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ardupilot/libraries/AP_GPS/AP_GPS_NMEA.cpp

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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
//
// 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.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
/// @file AP_GPS_NMEA.cpp
/// @brief NMEA protocol parser
///
/// This is a lightweight NMEA parser, derived originally from the
/// TinyGPS parser by Mikal Hart.
///
#include <FastSerial.h>
#include <AP_Common.h>
#include <avr/pgmspace.h>
#include <ctype.h>
#include <stdint.h>
#include "AP_GPS_NMEA.h"
// SiRF init messages //////////////////////////////////////////////////////////
//
// Note that we will only see a SiRF in NMEA mode if we are explicitly configured
// for NMEA. GPS_AUTO will try to set any SiRF unit to binary mode as part of
// the autodetection process.
//
const prog_char AP_GPS_NMEA::_SiRF_init_string[] PROGMEM =
"$PSRF103,0,0,1,1*25\r\n" // GGA @ 1Hz
"$PSRF103,1,0,0,1*25\r\n" // GLL off
"$PSRF103,2,0,0,1*26\r\n" // GSA off
"$PSRF103,3,0,0,1*27\r\n" // GSV off
"$PSRF103,4,0,1,1*20\r\n" // RMC off
"$PSRF103,5,0,1,1*20\r\n" // VTG @ 1Hz
"$PSRF103,6,0,0,1*22\r\n" // MSS off
"$PSRF103,8,0,0,1*2C\r\n" // ZDA off
"$PSRF151,1*3F\r\n" // WAAS on (not always supported)
"$PSRF106,21*0F\r\n" // datum = WGS84
"";
// MediaTek init messages //////////////////////////////////////////////////////
//
// Note that we may see a MediaTek in NMEA mode if we are connected to a non-DIYDrones
// MediaTek-based GPS.
//
const prog_char AP_GPS_NMEA::_MTK_init_string[] PROGMEM =
"$PMTK314,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0*28\r\n" // GGA & VTG once every fix
"$PMTK330,0*2E\r\n" // datum = WGS84
"$PMTK313,1*2E\r\n" // SBAS on
"$PMTK301,2*2E\r\n" // use SBAS data for DGPS
"";
// ublox init messages /////////////////////////////////////////////////////////
//
// Note that we will only see a ublox in NMEA mode if we are explicitly configured
// for NMEA. GPS_AUTO will try to set any ublox unit to binary mode as part of
// the autodetection process.
//
// We don't attempt to send $PUBX,41 as the unit must already be talking NMEA
// and we don't know the baudrate.
//
const prog_char AP_GPS_NMEA::_ublox_init_string[] PROGMEM =
"$PUBX,40,gga,0,1,0,0,0,0*7B\r\n" // GGA on at one per fix
"$PUBX,40,vtg,0,1,0,0,0,0*7F\r\n" // VTG on at one per fix
"$PUBX,40,rmc,0,0,0,0,0,0*67\r\n" // RMC off (XXX suppress other message types?)
"";
// NMEA message identifiers ////////////////////////////////////////////////////
//
const char AP_GPS_NMEA::_gprmc_string[] PROGMEM = "GPRMC";
const char AP_GPS_NMEA::_gpgga_string[] PROGMEM = "GPGGA";
const char AP_GPS_NMEA::_gpvtg_string[] PROGMEM = "GPVTG";
// Convenience macros //////////////////////////////////////////////////////////
//
#define DIGIT_TO_VAL(_x) (_x - '0')
// Constructors ////////////////////////////////////////////////////////////////
AP_GPS_NMEA::AP_GPS_NMEA(Stream *s) :
GPS(s)
{
FastSerial *fs = (FastSerial *)_port;
// Re-open the port with enough receive buffering for the messages we expect
// and very little tx buffering, since we don't care about sending.
// Leave the port speed alone as we don't actually know at what rate we're running...
