Emery Premeaux / Mbed 2 deprecated GPS_U-blox_NEO-M8N

GPS NMEA sentence reader for Nucleo boards.

Dependencies:   mbed MODSERIAL

I had a lot of trouble getting other GPS examples to work. So I took Edoardo De Marchi's code from 2014 and hacked it until it was working on newer hardware.

Advice:

  • Start with confirming the module works in U-Center, and know the baud rate. Many older libraries assume 9600. Newer modules run at higher baud rates
  • Use a good terminal program and confirm you have human readable messages starting with "$GNGGA" or "$GPGSV" or similar.

Comments in code include links to NMEA sentence guides:

Most libraries do not include sentence filters for the types of sentences output by my M8N (and perhaps other modules as well)

Most older versions of the MODSERIAL library do not update properly to support STM32. I have found and included a version of the lib which will compile without errors. However, when using it in my code, the NMEA sentence gets corrupted somehow (for example showing some HUGE [6 digit] Satellite count, etc.

main.cpp

Committer:
epremeaux
Date:
2019-07-04
Revision:
2:c16325a7d225
Parent:
1:acd907fbcbae

File content as of revision 2:c16325a7d225:

/*
 * Author: Edoardo De Marchi
 * Date: 22-08-14
 * Notes: Firmware for GPS U-Blox NEO-6M
 *
 * Modified: Emery Premeaux
 * Date: July 2019
 * Written for: Nucleo F401RE & NEO-M8N
 *
 * Updated MODSERIAL library now compiles without errors but data seems corrupted.
 *
 * NMEA sentences:  https://www.gpsinformation.org/dale/nmea.htm#nmea
 * 
*/

#include "mbed.h"
//#include "MODSERIAL.h"

//MODSERIAL pc(USBTX,USBRX);
//MODSERIAL gps(D8, D2);

Serial pc(USBTX,USBRX);
Serial gps(D8, D2);

char cDataBuffer[500];
int i = 0;
int h_time,m_time,s_time;

void Init();
void parse(char *cmd, int n);
void parseTime (float timeval);


void Init()
{
    gps.baud(115200);
     pc.baud(115200);
    pc.printf("Init OK\n");
}



int main() 
{   
    Init();
    char c;

    while(true) 
    {
        if(gps.readable())
        { 
            if(gps.getc() == '$');           // wait a $
            {
                for(int i=0; i<sizeof(cDataBuffer); i++)
                {
                    c = gps.getc();
                    if( c == '\r' )
                    {
                        //pc.printf("%s\n", cDataBuffer);
                        parse(cDataBuffer, i);
                        i = sizeof(cDataBuffer);
                    }
                    else
                    {
                        cDataBuffer[i] = c;
                    }                 
                }
            }
         } 
    }
}

/* 
 * NMEA sentences:  https://www.gpsinformation.org/dale/nmea.htm#nmea
 *                  http://navspark.mybigcommerce.com/content/NMEA_Format_v0.1.pdf
 */
void parse(char *cmd, int n)
{   
    char ns, ew, tf, status;
    int fq, nst, fix, date;                                     // fix quality, Number of satellites being tracked, 3D fix
    float latitude, longitude, timefix, speed, altitude;
    
    // Global Positioning System Fix Data
    if(strncmp(cmd,"$GPGGA", 6) == 0) 
    {
        sscanf(cmd, "$GPGGA,%f,%f,%c,%f,%c,%d,%d,%*f,%f", &timefix, &latitude, &ns, &longitude, &ew, &fq, &nst, &altitude);
        pc.printf("GPGGA Fix taken at: %f, Latitude: %f %c, Longitude: %f %c, Fix quality: %d, Number of sat: %d, Altitude: %f M\n", timefix, latitude, ns, longitude, ew, fq, nst, altitude);
    }
    
    // Satellite status
     else if(strncmp(cmd,"$GPGSA", 6) == 0) 
    {
        sscanf(cmd, "$GPGSA,%c,%d,%d", &tf, &fix, &nst);
        pc.printf("GPGSA Type fix: %c, 3D fix: %d, number of sat: %d\r\n", tf, fix, nst);
    }
    
    // Geographic position, Latitude and Longitude
    else if(strncmp(cmd,"$GPGLL", 6) == 0) 
    {
        sscanf(cmd, "$GPGLL,%f,%c,%f,%c,%f", &latitude, &ns, &longitude, &ew, &timefix);
        pc.printf("GPGLL Latitude: %f %c, Longitude: %f %c, Fix taken at: %f\n", latitude, ns, longitude, ew, timefix);
    }
    
    // Geographic position, Latitude and Longitude
    else if(strncmp(cmd,"$GPRMC", 6) == 0) 
    {
        sscanf(cmd, "$GPRMC,%f,%c,%f,%c,%f,%c,%f,,%d", &timefix, &status, &latitude, &ns, &longitude, &ew, &speed, &date);
        pc.printf("GPRMC Fix taken at: %f, Status: %c, Latitude: %f %c, Longitude: %f %c, Speed: %f, Date: %d\n", timefix, status, latitude, ns, longitude, ew, speed, date);
    }
    
    // 
    else if(strncmp(cmd,"$GNVTG", 6) == 0) 
    {
     //   pc.printf("its a Vector Track message.\n");
    }
    
    else if(strncmp(cmd,"$GNGGA", 6) == 0) 
    {
        sscanf(cmd, "$GNGGA,%f,%f,%c,%f,%c,%d,%d,%*f,%f", &timefix, &latitude, &ns, &longitude, &ew, &fq, &nst, &altitude);
        pc.printf("GNGGA Fix taken at: %f, Latitude: %f %c, Longitude: %f %c, Fix quality: %d, Number of sat: %d, Altitude: %f M\n", timefix, latitude, ns, longitude, ew, fq, nst, altitude);
        parseTime(timefix);
        pc.printf("Time: %d:%d:%d\n", h_time, m_time, s_time);
    }
    
    else if(strncmp(cmd,"$GNGSA", 6) == 0) 
    {
        sscanf(cmd, "$GNGSA,%c,%d,%d", &tf, &fix, &nst);
        pc.printf("GNGSA Type fix: %c, 3D fix: %d, number of sat: %d\r\n", tf, fix, nst);
    }
    
    else if(strncmp(cmd,"$GPGSV", 6) == 0) 
    {
     //   pc.printf("its a Satellite details message.\n");
    }
    
    else if(strncmp(cmd,"$GNGLL", 6) == 0) 
    {
        sscanf(cmd, "$GNGLL,%f,%c,%f,%c,%f", &latitude, &ns, &longitude, &ew, &timefix);
        pc.printf("GNGLL Latitude: %f %c, Longitude: %f %c, Fix taken at: %f\n", latitude, ns, longitude, ew, timefix);
    }
    
    else
    {
   //     pc.printf("Unknown message type\n");
    }
}

void parseTime (float timeval)
{
    //format utc time to beijing time,add 8 time zone
                float time = timeval + 80000.00f;
                h_time = int(time) / 10000;
                m_time = (int(time) % 10000) / 100;
                s_time = int(time) % 100;
}