Nen Emulator

NES emulator, written in Rust. High mappers compatibility, FDS support.

Download

Download is avaible in the releases section. An eframe frontend with egui is available, with a GUI and a lot of user functionality. A SDL2 and SDL3 frontend for the emulator is avaible, with very basic user functionality. A (WIP) WASM frontend is also avaible here: https://comba92.github.io/nen-emulator/frontend-wasm/index.html

Usage (eframe frontend)

Game ROMs can be loaded by dragging and dropping the files into the window, or by using the file dialog in the top bar.

[!TIP] Zip files are supported.

Controls

[!TIP] Both keyboards and controllers are supported. [!TIP] Controls can be changed in the keybids menu.

Keyboard	Button
S	A button
A	B button
W	Start
E	Select
ArrowKeys	You know what they do!
P	Pause/unpause the emulator
R	Reset current game
M	Mute/unmute sound
0	Save state
9	Load state

Features

The emulator supports all the basic NES features you'd expect from a NES emulator. - [x] The 6502 CPU is emulated with most of its quirks. - [x] PPU pixel rendering emulation. Emulates the LoopyRegister behaviour and the pixel fethcer. - [x] The APU channels are all fully emulated. - [x] Both NTSC and PAL games are supported. - [x] The Famicon Disk System is supported. - [x] Custom color palettes are supported - [x] Games with tricky and obscure behaviour run correctly, except for one or two exceptions. - [x] RAM random initializing for games which uses it to seed RNG - [x] Saving/loading of battery RAM when the game is changed or the emulator is closed. - [x] Savestates - [x] Setting to disable the sprites limit for scanline.

Compatibility

• iNes and NES2.0 headers are supported.
• Headerless ROMs are supported thanks to a games database.
• FDS disks roms for the Famicom Disk System are supported.
• Zip files are supported.

Supported Mappers

The most popular

• [x] 00. NROM
• [x] 01. MMC1
• [x] 02. UxROM
• [x] 03. CNROM
• [x] 04. MMC3
• [x] 07. AxROM
• [x] 66. GxROM

Other mappers

• [x] 01. MMC1 SxROM variants
• [x] 04. MMC6 (used for Startropics and Startropics II)
• [x] 05. MMC5
• Note: PCM channel not implemented (only one game seems to be using it)
• Note: Vertical split functionality not implemented (almost no game seems to use it, or use it in very obscure parts like rare cutscenes)
• [x] 09. MMC2 (used for Punch-Out!!)
• [x] 10. MMC4
• [x] 11. ColorDreams
• [x] 13. CPROM (only used for Videomation, a painting program for NES)
• [ ] 16, Bandai FCG
• Note: Something is implemented but not usable, graphical glitches
• [x] 19. Namcot 129/163
• [x] 20 Famicon Disk System
• [x] 21, 22, 23, 25. VRC2 and VRC4
• [x] 24. VRC6a (only used for Akumajou Densetsu - Japanese version of Castlevania III with enhanced audio)
• [x] 26. VRC6b (used for Madara and Esper Dream 2)
• [x] 29 Various Homebrews
• [ ] 30. UNROM512
• Note: flashable board PRG not implemented
• [x] 31. NSF (music compilations roms)
• [x] 34. BNROM/NINA-001
• [x] 40. NTDEC 27x2
• [x] 67. Sunsoft-3
• [x] 68. Sunsoft-4
• Note: Nantettatte!! Baseball (J) licensing IC not implemented
• [x] 69. Sunsoft5 FME-7 / Sunsoft 5a/5b
• [x] 70. Bandai-74
• [x] 71. Codemasters
• [x] 73. VRC3 (used for Salamander)
• [x] 75. VRC1
• [x] 76. Namcot-3446 (only used for Megami Tensei: Digital Devil Story)
• [x] 77. Napoleon Senki
• [x] 78. Irem 74HC (only used for Holy Diver and Cosmo Carrier)
• [x] 79. NINA-003-006
• [x] 85. VRC7 (used for Lagrange Point and Tiny Toon Adventures 2 (J))
• Note: audio chip not implemented (only used by Lagrange Point)
• [x] 87. J87
• [x] 88. Namcot 118
• [x] 89. Sunsoft89 (only used by Tenka no Goikenban: Mito Koumon)
• [x] 93. Sunsoft93
• [x] 94. UNROM (only used for Senjou no Ookami - Japanese version of Commando)
• [x] 95. Namcot-3425 (only used for Dragon Buster (J))
• [x] 97. Irem TAM-S1 (only used by Kaiketsu Yanchamaru)
• [x] 101. J87 (only used for Urusei Yatsura - Lum no Wedding Bell)
• [ ] 111. GTROM
• Note: flashable board PRG not implemented
• [x] 152. Bandai/Taito 74
• [x] 154. Namcot-3453 (only used for Devil Man)
• [x] 177. BNROM Hengedianzi
• [x] 180. UNROM (only used for Crazy Climber)
• [x] 184 Sunsoft-1
• [x] 206. Namco 118/Tengen MIMIC-1
• [x] 210. Namco 175/340
• [x] 232 Codemasters
• [x] 241. BxROM Hengedianzi

