Hi to all,
I have added "development mode credit counters" to the program which are needed when Universe Bios on AES (Home) systems "simulates" MVS (Arcade) mode.
Also, "Free Play mode" on MVS systems (hard dip switch 6 active) is now handled correctly (boots into AES mode with default or previously saved MVS soft dip data ).

I have tested the USER SUBROUTINE program with any available BIOS in different emulators and I can confirm that it works on the following "real" systems:
MVS MV-2F - Universe Bios 3.2
MVS MV-2F - EUR stock bios
MVS MV-1C - UniBios 3.1
MVS MV-1C - EUR stock bios
MVS MV-1FZ - EUR stock bios
AES - UniBios 3.1

The program is missing a memory card save function and it needs a routine for handling highscore saves (score sorting, user input of 3-letter initials) but anyway
here is the code of the actual version. Feel free to use this code for your game dev projects.

http://www.neohomebrew.com/downloads/main.c
http://www.neohomebrew.com/downloads/crt0_cart.s
http://www.neohomebrew.com/downloads/common_crt0_cart.s