communication device class (CDC) issue with Read

Question

Im trying to use the readfile function to read data from a CDC device in the WinCE environment.

BOOL WINAPI ReadFile(
  _In_         HANDLE hFile,
  _Out_        LPVOID lpBuffer,
  _In_         DWORD nNumberOfBytesToRead,
  _Out_opt_    LPDWORD lpNumberOfBytesRead,
  _Inout_opt_  LPOVERLAPPED lpOverlapped
);

I would like to know what is the size limit for the readbuf. I am sending the block of 256 bytes of data for 100 times, the parameter lpNumberOfBytesRead from the ReadFile returns 173 bytes on the first try, and 0 all other 99 times. Please let me know what I am missing. Also what is the size limit for the 'writebuf'? below is code for the port open

    BOOL PortOpen()
    {
    Close();

ComPort = INVALID_HANDLE_VALUE;
    COMMTIMEOUTS ct;




ComPort=CreateFile (TEXT("COM1:"), GENERIC_READ | GENERIC_WRITE,
                     0, NULL, OPEN_EXISTING, 0, NULL);



if (ComPort != INVALID_HANDLE_VALUE) {

    dcb.DCBlength = sizeof (dcb);
    GetCommState (hLocal, &dcb);
    dcb.BaudRate = 115200;
    dcb.fParity = FALSE;
    dcb.fNull = FALSE;
    dcb.StopBits = ONESTOPBIT;
    dcb.Parity = NOPARITY;
    dcb.ByteSize = 8;
    SetCommState (ComPort, &dcb);


    ct.ReadIntervalTimeout = 0;
    ct.ReadTotalTimeoutMultiplier = 0;
    ct.ReadTotalTimeoutConstant = 0;
    ct.WriteTotalTimeoutMultiplier = 0;
    ct.WriteTotalTimeoutConstant = 0;
    SetCommTimeouts (hLocal, &ct);

}

Liang

Answer 1

Thank you for the reply! my problem has been resolved. WindowCE does not support the overlapped I/O, the read and write needed to be in the separated thread. Also, to avoid the race condition, I used semaphore.

Liang