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/*
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/AP_Common.h>
#include <ctype.h>
#include <stdint.h>
#include <stdlib.h>
#include "AP_GPS_NMEA.h"
extern const AP_HAL::HAL& hal;
// optionally log all NMEA data for debug purposes
// #define NMEA_LOG_PATH "nmea.log"
#ifdef NMEA_LOG_PATH
#include <stdio.h>
#endif
// Convenience macros //////////////////////////////////////////////////////////
//
#define DIGIT_TO_VAL(_x) (_x - '0')
#define hexdigit(x) ((x)>9?'A'+((x)-10):'0'+(x))
bool AP_GPS_NMEA::read(void)
{
int16_t numc;
bool parsed = false;
numc = port->available();
while (numc--) {
char c = port->read();
#ifdef NMEA_LOG_PATH
static FILE *logf = nullptr;
if (logf == nullptr) {
logf = fopen(NMEA_LOG_PATH, "wb");
}
if (logf != nullptr) {
::fwrite(&c, 1, 1, logf);
}
#endif
if (_decode(c)) {
parsed = true;
}
}
return parsed;
}
bool AP_GPS_NMEA::_decode(char c)
{
bool valid_sentence = false;
_sentence_length++;
switch (c) {
case ',': // term terminators
_parity ^= c;
FALLTHROUGH;
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;
_sentence_length = 1;
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';
}
int32_t AP_GPS_NMEA::_parse_decimal_100(const char *p)
{
char *endptr = nullptr;
long ret = 100 * strtol(p, &endptr, 10);
int sign = ret < 0 ? -1 : 1;
if (ret >= (long)INT32_MAX) {
return INT32_MAX;
}
if (ret <= (long)INT32_MIN) {
return INT32_MIN;
}
if (endptr == nullptr || *endptr != '.') {
return ret;
}
if (isdigit(endptr[1])) {
ret += sign * 10 * DIGIT_TO_VAL(endptr[1]);
if (isdigit(endptr[2])) {
ret += sign * DIGIT_TO_VAL(endptr[2]);
if (isdigit(endptr[3])) {
ret += sign * (DIGIT_TO_VAL(endptr[3]) >= 5);
}
}
}
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_RMC_ms == 0 ||
_last_GGA_ms == 0) {
return false;
}
uint32_t now = AP_HAL::millis();
if (now - _last_RMC_ms > 150 ||
now - _last_GGA_ms > 150) {
return false;
}
if (_last_VTG_ms != 0 &&
now - _last_VTG_ms > 150) {
return false;
}
// prevent these messages being used again
if (_last_VTG_ms != 0) {
_last_VTG_ms = 1;
}
_last_GGA_ms = 1;
_last_RMC_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) {
uint32_t now = AP_HAL::millis();
switch (_sentence_type) {
case _GPS_SENTENCE_RMC:
_last_RMC_ms = now;
//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 = wrap_360(_new_course*0.01f);
make_gps_time(_new_date, _new_time * 10);
set_uart_timestamp(_sentence_length);
state.last_gps_time_ms = now;
fill_3d_velocity();
break;
case _GPS_SENTENCE_GGA:
_last_GGA_ms = now;
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;
switch(_new_quality_indicator) {
case 0: // Fix not available or invalid
state.status = AP_GPS::NO_FIX;
break;
case 1: // GPS SPS Mode, fix valid
state.status = AP_GPS::GPS_OK_FIX_3D;
break;
case 2: // Differential GPS, SPS Mode, fix valid
state.status = AP_GPS::GPS_OK_FIX_3D_DGPS;
break;
case 3: // GPS PPS Mode, fix valid
state.status = AP_GPS::GPS_OK_FIX_3D;
break;
case 4: // Real Time Kinematic. System used in RTK mode with fixed integers
state.status = AP_GPS::GPS_OK_FIX_3D_RTK_FIXED;
break;
case 5: // Float RTK. Satellite system used in RTK mode, floating integers
state.status = AP_GPS::GPS_OK_FIX_3D_RTK_FLOAT;
break;
case 6: // Estimated (dead reckoning) Mode
state.status = AP_GPS::NO_FIX;
break;
default://to maintain compatibility with MAV_GPS_INPUT and others
state.status = AP_GPS::GPS_OK_FIX_3D;
break;
}
break;
case _GPS_SENTENCE_VTG:
_last_VTG_ms = now;
state.ground_speed = _new_speed*0.01f;
state.ground_course = wrap_360(_new_course*0.01f);
fill_3d_velocity();
// VTG has no fix indicator, can't change fix status
break;
}
} else {
switch (_sentence_type) {
case _GPS_SENTENCE_RMC:
case _GPS_SENTENCE_GGA:
// 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) {
/*
The first two letters of the NMEA term are the talker
ID. The most common is 'GP' but there are a bunch of others
that are valid. We accept any two characters here.
