File content as of revision 2:8cb6a0a77e56:

/*
 ******************************************************************************
 * @file    ManchesterUART.cpp
 * @author  Zoltan Hudak
 * @version
 * @date    2017-Nov-22
 * @brief   Manchester code over UART for mbed
 ******************************************************************************
 * @attention
 *
 * <h2><center>&copy; COPYRIGHT(c) 2017 Zoltan Hudak <hudakz@outlook.com>
 *
 * All rights reserved.

 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/>.
 */
/*
 * This library implements Manchester code using UART serial connection. Each
 * data byte is encoded into two bytes representing two nibbles of the original
 * data byte. These two bytes are then sent over UART serial link connection.
 * The receiver reconstructs the original data byte from the two bytes received.
 * A start and stop pattern are sent to signify the begin and end of a message.
 *
 * The library is based on the article published by Adrian Mills:
 * http://www.quickbuilder.co.uk/qb/articles/Manchester_encoding_using_RS232.pdf
 */
#include "ManchesterUART.h"
#include "ManchesterMsg.h"

/**
 * @brief   Transmits message
 * @note
 * @param   msg Message to transmit
 * @retval
 */
void ManchesterUART::transmit(ManchesterMsg& msg)
{
    _data = msg.data;
    _len = msg.len;

    for (uint8_t i = 0; i < _preamble; i++)
        _serial.putc(START);
    for (uint32_t i = 0; i < _len; i++)
    {
        transmitByte(_data[i]);
    }

    _serial.putc(STOP);
}

/**
 * @brief   Transmits a byte
 * @note
 * @param   data The byte to transmit
 * @retval
 */
void ManchesterUART::transmitByte(uint8_t data)
{
    uint8_t encoded;

    for (uint8_t i = 0; i < 2; i++)
    {
        encoded = 0;                    // manchester encoded byte
        for (uint8_t j = 0; j < 4; j++)
        {
            encoded >>= 2;
            if (data & 0b00000001)
                encoded |= 0b01000000;  // 1->0
            else
                encoded |= 0b10000000;  // 0->1
            data >>= 1;
        }

        _serial.putc(encoded);
    }
}

/**
 * @brief   Receives message
 * @note    Waits until a message is received or error occured
 * @param   msg   Container to store the received message in
 * @retval  true  On success
 *          false Otherwise
 */
bool ManchesterUART::receive(ManchesterMsg& msg)
{
    uint8_t byte1, byte2;
    bool    byte1Received;
    
    _error = NO_ERROR;
    _data = msg.data;
    _len = 0;
    _maxLen = msg.maxLen();
    
    if (!_serial.readable())
        return false;

    _timeout.attach(callback(this, &ManchesterUART::rxTimeout), _rxTimeout);
    
    //
    // wait for START pattern
    do {
        byte1 = _serial.getc();
        if (_error)
        {
            if (_error != RX_TIMEOUT)
                _timeout.detach();
            msg.len = 0;
            return false;
        }
    } while (byte1 != START);
    //
    // read START pattern
    do {
        byte1 = _serial.getc();
        if (_error)
        {
            if (_error != RX_TIMEOUT)
                _timeout.detach();
            msg.len = 0;
            return false;
        }
    } while (byte1 == START);

    byte1Received = true;   // byte1 available from the loop above

    while (true)
    {
        if (byte1Received)
            byte1Received = false;
        else
        {
            byte1 = _serial.getc();
            if (byte1 == STOP)
                break;
            if (_len > _maxLen - 1)
            {
                _error = BUF_OVERRUN;
                break;
            }
        }

        byte2 = _serial.getc();
        if (byte2 == STOP)
        {
            _error = ILLEGAL_CODE;
            break;
        }

        _data[_len++] = (getNibble(byte1)) | (getNibble(byte2) << 4);
        if (_error)
            break;
    }

    if (_error != RX_TIMEOUT)
        _timeout.detach();

    if (_error)
    {
        msg.len = 0;
        return false;
    }
    else
    {
        msg.len = _len;
        return true;
    }
}

/**
 * @brief   ISR handling 'reception timeout'
 * @note    Called when receiving a message takes longer than limit.
 *          Signals 'timeout error' by setting error flag.
 * @param
 * @retval
 */
void ManchesterUART::rxTimeout(void)
{
    _timeout.detach();
    _error = RX_TIMEOUT;
}

/**
 * @brief   Gets a nibble of received byte
 * @note    Checks for illegal codes/patterns
 * @param   nibble  A byte received over UART (Manchester encoded nibble)
 * @retval  Decoded nibble
 */
uint8_t ManchesterUART::getNibble(uint8_t encoded)
{
    uint8_t decoded, pattern;

    decoded = 0;
    for (int i = 0; i < 4; i++)
    {
        decoded >>= 1;
        pattern = encoded & 0b000011;
        if (pattern == 0b00000001)  // 1
            decoded |= (0b00000001 << 3);
        else
        if (pattern == 0b00000010)  // 0
            decoded &= ~(0b00000001 << 3);
        else
        {
            _error = ILLEGAL_CODE;
            break;
        }

        encoded >>= 2;
    }

    return decoded;
}