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)&buffs[0].front(),num_rx_samps

//variables to be set by po
std::string args, sync, subdev, channel_list,file,file0,file1;
double seconds_in_future, freq;
size_t total_num_samps;
double rate,gain,tx_gain;
std::ofstream outfile,outfile2;

//setup the program options
po::options_description desc("Allowed options");
desc.add_options()
    ("help", "help message")
    ("args", po::value<std::string>(&args)->default_value(""), "single uhd device address args")
    ("file", po::value<std::string>(&file)->default_value("measure0-1"), "name of the file to write binary samples to")
    ("secs", po::value<double>(&seconds_in_future)->default_value(1.0), "number of seconds in the future to receive")
    ("nsamps", po::value<size_t>(&total_num_samps)->default_value(10000), "total number of samples to receive")
    ("rate", po::value<double>(&rate)->default_value(8e6), "rate of incoming samples")
    ("sync", po::value<std::string>(&sync)->default_value("b210"), "synchronization method: now, pps, mimo")
    ("freq", po::value<double>(&freq)->default_value(800e6), "RF center frequency in Hz")
    ("gain", po::value<double>(&gain), "gain for the RF chain")
    ("tx-gain", po::value<double>(&tx_gain), "gain for the TX in calibration Mode")
    ("subdev", po::value<std::string>(&subdev), "subdev spec (homogeneous across motherboards)")
    ("v", "specify to enable inner-loop verbose")
    ("calc","specify to enable transmitting and recording of calibration data")
    ("channels", po::value<std::string>(&channel_list)->default_value("0"), "which channel(s) to use (specify \"0\", \"1\", \"0,1\", etc)")
;
po::variables_map vm;
po::store(po::parse_command_line(argc, argv, desc), vm);
po::notify(vm);

//print the help message
if (vm.count("help")){
    std::cout << boost::format("UHD RX Multi Samples %s") % desc << std::endl;
    std::cout <<
    "    This is a demonstration of how to receive aligned data from multiple channels.\n"
    "    This example can receive from multiple DSPs, multiple motherboards, or both.\n"
    "    The MIMO cable or PPS can be used to synchronize the configuration. See --sync\n"
    "\n"
    "    Specify --subdev to select multiple channels per motherboard.\n"
    "      Ex: --subdev=\"0:A 0:B\" to get 2 channels on a Basic RX.\n"
    "\n"
    "    Specify --args to select multiple motherboards in a configuration.\n"
    "      Ex: --args=\"addr0=192.168.10.2, addr1=192.168.10.3\"\n"
    << std::endl;
    return ~0;
}

bool verbose = vm.count("v") == 1;
bool calibration = vm.count("calc") == 1;


/**************** RX Init *************************************************/
//create a usrp device
std::cout << std::endl;
std::cout << boost::format("Creating the usrp device with: %s...") % args << std::endl;
uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(args);

usrp->set_master_clock_rate(30e6); //less then 30.72e6 //Möglichkeit 1: Variable Clock-Rate
//always select the subdevice first, the channel mapping affects the other settings
if (vm.count("subdev")){
    uhd::usrp::subdev_spec_t subdevClass = subdev;
    std::cout << subdevClass.to_pp_string() << std::endl;
    usrp->set_rx_subdev_spec(subdevClass); //sets across all mboards
}

std::cout << boost::format("Using Device: %s") % usrp->get_pp_string() << std::endl;

//set the rx sample rate (sets across all channels)
std::cout << boost::format("Setting RX Rate: %f Msps... ") % (rate/1e6) << std::endl;
usrp->set_rx_rate(rate);
std::cout << boost::format("Actual RX Rate: %f Msps...") % (usrp->get_rx_rate()/1e6) << std::endl << std::endl;

//set center Frequency
std::cout << boost::format("Setting RX Freq: %f MHz...") % (freq/1e6) << std::endl;
uhd::tune_request_t tune_request(freq);
for(size_t i=0;i<usrp->get_rx_num_channels();i++)
    usrp->set_rx_freq(tune_request,i);
std::cout << boost::format("Actual RX Freq: %f MHz...") % (usrp->get_rx_freq(1)/1e6) << std::endl << std::endl;

