This board, along with others has taken me some time to get around to testing.
This is the simplest of the expansion cards i've designed for Y Ddraig. It supports 2 controllers and consists of a Xilinx XC9536 CPLD for handling the bus interface and supplying the SELECT lines to the Joypads and 2 latches for reading back data.
Other than few false starts in understanding how the controllers are read, then it works very well. I’ve only tested it so far with the 6-button controllers as they are the only ones I have available but as they are the more complex ones to read, I’m fairly confident that the 3-button controllers will work fine.