@Nightfire Just noticed your question been a while., but I have to do this in my gpi case.

Controls

Joystick axis Should just work
joystick_1_vert joy0 axis1
joystick_1_horiz joy0 axis0

In Game Buttons
left_button_1 key32 joy0_1
right_button_1 key109 joy0_0

Start Buttons
Colecovision has a numeric keypad to start game 1-9. Also *, 0 and # Key.
This is where jsTest comes in handy. The # from jsTest should be appended to joy0_

key1_1 key49 joy0_7
key2_1 key50 joy0_6
key3_1 key51 joy0_3
key4_1 key52 joy0_2
key5_1 key53 joy0_4
key6_1 key54 joy0_5
key7_1 key55
key8_1 key56
key9_1 key57
key*_1 key111
key0_1 key48
key#_1 key112

key_save key1073741882 joy0_6 joy0_5
key_restore key1073741883 joy0_6 joy0_4
key_exit key1073741939 joy0_6 joy0_7
key_pause key1073741884
key_reset key8
key_screenshot key1073741891

https://sites.google.com/site/gregsqna/gaming/handhelds/retroflaggpi/emu/colecovision