i found the file:
/home/pi/osmose_files/osmose.ini

PAD1_UP       = SDLK_UP
PAD1_DOWN     = SDLK_DOWN
PAD1_LEFT     = SDLK_LEFT
PAD1_RIGHT    = SDLK_RIGHT
PAD1_BUTTON_A = SDLK_LCTRL
PAD1_BUTTON_B = SDLK_LALT

#
# Second Player PAD:
#

PAD2_UP       = SDLK_KP5
PAD2_DOWN     = SDLK_KP2
PAD2_LEFT     = SDLK_KP1
PAD2_RIGHT    = SDLK_KP3
PAD2_BUTTON_A = SDLK_n
PAD2_BUTTON_B = SDLK_b

#
# GAME GEAR Specific:
#

GAMEGEAR_START = SDLK_RETURN

but if i change something here, nothing will change in the game…

other question: why do i have to change something in the retroarch.cfg if geamegear runs under osmose ?