This is a lightweight NMEA parser written in C#. It was designed for use with a Netduino, an "open-source electronics platform" that runs the .NET Micro Framework. With a 48MHz ARM processor and only about 60KB of RAM, it is extremely resource constrained. None of the existing NMEA parsers fit my requirements for such a low powered device.
NMEA is the common name for NMEA 0183: a specification that defines a protocol for communication between electronic devices, like most GPS units. By default, NMEA compatible GPS devices communicate over a serial port at 4800 baud, 8N1.
To use, simply create a Parser instance and feed bytes to its parse() method. When
the parse method returns true, a full sentence has been parsed and is available
in the cmd property. The length of the command is available in the offset property.
Currently, the Parser allocates a 1k buffer to hold the parsed commands. This is probably far more than is actually required; if you find that you're running out of memory, feel free to tune this.
Example:
byte[] in;
for (int i = 0; i < in.Length; i++) {
if (parser.parse(in[i])) {
System.Console.Write("Parsed a full sentence!");
}
}The Parser object itself does not fetch data, so you'll be responsible for getting data from whatever source you'd like to use. For example, to provide the Parser data from a serial port:
namespace gps_test
{
public class Program
{
static NMEA.Parser parser = new NMEA.Parser();
private static void onRecv(Object sender, SerialDataReceivedEventArgs args) {
SerialPort input = (SerialPort)sender;
int avail = input.BytesToRead;
while (avail-- > 0) {
if (parser.parse(input.ReadByte())) {
Debug.Print(new String(Encoding.UTF8.GetChars(parser.cmd)));
}
}
}
public static void Main() {
SerialPort input = new SerialPort(SerialPorts.COM1, 4800, 0, 8, StopBits.One);
input.DataReceived += onRecv;
input.Open();
while (true);
}
}
}While parsing each sentence, the parser records the starting offset of each field. You can retrieve the value of specific fields using the get* methods on the parser object.
For examples of parsing specific NMEA sentences, see the examples directory.
To learn more about the NMEA format, see: