Folks – I’ve been faffing around all evening and this is the best I’ve managed :
Open file mupen64plus.cfg in nano using the command :
sudo nano /opt/retropie/configs/n64/mupen64plus.cfg
Go to the line ‘VideoPlugin = “mupen64plus-video-n64″‘ under [UI-Console] and change “n64” to “rice”.
Save (Ctrl-x)
Launch the emulator. Exit the emulator.
Re-open mupen64plus.cfg in nano – there is a new section called [Video-Rice], change the line ‘ScreenUpdateSetting = 6’ to ‘ScreenUpdateSetting = 4’
Save (Ctrl-x)
Load up and play two player mariokart. Doesn’t seem to run quite as well – audio is a bit jittery, but that might be because of the two player…
Also worth noting that the only place that seems to make a difference adding new controllers is the InputAutoCfg.ini file in the same folder. I was pulling my hair out for ages because guides on the internet all seem to point you to the wrong place… and there are two identically named files with the same content in my install. Hope this helps. To give credit where it is due, my final clue came from this page : http://www.raspberrypi.org/forums/viewtopic.php?f=78&t=6761&start=200
