mayhem-firmware/firmware/common/manchester.cpp

/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * 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 2, 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; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "manchester.hpp"

#include "string_format.hpp"

size_t ManchesterBase::symbols_count() const {
    return packet.size() / 2;
}

DecodedSymbol ManchesterDecoder::operator[](const size_t index) const {
    const size_t encoded_index = index * 2;
    if ((encoded_index + 1) < packet.size()) {
        const auto value = packet[encoded_index + sense];
        const auto error = packet[encoded_index + 0] == packet[encoded_index + 1];
        return {value, error};
    } else {
        return {0, 1};
    }
}

DecodedSymbol BiphaseMDecoder::operator[](const size_t index) const {
    const size_t encoded_index = index * 2;
    if ((encoded_index + 1) < packet.size()) {
        const auto value = packet[encoded_index + 0] != packet[encoded_index + 1];
        const uint_fast8_t error = encoded_index ? (packet[encoded_index - 1] == packet[encoded_index + 0]) : 0;
        return {value, error};
    } else {
        return {0, 1};
    }
}

FormattedSymbols format_symbols(
    const ManchesterBase& decoder) {
    const size_t payload_length_decoded = decoder.symbols_count();
    const size_t payload_length_hex_characters = (payload_length_decoded + 3) / 4;
    const size_t payload_length_symbols_rounded = payload_length_hex_characters * 4;

    std::string hex_data;
    std::string hex_error;
    hex_data.reserve(payload_length_hex_characters);
    hex_error.reserve(payload_length_hex_characters);

    uint_fast8_t data = 0;
    uint_fast8_t error = 0;
    for (size_t i = 0; i < payload_length_symbols_rounded; i++) {
        const auto symbol = decoder[i];

        data <<= 1;
        data |= symbol.value;

        error <<= 1;
        error |= symbol.error;

        if ((i & 3) == 3) {
            hex_data += to_string_hex(data & 0xf, 1);
            hex_error += to_string_hex(error & 0xf, 1);
        }
    }

    return {hex_data, hex_error};
}

void manchester_encode(uint8_t* dest, uint8_t* src, const size_t length, const size_t sense) {
    uint8_t part = sense ? 0 : 0xFF;

    for (size_t c = 0; c < length; c++) {
        if ((src[c >> 3] << (c & 7)) & 0x80) {
            *(dest++) = part;
            *(dest++) = ~part;
        } else {
            *(dest++) = ~part;
            *(dest++) = part;
        }
    }
}