Refactor bit pattern matching.

Remove AccessCodeCorrelator, Unstuff classes.

firmware/baseband/Makefile

@@ -140,7 +140,6 @@ CPPSRC = main.cpp \
          proc_wideband_spectrum.cpp \
          dsp_squelch.cpp \
          clock_recovery.cpp \
-         access_code_correlator.cpp \
          packet_builder.cpp \
          dsp_fft.cpp \
          dsp_fir_taps.cpp \

firmware/baseband/access_code_correlator.cpp

@@ -1,34 +0,0 @@
-/*
- * Copyright (C) 2014 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 "access_code_correlator.hpp"
-
-void AccessCodeCorrelator::configure(
-	const uint32_t new_code,
-	const size_t new_code_length,
-	const size_t new_maximum_hamming_distance
-) {
-	if( new_code_length <= 32 ) {
-		code = new_code;
-		mask = mask_value(new_code_length);
-		maximum_hamming_distance = new_maximum_hamming_distance;
-	}
-}

firmware/baseband/access_code_correlator.hpp

@@ -1,57 +0,0 @@
-/*
- * Copyright (C) 2014 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 __ACCESS_CODE_CORRELATOR_H__
-#define __ACCESS_CODE_CORRELATOR_H__
-
-#include <cstdint>
-#include <cstddef>
-
-class AccessCodeCorrelator {
-public:
-	void configure(
-		const uint32_t new_code,
-		const size_t new_code_length,
-		const size_t new_maximum_hamming_distance
-	);
-
-	bool operator()(
-		const uint_fast8_t in
-	) {
-		history = (history << 1) | (in & 1);
-		const auto delta_bits = (history ^ code) & mask;
-		//const size_t count = __builtin_popcountll(delta_bits);
-		const size_t count = __builtin_popcountl(delta_bits);
-		return (count <= maximum_hamming_distance);
-	}
-
-private:
-	uint32_t code { 0 };
-	uint32_t mask { 0 };
-	uint32_t history { 0 };
-	size_t maximum_hamming_distance { 0 };
-
-	static constexpr uint32_t mask_value(const size_t n) {
-		return static_cast<uint32_t>((1ULL << n) - 1ULL);
-	}
-};
-
-#endif/*__ACCESS_CODE_CORRELATOR_H__*/

firmware/baseband/main.cpp

@@ -59,7 +59,6 @@
 #include "proc_wideband_spectrum.hpp"
 
 #include "clock_recovery.hpp"
-#include "access_code_correlator.hpp"
 #include "packet_builder.hpp"
 
 #include "message_queue.hpp"

firmware/baseband/packet_builder.cpp

@@ -22,11 +22,12 @@
 #include "packet_builder.hpp"
 
 void PacketBuilder::configure(
-	uint32_t unstuffing_pattern,
-	size_t unstuffing_length,
+	const BitPattern preamble,
+	const BitPattern unstuff,
 	size_t new_payload_length
 ) {
-	unstuff.configure(unstuffing_pattern, unstuffing_length);
+	preamble_pattern = preamble;
+	unstuff_pattern = unstuff;
 
 	if( new_payload_length <= payload.size() ) {
 		payload_length = new_payload_length;
@@ -37,6 +38,5 @@ void PacketBuilder::configure(
 
 void PacketBuilder::reset_state() {
 	bits_received = 0;
-	unstuff.reset();
-	state = State::AccessCodeSearch;
+	state = State::Preamble;
 }

firmware/baseband/packet_builder.hpp

@@ -26,37 +26,38 @@
 #include <cstddef>
 #include <bitset>
 
-#include "symbol_coding.hpp"
+#include "bit_pattern.hpp"
 
 class PacketBuilder {
 public:
 	void configure(
-		uint32_t unstuffing_pattern,
-		size_t unstuffing_length,
+		const BitPattern preamble,
+		const BitPattern unstuffing,
 		size_t new_payload_length
 	);
 
 	template<typename PayloadHandler>
 	void execute(
 		const uint_fast8_t symbol,
-		const bool access_code_found,
 		PayloadHandler payload_handler
 	) {
+		bit_history.add(symbol);
+
 		switch(state) {
-		case State::AccessCodeSearch:
-			if( access_code_found ) {
+		case State::Preamble:
+			if( found_preamble() ) {
 				state = State::Payload;
 			}
 			break;
 
 		case State::Payload:
-			if( bits_received < payload_length ) {
-				if( !unstuff.is_stuffing_bit(symbol) ) {
-					payload[bits_received++] = symbol;
-				}
-			} else {
+			if( found_end_flag() || packet_truncated() ) {
 				payload_handler(payload, bits_received);
 				reset_state();
+			} else {
+				if( !found_stuffing_bit() ) {
+					payload[bits_received++] = symbol;
+				}
 			}
 			break;
 
@@ -68,15 +69,35 @@ public:
 
 private:
 	enum State {
-		AccessCodeSearch,
+		Preamble,
 		Payload,
 	};
 
