/*! \file nmea.c \brief NMEA protocol function library. */
//*****************************************************************************
//
// File Name : 'nmea.c'
// Title : NMEA protocol function library
// Author : Pascal Stang - Copyright (C) 2002
// Created : 2002.08.27
// Revised : 2002.08.27
// Version : 0.1
// Target MCU : Atmel AVR Series
// Editor Tabs : 4
//
// NOTE: This code is currently below version 1.0, and therefore is considered
// to be lacking in some functionality or documentation, or may not be fully
// tested. Nonetheless, you can expect most functions to work.
//
// This code is distributed under the GNU Public License
// which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************
#ifndef WIN32
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#endif
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include "global.h"
#include "buffer.h"
#include "rprintf.h"
#include "gps.h"
#include "nmea.h"
// Program ROM constants
// Global variables
extern GpsInfoType GpsInfo;
u08 NmeaPacket[NMEA_BUFFERSIZE];
void nmeaInit(void)
{
}
u08* nmeaGetPacketBuffer(void)
{
return NmeaPacket;
}
u08 nmeaProcess(cBuffer* rxBuffer)
{
u08 foundpacket = NMEA_NODATA;
u08 startFlag = FALSE;
//u08 data;
u16 i,j;
// process the receive buffer
// go through buffer looking for packets
while(rxBuffer->datalength)
{
// look for a start of NMEA packet
if(bufferGetAtIndex(rxBuffer,0) == '$')
{
// found start
startFlag = TRUE;
// when start is found, we leave it intact in the receive buffer
// in case the full NMEA string is not completely received. The
// start will be detected in the next nmeaProcess iteration.
// done looking for start
break;
}
else
bufferGetFromFront(rxBuffer);
}
// if we detected a start, look for end of packet
if(startFlag)
{
for(i=1; i<(rxBuffer->datalength)-1; i++)
{
// check for end of NMEA packet <CR><LF>
if((bufferGetAtIndex(rxBuffer,i) == '\r') && (bufferGetAtIndex(rxBuffer,i+1) == '\n'))
{
// have a packet end
// dump initial '$'
bufferGetFromFront(rxBuffer);
// copy packet to NmeaPacket
for(j=0; j<(i-1); j++)
{
// although NMEA strings should be 80 characters or less,
// receive buffer errors can generate erroneous packets.
// Protect against packet buffer overflow
if(j<(NMEA_BUFFERSIZE-1))
NmeaPacket[j] = bufferGetFromFront(rxBuffer);
else
bufferGetFromFront(rxBuffer);
}
// null terminate it
NmeaPacket[j] = 0;
// dump <CR><LF> from rxBuffer
bufferGetFromFront(rxBuffer);
bufferGetFromFront(rxBuffer);
#ifdef NMEA_DEBUG_PKT
rprintf("Rx NMEA packet type: ");
rprintfStrLen(NmeaPacket, 0, 5);
rprintfStrLen(NmeaPacket, 5, (i-1)-5);
rprintfCRLF();
#endif
// found a packet
// done with this processing session
foundpacket = NMEA_UNKNOWN;
break;
}
}
}
if(foundpacket)
{
// check message type and process appropriately
if(!strncmp(NmeaPacket, "GPGGA", 5))
{
// process packet of this type
nmeaProcessGPGGA(NmeaPacket);
// report packet type
foundpacket = NMEA_GPGGA;
}
else if(!strncmp(NmeaPacket, "GPVTG", 5))
{
// process packet of this type
nmeaProcessGPVTG(NmeaPacket);
// report packet type
foundpacket = NMEA_GPVTG;
}
}
else if(rxBuffer->datalength >= rxBuffer->size)
{
// if we found no packet, and the buffer is full
// we're logjammed, flush entire buffer
bufferFlush(rxBuffer);
}
return foundpacket;
}
void nmeaProcessGPGGA(u08* packet)
{
u08 i;