//
fs->begin(0, 200, 16);
}
// Public Methods //////////////////////////////////////////////////////////////
void AP_GPS_NMEA::init(void)
{
BetterStream *bs = (BetterStream *)_port;
// send the SiRF init strings
bs->print_P((const prog_char_t *)_SiRF_init_string);
// send the MediaTek init strings
bs->print_P((const prog_char_t *)_MTK_init_string);
// send the ublox init strings
bs->print_P((const prog_char_t *)_ublox_init_string);
idleTimeout = 1200;
}
bool AP_GPS_NMEA::read(void)
{
int numc;
bool parsed = false;
numc = _port->available();
while (numc--) {
if (_decode(_port->read())) {
parsed = true;
}
}
return parsed;
}
bool AP_GPS_NMEA::_decode(char c)
{
bool valid_sentence = false;
switch (c) {
case ',': // term terminators
_parity ^= c;
case '\r':
case '\n':
case '*':
if (_term_offset < sizeof(_term)) {
_term[_term_offset] = 0;
valid_sentence = _term_complete();
}
++_term_number;
_term_offset = 0;
_is_checksum_term = c == '*';
return valid_sentence;
case '$': // sentence begin
_term_number = _term_offset = 0;
_parity = 0;
_sentence_type = _GPS_SENTENCE_OTHER;
_is_checksum_term = false;
_gps_data_good = false;
return valid_sentence;
}
// ordinary characters
if (_term_offset < sizeof(_term) - 1)
_term[_term_offset++] = c;
if (!_is_checksum_term)
_parity ^= c;
return valid_sentence;
}
//
// internal utilities
//
int AP_GPS_NMEA::_from_hex(char a)
{
if (a >= 'A' && a <= 'F')
return a - 'A' + 10;
else if (a >= 'a' && a <= 'f')
return a - 'a' + 10;
else
return a - '0';
}
unsigned long AP_GPS_NMEA::_parse_decimal()
{
char *p = _term;
unsigned long ret = 100UL * atol(p);
while (isdigit(*p))
++p;
if (*p == '.') {
if (isdigit(p[1])) {
ret += 10 * (p[1] - '0');
if (isdigit(p[2]))
ret += p[2] - '0';
}
}
return ret;
}
unsigned long AP_GPS_NMEA::_parse_degrees()
{
char *p, *q;
uint8_t deg = 0, min = 0;
unsigned int frac_min = 0;
// scan for decimal point or end of field
for (p = _term; isdigit(*p); p++)
;
q = _term;
// convert degrees
while ((p - q) > 2) {
if (deg)
deg *= 10;
deg += DIGIT_TO_VAL(*q++);
}
// convert minutes
while (p > q) {
if (min)
min *= 10;
min += DIGIT_TO_VAL(*q++);
}
// convert fractional minutes
// expect up to four digits, result is in
// ten-thousandths of a minute
if (*p == '.') {
q = p + 1;
for (int i = 0; i < 4; i++) {
frac_min *= 10;
if (isdigit(*q))
frac_min += *q++ - '0';
}
}
return deg * 100000UL + (min * 10000UL + frac_min) / 6;
}
// Processes a just-completed term
// Returns true if new sentence has just passed checksum test and is validated
bool AP_GPS_NMEA::_term_complete()
{
// handle the last term in a message
if (_is_checksum_term) {
uint8_t checksum = 16 * _from_hex(_term[0]) + _from_hex(_term[1]);
if (checksum == _parity) {
if (_gps_data_good) {
switch (_sentence_type) {
case _GPS_SENTENCE_GPRMC:
time = _new_time;
date = _new_date;
latitude = _new_latitude * 100; // degrees*10e5 -> 10e7
longitude = _new_longitude * 100; // degrees*10e5 -> 10e7
ground_speed = _new_speed;
ground_course = _new_course;
fix = true;
break;
case _GPS_SENTENCE_GPGGA:
altitude = _new_altitude;
time = _new_time;
latitude = _new_latitude * 100; // degrees*10e5 -> 10e7
longitude = _new_longitude * 100; // degrees*10e5 -> 10e7
num_sats = _new_satellite_count;
hdop = _new_hdop;
fix = true;
break;
case _GPS_SENTENCE_GPVTG:
ground_speed = _new_speed;
ground_course = _new_course;
// VTG has no fix indicator, can't change fix status
break;
}
} else {
switch (_sentence_type) {
case _GPS_SENTENCE_GPRMC:
case _GPS_SENTENCE_GPGGA:
// Only these sentences give us information about
// fix status.
