File content as of revision 0:e076052bcffd:

/*
 ******************************************************************************
 * @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;

    _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 recvByte1, recvByte2;

    _error = NO_ERROR;
    _data = msg.data;
    _len = 0;
    _maxLen = msg.maxLen();
    _timeout.attach(callback(this, &ManchesterUART::rxTimeout), _timeout_sec);

    do {
        recvByte1 = _serial.getc();
        if (_error) {
            if (_error != RX_TIMEOUT)
                _timeout.detach();
            msg.len = 0;
            return false;
        }
    } while (recvByte1 != START);    // wait for START pattern
    
    
    while (true) {
        recvByte1 = _serial.getc();
        if (recvByte1 == STOP)
            break;           
        if (_len > _maxLen - 1) {
            _error = BUF_OVERRUN;
            break;
        }
        
        recvByte2 = _serial.getc();
        if (recvByte2 == STOP) {
            _error = ILLEGAL_CODE;
            break;
        }        
        _data[_len++] = (getNibble(recvByte1)) | (getNibble(recvByte2) << 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 & 0b11;
        if (pattern == 0b1)    // 1
            decoded |= (0b01 << 3);
        else
        if (pattern == 0b10)    // 0
            decoded &= ~(0b1 << 3);
        else {
            _error = ILLEGAL_CODE;
            break;
        }
        encoded >>= 2;
    }
    
    return decoded;
}