MyCarTrek600: NMEA logging

A little bit experimental...


#include <stdio.h>
#include <windows.h>
/*
** CarTrek 600 NMEA logger (code inspired by gosmore)
**    still a little bit experimental...
*/
#define prog_name  TEXT("nmealog")
void msg(char *str1, char *str2)
    {
    static char    txtbuf[512];
    static wchar_t    wtxtbuf[512];

    sprintf(txtbuf, "%s %s (GetLastError()=%ld)", str1, str2, GetLastError());
    mbstowcs(&wtxtbuf[0], &txtbuf[0], strlen(txtbuf)+1);
    MessageBox(0, &wtxtbuf[0], prog_name, MB_OK);
    }
/*
** NMEA module
**    NMEA_init()
**    NMEA_close()
**    n = NMEA_read(buf, size)
*/
HANDLE NMEA_handle;
#define port_name TEXT("COM7:")
#define port_rate CBR_57600
int NMEA_init()
    {
    COMMTIMEOUTS commTiming;
    DCB portState;

    if ((NMEA_handle = CreateFile (port_name, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, 0)) == INVALID_HANDLE_VALUE)
        {
        MessageBox(0, TEXT("Can't open port COMx:"), prog_name, MB_OK);
        return(0);
        }
    if (!GetCommTimeouts(NMEA_handle, &commTiming))
        {
        MessageBox(0, TEXT("Can't GetCommTimeouts"), prog_name, MB_OK);
        CloseHandle(NMEA_handle);
        return(0);
        }
    commTiming.ReadIntervalTimeout = 20;
    commTiming.ReadTotalTimeoutMultiplier = 0;
    commTiming.ReadTotalTimeoutConstant = 200; /* Bailout when nothing on the port */
    commTiming.WriteTotalTimeoutMultiplier=5; /* No writing */
    commTiming.WriteTotalTimeoutConstant=5;
    if (!SetCommTimeouts(NMEA_handle, &commTiming))
        {
        MessageBox(0, TEXT("Can't SetCommTimeouts"), prog_name, MB_OK);
        CloseHandle(NMEA_handle);
        return(0);
        }
    if(!GetCommState(NMEA_handle, &portState))
        {
        MessageBox(0, TEXT("Can't GetCommState"), prog_name, MB_OK);
        CloseHandle(NMEA_handle);
        return(0);
        }
    portState.BaudRate = port_rate;
    if(!SetCommState(NMEA_handle, &portState))
        {
        MessageBox(0, TEXT("Can't GetCommState"), prog_name, MB_OK);
        CloseHandle(NMEA_handle);
        return(0);
        }
    PurgeComm(NMEA_handle, PURGE_RXCLEAR); /* Baud rate wouldn't change without this ! (?) */
    return(1);
    }
int NMEA_close()
    {
    return(CloseHandle(NMEA_handle));
    }
int NMEA_read(char *buf, int n)
    {
    DWORD    nr;
    char    stuff[80];

    if (!ReadFile(NMEA_handle, buf, n, &nr, NULL))
        {
        MessageBox(0, TEXT("Can't ReadFile"), prog_name, MB_OK);
        return(-1);
        }
    else    {
        n = nr;
        return(n);
        }
    }
/*===================================================================*/
/* LOG module
**
*/
char    *LOG_fname="\\SDMMC\\NMEAlog.txt";
FILE    *LOG_stream;
int LOG_init()
    {
    if ((LOG_stream=fopen(LOG_fname, "a+")) == NULL)
        {
        msg("Can't fopen()", LOG_fname);
        return(0);
        }
    fprintf(LOG_stream, "===== New log =====\n");
    return(1);
    }
int LOG_close()
    {
    return(fclose(LOG_stream));
    }
int LOG_write(char *buf, int len)
    {
    if (fwrite(buf, 1, len, LOG_stream) != len)
        msg("Can't write LOG_stream", LOG_fname);
    return(len);
    }
/*===================================================================*/
#define MAXLOG (100)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
    {
    wchar_t argv0[80];
    char    buf[512];
    int    n, count;

    GetModuleFileName (NULL, argv0, sizeof (argv0) / sizeof (argv0[0]));
    MessageBox(0, argv0, L"CeGCC says...", MB_OK);

    NMEA_init();
    if (LOG_init())
        {
        for (count = 0; count < MAXLOG; )
            {
            if ((n = NMEA_read(&buf[0], sizeof(buf))) < 0)
                {
                msg("Can't read NMEA", "");
                break;
                }
            if (n > 0)
                {
                if (LOG_write(&buf[0], n) != n)
                    {
                    msg("Can't write LOG", "");
                    break;
                    }
                count++;
                }
            }
        }
    LOG_close();
    NMEA_close();
    }

I get stuff like :


$GPRMC,110034.02,V,0000.0000,N,00000.0000,E,,,010103,,W,N*17^M
$GPGSA,A,1,,,,,,,,,,,,,60.000,60.000,60.000*06^M
$GPGSV,5,1,20,1,5,322,,5,15,296,,6,5,,,7,5,,*45^M
$GPGSV,5,2,20,8,5,,,9,41,12,,10,16,156,,11,5,,*4F^M
$GPGSV,5,3,20,14,23,316,,15,71,187,,16,10,282,,18,5,,*73^M
$GPGSV,5,4,20,21,5,,,22,1,273,,24,34,172,,25,5,,*4C^M
$GPGSV,5,5,20,26,5,,,28,5,,,30,23,4,,31,41,14,*41^M
$GPGGA,110039.02,0000.0000,N,00000.0000,E,,,60.000,,M,,M,,*53^M
$GPRMC,110039.02,V,0000.0000,N,00000.0000,E,,,010103,,W,N*1A^M

which is encouraging.
See
* Wikipedia->NMEA 0183
** NMEA reference Manual1.pdf SiRF Technology inc.
* Wikipedia->Dilution of precision
----
Three GPS, same location, same time. xy in meters (-75 is CarTrek (green); -64,-89 are Connex (red & blue))

xy plot