seniordesign-firmware Changeset - e5c11279c2a0

Changeset - e5c11279c2a0

Parent rev.

Child rev.

[Not reviewed]

default

0 1 0

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 20 insertions and 2 deletions:

master/master/lib/trackuinoGPS/gpsMKa.c

0 comments (0 inline, 0 general)

master/master/lib/trackuinoGPS/gpsMKa.c

➞

Show inline comments

 /*
 * gpsMKa.c
+*
 * Created: 11/15/2012 12:02:38 PM
 *  Author: mkanning
 */
 #include <stdbool.h>
 #include <avr/io.h>
 #include "gpsMKa.h"
 #include "../serial.h"
 // holds the byte ALREADY PARSED. includes starting character
 int bytesReceived = 0;
 //data (and checksum) of most recent transmission
 char data[16];
 //used to skip over bytes during parse
 int skipBytes = 0;
 //used to index data arrays during data collection
 int numBytes = 0;
 //variables to store data from transmission
 //least significant digit is stored at location 0 of arrays
 uint8_t tramsmissionType[5];
 uint8_t timestamp[9];	//hhmmss.ss
 uint8_t latitude[8];	//lllll.lla
 uint8_t longitude[8];	//yyyyy.yyb
 uint8_t quality;		//quality for GGA and validity for RMC
 uint8_t numSatellites[2];
 uint8_t hdop[4];		//xx.x
 uint8_t altitude[8];	//xxxxxx.x
 uint8_t wgs84Height[6];	//sxxx.x
 uint8_t lastUpdated[6];	//blank - included for testing
 uint8_t stationID[6];	//blank - included for testing
 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,
 	GGA_HDOP,
 	GGA_ALTITUDE,
 	GGA_WGS84,
 	GGA_LAST_UPDATE,
 	GGA_STATION_ID,
 	//RMC data fields
 	RMC_TIME,
 	RMC_VALIDITY,
 	RMC_LATITUDE,
 	RMC_LONGITUDE,
 	RMC_KNOTS,
 	RMC_COURSE,
 	RMC_DATE,
 	RMC_MAG_VARIATION,
 }decodeState;
 //// MKa GPS transmission parser START
 void parse_gps_transmission(void){
 	// Pull byte off of the buffer
 	char byte = 'a';// serial1_readChar();
 	if(byte == '$') //start of transmission sentence
+	{
 		decodeState = GET_TYPE;
 		numBytes = 0; //prep for next phases
 		skipBytes = 0;
 		calculatedChecksum = 0;
+	}
 	//parse transmission type
 	else if (decodeState == GET_TYPE)
+	{
 		tramsmissionType[numBytes] = byte;
 		numBytes++;
 		if(byte == ',') //end of this data type
+		{
 			if (tramsmissionType[2] == 'G' &&
@@ @@ -365,86 +366,103 @@ void parse_gps_transmission(void){ @@
 	else if(decodeState == RMC_KNOTS)
+	{
 		if (byte == ',') //end of this data type
+		{
 			decodeState = RMC_COURSE;
 			numBytes = 0; //prep for next phase of parse
+		}
 		else //store data
+		{
 			knots[numBytes]= byte; //adjust number of bytes to fit array
 			numBytes++;
+		}
+	}
 	//course
 	else if(decodeState == RMC_COURSE)
+	{
 		if (byte == ',') //end of this data type
+		{
 			decodeState = RMC_DATE;
 			numBytes = 0; //prep for next phase of parse
+		}
 		else //store data
+		{
 			course[numBytes] = byte; //adjust number of bytes to fit array
 			numBytes++;
+		}
+	}
 	//date
 	else if(decodeState == RMC_DATE)
+	{
 		if (byte == ',') //end of this data type
+		{
 			decodeState = RMC_MAG_VARIATION;
 			skipBytes = 0; //prep for next phase of parse
 			numBytes = 0;
+		}
 		else //store data
+		{
 			datestamp[numBytes] = byte; //adjust number of bytes to fit array
 			numBytes++;
+		}
+	}
 	//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
+		{
 			variation[numBytes] = byte; //adjust number of bytes to fit array
 			numBytes++;
+		}
+	}
 	///parses RMC transmissions END
 	//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++;
+		}
+	}
 	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
+}

0 comments (0 inline, 0 general)