From what i remember, the adapter on Mister FPGA will only work with 2 paddles and for older firmware like 8.5, you need to connected the paddles to port 2.  Unlike other software emulators, the MiSTer core does not support 2 paddles per gamepad and expects every player to be mapped to a separate gamepad. Other emulators let you use a single logical gamepad for multiple players by mapping different axis and buttons to different players.

When you put the iCode device in Mister mode, it will project the two paddles on port 2 to separate logical gamepads so the MiSTer can see them separately. The firmware does not yet support projecting both port 1 and 2 at same time to 4 logical gamepads for paddles.  I have this as a todo enhancement for a future firmware update and I will try to include this enhancement in V10 that i plan to release mid/late summer.

For 2 player operation, this video might help but as i said try port 2 if port 1 does not work on the 4 port unit. https://www.youtube.com/watch?v=swa8bvsxxdU

BTW, one way that will probably work today for 4 players on MiSTer is to use two separate iCode Devices. One for player 1&2 and one for player 3&4.

In the past, I purchased the "iCode Duo Plus USB Adapter"; it was okay, but I was unable to update it via USB (I will try again in a few days) in order to use the 8.5 version or above of the firmware.

The adapter is amazing for Windows or MAC OS X.

I would like to setup a 4 paddles (2 paddle controllers) with a iCode Game Adapter on Mister FPGA.

Is this adapter suitable and compatible with this goal?

4 Port Retro USB Adapter for Atari Joysticks and Paddles (Plus Edition)

Thanks in advance.

Marco