bool
PortWriteNMEA(Port &port, const char *line, OperationEnvironment &env)
{
assert(line != nullptr);
/* reasonable hard-coded timeout; do we need to make this a
parameter? */
const unsigned timeout_ms = 1000;
if (!port.Write('$') ||
!port.FullWrite(line, strlen(line), env, timeout_ms))
return false;
char checksum[16];
sprintf(checksum, "*%02X\r\n", NMEAChecksum(line));
return port.FullWrite(checksum, strlen(checksum), env, timeout_ms);
}
int
main(int argc, char **argv)
{
char buffer[1024];
const char *start = buffer;
while ((start = fgets(buffer, sizeof(buffer) - 3, stdin)) != NULL) {
const char *end = strchr(start, '*');
if (end == NULL) {
end = start + strlen(start);
while (end > start && (end[-1] == '\n' || end[-1] == '\r'))
--end;
}
printf("%.*s*%02x\n", (int)(end - buffer), buffer,
NMEAChecksum(start, end - start));
}
return 0;
}
char *GetLine() {
const auto src = buffer.Read();
char *const end = src.data + src.length;
/* a NMEA line starts with a dollar symbol ... */
char *dollar = std::find(src.data, end, '$');
if (dollar == end) {
buffer.Clear();
return nullptr;
}
char *start = dollar + 1;
/* ... and ends with an asterisk */
char *asterisk = std::find(start, end, '*');
if (asterisk + 3 > end)
/* need more data */
return nullptr;
/* verify the checksum following the asterisk (two hex digits) */
const uint8_t calculated_checksum = NMEAChecksum(start, asterisk - start);
const char checksum_buffer[3] = { asterisk[1], asterisk[2], 0 };
char *endptr;
const uint8_t parsed_checksum = strtoul(checksum_buffer, &endptr, 16);
if (endptr != checksum_buffer + 2 ||
parsed_checksum != calculated_checksum) {
buffer.Clear();
return nullptr;
}
buffer.Consume(asterisk + 3 - src.data);
*asterisk = 0;
return start;
}
bool
NMEAParser::ParseLine(const char *string, NMEAInfo &info)
{
assert(positive(info.clock));
if (string[0] != '$')
return false;
if (!NMEAChecksum(string))
return false;
NMEAInputLine line(string);
char type[16];
line.Read(type, 16);
if (IsAlphaASCII(type[1]) && IsAlphaASCII(type[2])) {
if (StringIsEqual(type + 3, "GSA"))
return GSA(line, info);
if (StringIsEqual(type + 3, "GLL"))
return GLL(line, info);
if (StringIsEqual(type + 3, "RMC"))
return RMC(line, info);
if (StringIsEqual(type + 3, "GGA"))
return GGA(line, info);
if (StringIsEqual(type + 3, "HDM"))
return HDM(line, info);
}
// if (proprietary sentence) ...
if (type[1] == 'P') {
// Airspeed and vario sentence
if (StringIsEqual(type + 1, "PTAS1"))
return PTAS1(line, info);
// FLARM sentences
if (StringIsEqual(type + 1, "PFLAE")) {
ParsePFLAE(line, info.flarm.error, info.clock);
return true;
}
if (StringIsEqual(type + 1, "PFLAV")) {
ParsePFLAV(line, info.flarm.version, info.clock);
return true;
}
if (StringIsEqual(type + 1, "PFLAA")) {
ParsePFLAA(line, info.flarm.traffic, info.clock);
return true;
}
if (StringIsEqual(type + 1, "PFLAU")) {
ParsePFLAU(line, info.flarm.status, info.clock);
return true;
}
// Garmin altitude sentence
if (StringIsEqual(type + 1, "PGRMZ"))
return RMZ(line, info);
return false;
}
return false;
}
