It works fine if I load the driver and specify the gamepad as a 3-Button Genesis controller (modprobe db9_gpio_rpi map=4,0), but if I specify a 6-Button gamepad (modprobe db9_gpio_rpi map=6,0) things get weird. Judging by the output of “jstest /dev/input/js0” it looks like some of the extra buttons (X, Y and Z) are being pressed dozens of times a second.
I double checked the connection schematic, the connectors themselves and the soldering on the DB9 connector, and everything _seems_ fine. Both controllers are third-party (cheap chinese clones bought on DealExtreme), but they do work fine on a real Genesis and a Sega Master System.
Does anyone have experience with this interface, or ideas on what might be wrong?