//set the rf gain
if (vm.count("gain")){
    for(size_t i=0;i<usrp->get_rx_num_channels();i++){
        std::cout << boost::format("Setting RX Gain for Channel %d: %f dB...") % i % gain << std::endl;
        usrp->set_rx_gain(gain,i);
        std::cout << boost::format("Actual RX Gain: %f dB...") % usrp->get_rx_gain() << std::endl << std::endl;
    }
}

//open files to write
if(calibration) file+=".calc"; //Kalibrierdaten mit Endung .calc
else    file+=".dat";   //Messdaten mit Endung.dat
file0 = file;
file1 = file;
file0 += "0";
file1 += "1";

outfile.open(file0.c_str(), std::ofstream::binary);
if(usrp->get_rx_num_channels()>1){
    outfile2.open(file1.c_str(),std::ofstream::binary);
}


/**************** Recieve Start ******************************************/
//create a receive streamer
//linearly map channels (index0 = channel0, index1 = channel1, ...)
uhd::stream_args_t stream_args("sc16"); //complex short

//stream_args.channels = channel_nums;
for (size_t i = 0; i < usrp->get_rx_num_channels(); i++)
    stream_args.channels.push_back(i);
uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

//setup streaming
std::cout << std::endl;
std::cout << boost::format(
    "Begin receiving of %u samples. Start in %f seconds in the future..."
) % total_num_samps % seconds_in_future << std::endl;
uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
stream_cmd.num_samps = total_num_samps;
stream_cmd.stream_now = false;
stream_cmd.time_spec = uhd::time_spec_t(seconds_in_future) + usrp->get_time_now();
rx_stream->issue_stream_cmd(stream_cmd); //tells all channels to stream

//meta-data will be filled in by recv()
uhd::rx_metadata_t md;

//allocate buffers to receive with samples (one buffer per channel)
const size_t samps_per_buff = rx_stream->get_max_num_samps();
std::vector<std::vector<std::complex<short> > > buffs(
    usrp->get_rx_num_channels(), std::vector<std::complex<short> >(samps_per_buff)
);

//create a vector of pointers to point to each of the channel buffers
std::vector<std::complex<short> *> buff_ptrs;
for (size_t i = 0; i < buffs.size(); i++) buff_ptrs.push_back(&buffs[i].front());

//the first call to recv() will block this many seconds before receiving
double timeout = seconds_in_future + 1; //timeout (delay before receive + padding)

size_t num_acc_samps = 0; //number of accumulated samples
while(num_acc_samps < total_num_samps){
    //receive a single packet
    size_t num_rx_samps = rx_stream->recv(
        buff_ptrs, samps_per_buff, md, timeout
    );

    //use a small timeout for subsequent packets
    timeout = 0.1;

    //handle the error code
    if (md.error_code == uhd::rx_metadata_t::ERROR_CODE_TIMEOUT) break;
    if (md.error_code != uhd::rx_metadata_t::ERROR_CODE_NONE){
        throw std::runtime_error(str(boost::format(
            "Receiver error %s"
        ) % md.strerror()));
    }

    if(verbose) std::cout << boost::format(
        "Received packet: %u samples, %u full secs, %f frac secs"
    ) % num_rx_samps % md.time_spec.get_full_secs() % md.time_spec.get_frac_secs() << std::endl;

    //Schreiben der gelesenen Werte in die Dateien
    if(outfile.is_open())
        outfile.write((const char *)&buffs[0].front(),num_rx_samps*sizeof(buffs[0].front()));
    if(outfile2.is_open())
        outfile2.write((const char *)&buffs[1].front(),num_rx_samps*sizeof(buffs[1][0]));

    num_acc_samps += num_rx_samps;
}

if (num_acc_samps < total_num_samps) std::cerr << "Receive timeout before all samples received..." << std::endl;
/**************************** Recieve End *******************************************************/
if(outfile.is_open())
    outfile.close();
if(outfile2.is_open())
    outfile2.close();

//finished
std::cout << std::endl << "Done! Mine" << std::endl << std::endl;

return EXIT_SUCCESS;

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Phase Offset between USRP-B210 Channels