AIS decoding and really bad UI.

The decoder needs a serious refactoring/decoupling.
The UI just dumps bits of the received packets into a console window, whcih scrolls too quickly in an AIS-dense area with a good antenna.

firmware/application/Makefile

@@ -167,6 +167,7 @@ CPPSRC = main.cpp \
          ui_spectrum.cpp \
          receiver_model.cpp \
          spectrum_color_lut.cpp \
+         ais_baseband.cpp \
          ../common/utility.cpp \
          ../common/chibios_cpp.cpp \
          ../common/debug.cpp \

firmware/application/ui_receiver.cpp

@@ -27,6 +27,8 @@
 #include "portapack.hpp"
 using namespace portapack;
 
+#include "ais_baseband.hpp"
+
 namespace ui {
 
 /* BasebandBandwidthField ************************************************/
@@ -496,8 +498,8 @@ ReceiverView::~ReceiverView() {
 void ReceiverView::on_show() {
 	context().message_map.register_handler(Message::ID::FSKPacket,
 		[this](Message* const p) {
-			auto message = static_cast<FSKPacketMessage*>(p);
+			const auto message = static_cast<const FSKPacketMessage*>(p);
-			(void)message;
+			this->on_packet_ais(*message);
 		}
 	);
 }
@@ -506,7 +508,13 @@ void ReceiverView::on_hide() {
 	context().message_map.unregister_handler(Message::ID::FSKPacket);
 }
 
+void ReceiverView::on_packet_ais(const FSKPacketMessage& message) {
+	const auto result = baseband::ais::packet_decode(message.packet.payload, message.packet.bits_received);
 
+	auto console = reinterpret_cast<Console*>(widget_content.get());
+	if( result.first == "OK" ) {
+		console->writeln(result.second);
+	}
 }
 
 void ReceiverView::focus() {

firmware/application/ui_receiver.hpp

@@ -415,6 +415,7 @@ private:
 			{ " AM ", 0 },
 			{ "NFM ", 1 },
 			{ "WFM ", 2 },
+			{ "AIS ", 3 },
 			{ "SPEC", 4 },
 		}
 	};
@@ -470,6 +471,8 @@ private:
 	void on_headphone_volume_changed(int32_t v);
 //	void on_baseband_oversampling_changed(int32_t v);
 	void on_edit_frequency();
+
+	void on_packet_ais(const FSKPacketMessage& message);
 };
 
