Assuming you are using fba to run Neo Geo:
I set my select button which adds credits here (depends on your control pad for the right number)
/opt/retropie/emulators/pifba/fba2x.cfg
[Joystick]
# Get codes from "jstest /dev/input/js0"
# from package "joystick"
A_1=0
B_1=1
X_1=2
Y_1=3
L_1=4
R_1=5
START_1=7
SELECT_1=6
#Joystick axis
JA_LR=0
JA_UD=1
