first working nfm chain using pycsdr

csdr/chain/demodulator.py

@@ -0,0 +1,56 @@
+from csdr.chain import Chain
+from pycsdr.modules import Shift, FirDecimate, Bandpass, Squelch, FractionalDecimator
+from abc import ABCMeta, abstractmethod
+
+
+class Demodulator(Chain, metaclass=ABCMeta):
+    @abstractmethod
+    def setLastDecimation(self, decimation: Chain):
+        pass
+
+
+class DemodulatorChain(Chain):
+    def __init__(self, samp_rate: int, audioRate: int, shiftRate: float, demodulator: Demodulator):
+        self.shift = Shift(shiftRate)
+
+        decimation, fraction = self._getDecimation(samp_rate, audioRate)
+        if_samp_rate = samp_rate / decimation
+        transition = 0.15 * (if_samp_rate / float(samp_rate))
+        self.decimation = FirDecimate(decimation, transition)
+
+        bp_transition = 320.0 / if_samp_rate
+        self.bandpass = Bandpass(bp_transition, use_fft=True)
+
+        self.squelch = Squelch(5)
+
+        if fraction != 1.0:
+            demodulator.setLastDecimation(Chain(FractionalDecimator(fraction)))
+
+        workers = [
+            self.shift,
+            self.decimation,
+            self.bandpass,
+            self.squelch,
+            demodulator
+        ]
+
+        super().__init__(*workers)
+
+    def setShiftRate(self, rate: float):
+        self.shift.setRate(rate)
+
+    def setSquelchLevel(self, level: float):
+        self.squelch.setSquelchLevel(level)
+
+    def setBandpass(self, low_cut: float, high_cut: float):
+        self.bandpass.setBandpass(low_cut, high_cut)
+
+    def _getDecimation(self, input_rate, output_rate):
+        if output_rate <= 0:
+            raise ValueError("invalid output rate: {rate}".format(rate=output_rate))
+        decimation = 1
+        target_rate = output_rate
+        while input_rate / (decimation + 1) >= target_rate:
+            decimation += 1
+        fraction = float(input_rate / decimation) / output_rate
+        return decimation, fraction