Building

Building requires, of course, Rust and it's development tools.

Three frontends are avaible. The eframe frontend is the default one. To build it:

cargo run -r
cargo run -r --features=persistence # enable savestates feature
cargo run -r --features=opengl # use opengl graphical backend for eframe

A SDL2 and a SDL3 frontends are also available. They are their own separate package, so the -p flag is needed. To build them:

cargo build -r -p nenemu_sdl2 # Dynamically linked with SDL2, no savestates feature
cargo build -r -p nenemu_sdl2 --features="static"  # Statically linked with SDL2

The WASM frontend is still WIP, but already avaible here: https://comba92.github.io/nen-emulator/frontend-wasm/index.html

Various resources (not updated)

This section contains some of the resources I've used during development. Sadly I didn't keep track of all of them. I did found a lot of interesting articles, blogs, and readings, but forgot to add them here.

• https://www.nesdev.org/wiki
• https://www.nesdev.org/NESDoc.pdf
• https://www.copetti.org/writings/consoles/nes/

Design

• https://gendev.spritesmind.net/forum/viewtopic.php?p=35653&sid=8395d8875e87653545c0905281b093a0#p35653
• https://gist.github.com/adamveld12/d0398717145a2c8dedab
• https://www.nesdev.org/wiki/Catch-up
• https://www.reddit.com/r/EmuDev/comments/10m9had/cpu_ppu_timing_catch_up_method/

CPU

• https://www.nesdev.org/6502.txt
• https://www.nesdev.org/6502_cpu.txt
• https://bugzmanov.github.io/nes_ebook/chapter_3.html
• http://www.6502.org/users/obelisk/6502
• https://www.pagetable.com/c64ref/6502
• https://www.masswerk.at/6502/6502_instruction_set.html

Illegal Opcodes

• https://www.nesdev.org/undocumented_opcodes.txt

Correct XAA

• http://www.ffd2.com/fridge/docs/6502-NMOS.extra.opcodes
• https://www.nesdev.org/the%20%27B%27%20flag%20&%20BRK%20instruction.txt

Memory

• https://en.wikibooks.org/wiki/NES_Programming/Memory_Map
• https://www.nesdev.org/wiki/CPU_memory_map
• https://www.nesdev.org/wiki/PPU_memory_map
• https://emudev.de/nes-emulator/cartridge-loading-pattern-tables-and-ppu-registers/

Ppu

• https://bugzmanov.github.io/nes_ebook/chapter_6.html
• https://austinmorlan.com/posts/nes_rendering_overview/
• https://leeteng.com/blog/content/writing-nes-emulator
• https://emudev.de/nes-emulator/palettes-attribute-tables-and-sprites/
• https://www.youtube.com/watch?v=-THeUXqR3zY

Mappers

• https://mapper.nes.science/
• https://bumbershootsoft.wordpress.com/2022/10/22/nes-beyond-40kb/

APU

• https://emudev.de/nes-emulator/charming-sound-the-apu/
• https://www.slack.net/~ant/nes-emu/apu_ref.txt
• https://nesmaker.nerdboard.nl/2022/03/25/the-apu/

Tests

• https://www.nesdev.org/wiki/Emulator_tests
• https://www.nesdev.org/wiki/Tricky-to-emulate_games
• https://github.com/SingleStepTests/ProcessorTests/tree/main/nes6502
• https://github.com/PyAndy/Py3NES/issues/1