 } /* namespace ui */

firmware/common/ais_baseband.cpp

@@ -0,0 +1,371 @@
+/*
+ * 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 "ais_baseband.hpp"
+
+#include <cstdint>
+#include <cstddef>
+#include <cstdlib>
+#include <string>
+
+#include "crc.hpp"
+
+// TODO: Move string formatting elsewhere!!!
+#include "ui_widget.hpp"
+
+namespace baseband {
+
+template<typename T, typename BitRemap>
+class FieldReader {
+public:
+	constexpr FieldReader(
+		const T& data
+	) : data { data }
+	{
+	}
+
+	uint32_t read(const size_t start_bit, const size_t length) const {
+		uint32_t value = 0;
+		for(size_t i=start_bit; i<(start_bit + length); i++) {
+			value = (value << 1) | data[bit_remap(i)];
+		}
+		return value;
+	}
+
+private:
+	const T& data;
+	const BitRemap bit_remap { };
+};
+
+namespace ais {
+
+struct BitRemap {
+	size_t operator()(const size_t bit_index) const {
+		return bit_index ^ 7;
+	}
+};
+
+struct CRCBitRemap {
+	size_t operator()(const size_t bit_index) const {
+		return bit_index;
+	}
+};
+
+using FieldReader = baseband::FieldReader<std::bitset<1024>, BitRemap>;
+using CRCFieldReader = baseband::FieldReader<std::bitset<1024>, CRCBitRemap>;
+
+struct PacketLengthRange {
+	constexpr PacketLengthRange(
+	) : min_bytes { 0 },
+		max_bytes { 0 }
+	{
+	}
+
+	constexpr PacketLengthRange(
+		const uint16_t min_bits,
+		const uint16_t max_bits
+	) : min_bytes { static_cast<uint8_t>(min_bits / 8U) },
+		max_bytes { static_cast<uint8_t>(max_bits / 8U) }
+	{
+		// static_assert((min_bits & 7) == 0, "minimum bits not a multiple of 8");
+		// static_assert((max_bits & 7) == 0, "minimum bits not a multiple of 8");
+	}
+
+	bool contains(const size_t bit_count) const {
+		return !is_above(bit_count) && !is_below(bit_count);
+	}
+
+	bool is_above(const size_t bit_count) const {
+		return (min() > bit_count);
+	}
+
+	bool is_below(const size_t bit_count) const {
+		return (max() < bit_count);
+	}
+
+	size_t min() const {
+		return min_bytes * 8;
+	}
+	
+	size_t max() const {
+		return max_bytes * 8;
+	}
+
+private:
+	const uint8_t min_bytes;
+	const uint8_t max_bytes;
+};
+
+static constexpr std::array<PacketLengthRange, 64> packet_length_range { {
+	{    0,    0 },	// 0
+	{  168,  168 },	// 1
+	{  168,  168 },	// 2
+	{  168,  168 }, // 3
+	{  168,  168 }, // 4
+	{  424,  424 }, // 5
+	{    0,    0 }, // 6
+	{    0,    0 }, // 7
+	{    0, 1008 }, // 8
+	{    0,    0 }, // 9
+	{    0,    0 }, // 10
+	{    0,    0 }, // 11
+	{    0,    0 }, // 12
+	{    0,    0 }, // 13
+	{    0,    0 }, // 14
+	{    0,    0 }, // 15
+	{    0,    0 }, // 16
+	{    0,    0 }, // 17
+	{  168,  168 }, // 18
+	{    0,    0 }, // 19
+	{   72,  160 }, // 20
+	{  272,  360 }, // 21
+	{  168,  168 }, // 22
+	{  160,  160 }, // 23
+	{  160,  168 }, // 24
+	{    0,  168 }, // 25
+	{    0,    0 }, // 26
+	{    0,    0 }, // 27
+	{    0,    0 }, // 28
+	{    0,    0 }, // 29
+	{    0,    0 }, // 30
+	{    0,    0 }, // 31
+} };
+
+struct PacketLengthValidator {
+	bool operator()(const uint_fast8_t message_id, const size_t length) {
+		return packet_length_range[message_id].contains(length);
+	}
+};
+
+struct PacketTooLong {
+	bool operator()(const uint_fast8_t message_id, const size_t length) {
+		return packet_length_range[message_id].is_below(length);
+	}
+};
+
+struct CRCCheck {
+	bool operator()(const std::bitset<1024>& payload, const size_t data_length) {
+		CRCFieldReader field_crc { payload };
+		CRC<uint16_t> ais_fcs { 0x1021 };
+		
+		uint16_t crc_calculated = 0xffff;
+		
+		for(size_t i=0; i<data_length + 16; i+=8) {
+			if( i == data_length ) {
+				crc_calculated ^= 0xffff;
+			}
+			const uint8_t byte = field_crc.read(i, 8);
+			crc_calculated = ais_fcs.calculate_byte(crc_calculated, byte);
+		}
+
+		return crc_calculated == 0x0000;
+	}
+};
+
+static int32_t ais_latitude_normalized(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	// Shifting and dividing is to sign-extend the source field.
+	// TODO: There's probably a more elegant way to do it.
+	return static_cast<int32_t>(field.read(start_bit, 27) << 5) / 32;
+}
+
+static int32_t ais_longitude_normalized(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	// Shifting and dividing is to sign-extend the source field.
+	// TODO: There's probably a more elegant way to do it.
+	return static_cast<int32_t>(field.read(start_bit, 28) << 4) / 16;
+}
+
+static std::string ais_format_latlon_normalized(const int32_t normalized) {
+	const int32_t t = (normalized * 5) / 3;
+	const int32_t degrees = t / (100 * 10000);
+	const int32_t fraction = std::abs(t) % (100 * 10000);
+	return ui::to_string_dec_int(degrees) + "." + ui::to_string_dec_int(fraction, 6, '0');
+}
+
