw.h

 */

void rs485_init(uint16_t baud) {

	// Set baud rate

	UBRRH = (uint8_t)(baud>>8);

	UBRRL = (uint8_t)baud;

	// Enable RX/TX

	UCSRB = _BV(RXEN) | _BV(TXEN);

	// Enable the TXEN pin as output

	DDRD |= TX_EN;

    rs485_toggle_transmit(RS485_TX_OFF);

}

/**

 * @brief Non-blocking receive

 * 

 * Receives a byte from the UART if one exists. If none exist the function

 * will return an error code immediately. If there is a byte to receive,

 * it will be placed in a passed in pointer and return.

 *

 * @pre The RS485 TXEN line is not enabled

 * @param output_byte Byte to store the received message

 * @return 0 on success, negative if there is nothing to receive

 */

int8_t rs485_get_byte(uint8_t *output_byte) {

    if (UCSRA & _BV(RXC)) {

        *output_byte = UDR;

        return 0;

    } else {

        return -1;

    }

}

/**

 * @brief Blocking send

 *

 * Sends the byte in data onto the network. The function will block until

 * the transmit is complete so that the transmit enable line can be toggled

 * safely. It will wait until any current transmission completes before sending

 * and will wait until it completes before returning. The RS485 TX enable line

 * is automatically toggled by the function and should not be done so

 * outside the function.

 *

 * @param data The byte to send

 */

void rs485_send_byte(uint8_t data) {

	//Waits until current transmit is done

    while (!(UCSRA & _BV(UDRE)));

    // Enable writes and send

	rs485_toggle_transmit(RS485_TX_ON);

    UDR = data;

    // Waits until the transmit is done

    while(!(UCSRA & _BV(TXC)));

    rs485_toggle_transmit(RS485_TX_OFF);

    UCSRA |= _BV(TXC);

	return;

}

/**

 * @brief Toggles the RS485 TXEN line

 *

 * This function should not be used outside of this file

 *

 * @param state Whether to turn the pin on or off

 */

void rs485_toggle_transmit(uint8_t state) {

	if (state == RS485_TX_ON) {

		PORTD |= TX_EN;

	} else {

		PORTD &= ~TX_EN;

	}

}