Differences

This shows you the differences between two versions of the page.

--- code:interrupt_driven_tsip [2008/06/16 01:49] – laurenceb
+++ code:interrupt_driven_tsip [2008/10/11 11:28] (current) – laurenceb
@@ Line 3: / Line 3: @@
 extern gps_type Gps;
-// Interrupt driven TSIP (lassen iq) parser for Atmel AVR
+// Interrupt driven TSIP (lassen iq) parser for Atmel AVR (state machine based)
-ISR(USART_RX_vect)			//UART interrupt on mega xx8 series
+#define ETX 0x03			//as defined in TSIP specs
+#define DLE 0x10
+//8O1 send routine for initial setup
+int suart_send(char c)
 {
-	static u08 LLA;
+	u08 n;
-	static u08 VENU;
+	u08 p=FALSE;		//odd parity
-	static u08 placemark;
+	CLEAR;				//start bit
-	static gps_type gps;
+	delay;
-	static u08 *d;
+	for(n=0;n<8;n++)		//the data
-	static u08 odd;
-	char c=UDR0;
-	if(odd)				//destuffing; a double <DLE> in the data will cause one to be overwritten
 	{
-		placemarker++;
+		if(c & 0x01)
+		{
+			SET;		//update parity
+			p=!p;
+		}
+		else
+		{
+			CLEAR;
+		}
+		c>>=1;
+		delay;
 	}
-	if(c==0x10)			//keep track of number of <DLE>
+	if(p)				//the parity
 	{
-		odd=!odd;
+		SET;
-	)
+	}
-	if(c==0x03 && !odd)		//<ETX> end of a packet ie a new one is coming- there are even <DLE> in a packet
+	else
 	{
-		placemarker=0;
+		CLEAR;
-		LLA=FALSE;
-		VENU=FALSE;		//we dont know what sort of packet it is yet
-		odd=FALSE;		//no <DLE> so far, i.e. an even number of <DLE>
 	}
-	else if(placemarker==1)		//packet id
+	delay;
+	SET;				//stop bit
+	delay;
+	return 0;
+}
+ISR(USART_RX_vect)			//UART interrupt on mega xx8 series
+{
+	static u08 id;
+	static u08 placemarker;
+	static gps_type gps;
+	static u08 state;		//state machine
+	u08 *d=(u08*)&gps;		//points to our data
+	if(UCSR0A & (BV(FE0)|BV(UPE0)))	//a framing or parity error causes us to drop the packet
 	{
-		switch(c)
+		state=0;
-		{
-			case 0x4A:
-				LLA=TRUE;
-			break;
-			case 0x56:
-				VENU=TRUE;
-			break;
-			default:	//unknown packet, leave it
-		}
 	}
-	if(LLA)
+	char c=UDR0;
+	if(state==2 || state==4)				//the two states where we can write something
 	{
-		switch(placemarker)
+		if(!placemarker && id==0x6D)		//start of packet - the status byte
 		{
-			case 3:
+			gps.status= c & 0x0F;		//number from 0 to 7, 0=undefined, 7=ground station,4 3D
-			d=&gps.latitude;
+			gps.nosats=(c & 0xF0)>>4;	//number of tracked satellites
-			break;
-			case 7:
-			d=&gps.longitude;
-			break;
-			case 11:
-			d=&gps.altitude;
-			break;
-			default:
-		}
-		if(d==&gps.latitude)
-		{
-			memcpy(d+placemarker-3,&c,1);
 		}
-		if(d==&gps.longitude)
+		else if(id==0x4A)	//lla(time) packet - 4 floats
 		{
-			memcpy(d+placemarker-7,&c,1);
+			if(placemarker<12)				//lla
+			{
+				d[27-placemarker]=c;
+			}
+			if(placemarker>15 && placemarker<20)	//time
+			{
+				d[31-placemarker]=c;		//time of fix
+			}
 		}
-		if(d==&gps.latitude)
+		else if(id==0x56 && placemarker<12)  //enu packet - 3 floats
 		{
-			memcpy(d+placemarker-11,&c,1);
+			d[11-placemarker]=c;
 		}
-		if(placemarker==14)
+		else if(placemarker>27)				//max 7 floats
 		{
-			LLA=FALSE;
+			state=0;					//we had too much data, something is wrong
 		}
+		placemarker++;					//incr placeholder
 	}
-	if(VENU)
+	switch(state)		//run the state machine
 	{
-		switch(placemarker)
+		case 0:
+		if(c==DLE)		//wait for a dle before proceeding
 		{
-			case 3:
+			state=1;
-			d=&gps.veast;
-			break;
-			case 7:
-			d=&gps.vnorth;
-			break;
-			case 11:
-			d=&gps.vup;
-			break;
-			default:
-		}
-		if(d==&gps.veast)
-		{
-			memcpy(d+placemarker-3,&c,1);
 		}
-		if(d==&gps.vnorth)
+		break;
+		case 1:
+		placemarker=0;
+		if(c==0x4A || c==0x6D || c==0x56)		//packet ids
 		{
-			memcpy(d+placemarker-7,&c,1);
+			state=2;
+			id=c;
 		}
-		if(d==&gps.vup)
+		else					//unknown or not something we are interested in
 		{
-			memcpy(d+placemarker-11,&c,1);
+			state=0;
+		}
+		break;
+		case 2:
+		if(c==DLE)				//a dle in the data?
+		{
+			state=3;
 		}
-		if(placemarker==14)
+		break;
+		case 3:
+		if(c==ETX)
 		{
-			toggle_pin;		//toggles pin D5 - flashing LED tells us gps is working
+			state=0;				//end of packet - we arent in one
-			if(!Gps.packetflag)	//main has unlocked the data
+			if(id==0x6D)			//the 0x6D packet is sent after a fix calculation or at 1Hz
 			{
-				Gps.packetflag=TRUE;	//this is usually the last interesting part of the fix info to come through
+				gps.packetflag=TRUE;//TRUE==1
-				Gps=gps;		//copy into the global variable
+				toggle_pin;			//toggles pin D5 - flashing LED tells us gps is working
-				VENU=FALSE;		//dont need to run again
+				if(!Gps.packetflag)		//main has unlocked the data
+					{
+						Gps=gps;		//copy into the global variable
+					}
 			}
 		}
+		else if(c==DLE)				//double stuffed dle
+		{
+			state=4;
+		}
+		else						//this shouldnt happen
+		{
+			state=0;
+		}
+		break;
+		case 4:
+		if(c==ETX || c==DLE)		//state 4 shouldnt get either of these
+		{
+			state=0;
+		}
+		break;
+		default:					//something wrong, go to 0
+		state=0;
 	}
 }</code>