+static std::string ais_format_latitude(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	const auto value = static_cast<int32_t>(field.read(start_bit, 27) << 5) / 32;
+	return ais_format_latlon_normalized(value);
+}
+
+static std::string ais_format_longitude(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	const auto value = static_cast<int32_t>(field.read(start_bit, 28) << 4) / 16;
+	return ais_format_latlon_normalized(value);
+}
+
+struct ais_datetime {
+	uint16_t year;
+	uint8_t month;
+	uint8_t day;
+	uint8_t hour;
+	uint8_t minute;
+	uint8_t second;
+};
+
+static ais_datetime ais_get_datetime(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	return {
+		static_cast<uint16_t>(field.read(start_bit +  0, 14)),
+		static_cast<uint8_t >(field.read(start_bit + 14,  4)),
+		static_cast<uint8_t >(field.read(start_bit + 18,  5)),
+		static_cast<uint8_t >(field.read(start_bit + 23,  5)),
+		static_cast<uint8_t >(field.read(start_bit + 28,  6)),
+		static_cast<uint8_t >(field.read(start_bit + 34,  6)),
+	};
+}
+
+static std::string ais_format_datetime(
+	const FieldReader& field,
+	const size_t start_bit
+) {
+	const auto datetime = ais_get_datetime(field, start_bit);
+	return ui::to_string_dec_uint(datetime.year, 4) + "/" +
+		ui::to_string_dec_uint(datetime.month, 2, '0') + "/" +
+		ui::to_string_dec_uint(datetime.day, 2, '0') + " " +
+		ui::to_string_dec_uint(datetime.hour, 2, '0') + ":" +
+		ui::to_string_dec_uint(datetime.minute, 2, '0') + ":" +
+		ui::to_string_dec_uint(datetime.second, 2, '0');
+}
+
+static char ais_char_to_ascii(const uint8_t c) {
+	return (c ^ 32) + 32;
+}
+
+static std::string ais_read_text(
+	const FieldReader& field,
+	const size_t start_bit,
+	const size_t character_count
+) {
+	std::string result;
+	const size_t character_length = 6;
+	const size_t end_bit = start_bit + character_count * character_length;
+	for(size_t i=start_bit; i<end_bit; i+=character_length) {
+		result += ais_char_to_ascii(field.read(i, character_length));
+	} 
+
+	return result;
+}
+
+static std::string ais_format_navigational_status(const unsigned int value) {
+	switch(value) {
+		case 0: return "under way w/engine";
+		case 1: return "at anchor";
+		case 2: return "not under command";
+		case 3: return "restricted maneuv";
+		case 4: return "constrained draught";
+		case 5: return "moored";
+		case 6: return "aground";
+		case 7: return "fishing";
+		case 8: return "sailing";
+		case 9: case 10: case 13: return "reserved";
+		case 11: return "towing astern";
+		case 12: return "towing ahead/along";
+		case 14: return "SART/MOB/EPIRB";
+		case 15: return "undefined";
+		default: return "unexpected";
+	}
+}
+
+decoded_packet packet_decode(const std::bitset<1024>& data, const size_t data_length) {
+	if( data_length < 38 ) {
+		return { "short " + ui::to_string_dec_uint(data_length, 3), "" };
+	}
+
+	const size_t extra_bits = data_length & 7;
+	if( extra_bits != 0 ) {
+		return { "extra bits " + ui::to_string_dec_uint(data_length, 3), "" };
+	}
+
+	FieldReader field { data };
+
+	const auto message_id = field.read(0, 6);
+
+	const size_t payload_length = data_length - 16;
+	PacketLengthValidator packet_length_valid;
+	if( !packet_length_valid(message_id, payload_length) ) {
+		return { "bad length " + ui::to_string_dec_uint(payload_length, 3), "" };
+	}
+
+	CRCCheck crc_ok;
+	if( !crc_ok(data, payload_length) ) {
+		return { "crc", "" };
+	}
+
+	const auto source_id = field.read(8, 30);
+	std::string result { ui::to_string_dec_uint(message_id, 2) + " " + ui::to_string_dec_uint(source_id, 10) };
+
+	switch(message_id) {
+	case 1:
+	case 2:
+	case 3:
+		{
+			const auto navigational_status = field.read(38, 4);
+			result += " " + ais_format_navigational_status(navigational_status);
+			result += " " + ais_format_latlon_normalized(ais_latitude_normalized(field, 89));
+			result += " " + ais_format_latlon_normalized(ais_longitude_normalized(field, 61));
+		}
+		break;
+
+	case 4:
+		{
+			result += " " + ais_format_datetime(field, 38);
+			result += " " + ais_format_latlon_normalized(ais_latitude_normalized(field, 107));
+			result += " " + ais_format_latlon_normalized(ais_longitude_normalized(field, 79));
+		}
+		break;
+
+	case 5:
+		{
+			const auto call_sign = ais_read_text(field, 70, 7);
+			const auto name = ais_read_text(field, 112, 20);
+			const auto destination = ais_read_text(field, 302, 20);
+			result += " \"" + call_sign + "\" \"" + name + "\" \"" + destination + "\""; 
+		}
+		break;
+
+	case 21:
+		{
+			const auto name = ais_read_text(field, 43, 20);
+			result += " \"" + name + "\" " + ais_format_latitude(field, 192) + " " + ais_format_longitude(field, 164);
+		}
+		break;
+
+	default:
+		break;
+	}
+
+	return { "OK", result };
+}
+
+} /* namespace ais */
+} /* namespace baseband */