fix = false;
}
}
// we got a good message
return true;
}
// we got a bad message, ignore it
return false;
}
// the first term determines the sentence type
if (_term_number == 0) {
if (!strcmp_P(_term, _gprmc_string)) {
_sentence_type = _GPS_SENTENCE_GPRMC;
} else if (!strcmp_P(_term, _gpgga_string)) {
_sentence_type = _GPS_SENTENCE_GPGGA;
} else if (!strcmp_P(_term, _gpvtg_string)) {
_sentence_type = _GPS_SENTENCE_GPVTG;
// VTG may not contain a data qualifier, presume the solution is good
// unless it tells us otherwise.
_gps_data_good = true;
} else {
_sentence_type = _GPS_SENTENCE_OTHER;
}
return false;
}
// 32 = RMC, 64 = GGA, 96 = VTG
if (_sentence_type != _GPS_SENTENCE_OTHER && _term[0]) {
switch (_sentence_type + _term_number) {
// operational status
//
case _GPS_SENTENCE_GPRMC + 2: // validity (RMC)
_gps_data_good = _term[0] == 'A';
break;
case _GPS_SENTENCE_GPGGA + 6: // Fix data (GGA)
_gps_data_good = _term[0] > '0';
break;
case _GPS_SENTENCE_GPVTG + 9: // validity (VTG) (we may not see this field)
_gps_data_good = _term[0] != 'N';
break;
case _GPS_SENTENCE_GPGGA + 7: // satellite count (GGA)
_new_satellite_count = atol(_term);
break;
case _GPS_SENTENCE_GPGGA + 8: // HDOP (GGA)
_new_hdop = _parse_decimal();
break;
// time and date
//
case _GPS_SENTENCE_GPRMC + 1: // Time (RMC)
case _GPS_SENTENCE_GPGGA + 1: // Time (GGA)
_new_time = _parse_decimal();
break;
case _GPS_SENTENCE_GPRMC + 9: // Date (GPRMC)
_new_date = atol(_term);
break;
// location
//
case _GPS_SENTENCE_GPRMC + 3: // Latitude
case _GPS_SENTENCE_GPGGA + 2:
_new_latitude = _parse_degrees();
break;
case _GPS_SENTENCE_GPRMC + 4: // N/S
case _GPS_SENTENCE_GPGGA + 3:
if (_term[0] == 'S')
_new_latitude = -_new_latitude;
break;
case _GPS_SENTENCE_GPRMC + 5: // Longitude
case _GPS_SENTENCE_GPGGA + 4:
_new_longitude = _parse_degrees();
break;
case _GPS_SENTENCE_GPRMC + 6: // E/W
case _GPS_SENTENCE_GPGGA + 5:
if (_term[0] == 'W')
_new_longitude = -_new_longitude;
break;
case _GPS_SENTENCE_GPGGA + 9: // Altitude (GPGGA)
_new_altitude = _parse_decimal();
break;
// course and speed
//
case _GPS_SENTENCE_GPRMC + 7: // Speed (GPRMC)
case _GPS_SENTENCE_GPVTG + 5: // Speed (VTG)
_new_speed = (_parse_decimal() * 514) / 1000; // knots-> m/sec, approximiates * 0.514
break;
case _GPS_SENTENCE_GPRMC + 8: // Course (GPRMC)
case _GPS_SENTENCE_GPVTG + 1: // Course (VTG)
_new_course = _parse_decimal();
break;
}
}
return false;
}
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