WaitCommEvent problem

From: marabo82 (marabo82_at_discussions.microsoft.com)
Date: 08/04/04 

Date: Wed, 4 Aug 2004 16:57:01 -0700

Hi All,

(Environment: SH3 device, PB 4.2)
My app is a Headless serial port App, it sends a trigger command to a
barcode scanner (via writefile , works fine)
the scanner sends the barcode ascii characters (all fine and Dundee) then i
have to write it to a file (so other app's can access it)

all that works perfect, however, i need my app to timeout if no data was
received within 3 seconds so that i am not waiting forever for the scanner to
send some data. (when i send the trigger command to the scanner, it will turn
on and attempt to capture barcode 4 ever, it will only send some data when it
captures barcode) i want my app to terminate if no data was received from the
scanner within 3 seconds

I am doing the COM port init, read, write all in the same UI (no seperate
threads, works perfect, juts want it to timeout)

i am using WaitCommEvent (hPort, &dwCommModemStatus, 0). i read in one of
the posting by Steve Maillet that
WaitCommEvent will timeout according to the timeout values set by
SetCommTimeouts(). However, this doesn't seem to work
, i think those values will only apply to ReadFile/WriteFile()

My approach was to set a timeout for the event to occur, and quit if it
doesn't occur within 3 seconds. i did the following:
  
        Time_out_event=CreateEvent(NULL,false,false,NULL);

And waited for that event to occur after i call WaitCommEvent().

<snap>
WaitCommEvent (hPort, &dwCommModemStatus, 0 ); //overlapped I/O is not
supported in windows CE
         // Re-specify the set of events to be monitored for the port
        SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING);
        //Wait for the event to occur for 3 seconds
        Time_out_result=WaitForSingleObject(Time_out_event,3000);

</snap>

However, WaitCommEvent never timeout -- if no data is received within 3
seconds, it will wait 4 ever--.
oddly, when the scanner gets some data, the WaitCommevent() will return and
WaitForSingleObject() will think
that WAIT_TIMEOUT event has occured instead WAIT_OBJECT_0 (which i believe
indicated that an event has occured)

here is the code:

        <code snap>
        HANDLE Time_out_event=0;
        DWORD Time_out_result=0;
        ...

        CommTimeouts.ReadIntervalTimeout = MAXWORD; //i also tried 1000, 0
        CommTimeouts.ReadTotalTimeoutMultiplier = 0;
        CommTimeouts.ReadTotalTimeoutConstant = 0;
        CommTimeouts.WriteTotalTimeoutMultiplier = 10;
        CommTimeouts.WriteTotalTimeoutConstant = 1000;

        ...

        SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING);
        
        // Wait for an event to occur for the port.
        Time_out_event=CreateEvent(NULL,false,false,NULL);
        if (Time_out_event== INVALID_HANDLE_VALUE)
        {
                // Could not create a Time out event
                PostMessage(HWND_BROADCAST,ERROR_BARCODE_MSG,0, 0);
                RETAILMSG(1,(TEXT("\r\nError: Unable to Create a Time Out Event \n")));
                //close the barcodemsg file
                CloseHandle(barcodemsg_file);
                //close serial port
                CloseHandle( hPort);
                return -1;
        }
        WaitCommEvent (hPort, &dwCommModemStatus, 0);
        
        // Re-specify the set of events to be monitored for the port
        SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING);
        
        //Wait for the event to occur for 3 seconds
        Time_out_result=WaitForSingleObject(Time_out_event,3000);
        
        switch(Time_out_result)
        {
        case WAIT_OBJECT_0 :
                //note: the program never go here, even if the scanner send the data
before 3 seconds have elapsed
                //in theory, the program should get here if data was received before 3
seconds.

                // Operation completed
                //// Re-specify the set of events to be monitored for the port
                //SetCommMask (hPort, EV_RXCHAR | EV_CTS | EV_DSR | EV_RLSD | EV_RING);
                
                RETAILMSG(1,(TEXT("\r\nSucccess: Operation Completed\n")));
                if (dwCommModemStatus & EV_RXCHAR)
                {
                        do
                        {
                                // Read the data from the serial port.
                                ReadFile (hPort, &byte, 1, &dwBytesTransferred, 0);
                                if (dwBytesTransferred == 1)
                                {
                                        WriteFile (barcodemsg_file,&byte,1,&dwNumBytesWritten,NULL);
                                
                                }
                        }while (dwBytesTransferred == 1);
                }
                
                // Retrieve modem control-register values.
                GetCommModemStatus (hPort, &dwCommModemStatus);
                ResetEvent ( Time_out_event );
                break;
        
        case WAIT_TIMEOUT:
                
                //note: the code end up here when the barcode sends the data, otherwise
                // WaitCommevent() will block 4 ever.
                //in theory, the code should only get here if Time_out_event has occurred

                //The time-out interval elapsed, and the objects state is nonsignaled
                PostMessage(HWND_BROADCAST,ERROR_BARCODE_MSG,0, 0);
                RETAILMSG(1,(TEXT("\r\nError: WaitCommEvent didn't succeed or timed
out\n")));
                //close the barcodemsg file
                CloseHandle(barcodemsg_file);
                //close serial port
                CloseHandle( hPort);
                exit(-1);
                break;
        }
</snap>

Any idea? will WaitSingleObject() ever work in windows CE?
do i have to Set/Reset Time_out_event somewhere?

Your help is greatly appreciated.

Mo
marabo82@hotmail.com

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