TetaNES Core for NES on iPhone & iPad | Retropa

Catalog systems and formats

Begin with the kind of file you actually hold, because TetaNES supports more of them than a plain cartridge core does. As an alternative to RusticoNES, it takes cartridges, disks and music: .nes, .fds, .nsf, .nsfe on the NES / Famicom line. Retropa tracks its own support list, which is shorter than the feature set of the upstream project at https://github.com/lukexor/tetanes. And it carries no games or BIOS of its own, so import only files you are entitled to use.

• NES / Famicom: .nes, .fds, .nsf, .nsfe

Music files are not cartridge games

NSF and NSFE hold NES music data, so a file that opens to silence instead of a title screen may be behaving. Play something and check the device volume and output before you call it broken. A music file will not gain a level select because you renamed it. The controls Retropa exposes are the app's own; a desktop player's interface is not part of the deal. For actual gameplay, pick a cartridge or disk image.

• Check device volume and audio output when testing music.
• Renaming an audio file cannot turn it into a cartridge image.
• UNIF extensions belong to RusticoNES's catalog entry, not TetaNES's.

Import a cartridge or disk image

Only import from the library once the file is genuinely on the device; an iCloud placeholder that looks present will fail. Then check that the app read it as NES. Famicom is the Japanese name for the same hardware; a Famicom Disk System image brings its own disk requirements on top. If TetaNES asks for a BIOS or reports a disk-data problem, satisfy that request. Swapping in an unrelated cartridge image solves nothing.

Test input and a repeatable scene

NES pads are small and predictable: directional pad, two action buttons, Start and Select. Confirm each one registers, and test a diagonal while you are there. Keep the default skin while you check controls, because a restyled layout can hide a dead direction. Then load the scene that misbehaves and watch it twice, once plain and once with a CRT effect. Scanlines change how detail looks, not what the core emulates.

Core switching and keeping progress

Reaching for TetaNES costs a Retropa Plus unlock, because changing cores sits behind it; playing NES itself does not. Ask first whether TetaNES even accepts the format you have, since a switch between cores is only meaningful where both lists overlap. Your choice sticks per game, and Retropa will not ask again next time. Before the test, archive the in-game save and any save states from the old core. One scene, two cores, then compare sound, picture and input.

• TetaNES save states belong to that implementation; keep them with TetaNES rather than moving them to another core.
• Preserve a tested game save before trying TetaNES; switching cores does not perform an automatic migration.
• Trying TetaNES does not convert the image or conjure a BIOS file.

An alternative is not a universal repair

TetaNES and RusticoNES diverge in both format lists and implementation. A swap tells you something only when your image is valid for both cores, and even then it isolates a timing or mapper difference rather than promising support for a cartridge board. Treat each core's save states as belonging to that core: keep them filed with it instead of moving them around like ordinary files.