CD-i uses UART and as it turns out all device are 1200 baud expect the keyboard (9600). The Mouse and Game pad are the same protocol and turns out the gamepad accept analog data. Interesting because no analog game pad was ever made. The switch on the controller changes the movement amount the d-pad issues. Normal is 1, when it is switched its 15 or so. So using an analog controller just makes good sense. Also because of this no mouse is needed unless you just want a mouse feel and can not afford a pippin controller. I feel there is a rummer’d fast mode games can put the controller in to to accept 9600 baud but I was not able to figure it out. Also besides the ID (0x4A) for controller start up there is a 0x2C that must be sent. No doc, or write up mentioned this but I had to do it. No idea what it means.
Ports are a mess, there is a lot of info on the net that explains where player to is used. With the OEM pads and later model (even with a splitter cable) I was unable to make player 2 work in the player 2 games. Seem this is also a mystery for now.