Sending trigger through parallel port, C++, Visual Studio 2010, Windows 7

Question

Hi, I have a problem that I am really stuck with, and I am novice to the task so any help would be extremely helpful.
I an trying to write to parallel port on my PC in order to send a trigger to EEG recording machine every time the new goal appears in a Virtual Reality game that I wrote in C++ (I want to record EEG brain signals while subjects are playing the game).
I tried to follow the instructions from here: http://msdn.microsoft.com/en-us/library/ff802693.aspx
I wrote the following code:
BOOL FileExists(LPCTSTR szPath)
DWORD dwAttrib = GetFileAttributes(szPath);
return (dwAttrib != INVALID_FILE_ATTRIBUTES && 
!(dwAttrib & FILE_ATTRIBUTE_DIRECTORY));
BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)
OVERLAPPED osWrite = {0};
DWORD dwWritten;
DWORD dwRes;
BOOL fRes;
// Create this write operation's OVERLAPPED structure's hEvent.
osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (osWrite.hEvent == NULL)
// error creating overlapped event handle
return FALSE;
// Issue write.
if (!WriteFile(ghComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {
if (GetLastError() != ERROR_IO_PENDING) {
// WriteFile failed, but isn't delayed. Report error and abort.
fRes = FALSE;
else
// Write is pending.
dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);
switch(dwRes)
// OVERLAPPED structure's event has been signaled.
case WAIT_OBJECT_0:
if (!GetOverlappedResult(ghComm, &osWrite, &dwWritten, FALSE))
fRes = FALSE;
else
// Write operation completed successfully.
fRes = TRUE;
break;
default:
// An error has occurred in WaitForSingleObject.
// This usually indicates a problem with the
// OVERLAPPED structure's event handle.
fRes = FALSE;
break;
else
// WriteFile completed immediately.
fRes = TRUE;
CloseHandle(osWrite.hEvent);
return fRes;
I get none of the specified errors, but game fails to start and it seems nothing gets written to parallel port. Any suggestions on how to proceed from here would be more than appreciated.
Thank you, Joanna

Answer 1

Hi, I have a problem that I am really stuck with, and I am novice to the task so any help would be extremely helpful.
I an trying to write to parallel port on my PC in order to send a trigger to EEG recording machine every time the new goal appears in a Virtual Reality game that I wrote in C++ (I want to record EEG brain signals while subjects are playing the game).
I tried to follow the instructions from here: http://msdn.microsoft.com/en-us/library/ff802693.aspx
I wrote the following code:
BOOL FileExists(LPCTSTR szPath)
DWORD dwAttrib = GetFileAttributes(szPath);
return (dwAttrib != INVALID_FILE_ATTRIBUTES && 
!(dwAttrib & FILE_ATTRIBUTE_DIRECTORY));
BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)
OVERLAPPED osWrite = {0};
DWORD dwWritten;
DWORD dwRes;
BOOL fRes;
// Create this write operation's OVERLAPPED structure's hEvent.
osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (osWrite.hEvent == NULL)
// error creating overlapped event handle
return FALSE;
// Issue write.
if (!WriteFile(ghComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {
if (GetLastError() != ERROR_IO_PENDING) {
// WriteFile failed, but isn't delayed. Report error and abort.
fRes = FALSE;
else
// Write is pending.
dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);
switch(dwRes)
// OVERLAPPED structure's event has been signaled.
case WAIT_OBJECT_0:
if (!GetOverlappedResult(ghComm, &osWrite, &dwWritten, FALSE))
fRes = FALSE;
else
// Write operation completed successfully.
fRes = TRUE;
break;
default:
// An error has occurred in WaitForSingleObject.
// This usually indicates a problem with the
// OVERLAPPED structure's event handle.
fRes = FALSE;
break;
else
// WriteFile completed immediately.
fRes = TRUE;
CloseHandle(osWrite.hEvent);
return fRes;
I get none of the specified errors, but game fails to start and it seems nothing gets written to parallel port. Any suggestions on how to proceed from here would be more than appreciated.
Thank you, Joanna