Ensure your BIOS file isn't corrupted and matches the version expected by the emulation core. To help narrow down your setup, please let me know:
I can provide step-by-step configuration files tailored to your device. Share public link
Years ago, a custom emulator called (based on MAME) was ported to 3DS. People would convert ROMs into individual CIAs using a tool called CIA Builder for Neo Geo .
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