nmea.cpp

/** @file nmea.cpp
 *  @brief NMEA Functions
 */
#include "nmea.h"
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>

/** @brief Parses GPGGA Message
 *  @author Paul Moggach
 *  @date 25MAR2019
 *  @param char * nmea Pointer to message
 *  @param gpgg_t * loc Pointer to output data structure
 */
void nmea_parse_gpgga(char *nmea, gpgga_t *loc) {
  char *p = nmea;

  p = strchr(p, ',') + 1; // time
  loc->utc = atof(p);

  p = strchr(p, ',') + 1;
  loc->latitude = atof(p);

  p = strchr(p, ',') + 1;
  switch (p[0]) {
  case 'N':
    loc->lat = 'N';
    break;
  case 'S':
    loc->lat = 'S';
    break;
  case ',':
    loc->lat = '\0';
    break;
  }

  p = strchr(p, ',') + 1;
  loc->longitude = atof(p);

  p = strchr(p, ',') + 1;
  switch (p[0]) {
  case 'W':
    loc->lon = 'W';
    break;
  case 'E':
    loc->lon = 'E';
    break;
  case ',':
    loc->lon = '\0';
    break;
  }

  p = strchr(p, ',') + 1;
  loc->quality = (uint8_t)atoi(p);

  p = strchr(p, ',') + 1;
  loc->satellites = (uint8_t)atoi(p);

  p = strchr(p, ',') + 1;

  p = strchr(p, ',') + 1;
  loc->altitude = atof(p);
}

/** @brief Parses GPRMC Message
 *  @author Paul Moggach
 *  @date 25MAR2019
 *  @param char * nmea Pointer to message
 *  @param gpgg_t * loc Pointer to output data structure
 */
void nmea_parse_gprmc(char *nmea, gprmc_t *loc) {
  char *p = nmea;

  p = strchr(p, ',') + 1; // skip time
  p = strchr(p, ',') + 1; // skip status
  p = strchr(p, ',') + 1;
  loc->latitude = atof(p);
  p = strchr(p, ',') + 1;
  switch (p[0]) {
  case 'N':
    loc->lat = 'N';
    break;
  case 'S':
    loc->lat = 'S';
    break;
  case ',':
    loc->lat = '\0';
    break;
  }

  p = strchr(p, ',') + 1;
  loc->longitude = atof(p);
  p = strchr(p, ',') + 1;
  switch (p[0]) {
  case 'W':
    loc->lon = 'W';
    break;
  case 'E':
    loc->lon = 'E';
    break;
  case ',':
    loc->lon = '\0';
    break;
  }

  p = strchr(p, ',') + 1;
  loc->speed = atof(p);

  p = strchr(p, ',') + 1;
  loc->course = atof(p);

  p = strchr(p, ',') + 1;
  loc->date = atof(p);
}

/** @brief Get the message type (GPGGA, GPRMC, etc..)
 *  @param message The NMEA message
 *  @return The type of message if it is valid
 */
uint8_t nmea_get_message_type(const char *message) {
  uint8_t checksum = 0;
  if ((checksum = nmea_valid_checksum(message)) != _EMPTY) {
    return checksum;
  }

  if (strstr(message, NMEA_GPGGA_STR) != NULL) {
    return NMEA_GPGGA;
  }

  if (strstr(message, NMEA_GPRMC_STR) != NULL) {
    return NMEA_GPRMC;
  }

  return NMEA_UNKNOWN;
}

/** @brief Checks Message Checksum
 *  @author Paul Moggach
 *  @date 25MAR2019
 *  @param char * nmea Pointer to message
 *  @return uint8_t Checksum
 */
uint8_t nmea_valid_checksum(const char *message) {
  uint8_t checksum = (uint8_t)strtol(strchr(message, '*') + 1, NULL, 16);

  char p;
  uint8_t sum = 0;
  ++message;
  while ((p = *message++) != '*') {
    sum ^= p;
  }

  if (sum != checksum) {
    return NMEA_CHECKSUM_ERR;
  }

  return _EMPTY;
}