A NES emulator written in C++
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README.md

NESChan - a cross-platform NES emulator for Windows/Mac

What is it

NesChan is a NES emulator I wrote just for fun. The idea of writing yet another NES emulator is inspired from a medium post I read recently. After reading nesdev wiki for a while I decided to give it a try mid-December 2017. It took me around week and half to get quite a few major titles perfectly (SMB, Super Contra, Shadow of the Ninja, etc). But it's still in its early stages and I'll update this when something changes.

See Super Mario Bros and Super Contra in action:

img img

NesChan supports both Windows and Mac:

img

What is the goal

Just for fun - it's fun learning about NES hardware, how the games work, and getting my favorite game working. It is almost as exciting as writing my own game - except I don't have to write any games. There is something magical about seeing the little pixel sprites moving around in screens.

I don't plan to create the greatest emulator ever. As far as I can see Mesen is as good as it gets.

Which platform is supported

Currently Windows and Mac. I've only tested on Windows 10 and mac OSX High Sierra but there is a good chance it should work in earlier versions. I haven't got around to try out linux yet but it should be relatively straight-forward given NesChan doesn't use any platform specific API nor libraries.

What NES functionality is supported

  • CPU - all official and most unofficial instructions, with accurate cycle emulation (but it can't stop mid-instruction).
  • PPU - rendering pipeline with goal of cycle accuracy. It's not exactly right yet but pretty close.
  • Mappers - 0, 1 (partial), and 4 (partial - no scanline counting / IRQ support)
  • Controllers - NES standard controller emulation only. Supports keyboard and game controllers. I've tested with my XBOX One controller.
  • APU - NYI. This is on top of my list.

What game does it run

It's still in its early stage and only supports a few mappers (0, 1, a part of 3) so it only supports a small set of games.

I've tested with following games:

  • Mapper 0
    • Donkey Kong - no problems
    • Balloon Fight - no problems
    • PopEye - no problems
    • Ice Climber - no problems
    • Super Mario Bros - no problems
  • Mapper 1
    • Dr Mario - no problems
    • Mega Man 2 - vertical transition is somewhat glitchy. Otherwise plays just fine
    • Ninja Gaiden - no problems
    • Metroid - freeze on start
  • Mapper 4
    • Shadow of the Ninja - no problems
    • Super Contra - first level boss fight background disappear. Otherwise works fine.
    • Super Mario Bros 2 - mario's eye is missing. Otherwise works.
    • Teenager Mutant Turtle 2 - freeze on start
    • Teenager Mutant Turtle 3 - freeze on start

How to build

Building on Windows

You'll need VS 2017 and SDL2. Support for clang on mac/linux isn't available yet but should be straight-forward.

  • Clone the repo
  • Download SDL development libraries SDL2-devel-2.0.7-VC.zip and unzip it into dep/sdl2
  • Open neschan.sln in VS 2017 and build x64 Debug/Release

Neschan.sln has 3 projects:

  • Neschan - the main app that implements main game/rendering loop and controller support. Currently uses SDL.
  • Neschanlib - static library that emulate NES hardware. Other clients written in other languages can simply link to this library statically or dynamically (NYI).
  • Test - using doctest with a combination of simple inline assembly and test roms (mostly from NesDev Emulator Tests)

Building on Mac

You'll need SDL2, XCode developer build tools, CMake.

  • Clone the repo
  • Download SDL development libraries for Mac SDL2-2.0.7.dmg and unzip it into dep/sdl2
  • Under neschan repo, create a bin directory
  • cd bin
  • cmake -DCMAKE_BUILD_TYPE=release ..
  • make

How to run

neschan.exe rom_path

Sorry. No fancy UI yet.

Next steps

In the order of "most likely" to "probably never going to happen"... :)

  • APU support - this one isn't too bad but I need to wrap my head around triangle waves, envelops, sweeps, delta modulations first...

  • More mappers and more game support - Ninja Gaiden 2/3 and TMNT 2/3 are on top of my list (which I suspect are due to missing IRQ support in mapper 4).

  • Add more test ROMs - it's way more effective to debug test ROMs than actual games! Not to mention they are good regression tests.

  • Save/Load states - enough said. Being able to go backward instantly would be even more awesome.

  • Port to other languages - just for learning about other languages.

  • Add proper UI - so far I've mostly stayed away from it and keep it just rendering (like a real game). But I've no intention to draw my own UI like a real game in SDL. I'm not yet sure which UI library I'm going to use yet - but it's probably not going to be MFC in 2017, and it should be cross-platform. Couple of ideas:

    • Electron.js - Write a UI in JS as well as a JS library to interop with C/C++ neschanlib (using N-API). Not sure about 2D rendering and controller support, though.
    • WinForms - Should work great on Windows + .NET desktop. Mono supports it too. Too bad .NET Core doesn't. It's pretty compelling - the only reason I don't want to go this route because I'm already pretty familiar with C#/.NET/WinForm.
    • Qt - I haven't played with QT much.
  • A built-in debugger - I realized this is basically a necesscity after debugging game / test ROMs. I frequently use Mesen's fantastic debugger to debug games to understand their behavior, viewing PPU memory/tiles/sprites and compare differences. It's extremely valuable to be able to see that glitching tile is index 0x80 and in address 0x1010. Having one built-in would greatly speed up development.

  • A development environment. Imagine a NES Studio built on top of Eclipse / VSCode / VS - making translation/hacking ROMs/writing your own ROMs much easier.

If you are interested in more details

I'm planning to write a series of technical posts talking about my experience.

  • Writing your own NES Emulator - overview
  • TODO - emulation strategy
  • TODO - CPU emulation
  • TODO - PPU emulation
  • TODO - APU emulation
  • TODO - Tieing it all together with SDL
  • TODO - iNES format, and Mappers

References