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--- code:interrupt_driven_nmea [2008/04/20 14:30] – laurenceb
+++ code:interrupt_driven_nmea [2013/04/18 20:00] (current) – Reports code isn't tested so just put a notice on there upu
@@ Line 1: / Line 1: @@
- This is a rather unconvensional approach to a NMEA parser - completely based on an ISR to parse the incoming bytes. It uses 2.2KB of code space and 44 bytes of RAM.
+**This code hasn't been tested and is believe not to work**
+This is a rather unconvensional approach to a NMEA parser - completely based on an ISR to parse the incoming bytes. It uses 1.9KB of code space and 44 bytes of RAM. Should run in less than 10us at 18MHz.
 <code c>#include "main.h"
 //global(s)
-extern gps_type gps;
+extern gps_type Gps;
 // Interrupt driven NMEA parser for Atmel AVR
-ISR(USART_RX_vect)			//UART interrupt on mega xx8 series
+ISR(USART_RX_vect)				//UART interrupt on mega xx8 series
 {
-	static char buffer[5];
+	static char buffer[6];
 	static u08 GGA;
 	static u08 RMC;
@@ Line 17: / Line 20: @@
 	static u08 bufferindex;
 	static u08 pointcount;
+	static gps_type gps;
 	char c=UDR0;
 	switch(c)
@@ Line 22: / Line 26: @@
 		case '$':			//start of a packet
 		  commacount=0;
-		  bufferindex=0;
-		  pointcount=0;
-		  stage=0;
-		  memset(buffer,' ',5);
 		  GGA=FALSE;
-		  RMC=FALSE;		//we dont know what sort of packet it is yet
+		  RMC=FALSE;			//we dont know what sort of packet it is yet
-		break;
+		case ',':			//we dont break as the code is shared
-		case ',':
+		  commacount++;			//note this means packet header is 1
-		  commacount++;
+		  bufferindex=0;		//wipe all these so they can be reused
-		  bufferindex=0;
 		  pointcount=0;
-		  stage=0;
+		  stage=FALSE;
+		  memset(buffer,' ',6);
 		break;
 		case '.':
-		  pointcount++;				//we need to be able to detect number of points in the case of altitude
+		  pointcount++;			//we need to be able to detect number of points in the case of altitude
 		break;
-		default:				//we have some of the CSV data
+		default:			//we have some of the CSV data
-		  if(bufferindex<5)		//dont mess up ! Dont overflow
+		  if(bufferindex<6)		//dont mess up ! Dont overflow
 		  {
-		    	buffer[bufferindex]=c;		//stick the character in our buffer
+		    	buffer[bufferindex]=c;	//stick the character in our buffer
 		  }
 		  if(GGA)
 		  {
-			if(commacount==2)		//the latitude from the GGA
+			switch(commacount)
 			{
-				if(bufferindex<1)
+				case 3:		//the latitude from the GGA
-				{
+				  if( (bufferindex<1  && !stage) || bufferindex<5)
+				  {
 					bufferindex++;
-				}
+				  }
-				else
+				  else
-				{
+				  {
 					if(!stage)
 					{
-						gps.latitude=(float)atoi(buffer);	//integer degrees
+						gps.latitude=(float)atoi(buffer);		// degrees
+						stage=TRUE;
 					}
-					if(stage==1)
+					else
 					{
-						gps.latitude+=minutes*(float)atoi(buffer);	//integer minutes
+						gps.latitude+=minutes*(float)atoi(buffer);	// minutes
 					}
-					if(stage==2)
+				  }
-					{
+				break;
-						gps.latitude+=0.01*minutes*(float)atoi(buffer);	//decimal degrees
+				case 4:
-					}
+				  if(c=='S')
-					memset(buffer,' ',5);
+				  {
-					stage++;
