3DS Virtual Console

There's two types of VC titles: regular VC titles, and dedicated GBA VC titles.

Regular VC

Regular VC titles: an emulator application + VC ROM in the NCCH RomFS(among other things in the RomFS). The emulator build includes support for all supported VC platforms, not specific to just the included ROM platform.

This emulator includes GBA support, however the GBA emulation for this this is somewhat slow. This was presumably implemented before AGB_FIRM was.

Unlike Wii VC, the 3DS VC ROMs for NES use the "TNES" header.

RomFS

• "rom:/rom/" This directory contains the ROM file(s). Filenames used under here don't matter: the filename is determined by the emulator app by doing a directory read.
• "rom:/shaders/" This directory contains GPU shaders used by the emulator app: .shbin, .csdr, and .obj.
• "rom:/VCM/" This directory contains graphics, audio, and text used by the emulator app.
• "rom:/agb.bin" GBA BIOS.
• "rom:/buildtime.txt" Emulator app build timestamp.
• "rom:/config.ini" Emulator configuration .ini, contains sections for all supported 3DS VC platforms.
• "rom:/<rom_name>.patch" rom_name = filename from the rom directory. This .ini contains patches for the ROM.
• "rom:/shader.shbin" GPU shader.

GBA VC

GBA VC is run by AGB_FIRM. RomFS isn't used for GBA VC titles, but can be found empty within GBA VC titles. The NCCH ExeFS contains the same files as a normal application. The ExeFS:/.code contains the GBA VC ROM followed by a 0x360 footer.

Footer

All values in the GBA VC Footer are Little Endian.

START	SIZE	DESCRIPTION
0x004	0x4	GBA ROM Filesize
0x008	0x2	Unknown
0x02A	0x2FA	Unknown
0x338	0x4	GBA ROM Filesize
0x344	0x4	GBA ROM Filesize
0x350	0x4	Magic '.CAA'
0x35A	0x2	GBA ROM Filesize per MB