"I bought this from a liquidated military surplus auction," the client said, his voice trembling. "They said it contains the source code for a cancelled 1990s console hybrid. But I can’t interface with it. The OS doesn’t see it. It’s like the port is invisible."

Once the driver is installed, the device acts as a . To control it, you send serial commands.

: Registers the hardware interface (e.g., rtl8xxxu or 8192eu for wireless cards) within the operating system to allow for networking or imaging functions. Hardware Compatibility & Features

It looks like you're asking for the of a driver related to "FF-USB 4-in-1" (likely a multi-function USB device, such as a card reader or adapter).