Simple test program: writing to OPM and VERA PSG registers, vblank interrupt. It (makefile) assumes you have cc65 and X16 emulator (x16emu.exe) in your PATH. It automatically calls the emulator and launches the PRG file.
Also I modified the bank RAM linker file a bit and demostrate how dummy function indeed ends up in B3.BIN (function isn't used, maybe later I will add demonstration of executing the code both from main RAM and banked RAM without any conflicts; to see it inside open file in hex editor to see that it's not empty like other Bx.BIN files). If I succeed in placing the code and data (dynamically too) in banked RAM, I will write a proper tracker for Commander X16 (since it's really overpowered audio-wise and ZSM is just a register dump which is bloat and not fun).