I’ve just realized that there are 2 (different ?) libretro cores named mednafen_psx_libretro.dll & beetle_psx_libretro.dll 
I didn’t realized until now that as I was updating the cores from the nightly build bot I ended up using one core or the other.
What are the differences between the 2 cores (branches ?) ?
I’ve noticed that beetle PSX doesn’t support rumble… ? Nor does it have a button combo to switch DualShock’s Analog Mode
On/Off when “Analog Mode toggle” is On ? Another thing I’ve noticed while playing Gran Turismo 2 is the lack of “environmental lighting” ?
I was racing on the Red Rock Valley Track when I’ve noticed how the asphalt on the track and the whole “atmosphere” on that track no
longer had that red-ish hue from the sky… The track was full bright grey and all the other assets were as well full bright “native colors”
Going back loading mednafen_psx_libretro.dll core, the track had it’s usual reddish tint/hue as it is on the actual PS1. Another thing I’ve
noticed on the real PS1 is that the track has darker or brighter lit areas (“from the sun”) depending in which section on the track you are.
Exiting the last corner on the track, you have the sun lighting the track very bright, while in other sections the track darkens. I didn’t see
this effect even on mednafen_psx_libretro core… or at least not so strong as it is on the real hardware. I’ve also made sure my TV didn’t
had any image enhancement effects like dynamic contrast or the like enabled at the time I’ve tested that track.
There seems to be lighting issues in general with the Beetle core right now. I posted an issue about it on GitHub a couple of hours ago.