Which NES mappers are supported?

NESpresso32 supports mapper 0 (NROM), mapper 1 (MMC1), mapper 2 (UNROM), mapper 3 (CNROM), and mapper 4 (MMC3). The OSD ROM browser flags ROMs with unsupported mappers before you try to load them.

Does every NES game work?

No. Compatibility is not guaranteed even for supported mappers. Games with unusual PRG/CHR size combinations, heavy sprite use, or strict timing dependencies may not run correctly on ESP32 hardware.

Why can some MMC3 games show glitches?

MMC3 uses a scanline counter driven by PPU A12 transitions to time IRQ interrupts. NESpresso32 MMC3 IRQ timing is approximate rather than cycle-accurate, which means games that rely on precise raster timing may show visual artifacts or incorrect behavior.

Is Kirby's Adventure fully supported?

Kirby's Adventure uses MMC3 and relies on timing-sensitive raster effects. Due to the approximate IRQ timing in the current MMC3 implementation, some effects may not behave correctly. The game may run but with visual glitches.

NESpresso32 Compatibility | NES Mappers on ESP32

Mapper support

Compatibility table

NESpresso32 supports mapper 0 (NROM), mapper 1 (MMC1), mapper 2 (UNROM), mapper 3 (CNROM), and mapper 4 (MMC3). Compatibility is not guaranteed even for supported mappers individual games may require specific timing or behavior not fully emulated.

No ROM download links are provided. Test with your own legally usable files or homebrew/test ROMs that permit use.

Mapper	Name	Status	Coverage	Notes
`0`	NROM	Supported	Stable baseline	Best target for early builds and timing checks. Works well with small PRG/CHR layouts.
`1`	MMC1	Supported	Core support	Serial register mapper with bank switching support for common MMC1 boards.
`2`	UNROM	Supported	Core support	PRG bank switching with CHR RAM. Suitable for many mid-size titles and homebrew builds.
`3`	CNROM	Supported	Core support	CHR bank switching support for compact games that use mapper 3 boards.
`4`	MMC3	Supported	In progress validation	IRQ and bank-switching behavior are supported, with ongoing compatibility testing recommended.

Notes on compatibility

Even within supported mappers, there are games that will not run correctly. Known problem areas:

Games with unusual PRG/CHR size combinations may not load correctly
PAL games flagged in the iNES header may run at wrong speed use use_lib_force_ntsc_timing
Games with sprite-heavy scenes may show slowdown due to the ESP32 timing budget
MMC3 IRQ timing is approximate some titles using raster effects may not work

The ROM browser in the OSD flags ROMs with unsupported mappers before you try to load them.

Frequently asked questions

Compatibility questions

Which NES mappers are supported?: NESpresso32 supports mapper 0 (NROM), mapper 1 (MMC1), mapper 2 (UNROM), mapper 3 (CNROM), and mapper 4 (MMC3). The OSD ROM browser flags ROMs with unsupported mappers before you try to load them.
Does every NES game work?: No. Compatibility is not guaranteed even for supported mappers. Games with unusual PRG/CHR size combinations, heavy sprite use, or strict timing dependencies may not run correctly on ESP32 hardware.
Why can some MMC3 games show glitches?: MMC3 uses a scanline counter driven by PPU A12 transitions to time IRQ interrupts. NESpresso32 MMC3 IRQ timing is approximate rather than cycle-accurate, which means games that rely on precise raster timing may show visual artifacts or incorrect behavior.
Is Kirby's Adventure fully supported?: Kirby's Adventure uses MMC3 and relies on timing-sensitive raster effects. Due to the approximate IRQ timing in the current MMC3 implementation, some effects may not behave correctly. The game may run but with visual glitches.

See the ROMs page for legal ROM guidance, or check open issues on GitHub for known bugs and progress.