Getting Started with UHD and C++

Application Note Number

AN-204

Revision History

Date	Author	Details
2016-05-01	Neel Pandeya Nate Temple	Initial creation

Abstract

This AN explains how to write and build C++ programs that use the UHD API.

Overview

This Application Note will walk through building a basic C++ program with UHD. This program will initialize, configure the USRP device, set the sample rate, frequency, gain, bandwidth, and select the antenna.

UHD Manual

The UHD Manual is hosted at http://files.ettus.com/manual/index.html and provides information on how to use the USRP devices and how to use the UHD API to connect to them through your own software. The manual is split into two parts: The device manual, and the UHD/API manual. The first part describes details of Ettus Research devices, motherboards and daughterboards, as well as aspects of using UHD. The second is meant for developers writing UHD-based applications, and includes descriptions of the API, sorted by namespaces, classes, and files.

Including Header Files

    #include <uhd/utils/thread_priority.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 <iostream>

UHD_SAFE_MAIN()

Defines a safe wrapper that places a catch-all around main. If an exception is thrown, it prints to stderr and returns.

    int UHD_SAFE_MAIN(int argc, char *argv[]) {
        ...
    }

set_thread_priority_safe()

Set the scheduling priority on the current thread. Same as set_thread_priority but does not throw on failure.

    uhd::set_thread_priority_safe();

Create Variables

    std::string device_args("addr=192.168.10.2");
    std::string subdev("A:0");
    std::string ant("TX/RX");
    std::string ref("internal");

    double rate(1e6);
    double freq(915e6);
    double gain(10);
    double bw(1e6);

Creating a USRP Object

Make a new multi usrp from the device address.

    uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(device_args);

Setting Motherboard Clocks

    // Lock mboard clocks
    std::cout << boost::format("Lock mboard clocks: %f") % ref << std::endl;
    usrp->set_clock_source(ref);

Selecting Sub Device

    //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;

Setting Sample Rate

    //set the sample rate
    if (rate <= 0.0) {
        std::cerr << "Please specify a valid sample rate" << std::endl;
        return ~0;
    }

    // set 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;

Setting Center Frequency

    // set freq
    std::cout << boost::format("Setting RX Freq: %f MHz...") % (freq / 1e6) << std::endl;
    uhd::tune_request_t tune_request(freq);
    usrp->set_rx_freq(tune_request);
    std::cout << boost::format("Actual RX Freq: %f MHz...") % (usrp->get_rx_freq() / 1e6) << std::endl << std::endl;

Setting RF Gain

    // set the rf gain
    std::cout << boost::format("Setting RX Gain: %f dB...") % gain << std::endl;
    usrp->set_rx_gain(gain);
    std::cout << boost::format("Actual RX Gain: %f dB...") % usrp->get_rx_gain() << std::endl << std::endl;

Setting IF Filter Bandwidth

    // set the IF filter bandwidth
    std::cout << boost::format("Setting RX Bandwidth: %f MHz...") % (bw / 1e6) << std::endl;
    usrp->set_rx_bandwidth(bw);
    std::cout << boost::format("Actual RX Bandwidth: %f MHz...") % (usrp->get_rx_bandwidth() / 1e6) << std::endl << std::endl;

Selecting Antenna

    std::cout << boost::format("Setting RX Antenna: %s") % ant << std::endl;
    usrp->set_rx_antenna(ant);
    std::cout << boost::format("Actual RX Antenna: %s") % usrp->get_rx_antenna() << std::endl << std::endl;

Exiting

    return EXIT_SUCCESS;

Full Example

#include <uhd/utils/thread_priority.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 <iostream>

int UHD_SAFE_MAIN(int argc, char *argv[]) {
    uhd::set_thread_priority_safe();

    std::string device_args("addr=192.168.10.2");
    std::string subdev("A:0");
    std::string ant("TX/RX");
    std::string ref("internal");

    double rate(1e6);
    double freq(915e6);
    double gain(10);
    double bw(1e6);

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

    // Lock mboard clocks
    std::cout << boost::format("Lock mboard clocks: %f") % ref << std::endl;
    usrp->set_clock_source(ref);
    
    //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 sample rate
    if (rate <= 0.0) {
        std::cerr << "Please specify a valid sample rate" << std::endl;
        return ~0;
    }

    // set 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;

    // set freq
    std::cout << boost::format("Setting RX Freq: %f MHz...") % (freq / 1e6) << std::endl;
    uhd::tune_request_t tune_request(freq);
    usrp->set_rx_freq(tune_request);
    std::cout << boost::format("Actual RX Freq: %f MHz...") % (usrp->get_rx_freq() / 1e6) << std::endl << std::endl;

    // set the rf gain
    std::cout << boost::format("Setting RX Gain: %f dB...") % gain << std::endl;
    usrp->set_rx_gain(gain);
    std::cout << boost::format("Actual RX Gain: %f dB...") % usrp->get_rx_gain() << std::endl << std::endl;

    // set the IF filter bandwidth
    std::cout << boost::format("Setting RX Bandwidth: %f MHz...") % (bw / 1e6) << std::endl;
    usrp->set_rx_bandwidth(bw);
    std::cout << boost::format("Actual RX Bandwidth: %f MHz...") % (usrp->get_rx_bandwidth() / 1e6) << std::endl << std::endl;

    // set the antenna
    std::cout << boost::format("Setting RX Antenna: %s") % ant << std::endl;
    usrp->set_rx_antenna(ant);
    std::cout << boost::format("Actual RX Antenna: %s") % usrp->get_rx_antenna() << std::endl << std::endl;

    return EXIT_SUCCESS;
}

CMake

Use the uhd/host/examples/init_usrp/CMakeLists.txt file as template - Add the names of your C++ source files to the add_executable(...) section - Put both modified CMakeLists.txt file and C++ file into an empty folder

Compile and Install

- Create a “build” folder and invoke CMake the usual way:

   mkdir build
   cd build
   cmake ../
   make

Running the Application

[example output]

Additional Example Programs

- Github UHD