i found this on the web:

~/.emulationstation/es_systems.cfg

DESCNAME=Sega Game Gear
...
COMMAND=/home/pi/RetroPie/emulators/osmose-0.8.1+rpi20121122/osmose %ROM% -joy -joy1 15 -joy2 14 -joystart 3 -tv -fs

...

are these command correct? How can i edit the Select Button for exit the Game with “Start + Secect”?
The GameGear has only 3 Buttons.