add VOR receiver module

decoder_modules/vor_receiver/src/vor_decoder.cpp

@@ -0,0 +1,50 @@
+#include "vor_decoder.h"
+
+#define STDDEV_NORM_FACTOR  1.813799364234218f // 2.0f * FL_M_PI / sqrt(12)
+
+namespace vor {
+    Decoder::Decoder(dsp::stream<dsp::complex_t>* in, double integrationTime) {
+        rx.init(in);
+        reshape.init(&rx.out, round(1000.0 * integrationTime), 0);
+        symSink.init(&reshape.out, dataHandler, this);
+    }
+
+    Decoder::~Decoder() {
+        // TODO
+    }
+
+    void Decoder::setInput(dsp::stream<dsp::complex_t>* in) {
+        rx.setInput(in);
+    }
+
+    void Decoder::start() {
+        rx.start();
+        reshape.start();
+        symSink.start();
+    }
+
+    void Decoder::stop() {
+        rx.stop();
+        reshape.stop();
+        symSink.stop();
+    }
+
+    void Decoder::dataHandler(float* data, int count, void* ctx) {
+        // Get the instance from context
+        Decoder* _this = (Decoder*)ctx;
+
+        // Compute the mean and standard deviation of the 
+        float mean, stddev;
+        volk_32f_stddev_and_mean_32f_x2(&stddev, &mean, data, count);
+        
+        // Compute the signal quality
+        float quality = std::max<float>(1.0f - (stddev / STDDEV_NORM_FACTOR), 0.0f);
+
+        // Convert the phase difference to a compass heading
+        mean = -mean;
+        if (mean < 0) { mean = 2.0f*FL_M_PI + mean; }
+
+        // Call the handler
+        _this->onBearing(mean, quality);
+    }
+}