Refactor SFFT.

include-gpl/dsp/fftfilt.h

@@ -67,7 +67,8 @@ private:
 public:
 	sfft(int len);
 	~sfft();
-	void run(const cmplx& input, cmplx *result);
+	void run(const cmplx& input);
+	void fetch(float *result);
 };
 
 #endif

plugins/channel/lora/lorademod.cpp

@@ -36,6 +36,8 @@ LoRaDemod::LoRaDemod(SampleSink* sampleSink) :
 	m_chirp = 0;
 	m_angle = 0;
 	m_bin = 0;
+	m_result = 0;
+	m_count = 0;
 
 	loraFilter = new sfft(LORA_SFFT_LEN);
 }
@@ -52,25 +54,28 @@ void LoRaDemod::configure(MessageQueue* messageQueue, Real Bandwidth)
 	cmd->submit(messageQueue, this);
 }
 
+// Detecting the header needs an sfft with the opposite rotation
 int  LoRaDemod::detect(Complex c)
 {
-	int i, result;
-	Real peak, mag;
-	cmplx bins[LORA_SFFT_LEN];
+	int i;
+	float peak;
+	float mag[LORA_SFFT_LEN];
 
-	// TODO: don`t need per-sample sliding FFT time resolution
-	loraFilter->run(c, bins);
-	peak = mag = 0;
-	result = 0;
+	loraFilter->run(c);
+	if (++m_count & 31)
+		return m_result;
+
+	// process spectrum every 32 samples
+	loraFilter->fetch(mag);
+	peak = 0.0f;
+	m_result = 0;
 	for (i = 0; i < LORA_SFFT_LEN; i++) {
-		mag = bins[i].real() * bins[i].real()
-			+ bins[i].imag() * bins[i].imag();
-		if (mag > peak) {
-			peak = mag;
-			result = i;
+		if (mag[i] > peak) {
+			peak = mag[i];
+			m_result = i;
 		}
 	}
-	return result;
+	return m_result;
 }
 
 void LoRaDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool pO)
@@ -91,7 +96,7 @@ void LoRaDemod::feed(SampleVector::const_iterator begin, SampleVector::const_ite
 
 			m_bin = (m_bin + newangle) & (LORA_SFFT_LEN - 1);
 			Complex nangle(cos(M_PI*2*m_bin/LORA_SFFT_LEN),sin(M_PI*2*m_bin/LORA_SFFT_LEN));
-			m_sampleBuffer.push_back(Sample(nangle.real() * 1000, nangle.imag() * 1000));
+			m_sampleBuffer.push_back(Sample(nangle.real() * 500, nangle.imag() * 500));
 			m_sampleDistanceRemain += (Real)m_sampleRate / m_Bandwidth;
 		}
 	}

plugins/channel/lora/lorademod.h

@@ -71,6 +71,8 @@ private:
 	int m_chirp;
 	int m_angle;
 	int m_bin;
+	int m_result;
+	int m_count;
 
 	sfft* loraFilter;
 

plugins/channel/lora/lorademodgui.cpp

@@ -136,6 +136,8 @@ LoRaDemodGUI::LoRaDemodGUI(PluginAPI* pluginAPI, QWidget* parent) :
 	ui->glSpectrum->setDisplayWaterfall(true);
 	ui->glSpectrum->setDisplayMaxHold(true);
 
+	setTitleColor(Qt::magenta);
+
 	m_channelMarker = new ChannelMarker(this);
 	m_channelMarker->setColor(Qt::magenta);
 	m_channelMarker->setBandwidth(7813);

plugins/channel/lora/lorademodgui.ui

@@ -40,7 +40,7 @@
      </widget>
     </item>
     <item row="1" column="0">
-     <widget class="QLabel" name="label">
+     <widget class="QLabel" name="mabel">
       <property name="text">
        <string>Spreading</string>
       </property>

sdrbase/dsp/fftfilt.cxx

@@ -224,22 +224,24 @@ sfft::~sfft()
 // Sliding FFT, cmplx input, cmplx output
 // FFT is computed for each value from first to last
 // Values are not stable until more than "len" samples have been processed.
-// Copies the frequencies to a pointer.
-void sfft::run(const cmplx& input, cmplx *result)
+void sfft::run(const cmplx& input)
 {
 	cmplx & de = delay[ptr];
 	const cmplx z( input.real() - k2 * de.real(), input.imag() - k2 * de.imag());
 	de = input;
 
-	++ptr ;
-	if( ptr >= fftlen ) ptr = 0 ;
+	if (++ptr >= fftlen)
+		ptr = 0;
 
-	// It is more efficient to have vrot and bins very close to each other.
-	for(	vrot_bins_pair
-			*itr = vrot_bins + first,
-			*end = vrot_bins + last ;
-		itr != end ;
-		++itr, result++ ) {
-		*result = itr->bins = (itr->bins + z) * itr->vrot;
-	}
+	for (vrot_bins_pair *itr = vrot_bins + first, *end = vrot_bins + last; itr != end ; ++itr)
+		itr->bins = (itr->bins + z) * itr->vrot;
 }
+
+// Copies the frequencies to a pointer.
+void sfft::fetch(float *result)
+{
+	for (vrot_bins_pair *itr = vrot_bins, *end = vrot_bins + last;  itr != end; ++itr, ++result)
+		*result = itr->bins.real() * itr->bins.real()
+                        + itr->bins.imag() * itr->bins.imag();
+}
+