seniordesign-firmware Changeset - e5c11279c2a0

Changeset - e5c11279c2a0

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mkanning@CL-ENS241-10.cedarville.edu - 12 years ago 2013-01-10 15:03:18
mkanning@CL-ENS241-10.cedarville.edu

checksum calculator and comparator for NMEA

1 file changed with 22 insertions and 4 deletions:

master/master/lib/trackuinoGPS/gpsMKa.c

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master/master/lib/trackuinoGPS/gpsMKa.c

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@@ @@ -39,19 +39,20 @@ uint8_t stationID[6]; //blank - included @@
 uint8_t checksum[2];	//xx
 uint8_t knots[5];		//xxx.xx
 uint8_t course[5];		//xxx.x
 uint8_t datestamp[6];	//ddmmyy
 uint8_t variation[6];	//xxx.xb
 int calculatedChecksum;
 int receivedChecksum;
 // transmission state machine
 enum decodeState {
 	//shared fields
 	INITIALIZE=0,
 	GET_TYPE,
-	GPS_CHECKSUM,	//need to find out how this is calculated/compared
+	GPS_CHECKSUM,	//XOR of all the bytes between the $ and the * (not including the delimiters themselves), written in hexadecimal
 	//GGA data fields
 	GGA_TIME,
 	GGA_LATITUDE,
 	GGA_LONGITUDE,
 	GGA_QUALITY,
 	GGA_SATELLITES,
@@ @@ -407,13 +408,13 @@ void parse_gps_transmission(void){ @@
+		}
+	}
 	//magnetic variation
 	else if(decodeState == RMC_MAG_VARIATION)
+	{
-		if (byte == ',') //end of this data type
+		if (byte == '*') //end of this data type
+		{
 			decodeState = GPS_CHECKSUM;
 			numBytes = 0; //prep for next phase of parse
+		}
 		else //store data
+		{
@@ @@ -426,24 +427,41 @@ void parse_gps_transmission(void){ @@
 	//checksum
 	else if (decodeState == GPS_CHECKSUM)
+	{
 		if (numBytes == 2) //end of data - terminating character ??
+		{
 			//checksum calculator for testing http://www.hhhh.org/wiml/proj/nmeaxor.html
 			//TODO: must determine what to do with correct and incorrect messages
 			receivedChecksum = checksum[0] + (checksum[1]*16);	//convert bytes to int
 			if(calculatedChecksum==receivedChecksum)
+			{
+			}
 			else
+			{
+			}
 			decodeState = INITIALIZE;
 			numBytes = 0; //prep for next phase of parse
+		}
 		else //store data
+		{
 			checksum[numBytes] = byte; //adjust number of bytes to fit array
 			numBytes++;
+		}
+	}
 	//input byte into running checksum
 	XORbyteWithChecksum(byte);
 	if (decodeState!=GPS_CHECKSUM && decodeState!=INITIALIZE)	//want bytes between '$' and '*'
+	{
 		//input byte into running checksum
 		XORbyteWithChecksum(byte);
+	}
+}
 /// MKa GPS transmission parser END
 void XORbyteWithChecksum(uint8_t byte){
 	calculatedChecksum ^= (int)byte; //this may need to be re-coded
+}

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