Tooltron

/**

 * @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>

 **/

#include <rs485_poll.h>

static void rs485_toggle_transmit(uint8_t state);

/**

 * @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

 */

static void rs485_toggle_transmit(uint8_t state) {

        if (state == RS485_TX_ON) {

                PORTD |= TX_EN;

        } else {

                PORTD &= ~TX_EN;

        }

}