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code:interrupt_driven_nmea [2008/04/17 12:58] – laurencebcode:interrupt_driven_nmea [2013/04/18 20:00] (current) – Reports code isn't tested so just put a notice on there upu
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- 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**
  
  
-<code c>#include "main.h"+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.
  
-// Interrupt driven NMEA parser for Atmel AVR 
  
-ISR(USART_RX_vect) //UART interrupt on mega xx8 series+<code c>#include "main.h" 
 +//global(s) 
 +extern gps_type Gps; 
 +  
 +// Interrupt driven NMEA parser for Atmel AVR 
 +  
 +ISR(USART_RX_vect) //UART interrupt on mega xx8 series
 { {
- static char buffer[5];+ static char buffer[6];
  static u08 GGA;  static u08 GGA;
  static u08 RMC;  static u08 RMC;
Line 15: Line 20:
  static u08 bufferindex;  static u08 bufferindex;
  static u08 pointcount;  static u08 pointcount;
 + static gps_type gps;
  char c=UDR0;  char c=UDR0;
  switch(c)  switch(c)
Line 20: Line 26:
  case '$': //start of a packet  case '$': //start of a packet
    commacount=0;    commacount=0;
-   bufferindex=0; 
-   pointcount=0; 
-   stage=0; 
-   memset(buffer,' ',5); 
    GGA=FALSE;    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;    pointcount=0;
-   stage=0;+   stage=FALSE; 
 +   memset(buffer,' ',6);
  break;  break;
  case '.':  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;                      THIS is deliberate, we want to run when we get a decimal point. + break;                       
- default: //we have some of the CSV data + default: //we have some of the CSV data 
-   if(bufferindex<5) //dont mess up ! +   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(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++;  bufferindex++;
- } +   } 
- else +   else 
- {+   {
  if(!stage)  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++;  bufferindex++;
- } +   } 
- else +   else 
- {+   {
  if(!stage)  if(!stage)
  {   {
- gps.longitude=(float)atoi(buffer); //integer degrees + gps.longitude=(float)atoi(buffer); // degrees 
- } + stage=TRUE;
- if(stage==1) +
- { +
- gps.longitude+=minutes*(float)atoi(buffer); //integer minutes +
- } +
- if(stage==2) +
- { +
- gps.longitude+=0.01*minutes*(float)atoi(buffer); //decimal degrees +
- }  +
- memset(buffer,' ',5); +
- stage++; +
- } +
- } +
- if(commacount==5 && c=='W') +
- { +
- gps.longitude=-gps.longitude; +
- } +
- if(commacount==6) +
- { +
- gps.status=atoi(&c); +
- } +
- if(commacount==9) +
- { +
- if(stage) //decimal altitude +
- { +
- gps.altitude+=((float)atoi(&c))*0.1; +
- memset(buffer,' ',5); +
- } +
- else +
- { +
- if(!pointcount) //wait until we get to a decimal point  +
- { +
- bufferindex++;+
  }  }
  else  else
  {  {
- gps.altitude=(float)atoi(buffer); + gps.longitude+=minutes*(float)atoi(buffer); // minutes
- memset(buffer,' ',5); +
- stage++;+
  }  }
- }+   } 
 + break; 
 + case 6: 
 +   if(c=='W') 
 +   { 
 + gps.longitude=-gps.longitude; 
 +   } 
 + break; 
 + case 7: 
 +   gps.status=atoi(&c); 
 + break; 
 + case 10: 
 +   if(!pointcount) //wait until we get to a decimal point  
 +   { 
 + bufferindex++; 
 +   } 
 +   else 
 +   { 
 + gps.altitude=(float)atoi(buffer)*0.1; //last char in buffer will be after dp 
 +   }
  }  }
    }    }
    else if(RMC)    else if(RMC)
    {    {
- if(commacount==7) //speed in knots+ if(commacount==8) //speed in knots
  {   {
- if(stage)+ if(!pointcount)
  {  {
- gps.speed+=((float)atoi(&c))*0.1; + bufferindex++;
- memset(buffer,' ',5);+
  }  }
  else  else
  {  {
- if(!pointcount) + gps.speed=(float)atoi(buffer)*0.1;
- { +
- bufferindex++; +
- } +
- else +
- { +
- gps.speed=(float)atoi(buffer); +
- memset(buffer,' ',5); +
- stage++; +
- }+
  }  }
  }   }
- if(commacount==8) //the heading field+ if(commacount==9) //the heading
  {  {
- if(stage)+  
 + if(!pointcount)
  {  {
- gps.heading+=((float)atoi(&c))*0.1; + bufferindex++;
- memset(buffer,' ',5); +
- gps.packetflag=TRUE; //this is usually the last interesting part of the fix info to come through+
  }  }
  else  else
  {  {
- if(!pointcount) + gps.heading=(float)atoi(buffer)*0.1; 
- { + toggle_pin; //toggles pin D5 - flashing LED 
- bufferindex++; + if(!Gps.packetflag) //main has unlocked the data
- } +
- else+
  {  {
- gps.heading=(float)atoi(buffer); + Gps.packetflag=TRUE; //this is usually the last interesting part of the fix info to come through 
- memset(buffer,' ',5); + Gps=gps; //copy into the global variable
- stage++;+
  }  }
  }  }
  }  }
    }    }
-   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> </code>
code/interrupt_driven_nmea.1208437081.txt.gz · Last modified: 2008/07/19 23:31 (external edit)
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