Method decodeDataRecord

arch/apple2/decoder.cc:122–172

    }

    void decodeDataRecord() override
    {
        /* Check ID. */

        if (readRaw24() != APPLE2_DATA_RECORD)
            return;

        // Sometimes there's a 1-bit gap between APPLE2_DATA_RECORD and
        // the data itself.  This has been seen on real world disks
        // such as the Apple II Operating System Kit from Apple2Online.
        // However, I haven't seen it described in any of the various
        // references.
        //
        // This extra '0' bit would not affect the real disk interface,
        // as it was a '1' reaching the top bit of a shift register
        // that triggered a byte to be available, but it affects the
        // way the data is read here.
        //
        // While the floppies tested only seemed to need this applied
        // to the first byte of the data record, applying it
        // consistently to all of them doesn't seem to hurt, and
        // simplifies the code.

        /* Read and decode data. */

        auto readApple8 = [&]()
        {
            auto result = 0;
            while ((result & 0x80) == 0)
            {
                auto b = readRawBits(1);
                if (b.empty())
                    break;
                result = (result << 1) | b[0];
            }
            return result;
        };

        constexpr unsigned recordLength = APPLE2_ENCODED_SECTOR_LENGTH + 2;
        uint8_t bytes[recordLength];
        for (auto& byte : bytes)
        {
            byte = readApple8();
        }

        // Upgrade the sector from MISSING to BAD_CHECKSUM.
        // If decode_crazy_data succeeds, it upgrades the sector to
        // OK.
        _sector->status = Sector::BAD_CHECKSUM;
        _sector->data = decode_crazy_data(&bytes[0], _sector->status);
    }
};

std::unique_ptr<Decoder> createApple2Decoder(const DecoderProto& config)