Merge pull request #1288 from gqrx-sdr/rx-fft-fix-zeros

Don't run FFTs until enough samples have arrived

resources/news.txt

@@ -29,6 +29,7 @@
   IMPROVED: Reduced CPU utilization of demodulators.
   IMPROVED: Properly handle smooth scrolling.
   IMPROVED: Shorten band names to fit in narrow spaces.
+  IMPROVED: Delay plot & waterfall drawing until samples arrive from hardware.
    CHANGED: Frequency zoom slider zooms around center of display.
    CHANGED: Disallow scrolling beyond the FFT frequency limits.
    CHANGED: Default narrow FM deviation increased to 5 kHz.

src/applications/gqrx/mainwindow.cpp

@@ -1499,9 +1499,8 @@ void MainWindow::iqFftTimeout()
     }
     d_last_fft_ms = now_ms;
 
-    rx->get_iq_fft_data(d_iqFftData.data());
-
-    ui->plotter->setNewFftData(d_iqFftData.data(), fftsize);
+    if (rx->get_iq_fft_data(d_iqFftData.data()) >= 0)
+        ui->plotter->setNewFftData(d_iqFftData.data(), fftsize);
 }
 
 /** Audio FFT plot timeout. */
@@ -1519,9 +1518,8 @@ void MainWindow::audioFftTimeout()
     if (!d_have_audio || !uiDockAudio->isVisible())
         return;
 
-    rx->get_audio_fft_data(d_audioFftData.data());
-
-    uiDockAudio->setNewFftData(d_audioFftData.data(), fftsize);
+    if (rx->get_audio_fft_data(d_audioFftData.data()) >= 0)
+        uiDockAudio->setNewFftData(d_audioFftData.data(), fftsize);
 }
 
 /** RDS message display timeout. */

src/applications/gqrx/receiver.cpp

@@ -751,9 +751,9 @@ void receiver::set_iq_fft_window(int window_type, bool normalize_energy)
 }
 
 /** Get latest baseband FFT data. */
-void receiver::get_iq_fft_data(float* fftPoints)
+int receiver::get_iq_fft_data(float* fftPoints)
 {
-    iq_fft->get_fft_data(fftPoints);
+    return iq_fft->get_fft_data(fftPoints);
 }
 
 unsigned int receiver::audio_fft_size() const
@@ -762,9 +762,9 @@ unsigned int receiver::audio_fft_size() const
 }
 
 /** Get latest audio FFT data. */
-void receiver::get_audio_fft_data(float* fftPoints)
+int receiver::get_audio_fft_data(float* fftPoints)
 {
-    audio_fft->get_fft_data(fftPoints);
+    return audio_fft->get_fft_data(fftPoints);
 }
 
 receiver::status receiver::set_nb_on(int nbid, bool on)

src/applications/gqrx/receiver.h

@@ -163,8 +163,8 @@ class receiver
     void        set_iq_fft_size(int newsize);
     unsigned int iq_fft_size(void) const;
     void        set_iq_fft_window(int window_type, bool normalize_energy);
-    void        get_iq_fft_data(float* fftPoints);
-    void        get_audio_fft_data(float* fftPoints);
+    int         get_iq_fft_data(float* fftPoints);
+    int         get_audio_fft_data(float* fftPoints);
     unsigned int audio_fft_size(void) const;
 
     /* Noise blanker */

src/dsp/rx_fft.cpp

@@ -48,6 +48,7 @@ rx_fft_c::rx_fft_c(unsigned int fftsize, double quad_rate, int wintype, bool nor
           gr::io_signature::make(1, 1, sizeof(gr_complex)),
           gr::io_signature::make(0, 0, 0)),
       d_fftsize(fftsize),
+      d_startup_samples(0),
       d_quadrate(quad_rate),
       d_wintype(-1),
       d_normalize_energy(false)
@@ -110,6 +111,9 @@ int rx_fft_c::work(int noutput_items,
             d_reader->update_read_pointer(items_to_copy - d_writer->space_available());
         memcpy(d_writer->write_pointer(), in, sizeof(gr_complex) * items_to_copy);
         d_writer->update_write_pointer(items_to_copy);
+
+        if (d_startup_samples < d_writer->bufsize())
+            d_startup_samples += items_to_copy;
     }
 
     return noutput_items;
@@ -119,7 +123,7 @@ int rx_fft_c::work(int noutput_items,
  *  \param fftPoints Buffer to copy FFT data
  *  \param fftSize Current FFT size (output).
  */
-void rx_fft_c::get_fft_data(float* fftPoints)
+int rx_fft_c::get_fft_data(float* fftPoints)
 {
     std::chrono::time_point<std::chrono::steady_clock> now = std::chrono::steady_clock::now();
     std::chrono::duration<double> diff = now - d_lasttime;
@@ -130,6 +134,10 @@ void rx_fft_c::get_fft_data(float* fftPoints)
         std::lock_guard<std::mutex> lock(d_in_mutex);
 
         d_reader->update_read_pointer(std::min((int)(diff.count() * d_quadrate * 1.001), d_reader->items_available() - MAX_FFT_SIZE));
+
+        if (d_startup_samples < d_reader->items_available() - (MAX_FFT_SIZE - d_fftsize))
+            return -1;
+
         apply_window(d_fftsize);
     }
 
