// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- /* 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 3 of the License, 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. If not, see . */ // // NMEA parser, adapted by Michael Smith from TinyGPS v9: // // TinyGPS - a small GPS library for Arduino providing basic NMEA parsing // Copyright (C) 2008-9 Mikal Hart // All rights reserved. // // /// @file AP_GPS_NMEA.h /// @brief NMEA protocol parser /// /// This is a lightweight NMEA parser, derived originally from the /// TinyGPS parser by Mikal Hart. It is frugal in its use of memory /// and tries to avoid unnecessary arithmetic. /// /// The parser handles GPGGA, GPRMC and GPVTG messages, and attempts to be /// robust in the face of occasional corruption in the input stream. It /// makes a basic effort to configure GPS' that are likely to be connected in /// NMEA mode (SiRF, MediaTek and ublox) to emit the correct message /// stream, but does not validate that the correct stream is being received. /// In particular, a unit emitting just GPRMC will show as having a fix /// even though no altitude data is being received. /// /// GPVTG data is parsed, but as the message may not contain the the /// qualifier field (this is common with e.g. older SiRF units) it is /// not considered a source of fix-valid information. /// #ifndef __AP_GPS_NMEA_H__ #define __AP_GPS_NMEA_H__ #include "AP_GPS.h" /// NMEA parser /// class AP_GPS_NMEA : public AP_GPS_Backend { public: AP_GPS_NMEA(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port); /// Checks the serial receive buffer for characters, /// attempts to parse NMEA data and updates internal state /// accordingly. bool read(); static bool _detect(struct NMEA_detect_state &state, uint8_t data); private: /// Coding for the GPS sentences that the parser handles enum _sentence_types { //there are some more than 10 fields in some sentences , thus we have to increase these value. _GPS_SENTENCE_GPRMC = 32, _GPS_SENTENCE_GPGGA = 64, _GPS_SENTENCE_GPVTG = 96, _GPS_SENTENCE_OTHER = 0 }; /// Update the decode state machine with a new character /// /// @param c The next character in the NMEA input stream /// @returns True if processing the character has resulted in /// an update to the GPS state /// bool _decode(char c); /// Return the numeric value of an ascii hex character /// /// @param a The character to be converted /// @returns The value of the character as a hex digit /// int16_t _from_hex(char a); /// Parses the current term as a NMEA-style decimal number with /// up to two decimal digits. /// /// @returns The value expressed by the string in _term, /// multiplied by 100. /// uint32_t _parse_decimal_100(); /// Parses the current term as a NMEA-style degrees + minutes /// value with up to four decimal digits. /// /// This gives a theoretical resolution limit of around 1cm. /// /// @returns The value expressed by the string in _term, /// multiplied by 1e7. /// uint32_t _parse_degrees(); /// Processes the current term when it has been deemed to be /// complete. /// /// Each GPS message is broken up into terms separated by commas. /// Each term is then processed by this function as it is received. /// /// @returns True if completing the term has resulted in /// an update to the GPS state. bool _term_complete(); /// return true if we have a new set of NMEA messages bool _have_new_message(void); uint8_t _parity; ///< NMEA message checksum accumulator bool _is_checksum_term; ///< current term is the checksum char _term[15]; ///< buffer for the current term within the current sentence uint8_t _sentence_type; ///< the sentence type currently being processed uint8_t _term_number; ///< term index within the current sentence uint8_t _term_offset; ///< character offset with the term being received bool _gps_data_good; ///< set when the sentence indicates data is good // The result of parsing terms within a message is stored temporarily until // the message is completely processed and the checksum validated. // This avoids the need to buffer the entire message. int32_t _new_time; ///< time parsed from a term int32_t _new_date; ///< date parsed from a term int32_t _new_latitude; ///< latitude parsed from a term int32_t _new_longitude; ///< longitude parsed from a term int32_t _new_altitude; ///< altitude parsed from a term int32_t _new_speed; ///< speed parsed from a term int32_t _new_course; ///< course parsed from a term uint16_t _new_hdop; ///< HDOP parsed from a term uint8_t _new_satellite_count; ///< satellite count parsed from a term uint32_t _last_GPRMC_ms = 0; uint32_t _last_GPGGA_ms = 0; uint32_t _last_GPVTG_ms = 0; /// @name Init strings /// In ::init, an attempt is made to configure the GPS /// unit to send just the messages that we are interested /// in using these strings //@{ static const prog_char _SiRF_init_string[]; ///< init string for SiRF units static const prog_char _MTK_init_string[]; ///< init string for MediaTek units static const prog_char _ublox_init_string[]; ///< init string for ublox units //@} /// @name GPS message identifier strings //@{ static const prog_char _gprmc_string[]; static const prog_char _gpgga_string[]; static const prog_char _gpvtg_string[]; //@} static const prog_char _initialisation_blob[]; }; #endif // __AP_GPS_NMEA_H__