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code:interrupt_driven_nmea [2008/04/23 00:43] – 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** 
 + 
 + 
 +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" <code c>#include "main.h"
 //global(s) //global(s)
-extern gps_type gps; +extern gps_type Gps; 
 + 
 // Interrupt driven NMEA parser for Atmel AVR // 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[6];  static char buffer[6];
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  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 22: Line 26:
  case '$': //start of a packet  case '$': //start of a packet
    commacount=0;    commacount=0;
-   bufferindex=0; 
-   pointcount=0; 
-   stage=FALSE; 
-   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=FALSE;    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;                        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(GGA)
Line 47: Line 47:
  switch(commacount)  switch(commacount)
  {   {
- case 2: //the latitude from the GGA+ case 3: //the latitude from the GGA
    if( (bufferindex<1  && !stage) || bufferindex<5)    if( (bufferindex<1  && !stage) || bufferindex<5)
    {    {
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  if(!stage)  if(!stage)
  {   {
- gps.latitude=(float)atoi(buffer); // degrees+ gps.latitude=(float)atoi(buffer); // degrees
  stage=TRUE;  stage=TRUE;
  }  }
Line 63: Line 63:
  gps.latitude+=minutes*(float)atoi(buffer); // minutes  gps.latitude+=minutes*(float)atoi(buffer); // minutes
  }  }
- memset(buffer,' ',6); 
    }    }
  break;  break;
- case 3:+ case 4:
    if(c=='S')    if(c=='S')
    {    {
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    }    }
  break;  break;
- case 4:+ case 5:
    if( (bufferindex<1 && !stage) || bufferindex<5)    if( (bufferindex<1 && !stage) || bufferindex<5)
    {    {
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  if(!stage)  if(!stage)
  {   {
- gps.longitude=(float)atoi(buffer); //integer degrees+ gps.longitude=(float)atoi(buffer); // degrees
  stage=TRUE;  stage=TRUE;
  }  }
  else  else
  {  {
- gps.longitude+=minutes*(float)atoi(buffer); //integer minutes+ gps.longitude+=minutes*(float)atoi(buffer); // minutes
  }  }
- memset(buffer,' ',6); 
    }    }
  break;  break;
- case 5:+ case 6:
    if(c=='W')    if(c=='W')
    {    {
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    }    }
  break;  break;
- case 6:+ case 7:
    gps.status=atoi(&c);    gps.status=atoi(&c);
  break;  break;
- case 9:+ case 10:
    if(!pointcount) //wait until we get to a decimal point     if(!pointcount) //wait until we get to a decimal point
    {    {
Line 108: Line 106:
    {    {
  gps.altitude=(float)atoi(buffer)*0.1; //last char in buffer will be after dp  gps.altitude=(float)atoi(buffer)*0.1; //last char in buffer will be after dp
- memset(buffer,' ',5); 
    }    }
  }  }
Line 114: Line 111:
    else if(RMC)    else if(RMC)
    {    {
- if(commacount==7) //speed in knots+ if(commacount==8) //speed in knots
  {   {
  if(!pointcount)  if(!pointcount)
Line 123: Line 120:
  {  {
  gps.speed=(float)atoi(buffer)*0.1;  gps.speed=(float)atoi(buffer)*0.1;
- memset(buffer,' ',5); 
  }  }
  }   }
- if(commacount==8) //the heading field+ if(commacount==9) //the heading
  {  {
- + 
  if(!pointcount)  if(!pointcount)
  {  {
Line 136: Line 132:
  {  {
  gps.heading=(float)atoi(buffer)*0.1;  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 if(!commacount) //the header+   else if(!commacount) //the header
    {     {
  if(bufferindex<4)  if(bufferindex<4)
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  RMC=TRUE;  RMC=TRUE;
  }  }
- memset(buffer,' ',6); //wipe the buffer so it can be reused 
  }  }
  }   }
  }  }
-} +}
 </code> </code>
code/interrupt_driven_nmea.1208911424.txt.gz · Last modified: 2008/07/19 23:31 (external edit)
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