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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: 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 <http://www.gnu.org/licenses/>.
*/
//
// 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.cpp
/// @brief NMEA protocol parser
///
/// This is a lightweight NMEA parser, derived originally from the
/// TinyGPS parser by Mikal Hart.
///
#include <AP_Common.h>
#include <AP_Progmem.h>
#include <ctype.h>
#include <stdint.h>
#include <stdlib.h>
#include "AP_GPS_NMEA.h"
extern const AP_HAL::HAL& hal;
// 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.
//
#define SIRF_INIT_MSG \
"$PSRF103,0,0,1,1*25\r\n" /* GGA @ 1Hz */ \
"$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.
//
#define MTK_INIT_MSG \
"$PMTK314,0,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n" /* RMC, GGA & VTG once every fix */ \
"$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 $PUBX,41 as the unit must already be talking NMEA
// and we don't know the baudrate.
//
#define UBLOX_INIT_MSG \
"$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?) */
const prog_char AP_GPS_NMEA::_initialisation_blob[] PROGMEM = SIRF_INIT_MSG MTK_INIT_MSG UBLOX_INIT_MSG;
// 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')
#define hexdigit(x) ((x)>9?'A'+(x):'0'+(x))
AP_GPS_NMEA::AP_GPS_NMEA(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
AP_GPS_Backend(_gps, _state, _port),
_parity(0),
_is_checksum_term(false),
_sentence_type(0),
_term_number(0),
_term_offset(0),
_gps_data_good(false)
{
gps.send_blob_start(state.instance, _initialisation_blob, sizeof(_initialisation_blob));
// this guarantees that _term is always nul terminated
memset(_term, 0, sizeof(_term));
}
bool AP_GPS_NMEA::read(void)
{
int16_t 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
//
int16_t 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';
}
uint32_t AP_GPS_NMEA::_parse_decimal_100()
{
char *p = _term;
uint32_t ret = 100UL * atol(p);
while (isdigit(*p))
++p;
if (*p == '.') {
if (isdigit(p[1])) {
ret += 10 * DIGIT_TO_VAL(p[1]);
if (isdigit(p[2]))
ret += DIGIT_TO_VAL(p[2]);
}
}
return ret;
}
/*
parse a NMEA latitude/longitude degree value. The result is in degrees*1e7
*/
uint32_t AP_GPS_NMEA::_parse_degrees()
{
char *p, *q;
uint8_t deg = 0, min = 0;
float frac_min = 0;
int32_t ret = 0;
// scan for decimal point or end of field
for (p = _term; *p && isdigit(*p); p++)
;
q = _term;
// convert degrees
while ((p - q) > 2 && *q) {
if (deg)
deg *= 10;
deg += DIGIT_TO_VAL(*q++);
}
// convert minutes
while (p > q && *q) {
if (min)
min *= 10;
min += DIGIT_TO_VAL(*q++);
}
// convert fractional minutes
if (*p == '.') {
q = p + 1;
float frac_scale = 0.1f;
while (*q && isdigit(*q)) {
frac_min += DIGIT_TO_VAL(*q) * frac_scale;
q++;
frac_scale *= 0.1f;
}
}
ret = (deg * (int32_t)10000000UL);
ret += (min * (int32_t)10000000UL / 60);
ret += (int32_t) (frac_min * (1.0e7f / 60.0f));
return ret;
}
/*
see if we have a new set of NMEA messages
*/
bool AP_GPS_NMEA::_have_new_message()
{
if (_last_GPRMC_ms == 0 ||
_last_GPGGA_ms == 0) {
return false;
}
uint32_t now = hal.scheduler->millis();
if (now - _last_GPRMC_ms > 150 ||
now - _last_GPGGA_ms > 150) {
return false;
}
if (_last_GPVTG_ms != 0 &&
now - _last_GPVTG_ms > 150) {
return false;
}
// prevent these messages being used again
if (_last_GPVTG_ms != 0) {
_last_GPVTG_ms = 1;
}
_last_GPGGA_ms = 1;
_last_GPRMC_ms = 1;
return true;
}
// 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;
state.location.lat = _new_latitude;
state.location.lng = _new_longitude;
state.ground_speed = _new_speed*0.01f;
state.ground_course_cd = _new_course;
make_gps_time(_new_date, _new_time * 10);
state.last_gps_time_ms = hal.scheduler->millis();
// To-Do: add support for proper reporting of 2D and 3D fix
state.status = AP_GPS::GPS_OK_FIX_3D;
fill_3d_velocity();
break;
case _GPS_SENTENCE_GPGGA:
state.location.alt = _new_altitude;
state.location.lat = _new_latitude;
state.location.lng = _new_longitude;
state.num_sats = _new_satellite_count;
state.hdop = _new_hdop;
// To-Do: add support for proper reporting of 2D and 3D fix
state.status = AP_GPS::GPS_OK_FIX_3D;
break;
case _GPS_SENTENCE_GPVTG:
state.ground_speed = _new_speed*0.01f;
state.ground_course_cd = _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.
state.status = AP_GPS::NO_FIX;
}
}
// see if we got a good message
return _have_new_message();
}
// 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;
_last_GPRMC_ms = hal.scheduler->millis();
} else if (!strcmp_P(_term, _gpgga_string)) {
_sentence_type = _GPS_SENTENCE_GPGGA;
_last_GPGGA_ms = hal.scheduler->millis();
} 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.
_last_GPVTG_ms = hal.scheduler->millis();
_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_100();
break;
// time and date
//
case _GPS_SENTENCE_GPRMC + 1: // Time (RMC)
case _GPS_SENTENCE_GPGGA + 1: // Time (GGA)
_new_time = _parse_decimal_100();
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_100();
break;
// course and speed
//
case _GPS_SENTENCE_GPRMC + 7: // Speed (GPRMC)
case _GPS_SENTENCE_GPVTG + 5: // Speed (VTG)
_new_speed = (_parse_decimal_100() * 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_100();
break;
}
}
return false;
}
/*
detect a NMEA GPS. Adds one byte, and returns true if the stream
matches a NMEA string
*/
bool
AP_GPS_NMEA::_detect(struct NMEA_detect_state &state, uint8_t data)
{
switch (state.step) {
case 0:
state.ck = 0;
if ('$' == data) {
state.step++;
}
break;
case 1:
if ('*' == data) {
state.step++;
} else {
state.ck ^= data;
}
break;
case 2:
if (hexdigit(state.ck>>4) == data) {
state.step++;
} else {
state.step = 0;
}
break;
case 3:
if (hexdigit(state.ck&0xF) == data) {
return true;
}
state.step = 0;
break;
}
return false;
}
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