I am using Ramon de Klein's CSerial library in order to open and manage a serial port from my C++ code.
My hardware implements a serial tu USB converter with an FTDI chip, so I am able to connect the serial port to a USB plug in my CPU. Once FTDI drivers are installed, a virtual COM port is shown at 'Device Manager' (Windows).
If I try to open it, it works.
But now I have installed a USB to ethernet server like this one. So I install its drivers and software, and after connecting some usb device to it, is is detected and also added as a virtual serial port to 'Device Manager' window.
But when I try to open the port, it doesn't work. It does work if I open the port with an HyperTerminal-like application, just as if it was a normal serial port, but not in my code.
CSerial library works as if it were creating a new file, and given LastErrorCode is 2: "File not found". This is the Open method from the CSerial library:
LONG CSerial::Open (LPCTSTR lpszDevice, DWORD dwInQueue, DWORD dwOutQueue, bool fOverlapped)
{
// Reset error state
m_lLastError = ERROR_SUCCESS;
// Check if the port isn't already opened
if (m_hFile)
{
m_lLastError = ERROR_ALREADY_INITIALIZED;
_RPTF0(_CRT_WARN,"CSerial::Open - Port already opened\n");
return m_lLastError;
}
// Open the device
m_hFile = ::CreateFile(lpszDevice,
GENERIC_READ|GENERIC_WRITE,
0,
0,
OPEN_EXISTING,
fOverlapped?FILE_FLAG_OVERLAPPED:0,
0);
if (m_hFile == INVALID_HANDLE_VALUE)
{
// Reset file handle
m_hFile = 0;
// Display error
m_lLastError = ::GetLastError();
_RPTF0(_CRT_WARN, "CSerial::Open - Unable to open port\n");
return m_lLastError;
}
#ifndef SERIAL_NO_OVERLAPPED
// We cannot have an event handle yet
_ASSERTE(m_hevtOverlapped == 0);
// Create the event handle for internal overlapped operations (manual reset)
if (fOverlapped)
{
m_hevtOverlapped = ::CreateEvent(0,true,false,0);
if (m_hevtOverlapped == 0)
{
// Obtain the error information
m_lLastError = ::GetLastError();
_RPTF0(_CRT_WARN,"CSerial::Open - Unable to create event\n");
// Close the port
::CloseHandle(m_hFile);
m_hFile = 0;
// Return the error
return m_lLastError;
}
}
#else
// Overlapped flag shouldn't be specified
_ASSERTE(!fOverlapped);
#endif
// Setup the COM-port
if (dwInQueue || dwOutQueue)
{
// Make sure the queue-sizes are reasonable sized. Win9X systems crash
// if the input queue-size is zero. Both queues need to be at least
// 16 bytes large.
_ASSERTE(dwInQueue >= 16);
_ASSERTE(dwOutQueue >= 16);
if (!::SetupComm(m_hFile,dwInQueue,dwOutQueue))
{
// Display a warning
long lLastError = ::GetLastError();
_RPTF0(_CRT_WARN,"CSerial::Open - Unable to setup the COM-port\n");
// Close the port
Close();
// Save last error from SetupComm
m_lLastError = lLastError;
return m_lLastError;
}
}
// Setup the default communication mask
SetMask();
// Non-blocking reads is default
SetupReadTimeouts(EReadTimeoutNonblocking);
// Setup the device for default settings
COMMCONFIG commConfig = {0};
DWORD dwSize = sizeof(commConfig);
commConfig.dwSize = dwSize;
if (::GetDefaultCommConfig(lpszDevice,&commConfig,&dwSize))
{
// Set the default communication configuration
if (!::SetCommConfig(m_hFile,&commConfig,dwSize))
{
// Display a warning
_RPTF0(_CRT_WARN,"CSerial::Open - Unable to set default communication configuration.\n");
}
}
else
{
// Display a warning
_RPTF0(_CRT_WARN,"CSerial::Open - Unable to obtain default communication configuration.\n");
}
// Return successful
return m_lLastError;
}
I don't understand why it doesn't work in the same way as plugging the USB directly to the computer: I always thought that it should work if the COM is listed in 'Device Manager', independently from where it is really connected.
On balance, the way data is comming from was:
RS232--->converted to USB--->USB CPU connector--->virtualized as RS232 in a COM port
And now is:
RS232--->converted to USB--->converted to ethernet by the "netUSB server"--->Ethernet/WiFi at the CPU--->virtualized as a USB device--->virtualized as RS232 in a COM port
Any help?