It should already have these defaults:
Arrow keys = D-pad
ZXASQW = BAYXLR
RShift = Select
Enter = Start
You can add additional binds in /opt/retropie/configs/all/retroarch.cfg:
input_player1_b = "z" input_player1_a = "x" input_player1_y = "a" input_player1_x = "s" input_player1_start = "enter" input_player1_select = "rshift" input_player1_l = "q" input_player1_r = "w" input_player1_left = "left" input_player1_right = "right" input_player1_up = "up" input_player1_down = "down" # input_player1_l2 = # input_player1_r2 = # input_player1_l3 = # input_player1_r3 = # input_player1_l_x_plus = # input_player1_l_x_minus = # input_player1_l_y_plus = # input_player1_l_y_minus = # input_player1_r_x_plus = # input_player1_r_x_minus = # input_player1_r_y_plus = # input_player1_r_y_minus =This works in conjunction with the gamepad. Right now I am playing Double Dragon (arcade, ddragonw.zip under lr-fbneo) using the d-pad to walk around and the keyboard to punch and kick.