Rework BitHistory, BitPattern, PacketBuilder.

Templatize PacketBuilder to optionally bit unstuff, and have flexible packet termination behavior.

firmware/baseband/packet_builder.cpp

@@ -20,18 +20,3 @@
  */
 
 #include "packet_builder.hpp"
-
-void PacketBuilder::configure(
-	const BitPattern preamble,
-	const BitPattern unstuff
-) {
-	preamble_pattern = preamble;
-	unstuff_pattern = unstuff;
-
-	reset_state();
-}
-
-void PacketBuilder::reset_state() {
-	bits_received = 0;
-	state = State::Preamble;
-}

firmware/baseband/packet_builder.hpp

@@ -29,21 +29,33 @@
 
 #include "bit_pattern.hpp"
 
+template<typename PreambleMatcher, typename UnstuffMatcher, typename EndMatcher>
 class PacketBuilder {
 public:
 	using PayloadType = std::bitset<1024>;
 	using PayloadHandlerFunc = std::function<void(const PayloadType& payload, const size_t bits_received)>;
 
 	PacketBuilder(
+		const PreambleMatcher preamble_matcher,
+		const UnstuffMatcher unstuff_matcher,
+		const EndMatcher end_matcher,
 		const PayloadHandlerFunc payload_handler
-	) : payload_handler { payload_handler }
+	) : payload_handler { payload_handler },
+		preamble(preamble_matcher),
+		unstuff(unstuff_matcher),
+		end(end_matcher)
 	{
 	}
 
 	void configure(
-		const BitPattern preamble,
+		const PreambleMatcher preamble_matcher,
-		const BitPattern unstuffing
+		const UnstuffMatcher unstuff_matcher
-	);
+	) {
+		preamble = preamble_matcher;
+		unstuff = unstuff_matcher;
+
+		reset_state();
+	}
 
 	void execute(
 		const uint_fast8_t symbol
@@ -52,25 +64,24 @@ public:
 
 		switch(state) {
 		case State::Preamble:
-			if( found_preamble() ) {
+			if( preamble(bit_history, bits_received) ) {
 				state = State::Payload;
 			}
 			break;
 
 		case State::Payload:
-			if( !found_stuffing_bit() ) {
+			if( !unstuff(bit_history, bits_received) ) {
 				payload[bits_received++] = symbol;
 			}
 
-			if( found_end_flag() ) {
+			if( end(bit_history, bits_received) ) {
-				payload_handler(payload, bits_received - 7);
+				payload_handler(payload, bits_received);
 				reset_state();
 			} else {
 				if( packet_truncated() ) {
 					reset_state();
 				}
 			}
-
 			break;
 
 		default:
@@ -89,30 +100,21 @@ private:
 		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);
-	}
-
 	const PayloadHandlerFunc payload_handler;
 
 	BitHistory bit_history;
-	BitPattern preamble_pattern { 0b0101010101111110, 16, 1 };
+	PreambleMatcher preamble;
-	BitPattern unstuff_pattern { 0b111110, 6 };
+	UnstuffMatcher unstuff;
-	BitPattern end_flag_pattern { 0b01111110, 8 };
+	EndMatcher end;
 
 	size_t bits_received { 0 };
 	State state { State::Preamble };
 	PayloadType payload;
 
-	void reset_state();
+	void reset_state() {
+		bits_received = 0;
+		state = State::Preamble;
+	}
 };
 
 #endif/*__PACKET_BUILDER_H__*/

firmware/baseband/proc_fsk.hpp

@@ -56,8 +56,11 @@ private:
 		[this](const float symbol) { this->consume_symbol(symbol); }
 	};
 	symbol_coding::NRZIDecoder nrzi_decode;
-	PacketBuilder packet_builder {
+	PacketBuilder<BitPattern, BitPattern, BitPattern> packet_builder {
-		[this](const PacketBuilder::PayloadType& payload, const size_t bits_received) {
+		{ 0b0101010101111110, 16, 1 },
+		{ 0b111110, 6 },
+		{ 0b01111110, 8 },
+		[this](const payload_t& payload, const size_t bits_received) {
 			this->payload_handler(payload, bits_received);
 		}
 	};

firmware/common/ais_baseband.cpp

@@ -299,7 +299,8 @@ static std::string ais_format_navigational_status(const unsigned int value) {
 decoded_packet packet_decode(const std::bitset<1024>& payload, const size_t payload_length) {
 	// TODO: Unstuff here, not in baseband!
 
-	const size_t data_and_fcs_length = payload_length;
+	// Subtract end flag (6 bits) + one unstuffing bit (occurs during end flag).
+	const size_t data_and_fcs_length = payload_length - 7;
 
 	if( data_and_fcs_length < 38 ) {
 		return { "short " + ui::to_string_dec_uint(data_and_fcs_length, 3), "" };

firmware/common/bit_pattern.hpp

@@ -25,8 +25,29 @@
 #include <cstdint>
 #include <cstddef>
 
+class BitHistory {
+public:
+	void add(const uint_fast8_t bit) {
+		history = (history << 1) | (bit & 1);
+	}
+
+	uint32_t value() const {
+		return history;
+	}
+
+private:
+	uint32_t history { 0 };
+};
+
 class BitPattern {
 public:
+	constexpr BitPattern(
+	) : code_ { 0 },
+		mask_ { 0 },
+		maximum_hanning_distance_ { 0 }
+	{
+	}
+	
 	constexpr BitPattern(
 		const uint32_t code,
 		const size_t code_length,
@@ -37,16 +58,10 @@ public:
 	{
 	}
 
-	uint32_t code() const {
+	bool operator()(const BitHistory& history, const size_t) const {
-		return code_;
+		const auto delta_bits = (history.value() ^ code_) & mask_;
-	}
+		const size_t count = __builtin_popcountl(delta_bits);
-
+		return (count <= maximum_hanning_distance_);
-	uint32_t mask() const {
-		return mask_;
-	}
-
-	size_t maximum_hanning_distance() const {
-		return maximum_hanning_distance_;
 	}
 
 private:
@@ -55,20 +70,4 @@ private:
 	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__*/