Method decompress_firmware_3

src/board_controller/openbci/ganglion.cpp:398–466

}

void Ganglion::decompress_firmware_3 (
    struct GanglionLib::GanglionData *data, float *last_data, double *acceleration, double *package)
{
    int bits_per_num = 0;
    unsigned char package_bits[160] = {0}; // 20 * 8
    for (int i = 0; i < 20; i++)
    {
        uchar_to_bits (data->data[i], package_bits + i * 8);
    }

    // 18 bit compression, sends 17 MSBs + sign bit of 24-bit sample
    if (data->data[0] >= 0 && data->data[0] < 100)
    {
        int last_digit = data->data[0] % 10;
        switch (last_digit)
        {
            // accel data is signed, so we must cast it to signed char
            // swap x and z, and invert z to convert to standard coordinate space.
            case 0:
                acceleration[2] = -accel_scale * (char)data->data[19];
                break;
            case 1:
                acceleration[1] = accel_scale * (char)data->data[19];
                break;
            case 2:
                acceleration[0] = accel_scale * (char)data->data[19];
                break;
            default:
                break;
        }
        bits_per_num = 18;
    }
    else if (data->data[0] >= 100 && data->data[0] < 200)
    {
        bits_per_num = 19;
    }

    // handle compressed data for 18 or 19 bits
    for (int i = 8, counter = 0; i < bits_per_num * 8; i += bits_per_num, counter++)
    {
        if (bits_per_num == 18)
        {
            last_data[counter] = (float)(cast_ganglion_bits_to_int32<18> (package_bits + i) << 6);
        }
        else
        {
            last_data[counter] = (float)(cast_ganglion_bits_to_int32<19> (package_bits + i) << 5);
        }
    }

    // add first encoded package
    package[board_descr["default"]["package_num_channel"].get<int> ()] = data->data[0];
    package[board_descr["default"]["eeg_channels"][0].get<int> ()] = eeg_scale * last_data[0];
    package[board_descr["default"]["eeg_channels"][1].get<int> ()] = eeg_scale * last_data[1];
    package[board_descr["default"]["eeg_channels"][2].get<int> ()] = eeg_scale * last_data[2];
    package[board_descr["default"]["eeg_channels"][3].get<int> ()] = eeg_scale * last_data[3];
    package[board_descr["default"]["accel_channels"][0].get<int> ()] = acceleration[0];
    package[board_descr["default"]["accel_channels"][1].get<int> ()] = acceleration[1];