+	bool packet_truncated() const {
+		return bits_received > payload.size();
+	}
+
+	bool found_preamble() const {
+		return bit_history.matches(preamble_pattern);
+	}
+
+	bool found_stuffing_bit() const {
+		return bit_history.matches(unstuff_pattern);
+	}
+
+	bool found_end_flag() const {
+		return bit_history.matches(end_flag_pattern);
+	}
+
+	BitHistory bit_history;
+	BitPattern preamble_pattern { 0b01010101010101010101111110, 26, 1 };
+	BitPattern unstuff_pattern { 0b111110, 6 };
+	BitPattern end_flag_pattern { 0b01111110, 8 };
+
 	size_t payload_length { 0 };
 	size_t bits_received { 0 };
-	State state { State::AccessCodeSearch };
+	State state { State::Preamble };
 	std::bitset<256> payload;
-	symbol_coding::Unstuff unstuff;
 
 	void reset_state();
 };

firmware/baseband/proc_fsk.cpp

@@ -45,14 +45,9 @@ FSKProcessor::~FSKProcessor() {
 void FSKProcessor::configure(const FSKConfiguration new_configuration) {
 	// TODO: Matched filter characteristics are hard-coded for the moment. YUCK!
 	clock_recovery.configure(sampling_rate / 4, new_configuration.symbol_rate);
-	access_code_correlator.configure(
-		new_configuration.access_code,
-		new_configuration.access_code_length,
-		new_configuration.access_code_tolerance
-	);
 	packet_builder.configure(
-		new_configuration.unstuffing_pattern,
-		new_configuration.unstuffing_length,
+		{ new_configuration.access_code, new_configuration.access_code_length, new_configuration.access_code_tolerance },
+		{ new_configuration.unstuffing_pattern, new_configuration.unstuffing_length },
 		new_configuration.packet_length
 	);
 }
@@ -117,11 +112,9 @@ void FSKProcessor::consume_symbol(
 
 	const uint_fast8_t sliced_symbol = (raw_symbol >= 0.0f) ? 1 : 0;
 	const auto decoded_symbol = nrzi_decode(sliced_symbol);
-	const bool access_code_found = access_code_correlator(decoded_symbol);
 
 	packet_builder.execute(
 		decoded_symbol,
-		access_code_found,
 		payload_handler_fn
 	);
 }

firmware/baseband/proc_fsk.hpp

@@ -31,7 +31,6 @@
 
 #include "clock_recovery.hpp"
 #include "symbol_coding.hpp"
-#include "access_code_correlator.hpp"
 #include "packet_builder.hpp"
 
 #include "message.hpp"
@@ -85,7 +84,6 @@ private:
 		[this](const float symbol) { this->consume_symbol(symbol); }
 	};
 	symbol_coding::NRZIDecoder nrzi_decode;
-	AccessCodeCorrelator access_code_correlator;
 	PacketBuilder packet_builder;
 
 	MessageHandlerMap& message_handlers;

firmware/baseband/symbol_coding.hpp

@@ -39,33 +39,6 @@ private:
 	uint_fast8_t last { 0 };
 };
 
-class Unstuff {
-public:
-	uint_fast8_t is_stuffing_bit(const uint_fast8_t symbol) {
-		history = (history << 1) | (symbol & 1);
-		return (history & mask) == match;
-	}
-
-	void configure(
-		const uint32_t pattern,
-		const size_t length
-	) {
-		// Ensure that length=0 (unstuffing disabled) never matches.
-		match = length ? pattern : 1;
-		mask = (1U << length) - 1;
-		reset();
-	}
-
-	void reset() {
-		history = 0;
-	}
-
-private:
-	uint32_t history { 0 };
-	uint32_t match { 0b111110 };
-	uint32_t mask  { 0b111111 };
-};
-
 } /* namespace symbol_coding */
 
 #endif/*__SYMBOL_CODING_H__*/

firmware/common/bit_pattern.hpp

@@ -0,0 +1,74 @@
+/*
+ * 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 __BIT_PATTERN_H__
+#define __BIT_PATTERN_H__
+
+#include <cstdint>
+#include <cstddef>
+
+class BitPattern {
+public:
+	constexpr BitPattern(
+		const uint32_t code,
+		const size_t code_length,
+		const size_t maximum_hanning_distance = 0
+	) : code_ { code },
+		mask_ { (1UL << code_length) - 1UL },
+		maximum_hanning_distance_ { maximum_hanning_distance }
+	{
+	}
+
+	uint32_t code() const {
+		return code_;
+	}
+
+	uint32_t mask() const {
+		return mask_;
+	}
+
+	size_t maximum_hanning_distance() const {
+		return maximum_hanning_distance_;
+	}
+
+private:
+	uint32_t code_;
+	uint32_t mask_;
+	size_t maximum_hanning_distance_;
+};
+
+class BitHistory {
+public:
+	void add(const uint_fast8_t bit) {
+		history = (history << 1) | (bit & 1);
+	}
+
+	bool matches(const BitPattern& pattern) const {
+		const auto delta_bits = (history ^ pattern.code()) & pattern.mask();
+		const size_t count = __builtin_popcountl(delta_bits);
+		return (count <= pattern.maximum_hanning_distance());
+	}
+
+private:
+	uint32_t history { 0 };
+};
+
+#endif/*__BIT_PATTERN_H__*/