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code:interrupt_driven_nmea [2008/04/12 19:07] – 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> +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.
-#include "global.h" +
-#include "avrlibdefs.h" +
-#include "avrlibtypes.h" +
-#include <avr/io.h> +
-#include <stdlib.h> +
-#include <stdio.h> +
-#include <string.h> +
-#include <avr/interrupt.h>+
  
  
 +<code c>#include "main.h"
 +//global(s)
 +extern gps_type Gps;
 + 
 // Interrupt driven NMEA parser for Atmel AVR // Interrupt driven NMEA parser for Atmel AVR
-//header file starts here +  
-#define minutes (float)1.0/60.0 +ISR(USART_RX_vect) //UART interrupt on mega xx8 series
-#define baudrate 4800 +
- +
-struct +
-{ +
- volatile float longitude; +
- volatile float latitude; +
- volatile float altitude; +
- volatile float speed; +
- volatile float heading; +
- volatile u08 packetflag;                                //packetflag lets us see when our packet has been updated +
- volatile u08 status; +
-} gps; +
-//end of header file +
- +
-int main() +
-{ +
-outb(UCSR0B, BV(RXCIE0)|BV(TXCIE0)|BV(RXEN0)|BV(TXEN0)); //mega xx8 registers - enable tx and rx, with interrupts +
-u16 bauddiv = ((F_CPU+(baudrate*8L))/(baudrate*16L)-1); +
-outb(UBRR0L, bauddiv); +
-outb(UBRR0H, bauddiv>>8); +
-} +
- +
-SIGNAL(SIG_USART_RECV) //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 47: 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 52: 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 
-   buffer[bufferindex]=c; //stick the character in our buffer +   if(bufferindex<6) //dont mess up ! Dont overflow 
 +   {  
 +     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 
 + if(!Gps.packetflag) //main has unlocked the data
  {  {
- bufferindex++; + 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 +
- { +
- gps.heading=(float)atoi(buffer); +
- memset(buffer,' ',5); +
- 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.1208027242.txt.gz · Last modified: 2008/07/19 23:31 (external edit)
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