// code should compile for any WinCE 3.x or higher based device
// some of the code was taken from Nick Gratton and Marshall Brian's book...
// Windows CE 3.0 Application Programming

// defines and includes
#define WIN32_LEAN_AND_MEAN  // Exclude rarely-used stuff from Windows headers
#include <windows.h>
// function headers
void openComPort();
DWORD WINAPI GPSReadThread(LPVOID);
void ParseRMC(LPTSTR szSentence);
// class level variables
HANDLE hGPSPort = INVALID_HANDLE_VALUE;

int WINAPI WinMain( HINSTANCE hInstance,
    HINSTANCE hPrevInstance,
    LPTSTR    lpCmdLine,
    int       nCmdShow)
{
 // open the port
openComPort();
// read some data and write it to file
GPSReadThread(NULL);
// close the port
if(hGPSPort != INVALID_HANDLE_VALUE)
{
 CloseHandle(hGPSPort);
 hGPSPort = INVALID_HANDLE_VALUE;
}
return 0;
}

void openComPort()
{

// hardcoded hear to COM port 1
hGPSPort = CreateFile (_T("COM1:"), // Port Name (Unicode compatible)
  GENERIC_READ | GENERIC_WRITE, // Open for Read-Write
           0,             // COM port cannot be shared
           NULL,          // Always NULL for Windows CE
           OPEN_EXISTING, // For communication resource
           0,             // Non-overlapped operation only
           NULL);         // Always NULL for Windows CE
 
if(hGPSPort == INVALID_HANDLE_VALUE)
{
 MessageBox(0, _T("Error Opening Comms Port."), _T(""), 0);
 return;
}

// set the timeouts to specify the behavior of reads and writes.
COMMTIMEOUTS ct;
ct.ReadIntervalTimeout = 1000; 
ct.ReadTotalTimeoutMultiplier = 0; 
   ct.ReadTotalTimeoutConstant = 0; 
   ct.WriteTotalTimeoutMultiplier = 10; 
   ct.WriteTotalTimeoutConstant = 1000;
if(!SetCommTimeouts(hGPSPort, &ct))
{
 MessageBox(0, _T("Error Setting Comm Timeouts."), _T(""), 0);
 CloseHandle(hGPSPort);
 hGPSPort = INVALID_HANDLE_VALUE;
 return;
}

// get the current communications parameters, and configure baud rate
DCB dcb;
dcb.DCBlength = sizeof(DCB);

if(!GetCommState(hGPSPort, &dcb))
{
 MessageBox(0, _T("Error Getting Comms State."), _T(""), 0);
 CloseHandle(hGPSPort);
 hGPSPort = INVALID_HANDLE_VALUE;
 return;
}
dcb.BaudRate = CBR_4800;
dcb.fOutxCtsFlow = FALSE;
dcb.fRtsControl     = RTS_CONTROL_DISABLE;
dcb.fDtrControl     = DTR_CONTROL_DISABLE;
dcb.fOutxDsrFlow    = FALSE;
dcb.fOutX           = TRUE; // XON/XOFF control
dcb.fInX            = TRUE;
dcb.ByteSize        = 8;
dcb.Parity          = NOPARITY;
dcb.StopBits        = ONESTOPBIT;

if(!SetCommState(hGPSPort, &dcb))
{
 
 MessageBox(0, _T("Error Setting Comms State."), _T(""), 0);
 CloseHandle(hGPSPort);
 hGPSPort = INVALID_HANDLE_VALUE;
 return;
}
// give time for data to arrive into comm port
Sleep(3000);

// now need to create the thread that will be reading the comms port
HANDLE hCommReadThread = CreateThread(NULL, 0, 
  GPSReadThread, NULL, 0, NULL);
if(hCommReadThread == NULL) 
{
 MessageBox(0, _T("Error Creating Thread."), _T(""), 0);
 CloseHandle(hGPSPort);
 hGPSPort = INVALID_HANDLE_VALUE;
 return;
}
else
{
 CloseHandle(hGPSPort);
 
