I decided to update my question, just in case someone comes back to look at this asking the same question I was.

I'm using joystick encoders instead of a keyboard encoder. What I found is that retroarch allows you to setup a mouse for use with the game. So my trackball goes in as mouse 1. Since I do not have a UI running on my setup, I don't actually need mouse buttons. I only need the trackball input for the games.

What all this means is that the retroarch setup will use a joystick along side the trackball... meaning the buttons going through the joystick controller work along side the track ball and I don't need extra buttong for left and right mouse clicks.

@dankcushions Preferably everywhere, because there isn't a huge palm rest area. Having the top row as the main buttons would result in less cramped finger placement.

Thanks for replying, I think I now have a remapping project ahead of me.

As mentioned in Post#1, we are now opening chapter: Curse of Configs

@Ashpool said in CP2020 - my DIY 2Player/Trackball Control Panel:

Since my last visit, the Page for the I-Pac got a major overhaul and the new Firmware 1.55 is now called "Multi-Mode" [... ...] the old "Gamepad enabled" FW139 is now called "Alternative Firmware (Mixed Mode)" [... ...] they are mentioning now:
"This is an alternative firmware version [... ...] Retropie does not work with this configuration. The standard multiMode version (above) enables one device type at a time on the host (plus mouse) and this is required for Retropie. [...]"
Sadly, that was the Firmware I've build my concepts on (and had tested on a PC, never thought Retropie couldn't cope with it).

Well, I've tried on a fresh retropie-buster-4.6-rpi4.img install with my old IPac Configuration (Joy(1/2), Buttons(1/2)1-7 + Start and Select as Gamepad and (1/2)SW8, (1/2)A and (1/2)B as keys and it was working just fine (Quicktest on some 2 player games in lr-mame2003: Both Players Gamepad Functions where fine (upon start the messages detected I-PAC2 on Port 0 and detected I-PAC2 on Port 1 flashed up and the keyboard keys where accepted fine from mame (ie. 1A (Button M in Post #9) set to TAB opened the Mame Menu). ... What I hadn't considered (as I had not assigned any "shifts" so far) was: The assignment of a switch to act as Gamepad, Keyboard or Mousebutton is a general one, so it cannot act as Gamepad (unshifted) and as a keyboard (shifted) [though I bet that would only be a Firmware-thing] :/

This would have been my intended configuration:
Seufz.jpg

As using Hat-(UDLR) and Buttons 8,11+ (WinIPAC can assign Buttonnumbers 1-28) as shifted assigns ain't going to be of any use (i believe?), I think i heed the advice from @theink in his wonderfull guide to setting up the IPAC2 as a keyboard controller and stick to keyboard only (though his argument that the I-PAC is only recognized as one controller in gamepad-mode appears (to me) to be void nowadays [at least for the Retropie Install mentioned above with an I-PAC 2 (Firmware 1.39) configured in WinIPACV2 (V1.0.8.12)])

Edit: And I haven't tried wether it is possible to assign keyboard keys as hotkeys (no hotkey-enable button set) or not... so that could have been the next boobytrap laid out for me within this battle ;>

@Clyde I loved playing Tron in the Arcades, but of course it's virtually impossible to play without the right controls. I've got a few full-size arcades and 1 Arcade1UP and running out of room for much else. Using the GRS products to build a custom Tron controller solved those problems.

@dizunuvezu You're welcome, I'm happy it as helpful for you!

@tuntav This may be information you already know, but both mine are detect as mice and the spinner overrides the mouse. The only way I get around is to find out what device number each mouse is (spinner is detected as mouse) and then start game, go into retroarch and set the mouse input to the number assigned to what mouse I want to use and then save the game settings (not the core settings).

For example, my spinner is device 0 and mouse is device 2. For a game like Centipede, I just go into Retroarch, set Mouse Input from 0 to 2 and save the game config so only affects that game.

Have done the same for AdvanceMame, but that does not use Retroarch but a config file.

Again, you may already know this, so I am sorry if I am repeating information you already know.

@813_alex That stick, like any arcade one with microswitches is quite noisy (but I like that). Also the stick itself (spring ?) makes noise when moving it. On the other hand that's a real 4-way ;-)

@sammylj Hmm. That escape exit situation sounds like you still have hotkeys enabled. Scan through your retroarch.cfg for hotkey and set it to "nul" or comment out the setting. I am running with a dedicated exit (escape) and I don't need to press anything else, just my single exit button.

@grant2258 Interesting approach. If I'll make another CP in the future (or even a Cab..) I surely will retry with Plexi.