unfortunately I have no idea on how to issue a pull request :( For sure I could describe and detail the installation steps, this is what I’m doing hereafter!
* to install the new Fullspeed, perfect-frame PCE-CD core (LINK)
1. download the zip archive provided in the link above
2. unzip it in some temp directory (this creates a “pce” directory)
3. copy the pce/cores/mednafen_pce_fast_libretro.so file over the /opt/retropie/emularcores/mednafen-pce/
$ sudo cp pce/cores/mednafen_pce_fast_libretro.so /opt/retropie/emularcores/mednafen-pce/
4. copy the retroarch binary from pce/retroarch to /opt/retropie/emulatorcores/Retroarch
$ sudo cp pce/retroarch /opt/retropie/emulatorcores/Retroarch/
5. copy over the retroarch core options file to the configs folder
$ sudo cp pce/cfg/.retroarch-core-options.cfg /opt/retropie/configs/all/
6a. edit EmulationStation “systems” file (vi .emulationstation/es_systems.cfg) and locate the PC Engine section. In the COMMAND line, look for libretro.so and replace it by mednafen_pce_fast_libretro.so.
6b. alternatively you could simply rename the new core file to libretro.so to replace the older one.
$ sudo mv /opt/retropie/emularcores/mednafen-pce/mednafen_pce_fast_libretro.so /opt/retropie/emularcores/mednafen-pce/libretro.so
* uae4all2 (LINK)
it seems that there is no way to configure a controller yet (conf hardcoded) so might be wise to wait a bit more to include it within Retropie?
hope this helps.