Use IFIR decimation for broadcast FM receiver.

firmware/baseband/dsp_decimate.cpp

@@ -618,6 +618,12 @@ buffer_c16_t DecimateBy2CIC3::execute(
 	return { dst.p, src.count / 2, src.sampling_rate / 2 };
 }
 
+void FIR64AndDecimateBy2Real::configure(
+	const std::array<int16_t, taps_count>& new_taps
+) {
+	std::copy(new_taps.cbegin(), new_taps.cend(), taps.begin());
+}
+
 buffer_s16_t FIR64AndDecimateBy2Real::execute(
 	buffer_s16_t src,
 	buffer_s16_t dst

firmware/baseband/dsp_decimate.hpp

@@ -76,11 +76,9 @@ class FIR64AndDecimateBy2Real {
 public:
 	static constexpr size_t taps_count = 64;
 
-	FIR64AndDecimateBy2Real(
+	void configure(
 		const std::array<int16_t, taps_count>& taps
-	) : taps(taps)
+	);
-	{
-	}
 
 	buffer_s16_t execute(
 		buffer_s16_t src,
@@ -89,7 +87,7 @@ public:
 
 private:
 	std::array<int16_t, taps_count + 2> z;
-	const std::array<int16_t, taps_count>& taps;
+	std::array<int16_t, taps_count> taps;
 };
 
 class FIRC8xR16x24FS4Decim4 {

firmware/baseband/dsp_fir_taps.hpp

@@ -182,6 +182,27 @@ constexpr fir_taps_real<32> taps_6k0_channel {
 	} },
 };
 
+// WFM 200KF8E emission type //////////////////////////////////////////////
+
+constexpr fir_taps_real<24> taps_200k_wfm_decim_0 = {
+	.pass_frequency_normalized = 100000.0f / 3072000.0f,
+	.stop_frequency_normalized = 484000.0f / 3072000.0f,
+	.taps = { {
+		    48,    -18,   -151,   -364,   -557,   -548,   -139,    789,
+		  2187,   3800,   5230,   6071,   6071,   5230,   3800,   2187,
+		   789,   -139,   -548,   -557,   -364,   -151,    -18,     48,
+	} },
+};
+
+constexpr fir_taps_real<16> taps_200k_wfm_decim_1 = {
+	.pass_frequency_normalized = 100000.0f / 768000.0f,
+	.stop_frequency_normalized = 284000.0f / 768000.0f,
+	.taps = { {
+		   -67,   -123,    388,    622,  -1342,  -2185,   4599,  14486,
+		 14486,   4599,  -2185,  -1342,    622,    388,   -123,    -67,
+	} },
+};
+
 /* Wideband audio filter */
 /* 96kHz int16_t input
  * -> FIR filter, <15kHz (0.156fs) pass, >19kHz (0.198fs) stop

firmware/baseband/proc_wfm_audio.cpp

@@ -23,8 +23,34 @@
 
 #include <cstdint>
 
+WidebandFMAudio::WidebandFMAudio() {
+	constexpr size_t baseband_fs = 3072000;
+
+	constexpr size_t decim_0_input_fs = baseband_fs;
+	constexpr size_t decim_0_decimation_factor = 4;
+	constexpr size_t decim_0_output_fs = decim_0_input_fs / decim_0_decimation_factor;
+
+	constexpr size_t decim_1_input_fs = decim_0_output_fs;
+	constexpr size_t decim_1_decimation_factor = 2;
+	constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1_decimation_factor;
+
+	constexpr size_t demod_input_fs = decim_1_output_fs;
+
+	decim_0.configure(taps_200k_wfm_decim_0.taps, 33554432);
+	decim_1.configure(taps_200k_wfm_decim_1.taps, 131072);
+	demod.configure(demod_input_fs, 75000);
+	audio_filter.configure(taps_64_lp_156_198.taps);
+}
+
 void WidebandFMAudio::execute(const buffer_c8_t& buffer) {
-	auto decimator_out = decimator.execute(buffer);
+	const buffer_c16_t dst_buffer {
+		dst.data(),
+		dst.size()
+	};
+
+	const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
+	const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
+	const auto decimator_out = decim_1_out;
 
 	const buffer_s16_t work_audio_buffer {
 		(int16_t*)decimator_out.p,
@@ -37,29 +63,24 @@ void WidebandFMAudio::execute(const buffer_c8_t& buffer) {
 	feed_channel_stats(channel);
 	//feed_channel_spectrum(channel);
 
-	/* 768kHz complex<int16_t>[512]
+	/* 384kHz complex<int16_t>[256]
 	 * -> FM demodulation
-	 * -> 768kHz int16_t[512] */
+	 * -> 384kHz int16_t[256] */
 	/* TODO: To improve adjacent channel rejection, implement complex channel filter:
 	 *		pass < +/- 100kHz, stop > +/- 200kHz
 	 */
 
 	auto audio_oversampled = demod.execute(decimator_out, work_audio_buffer);
 
-	/* 768kHz int16_t[512]
-	 * -> 4th order CIC decimation by 2, gain of 1
-	 * -> 384kHz int16_t[256] */
-	auto audio_8fs = audio_dec_1.execute(audio_oversampled, work_audio_buffer);
-
 	/* 384kHz int16_t[256]
 	 * -> 4th order CIC decimation by 2, gain of 1
 	 * -> 192kHz int16_t[128] */
-	auto audio_4fs = audio_dec_2.execute(audio_8fs, work_audio_buffer);
+	auto audio_4fs = audio_dec_1.execute(audio_oversampled, work_audio_buffer);
 
 	/* 192kHz int16_t[128]
 	 * -> 4th order CIC decimation by 2, gain of 1
 	 * -> 96kHz int16_t[64] */
-	auto audio_2fs = audio_dec_3.execute(audio_4fs, work_audio_buffer);
+	auto audio_2fs = audio_dec_2.execute(audio_4fs, work_audio_buffer);
 
 	/* 96kHz int16_t[64]
 	 * -> FIR filter, <15kHz (0.156fs) pass, >19kHz (0.198fs) stop, gain of 1

firmware/baseband/proc_wfm_audio.hpp

@@ -33,21 +33,19 @@
 
 class WidebandFMAudio : public BasebandProcessor {
 public:
-	WidebandFMAudio() {
+	WidebandFMAudio();
-		decimator.set_decimation_factor(ChannelDecimator::DecimationFactor::By4);
-	}
 
 	void execute(const buffer_c8_t& buffer) override;
 
 private:
-	ChannelDecimator decimator;
+	std::array<complex16_t, 512> dst;
+	dsp::decimate::FIRC8xR16x24FS4Decim4 decim_0;
+	dsp::decimate::FIRC16xR16x16Decim2 decim_1;
 
-	dsp::demodulate::FM demod { 768000, 75000 };
+	dsp::demodulate::FM demod;
 	dsp::decimate::DecimateBy2CIC4Real audio_dec_1;
 	dsp::decimate::DecimateBy2CIC4Real audio_dec_2;
-	dsp::decimate::DecimateBy2CIC4Real audio_dec_3;
+	dsp::decimate::FIR64AndDecimateBy2Real audio_filter;
-	const fir_taps_real<64>& audio_filter_taps = taps_64_lp_156_198;
-	dsp::decimate::FIR64AndDecimateBy2Real audio_filter { audio_filter_taps.taps };
 
 	IIRBiquadFilter audio_hpf { audio_hpf_30hz_config };
 	IIRBiquadFilter audio_deemph { audio_deemph_2122_6_config };