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firmware/common/ais_packet.hpp

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+/*
+ * 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 __AIS_PACKET_H__
+#define __AIS_PACKET_H__
+
+#include "baseband_packet.hpp"
+#include "field_reader.hpp"
+
+#include <cstdint>
+#include <cstddef>
+#include <string>
+
+namespace ais {
+
+struct DateTime {
+	uint16_t year;
+	uint8_t month;
+	uint8_t day;
+	uint8_t hour;
+	uint8_t minute;
+	uint8_t second;
+};
+
+template<size_t FieldSize, int32_t DegMax, uint32_t NAValue>
+struct LatLonBase {
+	constexpr LatLonBase(
+	) : LatLonBase { raw_not_available }
+	{
+	}
+	
+	constexpr LatLonBase(
+		const int32_t raw
+	) : raw_ { raw }
+	{
+	}
+
+	constexpr LatLonBase(
+		const LatLonBase& other
+	) : raw_ { other.raw_ }
+	{
+	}
+
+	int32_t normalized() const {
+		return static_cast<int32_t>(raw() << sign_extend_shift) / (1 << sign_extend_shift);
+	}
+
+	int32_t raw() const {
+		return raw_;
+	}
+
+	bool is_not_available() const {
+		return raw() == raw_not_available;
+	}
+
+	bool is_valid() const {
+		return (normalized() >= raw_valid_min) && (normalized() <= raw_valid_max);
+	}
+
+private:
+	int32_t raw_;
+
+	static constexpr size_t sign_extend_shift = 32 - FieldSize;
+
+	static constexpr int32_t raw_not_available = NAValue;
+	static constexpr int32_t raw_valid_min = -DegMax * 60 * 10000;
+	static constexpr int32_t raw_valid_max =  DegMax * 60 * 10000;
+};
+
+using Latitude = LatLonBase<27, 90, 0x3412140>;
+using Longitude = LatLonBase<28, 180, 0x6791AC0>;
+
+using RateOfTurn = int8_t;
+using SpeedOverGround = uint16_t;
+using CourseOverGround = uint16_t;
+using TrueHeading = uint16_t;
+
+using MMSI = uint32_t;
+
+class Packet {
+public:
+	constexpr Packet(
+		const baseband::Packet& packet
+	) : packet_ { packet },
+		field_ { packet_ }
+	{
+	}
+
+	size_t length() const;
+	
+	bool is_valid() const;
+
+	Timestamp received_at() const;
+
+	uint32_t message_id() const;
+	MMSI user_id() const;
+	MMSI source_id() const;
+
+	uint32_t read(const size_t start_bit, const size_t length) const;
+
+	std::string text(const size_t start_bit, const size_t character_count) const;
+
+	DateTime datetime(const size_t start_bit) const;
+
+	Latitude latitude(const size_t start_bit) const;
+	Longitude longitude(const size_t start_bit) const;
+
+	bool crc_ok() const;
+
+private:
+	using Reader = FieldReader<baseband::Packet, BitRemapByteReverse>;
+	using CRCReader = FieldReader<baseband::Packet, BitRemapNone>;
+	
+	const baseband::Packet packet_;
+	const Reader field_;
+
+	const size_t fcs_length = 16;
+
+	size_t data_and_fcs_length() const;
+	size_t data_length() const;
+
+	bool length_valid() const;
+};
+
+} /* namespace ais */
+
+#endif/*__AIS_PACKET_H__*/