examples: Remove default --ref and --pps values

This changes the behaviour of the examples in a way that leaving
out the --ref argument will not force it to be 'internal'. Previously,
the following command:

    rx_samples_to_file --args type=xxx,clock_source=external

would still use the internal reference, because the default value for
--ref was internal, and no other value for --ref was provided. Even
worse, the following command:

    rx_samples_to_file --args \
        type=xxx,clock_source=external,time_source=external

might throw errors/warnings, because internal clock source plus external
time source is generally not supported, and the example would force the
clock source to be internal unless `--ref internal` was also provided.

For all cases that `clock_source` or `time_source` were not given as
a device argument, this is a no-op because `internal` is the default
value anyway.

In two examples, this includes minor code changes:
- In rfnoc_radio_loopback, if both --ref and --pps were given, we now
  use set_sync_source() to speed up setting the reference sources. On
  the N310/N300 series in particular, this saves a few seconds at
  initialization over the previous implementation (which set clock and
  time reference separately).
- In test_dboard_coercion, the code would fail without a default value
  for --ref, so we no longer require such a default value.

host/examples/rfnoc_radio_loopback.cpp

@@ -72,8 +72,8 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("rate", po::value<double>(&rate)->default_value(0.0), "Sampling rate")
         ("duration", po::value<double>(&total_time)->default_value(0), "total number of seconds to receive")
         ("int-n", "Tune USRP with integer-N tuning")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "clock reference (internal, external, mimo, gpsdo)")
-        ("pps", po::value<std::string>(&pps)->default_value("internal"), "PPS source (internal, external, mimo, gpsdo)")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, gpsdo, mimo)")
+        ("pps", po::value<std::string>(&pps), "PPS source (internal, external, mimo, gpsdo)")
     ;
     // clang-format on
     po::variables_map vm;
@@ -127,13 +127,16 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
     rx_radio_ctrl->enable_rx_timestamps(rx_timestamps, rx_chan);
 
     // Set time and clock reference
-    if (vm.count("ref")) {
+    if (vm.count("ref") && vm.count("pps")) {
+        for (size_t i = 0; i < graph->get_num_mboards(); ++i) {
+            graph->get_mb_controller(i)->set_sync_source(ref, pps);
+        }
+    } else if (vm.count("ref")) {
         // Lock mboard clocks
         for (size_t i = 0; i < graph->get_num_mboards(); ++i) {
             graph->get_mb_controller(i)->set_clock_source(ref);
         }
-    }
-    if (vm.count("pps")) {
+    } else if (vm.count("pps")) {
         // Lock mboard clocks
         for (size_t i = 0; i < graph->get_num_mboards(); ++i) {
             graph->get_mb_controller(i)->set_time_source(pps);

host/examples/rfnoc_replay_samples_from_file.cpp

@@ -75,7 +75,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("gain", po::value<double>(&gain), "gain for the RF chain")
         ("ant", po::value<std::string>(&ant), "antenna selection")
         ("bw", po::value<double>(&bw), "analog front-end filter bandwidth in Hz")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, mimo, gpsdo)")
     ;
     // clang-format on
     po::variables_map vm;

host/examples/rx_ascii_art_dft.cpp

@@ -48,7 +48,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("frame-rate", po::value<double>(&frame_rate)->default_value(5), "frame rate of the display (fps)")
         ("ref-lvl", po::value<float>(&ref_lvl)->default_value(0), "reference level for the display (dB)")
         ("dyn-rng", po::value<float>(&dyn_rng)->default_value(60), "dynamic range for the display (dB)")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "reference source (internal, external, gpsdo, mimo)")
         ("step", po::value<double>(&step)->default_value(1e6), "tuning step for rate/bw/freq")
         ("show-controls", po::value<bool>(&show_controls)->default_value(true), "show the keyboard controls")
         ("int-n", "tune USRP with integer-N tuning")

host/examples/rx_samples_to_file.cpp

@@ -379,7 +379,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("subdev", po::value<std::string>(&subdev), "subdevice specification")
         ("channels,channel", po::value<std::string>(&channels)->default_value("0"), "which channel(s) to use (specify \"0\", \"1\", \"0,1\", etc)")
         ("bw", po::value<double>(&bw), "analog frontend filter bandwidth in Hz")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "reference source (internal, external, mimo)")
         ("wirefmt", po::value<std::string>(&wirefmt)->default_value("sc16"), "wire format (sc8, sc16 or s16)")
         ("setup", po::value<double>(&setup_time)->default_value(1.0), "seconds of setup time")
         ("progress", "periodically display short-term bandwidth")

host/examples/rx_samples_to_udp.cpp

@@ -43,7 +43,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("bw", po::value<double>(&bw), "analog frontend filter bandwidth in Hz")
         ("port", po::value<std::string>(&port)->default_value("7124"), "server udp port")
         ("addr", po::value<std::string>(&addr)->default_value("192.168.1.10"), "resolvable server address")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, mimo, gpsdo)")
         ("int-n", "tune USRP with integer-N tuning")
     ;
     // clang-format on

