This allows you to fine-tune the searching to play either more, or less frames at the end of each scene. Debugging is turned off by default. It can be turned on by a command line parameter. This has nothing to do with the game, but it looks pretty darn cool. And, you don't need the DL board hooked up to use it.
Theory of operation is pretty simple.
The DL motherboard is wired to the PC parallel port with a custom-built cable. The PC parallel port is polled, looking for commands from the DL motherboard. When it gets a command, it is translated to the equivalent command for the new player and sent out the serial port. To complicate matters, the DL motherboard needs to see 2 signals, command and status, which the LD-V1000 sends out every 16.6 milliseconds. First the command strobe is sent.