firmware/common/ais_baseband.hpp

@@ -22,38 +22,14 @@
 #ifndef __AIS_BASEBAND_H__
 #define __AIS_BASEBAND_H__
 
-#include "crc.hpp"
-
 #include <cstdint>
 #include <cstddef>
 #include <complex>
 #include <array>
 #include <bitset>
+#include <utility>
 
 namespace baseband {
-
-template<typename T, typename BitRemap>
-class FieldReader {
-public:
-	constexpr FieldReader(
-		const T& data
-	) : data { data }
-	{
-	}
-
-	uint32_t read(const size_t start_bit, const size_t length) const {
-		uint32_t value = 0;
-		for(size_t i=start_bit; i<(start_bit + length); i++) {
-			value = (value << 1) | data[bit_remap(i)];
-		}
-		return value;
-	}
-
-private:
-	const T& data;
-	const BitRemap bit_remap { };
-};
-
 namespace ais {
 
 // RRC length should be about 4 x the symbol length to do a good job of
@@ -209,128 +185,9 @@ constexpr std::array<std::complex<float>, 128> rrc_taps_128_decim_1_p { {
 	{ -1.1001696231e-04f,  4.5570517881e-05f }, { -2.5877077742e-04f,  5.1472707944e-05f },
 } };
 
-struct BitRemap {
+using decoded_packet = std::pair<std::string, std::string>;
-	size_t operator()(const size_t bit_index) const {
-		return bit_index ^ 7;
-	}
-};
 
