void buildAndCheckSentence(unsigned char characterIn) {
// Full specification for NMEA0138 specifies a maximum sentence length
// of 255 characters. We're going to ignore this for half the length as
// we shouldn't get anything that big.
// This contains the function's state of whether
// it is currently building a sentence.
// 0 - Awaiting start character ($)
// 1 - Building sentence
// 2 - Building first checksum character
// 3 - Building second checksum character
//printf("char: %c\r\n",characterIn);
// We start recording a new sentence if we see a dollarsign.
// The sentenceIndex is hard-set to 1 so that multiple dollar-signs
// keep you at the beginning.
if (characterIn == '$') {
//printf("start character at least");
sentence[0] = characterIn;
sentenceIndex = 1;
sentenceState = 1;
} else if (sentenceState == 1) {
// Record every character that comes in now that we're building a sentence.
// Only stop if we run out of room or an asterisk is found.
sentence[sentenceIndex++] = characterIn;
if (characterIn == '*') {
sentenceState = 2;
} else if (sentenceIndex > 127) {
// If we've filled up the buffer, ignore the entire message as we can't store it all
sentenceState = 0;
sentenceIndex = 0;
}
} else if (sentenceState == 2) {
// Record the first ASCII-hex character of the checksum byte.
checksum = hex2char(characterIn) << 4;
sentenceState = 3;
} else if (sentenceState == 3) {
// Record the second ASCII-hex character of the checksum byte.
checksum |= hex2char(characterIn);
// Now that we've compiled a complete GPS sentence, let's check the checksum and parse it.
// This code currently only supports RMC and GGA messages.
if (checksum == getChecksum(sentence, sentenceIndex)) {
if (sentence[3] == 'R' &&
sentence[4] == 'M' &&
sentence[5] == 'C') {
parseRMC(sentence);
} else if (sentence[3] == 'G' &&
sentence[4] == 'G' &&
sentence[5] == 'A') {
parseGGA(sentence);
}
}
// We clear all state variables here regardless of success.
sentenceIndex = 0;
sentenceState = 0;
}
}
uint8_t GPS::parse(const char* nmea, const uint32_t now)
{
//Serial.print("P: ");
//Serial.println(nmea);
if (*nmea != '$') {
return PARSED_ERROR;
}
if (strstr(nmea, "$GPGGA") == nmea) {
if (strlen(nmea) < 65) return PARSED_UNKNOWN; // No fix
return parseGGA(nmea, now);
} else if (strstr(nmea, "$GPRMC") == nmea) {
if (strlen(nmea) < 65) return PARSED_UNKNOWN; // No fix
return parseRMC(nmea, now);
} else if (strstr(nmea, "$PMTK001") == nmea) {
return PARSED_ACK;
}
return PARSED_UNKNOWN;
}
bool GPS::parse(char *field)
{
if (strcmp(field, "$GPGGA") == 0)
{
currentSentence = SENTENCE_GGA;
currentField = FIELD_TIME;
return true;
}
else if (strcmp(field, "$GPRMC") == 0)
{
currentSentence = SENTENCE_RMC;
currentField = FIELD_TIME;
return true;
}
if (currentSentence == SENTENCE_GGA)
return parseGGA(field);
if (currentSentence == SENTENCE_RMC)
{
bool b = parseRMC(field);
if (fix && haveFirstLocation == false)
{
if (currentLatitude > 1.0)
lastLatitude = currentLatitude;
if (currentLongitude > 1.0)
lastLongitude = currentLongitude;
if (lastLatitude > 1.0 && lastLongitude > 1.0)
{
haveFirstLocation = true;
}
}
return b;
}
return false;
}
