Hi there,
I’ve got the Mayflash (HuiJia) n64 to USB adapter, which I’ve been trying to use on retropie. I did as ceuse said and tried to configure the controllers for retroarch with the above console commands, but it only allowed me to do the configuration with one of the controllers.
After that, when I ran any ROM each controller worked for initial selection things (where normally only player 1 would have control) and as soon as both players had controller, the second controller was unresponsive.
So I’m not sure I can say that I’m confident about the Mayflash adapter, unless someone can point out my mistakes?