com0com virtual port not found

Question

I have installed, apparently successfully, com0com v2.2.2.0 on a 64bit Windows 7 machine.

I run the command utility, like this:

command> install PortName=COM9 PortName=COM8
       CNCA0 PortName=COM9
       CNCB0 PortName=COM8
ComDB: COM8 - logged as "in use"
ComDB: COM9 - logged as "in use"

command> busynames COM?*
COM3
COM4
COM5
COM6
COM8
COM9
COMPOSITEBATTERY

Note: logged as "in use" is NOT an error message?

Then I try to open COM8 like this

m_hIDComDev = CreateFileA( szCodedPort, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, NULL );
if( m_hIDComDev == NULL  || m_hIDComDev == INVALID_HANDLE_VALUE ) {

    wchar_t * lpMsgBuf;
    DWORD dw = ::GetLastError(); 
    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR) &lpMsgBuf,
        0, NULL );

    myErrorMsg = (char*)malloc( 200 );
    sprintf(myErrorMsg,"Error creating connection %s ( %s ) %S",
        szPort,szCodedPort,lpMsgBuf);

This fails with

Error creating connection COM8 ( COM8 ) The system cannot find the file specified.

I have tried both "COM8" and "\\.\COM8".

Note that the exact same call to CreateFileA works perfectly on a 'real' COM port.

Q: Can someone tell me what the problem is?

A: On windows 7 64 bit you have to enable testing of unsigned drivers.

• Run a command prompt as administrator. ( It is not enough just to run from an account with admin privileges. See here for details of how to do this. )

• Type in the command bcdedit -set TESTSIGNING ON

• reboot. ( Windows will place a "test Mode" note on the bottom right of the desktop )

For Windows 8 this method does not work satisfactorily or easily. Here is some discussion of the issues and workarounds.

Alternatively you might want to try a signed version - I have NOT tried this myself.

Answer 1

Here are my points:

• Microsoft requires 64-bit drivers to be signed.
• com0com.sys (64bit) is a mere unsigned kernel-mode driver.

SoftWx has written an interesting tutorial on installing it on a 64 bit Windows 7 machine. You can fetch it here.

Answer 2

This is a very old post, but just to add some help if somebody stumbles across it like I did.

After Windows 10 Version 2004 you may need to disable Secure Boot in your BIOS.

I got a signed version 3.0 of the app from SourceForge, this worked perfectly on my one PC (Windows 10 Pro Version 2004). I just installed the app and two pairs of linked ports were immediately created.

On my laptop (Windows 10 Pro Version 20H2), I did not get the same results. No COM ports were created and in the device manager the devices could not be configured. After changing the BIOS setting, I reinstalled and all went smoothly.

Links for reference:

https://sourceforge.net/projects/com0com/

https://sourceforge.net/projects/signed-drivers/files/com0com/v3.0/

To answer @DaAwesomeP above (I do not have the rep to put it in the comments), there is a repo on GitHub https://github.com/paulakg4/com0com where I can see a changes.txt. If I compare the dates, it looks like the same version 3.0 in there.

Answer 3

In case anyone is referencing this, and interested in this topic, the 2.2.2.0 version of com0com is signed for 64-bit Windows. This removes the need to jump through the hoops of putting Windows in "test" mode.