*/
if (_term[0] < 'A' || _term[0] > 'Z' ||
_term[1] < 'A' || _term[1] > 'Z') {
_sentence_type = _GPS_SENTENCE_OTHER;
return false;
}
const char *term_type = &_term[2];
if (strcmp(term_type, "RMC") == 0) {
_sentence_type = _GPS_SENTENCE_RMC;
} else if (strcmp(term_type, "GGA") == 0) {
_sentence_type = _GPS_SENTENCE_GGA;
} else if (strcmp(term_type, "VTG") == 0) {
_sentence_type = _GPS_SENTENCE_VTG;
// 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_RMC + 2: // validity (RMC)
_gps_data_good = _term[0] == 'A';
break;
case _GPS_SENTENCE_GGA + 6: // Fix data (GGA)
_gps_data_good = _term[0] > '0';
_new_quality_indicator = _term[0] - '0';
break;
case _GPS_SENTENCE_VTG + 9: // validity (VTG) (we may not see this field)
_gps_data_good = _term[0] != 'N';
break;
case _GPS_SENTENCE_GGA + 7: // satellite count (GGA)
_new_satellite_count = atol(_term);
break;
case _GPS_SENTENCE_GGA + 8: // HDOP (GGA)
_new_hdop = (uint16_t)_parse_decimal_100(_term);
break;
// time and date
//
case _GPS_SENTENCE_RMC + 1: // Time (RMC)
case _GPS_SENTENCE_GGA + 1: // Time (GGA)
_new_time = _parse_decimal_100(_term);
break;
case _GPS_SENTENCE_RMC + 9: // Date (GPRMC)
_new_date = atol(_term);
break;
// location
//
case _GPS_SENTENCE_RMC + 3: // Latitude
case _GPS_SENTENCE_GGA + 2:
_new_latitude = _parse_degrees();
break;
case _GPS_SENTENCE_RMC + 4: // N/S
case _GPS_SENTENCE_GGA + 3:
if (_term[0] == 'S')
_new_latitude = -_new_latitude;
break;
case _GPS_SENTENCE_RMC + 5: // Longitude
case _GPS_SENTENCE_GGA + 4:
_new_longitude = _parse_degrees();
break;
case _GPS_SENTENCE_RMC + 6: // E/W
case _GPS_SENTENCE_GGA + 5:
if (_term[0] == 'W')
_new_longitude = -_new_longitude;
break;
case _GPS_SENTENCE_GGA + 9: // Altitude (GPGGA)
_new_altitude = _parse_decimal_100(_term);
break;
// course and speed
//
case _GPS_SENTENCE_RMC + 7: // Speed (GPRMC)
case _GPS_SENTENCE_VTG + 5: // Speed (VTG)
_new_speed = (_parse_decimal_100(_term) * 514) / 1000; // knots-> m/sec, approximiates * 0.514
break;
case _GPS_SENTENCE_RMC + 8: // Course (GPRMC)
case _GPS_SENTENCE_VTG + 1: // Course (VTG)
_new_course = _parse_decimal_100(_term);
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) {
state.step = 0;
return true;
}
state.step = 0;
break;
}
return false;
}
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