I have also resolved the issue with using a bluetooth controller for ScummVM. The write up is in the other post. In case you also need it:
https://retropie.org.uk/forum/topic/33334/scummvm-controller-help-needed

@mitu I see thx, so do you think this is very specific or maybe more common and with more roms? or do you even know of a compatibility list of lr-gpsp?

OK, so I was able to solve it; a couple of steps I think were necessary, the others I did as precautions.

Basically, the main issue was that my runcommand-onstart.sh and runcommand-onend.sh files were empty; these need lines to trigger xboxdrvstart.sh, which in turn should allow the GPI controls to be recognised by Mame4All. Here's what I did:

In /opt/retropie/configs/all/runcommand-onstart.sh I added the following:

#!/bin/sh

source /opt/retropie/configs/all/xboxdrvstart.sh > /dev/null 2>&1
sudo pkill -STOP mpg123 > /dev/null 2>&1
fbset -g 320 240 640 480 16

In /opt/retropie/configs/all/runcommand-onend.sh I added the following:

#!/bin/sh

source /opt/retropie/configs/all/xboxdrvend.sh > /dev/null 2>&1
sudo pkill -CONT mpg123 > /dev/null 2>&1
fbset -g 320 240 320 240 8
fbset -g 320 240 320 240 32

(the lines about mpg123 are, I think, related to background music or something like that; probably not needed, but I borrowed these from a pre-made GPI image so thought safer just to copy everything.)

Then, after a restart/reboot, I switched the GPi's D-Pad to axis mode by by pressing START+DPAD LEFT for 5 seconds, until the purple light flashed.

I deleted default.cfg in /opt/retropie/configs/mame-mame4all/cfg

Finally, I the went to GPI's 'Controls Updater Menu' and ran that script, just in case.

If I'm not mistaked, the Pi Zero W is already clocked at 1Ghz, so your overclock will not considerably improve the system's performance.
For GBA, use lr-gpsp or gpsp as emulators, for SNES, use pisnes as emulator - this should get perform better on the Pi Zero W.

@soldomino said in Questions about GPi:

I'm viewing the Pi using WinSCP, if that matters.

If you're using SSH to access your Pi, then you can look at/opt/retropie/configs/all/emulationstation/gamelists, it's basically the same folder.

Knowing that will help me whittle down what games I should put on there (SNES Doom, Star Fox, and really any Mode 7 stuff was lagging pretty bad)

I think that even with older/less accurate emulation, you won't be able to emulate SuperFX games full speed on a Pi 0.

Yay! @mitu you are awesome. Thank you!

It turns out that the GPi uses the "windowed" version of the settings, so I needed to add the following to /opt/retropie/configs/all/retroarch.cfg

menu_widget_scale_auto = "false" menu_widget_scale_factor_windowed = "2.75"

For what it's worth I had actually stumbled on this setting when messing around but I set the non-windowed value (because it's full screen... I assumed that meant it wasn't windowed) and when that didn't fix it I moved on.

Thanks all for your help. I found a good image for the Pi0 and dont have any problems now :)

Image: Super RetroPie

@suikodentir Care to share how exactly? It may help others in the future.

@joharibk hiding the boot text has nothing to do with Pegasus and this Pegasus Theme, even less.
Maybe you need to follow this tutorial of how to hide the boot text

@Chuck_B lol. There is a tad bit of slowdown, but nothing detrimental.

@mitu Thanks Bro, fixed!

@wkelley89 There is a dedicated reddit sub for the GPI case. Other people have had the same issue : https://www.reddit.com/r/retroflag_gpi/