Possible final fix for gqrx-sdr#1004

Partially reverting 8b4c2ef and fixing
DSP restart failure in MainWindow::on_actionIoConfig_triggered allows to
select different device/change sample rate/bandwidth/or other device
options without DSP freeze and device open failure.

Work around GNU Radio bug #3184

Resetting shared_ptr is not enough to close the device.
We have to switch to some other dummy osmosdr source, start the
top_block, then stop it and disconnect dummy source to really close the device.
This may fix some hackrf glitches (at least switching bias tee on the fly) too.

Fix white waterfall and no sound after playing back bad IQ file.

Workaround gnuradio blocks state corruption after device change by recreating dc_corr
(fixes white waterfall and no sound) and resetting the demod (fixes corrupted sound).
It looks like sometimes demodulators are not happy with bad samles too.
We should recreate the graph, temporarily switching out current
demodulator to prevent bad behavior.

src/applications/gqrx/mainwindow.cpp

@@ -1857,7 +1857,9 @@ int MainWindow::on_actionIoConfig_triggered()
 
     if (confres == QDialog::Accepted)
     {
-        if (ui->actionDSP->isChecked())
+        bool dsp_running = ui->actionDSP->isChecked();
+
+        if (dsp_running)
             // suspend DSP while we reload settings
             on_actionDSP_triggered(false);
 
@@ -1866,7 +1868,7 @@ int MainWindow::on_actionIoConfig_triggered()
         storeSession();
         loadConfig(m_settings->fileName(), false, false);
 
-        if (ui->actionDSP->isChecked())
+        if (dsp_running)
             // restsart DSP
             on_actionDSP_triggered(true);
     }

src/applications/gqrx/receiver.cpp

@@ -180,14 +180,29 @@ void receiver::stop()
  */
 void receiver::set_input_device(const std::string device)
 {
-    qDebug() << "Set input device:";
-    qDebug() << "  old:" << input_devstr.c_str();
-    qDebug() << "  new:" << device.c_str();
-
     std::string error = "";
 
     if (device.empty())
         return;
+    if (input_devstr.compare(device) == 0)
+    {
+#ifndef QT_NO_DEBUG_OUTPUT
+        qDebug() << "No change in input device:";
+        qDebug() << "  old: " << input_devstr.c_str();
+        qDebug() << "  new: " << device.c_str();
+#endif
+        return;
+    }
+    else
+    {
+#ifndef QT_NO_DEBUG_OUTPUT
+        qDebug() << "Set input device:";
+        qDebug() << "  old:" << input_devstr.c_str();
+        qDebug() << "  new:" << device.c_str();
+#endif
+    }
+
+
 
     input_devstr = device;
 
@@ -208,7 +223,18 @@ void receiver::set_input_device(const std::string device)
         tb->disconnect(src, 0, iq_swap, 0);
     }
 
+#if GNURADIO_VERSION < 0x030802
+    //Work around GNU Radio bug #3184
+    //temporarily connect dummy source to ensure that previous device is closed
+    src = osmosdr::source::make("file="+escape_filename(get_zero_file())+",freq=428e6,rate=96000,repeat=true,throttle=true");
+    tb->connect(src, 0, iq_swap, 0);
+    tb->start();
+    tb->stop();
+    tb->wait();
+    tb->disconnect(src, 0, iq_swap, 0);
+#else
     src.reset();
+#endif
 
     try
     {
@@ -218,6 +244,7 @@ void receiver::set_input_device(const std::string device)
     {
         error = x.what();
         src = osmosdr::source::make("file="+escape_filename(get_zero_file())+",freq=428e6,rate=96000,repeat=true,throttle=true");
+
     }
 
     if(src->get_sample_rate() != 0)
@@ -233,6 +260,12 @@ void receiver::set_input_device(const std::string device)
         tb->connect(src, 0, iq_swap, 0);
     }
 
+    //reset DSP IIR filters to safe initial state from possible runaway after
+    // playing bad IQ file
+    auto last_demod = d_demod;
+    set_demod(RX_DEMOD_OFF, true);
+    set_demod(last_demod);
+
     if (d_running)
         tb->start();
 
@@ -1315,6 +1348,7 @@ void receiver::connect_all(rx_chain type)
 
     if (d_dc_cancel)
     {
+        dc_corr = make_dc_corr_cc(d_decim_rate, 1.0);
         tb->connect(b, 0, dc_corr, 0);
         b = dc_corr;
     }
@@ -1342,6 +1376,8 @@ void receiver::connect_all(rx_chain type)
         break;
 
     default:
+        rx.reset();
+        rx = make_nbrx(d_quad_rate, d_audio_rate);
         break;
     }