char* endptr;
double degrees, minutesfrac;
#ifdef NMEA_DEBUG_GGA
rprintf("NMEA: ");
rprintfStr(packet);
rprintfCRLF();
#endif
// start parsing just after "GPGGA,"
i = 6;
// attempt to reject empty packets right away
if(packet[i]==',' && packet[i+1]==',')
return;
// get UTC time [hhmmss.sss]
GpsInfo.PosLLA.TimeOfFix.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: latitude
// get latitude [ddmm.mmmmm]
GpsInfo.PosLLA.lat.f = strtod(&packet[i], &endptr);
// convert to pure degrees [dd.dddd] format
minutesfrac = modf(GpsInfo.PosLLA.lat.f/100, °rees);
GpsInfo.PosLLA.lat.f = degrees + (minutesfrac*100)/60;
// convert to radians
GpsInfo.PosLLA.lat.f *= (M_PI/180);
while(packet[i++] != ','); // next field: N/S indicator
// correct latitute for N/S
if(packet[i] == 'S') GpsInfo.PosLLA.lat.f = -GpsInfo.PosLLA.lat.f;
while(packet[i++] != ','); // next field: longitude
// get longitude [ddmm.mmmmm]
GpsInfo.PosLLA.lon.f = strtod(&packet[i], &endptr);
// convert to pure degrees [dd.dddd] format
minutesfrac = modf(GpsInfo.PosLLA.lon.f/100, °rees);
GpsInfo.PosLLA.lon.f = degrees + (minutesfrac*100)/60;
// convert to radians
GpsInfo.PosLLA.lon.f *= (M_PI/180);
while(packet[i++] != ','); // next field: E/W indicator
// correct latitute for E/W
if(packet[i] == 'W') GpsInfo.PosLLA.lon.f = -GpsInfo.PosLLA.lon.f;
while(packet[i++] != ','); // next field: position fix status
// position fix status
// 0 = Invalid, 1 = Valid SPS, 2 = Valid DGPS, 3 = Valid PPS
// check for good position fix
if( (packet[i] != '0') && (packet[i] != ',') )
GpsInfo.PosLLA.updates++;
while(packet[i++] != ','); // next field: satellites used
// get number of satellites used in GPS solution
GpsInfo.numSVs = atoi(&packet[i]);
while(packet[i++] != ','); // next field: HDOP (horizontal dilution of precision)
while(packet[i++] != ','); // next field: altitude
// get altitude (in meters)
GpsInfo.PosLLA.alt.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: altitude units, always 'M'
while(packet[i++] != ','); // next field: geoid seperation
while(packet[i++] != ','); // next field: seperation units
while(packet[i++] != ','); // next field: DGPS age
while(packet[i++] != ','); // next field: DGPS station ID
while(packet[i++] != '*'); // next field: checksum
}
void nmeaProcessGPVTG(u08* packet)
{
u08 i;
char* endptr;
#ifdef NMEA_DEBUG_VTG
rprintf("NMEA: ");
rprintfStr(packet);
rprintfCRLF();
#endif
// start parsing just after "GPVTG,"
i = 6;
// attempt to reject empty packets right away
if(packet[i]==',' && packet[i+1]==',')
return;
// get course (true north ref) in degrees [ddd.dd]
GpsInfo.VelHS.heading.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: 'T'
while(packet[i++] != ','); // next field: course (magnetic north)
// get course (magnetic north ref) in degrees [ddd.dd]
//GpsInfo.VelHS.heading.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: 'M'
while(packet[i++] != ','); // next field: speed (knots)
// get speed in knots
//GpsInfo.VelHS.speed.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: 'N'
while(packet[i++] != ','); // next field: speed (km/h)
// get speed in km/h
GpsInfo.VelHS.speed.f = strtod(&packet[i], &endptr);
while(packet[i++] != ','); // next field: 'K'
while(packet[i++] != '*'); // next field: checksum
GpsInfo.VelHS.updates++;
}
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