}
}

// Thread function reads NMEA output from GPS device
DWORD WINAPI GPSReadThread(LPVOID)
{
DWORD dwBytesRead;
char szSentence[1000], c;
TCHAR szwcsSentence[1000];
int nc = 0;
int counter = 0;
SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_BELOW_NORMAL);
while(hGPSPort != INVALID_HANDLE_VALUE)
{

  if(!ReadFile(hGPSPort, &c, 1, &dwBytesRead, NULL))
  {
   MessageBox(0, _T("Error Reading comms port."), _T(""), 0);
   return 0;  // terminate thread on first error
  }
  if(dwBytesRead == 1)
  {
   
    if(c == '\n') // LF marks end of sentance
    {
    
      szSentence[nc - 1] = '\0';// remove trailing CR
      nc = 0;   // ready to read next sentence
      if(strlen(szSentence) < 6)
       ;
      else if(szSentence[0] != '$')
       ;
      else 
      {
       // have a sentence. convert to Unicode
       mbstowcs(szwcsSentence, szSentence, 1000);
       // find sentence ID
       if(wcsncmp(&szwcsSentence[3], _T("RMC"), 3) == 0)
       {
         
        ParseRMC(szwcsSentence);
         
        return 1;
       }
        
      }
    
     
    }
    else
     szSentence[nc++] = c;
 }

}
return 0;
}

// returns the next token from the sentence.
LPTSTR GetNextToken(LPTSTR lpSentence, LPTSTR lpToken)
{
lpToken[0] = '\0';
if(lpSentence == NULL) // empty sentence
 return NULL;
if(lpSentence[0] == '\0') // end of sentence
 return NULL;
if(lpSentence[0] == ',') // empty token
 return lpSentence + 1;
while(*lpSentence != ',' && *lpSentence != '\0' && *lpSentence != '*')
{
 *lpToken = *lpSentence;
 lpToken++;
 lpSentence++;
}
lpSentence++;  // skip over comma
*lpToken = '\0';
return lpSentence;
}


// Parses a RMC sentence which has the format:
// RMC,225446,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E*68
void ParseRMC(LPTSTR szSentence)
{
TCHAR szToken[20];
DWORD dwCheckSum = 0;
FILE* stream;
TCHAR* s = _T("|");
LPCWSTR seps = (const unsigned short *) s;
for(UINT i = 1; i < wcslen(szSentence) && szSentence[i] != '*'; i++)
 dwCheckSum ^= szSentence[i];
// lpNextTok points at ID $GPRMS, ignore this
szSentence = GetNextToken(szSentence, szToken);
// Time of Fix, convert to Unicode
szSentence = GetNextToken(szSentence, szToken);

// Navigation receiver (GPS) warning
szSentence = GetNextToken(szSentence, szToken);

// Latitude
szSentence = GetNextToken(szSentence, szToken);

   
// write lat. to file
stream = fopen( "\\location.txt", "w" );
   fputws( szToken, stream );
fputws( seps, stream );
fclose( stream );
// Latitude N or S
szSentence = GetNextToken(szSentence, szToken);

// write N/S. to file
stream = fopen( "\\location.txt", "a" );
   fputws( szToken, stream );
fputws( seps, stream );

// Longitude
szSentence = GetNextToken(szSentence, szToken);

// write lon. to file
   fputws( szToken, stream );
fputws( seps, stream );
// Longitude W or E
szSentence = GetNextToken(szSentence, szToken);

// write W/E. to file
   fputws( szToken, stream );
fputws( seps, stream );
fclose( stream );
}

quote:

if(hCommReadThread == NULL)
{
MessageBox(0, _T("Error Creating Thread."), _T(""), 0);
CloseHandle(hCommReadThread );
hCommReadThread = INVALID_HANDLE_VALUE;
return;
}
else
{
CloseHandle(hCommReadThread );

}