@@ -143,6 +151,8 @@ void rx_fft_c::get_fft_data(float* fftPoints)
         fftPoints[i] = static_cast<float>(std::norm(fftOut[i + d_fftsize/2]));
     for (unsigned int i = d_fftsize/2; i < d_fftsize; ++i)
         fftPoints[i] = static_cast<float>(std::norm(fftOut[i - d_fftsize/2]));
+
+    return 0;
 }
 
 /*! \brief Compute FFT on the available input data.
@@ -249,6 +259,7 @@ rx_fft_f::rx_fft_f(unsigned int fftsize, double audio_rate,
           gr::io_signature::make(1, 1, sizeof(float)),
           gr::io_signature::make(0, 0, 0)),
       d_fftsize(fftsize),
+      d_startup_samples(0),
       d_audiorate(audio_rate),
       d_wintype(-1),
       d_normalize_energy(false)
@@ -311,6 +322,9 @@ int rx_fft_f::work(int noutput_items,
             d_reader->update_read_pointer(items_to_copy - d_writer->space_available());
         memcpy(d_writer->write_pointer(), in, sizeof(float) * items_to_copy);
         d_writer->update_write_pointer(items_to_copy);
+
+        if (d_startup_samples < d_writer->bufsize())
+            d_startup_samples += items_to_copy;
     }
 
     return noutput_items;
@@ -320,7 +334,7 @@ int rx_fft_f::work(int noutput_items,
  *  \param fftPoints Buffer to copy FFT data
  *  \param fftSize Current FFT size (output).
  */
-void rx_fft_f::get_fft_data(float* fftPoints)
+int rx_fft_f::get_fft_data(float* fftPoints)
 {
     std::chrono::time_point<std::chrono::steady_clock> now = std::chrono::steady_clock::now();
     std::chrono::duration<double> diff = now - d_lasttime;
@@ -333,6 +347,10 @@ void rx_fft_f::get_fft_data(float* fftPoints)
             std::lock_guard<std::mutex> lock(d_in_mutex);
 
             d_reader->update_read_pointer(std::min((unsigned int)(diff.count() * d_audiorate * 1.001), d_reader->items_available() - d_fftsize));
+
+            if ((int)d_startup_samples < d_reader->items_available())
+                return -1;
+
             apply_window(d_fftsize);
         }
 
@@ -347,6 +365,8 @@ void rx_fft_f::get_fft_data(float* fftPoints)
         for (unsigned int i = d_fftsize/2; i < d_fftsize; ++i)
             fftPoints[i] = static_cast<float>(std::norm(fftOut[i - d_fftsize/2]));
     }
+
+    return 0;
 }
 
 /*! \brief Compute FFT on the available input data.
@@ -425,4 +445,4 @@ void rx_fft_f::update_window()
     if (d_normalize_energy)
         factor = std::sqrt(factor);
     volk_32f_s32f_normalize(d_window.data(), factor, d_fftsize);
-}
+}

src/dsp/rx_fft.h

@@ -94,7 +94,7 @@ class rx_fft_c : public gr::sync_block
              gr_vector_const_void_star &input_items,
              gr_vector_void_star &output_items);
 
-    void get_fft_data(float* fftPoints);
+    int get_fft_data(float* fftPoints);
 
     void set_window_type(int wintype, bool normalize_energy);
     int  get_window_type() const { return d_wintype; }
@@ -105,6 +105,7 @@ class rx_fft_c : public gr::sync_block
 
 private:
     unsigned int d_fftsize;   /*! Current FFT size. */
+    unsigned int d_startup_samples;
     double       d_quadrate;
     int          d_wintype;   /*! Current window type. */
     bool         d_normalize_energy;
@@ -172,7 +173,7 @@ class rx_fft_f : public gr::sync_block
              gr_vector_const_void_star &input_items,
              gr_vector_void_star &output_items);
 
-    void get_fft_data(float* fftPoints);
+    int get_fft_data(float* fftPoints);
 
     void set_window_type(int wintype, bool normalize_energy);
     int  get_window_type() const { return d_wintype; }
@@ -182,6 +183,7 @@ class rx_fft_f : public gr::sync_block
 
 private:
     unsigned int d_fftsize;   /*! Current FFT size. */
+    unsigned int d_startup_samples;
     double       d_audiorate;
     int          d_wintype;   /*! Current window type. */
     bool         d_normalize_energy;