+					gps.latitude=-gps.latitude;
-				}
+				  }
-			}
+				break;
-			if(commacount==3 && c=='S')
+				case 5:
-			{
+				  if( (bufferindex<1 && !stage) || bufferindex<5)
-				gps.latitude=-gps.latitude;
+				  {
-			}
-			if(commacount==4)
-			{
-				if( (stage && bufferindex<1) || bufferindex<2)
-				{
 					bufferindex++;
-				}
+				  }
-				else
+				  else
-				{
+				  {
 					if(!stage)
 					{
-						gps.longitude=(float)atoi(buffer);	//integer degrees
+						gps.longitude=(float)atoi(buffer);		// degrees
+						stage=TRUE;
 					}
-					if(stage==1)
+					else
 					{
-						gps.longitude+=minutes*(float)atoi(buffer);	//integer minutes
+						gps.longitude+=minutes*(float)atoi(buffer);	// minutes
 					}
-					if(stage==2)
+				  }
-					{
+				break;
-						gps.longitude+=0.01*minutes*(float)atoi(buffer);	//decimal degrees
+				case 6:
-					}
+				  if(c=='W')
-					memset(buffer,' ',5);
+				  {
-					stage++;
+					gps.longitude=-gps.longitude;
-				}
+				  }
-			}
+				break;
-			if(commacount==5 && c=='W')
+				case 7:
-			{
+				  gps.status=atoi(&c);
-				gps.longitude=-gps.longitude;
+				break;
-			}
+				case 10:
-			if(commacount==6)
+				  if(!pointcount)				//wait until we get to a decimal point
-			{
+				  {
-				gps.status=atoi(&c);
-			}
-			if(commacount==9)
-			{
-				if(!pointcount)				//wait until we get to a decimal point
-				{
 					bufferindex++;
-				}
+				  }
-				else
+				  else
-				{
+				  {
 					gps.altitude=(float)atoi(buffer)*0.1;	//last char in buffer will be after dp
-					memset(buffer,' ',5);
+				  }
-				}
 			}
 		  }
 		  else if(RMC)
 		  {
-			if(commacount==7)		//speed in knots
+			if(commacount==8)		//speed in knots
 			{
 				if(!pointcount)
@@ Line 129: / Line 120: @@
 				{
 					gps.speed=(float)atoi(buffer)*0.1;
-					memset(buffer,' ',5);
 				}
 			}
-			if(commacount==8)				//the heading field
+			if(commacount==9)		//the heading
 			{
 				if(!pointcount)
 				{
@@ Line 141: / Line 131: @@
 				else
 				{
-					gps.heading=(float)atoi(buffer);
+					gps.heading=(float)atoi(buffer)*0.1;
-					memset(buffer,' ',5);
+					toggle_pin;		//toggles pin D5 - flashing LED
-					gps.packetflag=TRUE;		//this is usually the last interesting part of the fix info to come through
+					if(!Gps.packetflag)	//main has unlocked the data
+					{
+						Gps.packetflag=TRUE;	//this is usually the last interesting part of the fix info to come through
+						Gps=gps;		//copy into the global variable
+					}
 				}
 			}
 		  }
-		  else
+		  else if(!commacount)			//the header
 		  {
-			if(commacount==0)	//the header
+			if(bufferindex<4)
 			{
-				if(bufferindex<4)
+				bufferindex++;		//increase the position in the buffer
+			}
+			else
+			{
+				if(buffer=="GPGGA ")	//the last character will be a space
 				{
-					bufferindex++;		//increase the position in the buffer
+					GGA=TRUE;
 				}
-				else
+				if(buffer=="GPRMC ")
 				{
-					if(buffer=="GPGGA")	//the last character will be a space
+					RMC=TRUE;
-					{
-						GGA=TRUE;
-					}
-					if(buffer=="GPRMC")
-					{
-						RMC=TRUE;
-					}
-					memset(buffer,' ',5);		//wipe the buffer so it can be reused
 				}
 			}
-		  }
+		 }
 	}
 }
 </code>