Using the UHD API for B210

Question

I'm trying to use the C++ UHD API for my B210. I've been following the examples, specifically the rx_samples_to_file and rx_timed_samples to create a receiver. I get an error however, when I'm try to set my gain for the channels.

If I call the program like this " ./uhd_basic --nsamps 2040 --rate 1e6 --freq 91.9e6 --channel 0 --gain 20" I get an error saying "IndexError: multi_usrp: RX channel 18446744073709551615 out of range for configured RX frontends". The part of the code that sets the gain is pretty identical to the examples, so I don't understand why the error appears. My end goal is to be able to replicate a GNU Radio flowgraph in the C++ API, but I'm stuck with this error. Any advice would be appreciated.

#include <uhd/utils/thread.hpp>
#include <uhd/utils/safe_main.hpp>
#include <uhd/usrp/multi_usrp.hpp>
#include <uhd/exception.hpp>
#include <uhd/types/tune_request.hpp>
#include <boost/program_options.hpp>
#include <boost/format.hpp>
#include <boost/thread.hpp>
#include <boost/algorithm/string.hpp>
#include <boost/filesystem.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/process.hpp>
#include <chrono> 
#include <complex>
include <csignal> 
#include <fstream> 
#include <iostream> 
#include <numeric>  
#include <regex> 
#include <Python.h>


using namespace std::literals::chrono_literals;
namespace po = boost::program_options;

std::mutex recv_mutex;

static bool stop_signal_called = false;
static bool overflow_message   = true;

// handler to stop streaming
void sig_int_handler(int)
{
    stop_signal_called = true;
}


int UHD_SAFE_MAIN(int argc, char* argv[])
{
     // variables to be set by po
    std::string args, subdev;
    std::string wire;
    double seconds_in_future;
    size_t total_num_samps;
    double rate, freq, gain;
    std::string channel_list;

    // setup the program options
    po::options_description desc("Allowed options");
    // clang-format off
    desc.add_options()
        ("help", "help message")
        ("args", po::value<std::string>(&args)->default_value(""), "single uhd device address args")
        ("wire", po::value<std::string>(&wire)->default_value(""), "the over the wire type, sc16, sc8, etc")
        ("secs", po::value<double>(&seconds_in_future)->default_value(1.5), "number of seconds in the future to receive")
        ("gain", po::value<double>(&gain), "gain for the RF chain")
        ("nsamps", po::value<size_t>(&total_num_samps)->default_value(10000), "total number of samples to receive")
        ("freq", po::value<double>(&freq)->default_value(0.0), "RF center frequency in Hz")
        ("rate", po::value<double>(&rate)->default_value(100e6/16), "rate of incoming samples")
        ("dilv", "specify to disable inner-loop verbose")
        ("channels", po::value<std::string>(&channel_list)->default_value("0"), "which channel(s) to use (specify \"0\", \"1\", \"0,1\", etc)")
    ;
    // clang-format on
    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, desc), vm);
    po::notify(vm);



    bool verbose = vm.count("dilv") == 0;

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

    // detect which channels to use
    std::vector<std::string> channel_strings;
    std::vector<size_t> channel_nums;
    boost::split(channel_strings, channel_list, boost::is_any_of("\"',"));
    for (size_t ch = 0; ch < channel_strings.size(); ch++) {
        size_t chan = std::stoi(channel_strings[ch]);
        if (chan >= usrp->get_tx_num_channels() or chan >= usrp->get_rx_num_channels()) {
            throw std::runtime_error("Invalid channel(s) specified.");
        } else
            channel_nums.push_back(std::stoi(channel_strings[ch]));
    }

    // set the rx sample rate
    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;

    std::cout << boost::format("Setting device timestamp to 0...") << std::endl;
    usrp->set_time_now(uhd::time_spec_t(0.0));

    // set the center frequency
    if (vm.count("freq")) { // with default of 0.0 this will always be true
        std::cout << boost::format("Setting RX Freq: %f MHz...") % (freq / 1e6) << std::endl;
    }

    //always select the subdevice first, the channel mapping affects the other settings
    std::cout << boost::format("subdev set to: %f") % subdev << std::endl;
    usrp->set_rx_subdev_spec(subdev);
    std::cout << boost::format("Using Device: %s") % usrp->get_pp_string() << std::endl;

    //set the rf gain
    if (vm.count("gain")) {
        std::cout << boost::format("Setting RX Gain: %f dB...") % gain << std::endl;
        usrp->set_rx_gain(gain, uhd::usrp::multi_usrp::ALL_CHANS);
        std::cout << boost::format("Actual RX Gain: %f dB...")
                         % usrp->get_rx_gain(channel_list[0])
                  << std::endl
                  << std::endl;
    }

    // print for debugging
    uhd::dict<std::string, std::string> info = usrp->get_usrp_rx_info();
    std::cout << "#####################################################" << std::endl;
    std::cout << info.get("mboard_name") << std::endl;
    std::cout << usrp->get_rx_num_channels()<< std::endl;
    std::cout << usrp->get_rx_subdev_name(1)<< std::endl;
    std::cout << usrp->get_rx_gain(1)<< std::endl;
    std::cout << usrp->get_rx_antenna() << std::endl;

    // create a receive streamer
    uhd::stream_args_t stream_args("fc32", wire); // complex floats
    stream_args.channels             = channel_nums;
    uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

    // setup streaming
    std::cout << std::endl;
    std::cout << boost::format("Begin streaming %u samples, %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);
    rx_stream->issue_stream_cmd(stream_cmd);

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

    // allocate buffer to receive with samples        
    std::vector<std::complex<float>> buff(rx_stream->get_max_num_samps());
    std::vector<void*> buffs;

    for (size_t ch = 0; ch < rx_stream->get_num_channels(); ch++)
        buffs.push_back(&buff.front()); // same buffer for each channel
    // the first call to recv() will block this many seconds before receiving
    double timeout = seconds_in_future + 0.1; // 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(buffs, buff0.size(), md, timeout, true);
        //size_t num_rx_samps1 = rx_stream->recv(buffs[1], buff.size(), md, timeout, true);

        // 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()));
        }
        ////////////////////////////  Start of DSP Code ///////////////////////////
        // do stuff
            }
        }

        //////////////////////////// End of DSP Code /////////////////////////////
        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;

        num_acc_samps += num_rx_samps;
    }

    if (num_acc_samps < total_num_samps)
        std::cerr << "Receive timeout before all samples received..." << std::endl;

    // finished

    std::cout << std::endl << "Done!" << std::endl << std::endl;
    delete A;
    return EXIT_SUCCESS;
}

Answer 1

I had this problem when using the example rx_samples_to_file function with a b205 mini. I was able to solve it by removing the second argument from usrp->set_rx_gain()

//usrp->set_rx_gain(gain, uhd::usrp::multi_usrp::ALL_CHANS);
usrp->set_rx_gain(gain);