Add TPMS initial demodulator implementation.

Right now, 2FSK, 19200 baud, +/-38400Hz deviation. No effort is made to check CRC/checksums or decode packets.

firmware/baseband/Makefile

@@ -139,6 +139,7 @@ CPPSRC = main.cpp \
          proc_wfm_audio.cpp \
          proc_ais.cpp \
          proc_wideband_spectrum.cpp \
+         proc_tpms.cpp \
          dsp_squelch.cpp \
          clock_recovery.cpp \
          packet_builder.cpp \

firmware/baseband/main.cpp

@@ -57,6 +57,7 @@
 #include "proc_wfm_audio.hpp"
 #include "proc_ais.hpp"
 #include "proc_wideband_spectrum.hpp"
+#include "proc_tpms.hpp"
 
 #include "clock_recovery.hpp"
 #include "packet_builder.hpp"
@@ -319,6 +320,10 @@ int main(void) {
 					baseband_processor = new WidebandSpectrum();
 					break;
 
+				case 5:
+					baseband_processor = new TPMSProcessor();
+					break;
+
 				default:
 					break;
 				}

firmware/baseband/proc_tpms.cpp

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "proc_tpms.hpp"
+
+#include "portapack_shared_memory.hpp"
+
+#include "i2s.hpp"
+using namespace lpc43xx;
+
+void TPMSProcessor::execute(buffer_c8_t buffer) {
+	/* 2.4576MHz, 2048 samples */
+
+	auto decimator_out = decimator.execute(buffer);
+
+	/* 76.8kHz, 64 samples */
+	feed_channel_stats(decimator_out);
+	/* No spectrum display while FSK decoding.
+	feed_channel_spectrum(
+		channel,
+		decimator_out.sampling_rate * channel_filter_taps.pass_frequency_normalized,
+		decimator_out.sampling_rate * channel_filter_taps.stop_frequency_normalized
+	);
+	*/
+
+	for(size_t i=0; i<decimator_out.count; i++) {
+		// TODO: No idea why implicit cast int16_t->float is not allowed.
+		const std::complex<float> sample {
+			static_cast<float>(decimator_out.p[i].real()),
+			static_cast<float>(decimator_out.p[i].imag())
+		};
+		if( mf.execute_once(sample) ) {
+			clock_recovery(mf.get_output());
+		}
+	}
+
+	i2s::i2s0::tx_mute();
+}
+
+void TPMSProcessor::consume_symbol(
+	const float raw_symbol
+) {
+	const uint_fast8_t sliced_symbol = (raw_symbol >= 0.0f) ? 1 : 0;
+	packet_builder.execute(sliced_symbol);
+}
+
+void TPMSProcessor::payload_handler(
+	const std::bitset<1024>& payload,
+	const size_t bits_received
+) {
+	TPMSPacketMessage message;
+	message.packet.payload = payload;
+	message.packet.bits_received = bits_received;
+	shared_memory.application_queue.push(message);
+}

firmware/baseband/proc_tpms.hpp

@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __PROC_TPMS_H__
+#define __PROC_TPMS_H__
+
+#include "baseband_processor.hpp"
+
+#include "channel_decimator.hpp"
+#include "matched_filter.hpp"
+
+#include "clock_recovery.hpp"
+#include "symbol_coding.hpp"
+#include "packet_builder.hpp"
+
+#include "message.hpp"
+
+#include <cstdint>
+#include <cstddef>
+#include <bitset>
+
+struct NeverMatch {
+	bool operator()(const BitHistory&, const size_t) const {
+		return false;
+	}
+};
+
+struct FixedLength {
+	bool operator()(const BitHistory&, const size_t symbols_received) const {
+		return symbols_received >= length;
+	}
+
+	const size_t length;
+};
+
+// Translate+rectangular filter
+// sample=153.6k, deviation=38400, symbol=19200
+// Length: 8 taps, 1 symbols, 2 cycles of sinusoid
+constexpr std::array<std::complex<float>, 8> rect_taps_153k6_1t_p { {
+	{  1.2500000000e-01f,  0.0000000000e+00f }, {  7.6540424947e-18f,  1.2500000000e-01f },
+	{ -1.2500000000e-01f,  1.5308084989e-17f }, { -2.2962127484e-17f, -1.2500000000e-01f },
+	{  1.2500000000e-01f, -3.0616169979e-17f }, {  3.8270212473e-17f,  1.2500000000e-01f },
+	{ -1.2500000000e-01f,  4.5924254968e-17f }, { -5.3578297463e-17f, -1.2500000000e-01f },
+} };
+
+class TPMSProcessor : public BasebandProcessor {
+public:
+	using payload_t = std::bitset<1024>;
+
+	void execute(buffer_c8_t buffer) override;
+
+private:
+	ChannelDecimator decimator { ChannelDecimator::DecimationFactor::By16 };
+	dsp::matched_filter::MatchedFilter mf { rect_taps_153k6_1t_p, 4 };
+
+	clock_recovery::ClockRecovery<clock_recovery::FixedErrorFilter> clock_recovery {
+		38400, 19200, { 0.0555f },
+		[this](const float symbol) { this->consume_symbol(symbol); }
+	};
+	PacketBuilder<BitPattern, NeverMatch, FixedLength> packet_builder {
+		{ 0b010101010101010101010101010110, 30, 1 },
+		{ },
+		{ 256 },
+		[this](const payload_t& payload, const size_t bits_received) {
+			this->payload_handler(payload, bits_received);
+		}
+	};
+
+	void consume_symbol(const float symbol);
+	void payload_handler(const payload_t& payload, const size_t bits_received);
+};
+
+#endif/*__PROC_TPMS_H__*/