host/examples/test_dboard_coercion.cpp

@@ -377,7 +377,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("gain-step", po::value<double>(&gain_step)->default_value(1.0), "Specify the delta between gain scans")
         ("tx", "Specify to test TX frequency and gain coercion")
         ("rx", "Specify to test RX frequency and gain coercion")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "Waveform type: internal, external, or mimo")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, mimo, gpsdo)")
         ("no-tx-gain", "Do not test TX gain")
         ("no-rx-gain", "Do not test RX gain")
         ("verbose", "Output every frequency and gain check instead of just final summary")
@@ -424,7 +424,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
                         and (usrp->get_rx_gain_range().stop() > 0);
     bool verbose = vm.count("verbose") > 0;
 
-    if (ref != "internal" and ref != "external" and ref != "mimo") {
+    if (!ref.empty() and ref != "internal" and ref != "external" and ref != "mimo") {
         std::cout << desc << std::endl;
         std::cout << "REF must equal internal, external, or mimo." << std::endl;
         return EXIT_FAILURE;
@@ -474,7 +474,10 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
     }
 
     // Setting clock source
-    usrp->set_clock_source(ref);
+    if (!ref.empty()) {
+        usrp->set_clock_source(ref);
+    }
+    ref = usrp->get_clock_source(0);
     std::this_thread::sleep_for(std::chrono::seconds(1));
 
     std::vector<std::string> sensor_names = usrp->get_mboard_sensor_names(0);

host/examples/tx_bursts.cpp

@@ -50,7 +50,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("channels", po::value<std::string>(&channel_list)->default_value("0"), "which channel(s) to use (specify \"0\", \"1\", \"0,1\", etc")
         ("int-n", "tune USRP with integer-n tuning")
         ("subdev", po::value<std::string>(&subdev), "subdevice specification")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "reference source (internal, external, gpsdo, mimo)")
         ("lo-offset", po::value<double>(&lo_offset)->default_value(0.0),
             "Offset for frontend LO in Hz (optional)")
         ("bw", po::value<double>(&bw), "analog frontend filter bandwidth in Hz")

host/examples/tx_samples_from_file.cpp

@@ -80,7 +80,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("ant", po::value<std::string>(&ant), "antenna selection")
         ("subdev", po::value<std::string>(&subdev), "subdevice specification")
         ("bw", po::value<double>(&bw), "analog frontend filter bandwidth in Hz")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "reference source (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, mimo, gpsdo)")
         ("wirefmt", po::value<std::string>(&wirefmt)->default_value("sc16"), "wire format (sc8 or sc16)")
         ("delay", po::value<double>(&delay)->default_value(0.0), "specify a delay between repeated transmission of file (in seconds)")
         ("channel", po::value<std::string>(&channel)->default_value("0"), "which channel to use")

host/examples/tx_waveforms.cpp

@@ -65,7 +65,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("bw", po::value<double>(&bw), "analog frontend filter bandwidth in Hz")
         ("wave-type", po::value<std::string>(&wave_type)->default_value("CONST"), "waveform type (CONST, SQUARE, RAMP, SINE)")
         ("wave-freq", po::value<double>(&wave_freq)->default_value(0), "waveform frequency in Hz")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "clock reference (internal, external, mimo, gpsdo)")
+        ("ref", po::value<std::string>(&ref), "clock reference (internal, external, mimo, gpsdo)")
         ("pps", po::value<std::string>(&pps), "PPS source (internal, external, mimo, gpsdo)")
         ("otw", po::value<std::string>(&otw)->default_value("sc16"), "specify the over-the-wire sample mode")
         ("channels", po::value<std::string>(&channel_list)->default_value("0"), "which channels to use (specify \"0\", \"1\", \"0,1\", etc)")

host/examples/txrx_loopback_to_file.cpp

@@ -230,7 +230,7 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
         ("rx-bw", po::value<double>(&rx_bw), "analog receive filter bandwidth in Hz")
         ("wave-type", po::value<std::string>(&wave_type)->default_value("CONST"), "waveform type (CONST, SQUARE, RAMP, SINE)")
         ("wave-freq", po::value<double>(&wave_freq)->default_value(0), "waveform frequency in Hz")
-        ("ref", po::value<std::string>(&ref)->default_value("internal"), "clock reference (internal, external, mimo)")
+        ("ref", po::value<std::string>(&ref), "reference source (internal, external, gpsdo, mimo)")
         ("otw", po::value<std::string>(&otw)->default_value("sc16"), "specify the over-the-wire sample mode")
         ("tx-channels", po::value<std::string>(&tx_channels)->default_value("0"), "which TX channel(s) to use (specify \"0\", \"1\", \"0,1\", etc)")
         ("rx-channels", po::value<std::string>(&rx_channels)->default_value("0"), "which RX channel(s) to use (specify \"0\", \"1\", \"0,1\", etc)")