It turns out City Patrolman runs on the UM6578 system with a custom lightgun and custom mapper, which shares a few things in common with NES/Famicom, but at the same time its completely different. The endeavor required to emulate such a beast is too much for this game right now. Sorry about that, of course - if it were just a nes/famicom game with a mapper we didn't support yet - it would be no problem!
best regards,
- dink