Com Ports

Hi,

I've been using the following code to open and read data from a com port

      h = CreateFile("Com1",
                           GENERIC_READ|GENERIC_WRITE,
                           0,NULL,
                           OPEN_EXISTING,FILE_FLAG_OVERLAPPED,NULL);

      if(h == INVALID_HANDLE_VALUE) {
         PrintError("Failed to open port",ComNumber);
         return;
      }

***** To read from the port

      COMMTIMEOUTS cto = { 2, 1, 1, 0, 0 };
            
      if(!SetCommTimeouts(h,&cto))
            PrintError("SetCommTimeouts failed",ComNumber);


      // create event for overlapped I/O
   osRead.hEvent = CreateEvent(NULL,FALSE,FALSE,NULL);
   if(osRead.hEvent == INVALID_HANDLE_VALUE)
      PrintError("CreateEvent failed", ComNumber);

   // wait for received characters
   if(!SetCommMask(h,EV_RXCHAR | EV_RLSD))
      PrintError("SetCommMask failed", ComNumber);

   Finished=FALSE;
   while( !Finished ) {
      // get the event mask
      if( !WaitCommEvent(h,&mask,&osRead) ) {
         DWORD e = GetLastError();
         if( e == ERROR_IO_PENDING ) {
            DWORD r;
            if( !GetOverlappedResult(h,&osRead,&r,TRUE) ) {
               PrintError("GetOverlappedResult failed",ComNumber);
               break;
            }
         } else {
            PrintError("WaitCommEvent failed", ComNumber);
            break;
         }
      }

      // if no event, then UI thread terminated with SetCommMask(h,0)
      if( mask == 0 ) {
         return ExitThread;
      }

      if( mask & EV_RLSD)
        {
              return CDLost;
        }
        else{
         char buf[10];
         DWORD read;

   

             do {
                  memset(buf,'\0',sizeof(buf));
             read = 0;
            if( !ReadFile(h,buf,sizeof(buf),&read,&osRead) ) {
               if( GetLastError() == ERROR_IO_PENDING ) {
                  if( !GetOverlappedResult(h,&osRead,&read,TRUE) ) {
                     PrintError("GetOverlappedResult failed", ComNumber);
                     break;
                  }
               } else {
                  PrintError("ReadFile failed", ComNumber);
                  break;
               }
            }
            if(read)
                  {
*** We have some data

All works ok.  The routine waits until data is received then reads it in.  If their is a change in CD signal this is also recognised.

The problem I have is I wish the GetOverlappedresult function to return after a set time interval.   Whether there is any data or not.

I have tried the following

      COMMTIMEOUTS cto = { 200, 1, 3000, 0, 0 };


    if(!SetCommTimeouts(h,&cto))
        PrintError("SetCommTimeouts failed",ComNumber);            
        if( !ReadFile(h,buf,MaxCharNumber,&read,&osRead) ) {
                        PrintError("ReadFile failed", ComNumber);
                        return FALSE;
                        break;
                  }

            if (read)
            {
            *** We have data      

Which works as required. I.E if after 3 seconds no data is received ReadFile returns with read=0, if data is received ReadFile returns straight away with the data.

But.  If i call  ReadFile again it returns straight away even when there is no data,  How do I get it to perform as it does the first time i called ReadFile.

Or can I change the first example code so that  GetOverLappedResult returns after a set interval.