Espruino/libs/misc/nmea.c

/*
 * This file is part of Espruino, a JavaScript interpreter for Microcontrollers
 *
 * Copyright (C) 2019 Gordon Williams <gw@pur3.co.uk>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * ----------------------------------------------------------------------------
 * NMEA decoder
 * ----------------------------------------------------------------------------
 */

#include "nmea.h"
#include "jswrap_date.h"

char *nmea_next_comma(char *nmea) {
  while (*nmea && *nmea!=',') nmea++; // find the comma
  return nmea;
}
double nmea_decode_latlon(char *nmea, char *comma) {
  if (*nmea==',') return NAN; // no reading
  char *dp = nmea;
  while (*dp && *dp!='.' && *dp!=',') dp++; // find decimal pt
  *comma = 0;
  double minutes = stringToFloat(&dp[-2]);
  *comma = ',';
  dp[-2] = 0;
  int x = stringToInt(nmea);
  return x+(minutes/60);
}
double nmea_decode_float(char *nmea, char *comma) {
  *comma = 0;
  double r = stringToFloat(nmea);
  *comma = ',';
  return r;
}
uint8_t nmea_decode_1(char *nmea) {
  return chtod(nmea[0]);
}
uint8_t nmea_decode_2(char *nmea) {
  return chtod(nmea[0])*10 + chtod(nmea[1]);
}
bool nmea_decode(NMEAFixInfo *gpsFix, const char *nmeaLine) {
  char buf[NMEA_MAX_SIZE];
  strcpy(buf, nmeaLine);
  char *nmea = buf, *nextComma;


  if (nmea[0]!='$' || nmea[1]!='G') return false; // not valid
  if (nmea[3]=='R' && nmea[4]=='M' && nmea[5]=='C') {
    // $GNRMC,161945.00,A,5139.11397,N,00116.07202,W,1.530,,190919,,,A*7E
    nmea = nmea_next_comma(nmea)+1;
    nextComma = nmea_next_comma(nmea);
    // time
    gpsFix->hour = nmea_decode_2(&nmea[0]);
    gpsFix->min = nmea_decode_2(&nmea[2]);
    gpsFix->sec = nmea_decode_2(&nmea[4]);
    gpsFix->ms = nmea_decode_2(&nmea[7]);
    // status
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);//?
    // lat + NS
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // lon + EW
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // speed
    gpsFix->speed = nmea_decode_float(nmea, nextComma);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // course
    gpsFix->course = nmea_decode_float(nmea, nextComma);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // date
    gpsFix->day = nmea_decode_2(&nmea[0]);
    gpsFix->month = nmea_decode_2(&nmea[2]);
    gpsFix->year = nmea_decode_2(&nmea[4]);
    // ....
  }
  if (nmea[3]=='G' && nmea[4]=='G' && nmea[5]=='A') {
    // $GNGGA,161945.00,5139.11397,N,00116.07202,W,1,06,1.29,71.1,M,47.0,M,,*64
    nmea = nmea_next_comma(nmea)+1;
    nextComma = nmea_next_comma(nmea);
    // time
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // LAT
    gpsFix->lat = nmea_decode_latlon(nmea, nextComma);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    if (*nmea=='S') gpsFix->lat=-gpsFix->lat;
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // LON
    gpsFix->lon = nmea_decode_latlon(nmea, nextComma);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    if (*nmea=='W') gpsFix->lon=-gpsFix->lon;
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // quality
    gpsFix->quality = nmea_decode_1(nmea);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // num satellites
    gpsFix->satellites = nmea_decode_2(nmea);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // dilution of precision
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // altitude
    gpsFix->alt = nmea_decode_float(nmea, nextComma);
    nmea = nextComma+1; nextComma = nmea_next_comma(nmea);
    // ....
  }
  if (nmea[3]=='G' && nmea[4]=='S' && nmea[5]=='V') {
    // loads of cool data about what satellites we have
  }
  if (nmea[3]=='G' && nmea[4]=='L' && nmea[5]=='L') {
    // Complete set of data received
    return true;
  }
  return false;
}


JsVar *nmea_to_jsVar(NMEAFixInfo *gpsFix) {
  JsVar *o = jsvNewObject();
  if (o) {
    jsvObjectSetChildAndUnLock(o, "lat", jsvNewFromFloat(gpsFix->lat));
    jsvObjectSetChildAndUnLock(o, "lon", jsvNewFromFloat(gpsFix->lon));
    jsvObjectSetChildAndUnLock(o, "alt", jsvNewFromFloat(gpsFix->alt));
    jsvObjectSetChildAndUnLock(o, "speed", jsvNewFromFloat(gpsFix->speed));
    jsvObjectSetChildAndUnLock(o, "course", jsvNewFromFloat(gpsFix->course));
    CalendarDate date;
    date.day = gpsFix->day;
    date.month = gpsFix->month-1; // 1 based to 0 based
    date.year = 2000+gpsFix->year;
    TimeInDay td;
    td.daysSinceEpoch = fromCalenderDate(&date);
    td.hour = gpsFix->hour;
    td.min = gpsFix->min;
    td.sec = gpsFix->sec;
    td.ms = gpsFix->ms;
    td.zone = 0; // jsdGetTimeZone(); - no! GPS time is always in UTC :)
    jsvObjectSetChildAndUnLock(o, "time", jswrap_date_from_milliseconds(fromTimeInDay(&td)));
    jsvObjectSetChildAndUnLock(o, "satellites", jsvNewFromInteger(gpsFix->satellites));
    jsvObjectSetChildAndUnLock(o, "fix", jsvNewFromInteger(gpsFix->quality));
  }
  return o;
}