-struct CRCBitRemap {
+decoded_packet packet_decode(const std::bitset<1024>& data, const size_t data_length);
-	size_t operator()(const size_t bit_index) const {
-		return bit_index;
-	}
-};
-
-using FieldReader = baseband::FieldReader<std::bitset<1024>, BitRemap>;
-using CRCFieldReader = baseband::FieldReader<std::bitset<1024>, CRCBitRemap>;
-
-struct PacketLengthRange {
-	constexpr PacketLengthRange(
-	) : min_bytes { 0 },
-		max_bytes { 0 }
-	{
-	}
-
-	constexpr PacketLengthRange(
-		const uint16_t min_bits,
-		const uint16_t max_bits
-	) : min_bytes { static_cast<uint8_t>(min_bits / 8U) },
-		max_bytes { static_cast<uint8_t>(max_bits / 8U) }
-	{
-		// static_assert((min_bits & 7) == 0, "minimum bits not a multiple of 8");
-		// static_assert((max_bits & 7) == 0, "minimum bits not a multiple of 8");
-	}
-
-	bool contains(const size_t bit_count) const {
-		return !is_above(bit_count) && !is_below(bit_count);
-	}
-
-	bool is_above(const size_t bit_count) const {
-		return (min() > bit_count);
-	}
-
-	bool is_below(const size_t bit_count) const {
-		return (max() < bit_count);
-	}
-
-	size_t min() const {
-		return min_bytes * 8;
-	}
-	
-	size_t max() const {
-		return max_bytes * 8;
-	}
-
-private:
-	const uint8_t min_bytes;
-	const uint8_t max_bytes;
-};
-
-constexpr std::array<PacketLengthRange, 64> packet_length_range { {
-	{    0,    0 },	// 0
-	{  168,  168 },	// 1
-	{  168,  168 },	// 2
-	{  168,  168 }, // 3
-	{  168,  168 }, // 4
-	{  424,  424 }, // 5
-	{    0,    0 }, // 6
-	{    0,    0 }, // 7
-	{    0, 1008 }, // 8
-	{    0,    0 }, // 9
-	{    0,    0 }, // 10
-	{    0,    0 }, // 11
-	{    0,    0 }, // 12
-	{    0,    0 }, // 13
-	{    0,    0 }, // 14
-	{    0,    0 }, // 15
-	{    0,    0 }, // 16
-	{    0,    0 }, // 17
-	{  168,  168 }, // 18
-	{    0,    0 }, // 19
-	{   72,  160 }, // 20
-	{  272,  360 }, // 21
-	{  168,  168 }, // 22
-	{  160,  160 }, // 23
-	{  160,  168 }, // 24
-	{    0,  168 }, // 25
-	{    0,    0 }, // 26
-	{    0,    0 }, // 27
-	{    0,    0 }, // 28
-	{    0,    0 }, // 29
-	{    0,    0 }, // 30
-	{    0,    0 }, // 31
-} };
-
-struct PacketLengthValidator {
-	bool operator()(const uint_fast8_t message_id, const size_t length) {
-		return packet_length_range[message_id].contains(length);
-	}
-};
-
-struct PacketTooLong {
-	bool operator()(const uint_fast8_t message_id, const size_t length) {
-		return packet_length_range[message_id].is_below(length);
-	}
-};
-
-struct CRCCheck {
-	bool operator()(const std::bitset<1024>& payload, const size_t data_length) {
-		CRCFieldReader field_crc { payload };
-		CRC<uint16_t> ais_fcs { 0x1021 };
-		
-		uint16_t crc_calculated = 0xffff;
-		
-		for(size_t i=0; i<data_length + 16; i+=8) {
-			if( i == data_length ) {
-				crc_calculated ^= 0xffff;
-			}
-			const uint8_t byte = field_crc.read(i, 8);
-			crc_calculated = ais_fcs.calculate_byte(crc_calculated, byte);
-		}
-
-		return crc_calculated == 0x0000;
-	}
-};
 
 } /* namespace ais */
 } /* namespace baseband */