🎮 NES Emulator written in Haskell
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ron-wolf and dbousamra Concatenate after building up String
Concatenate the pieces of the String in order to produce a valid result for `show`
Latest commit ec16e30 Aug 2, 2018



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Welcome to hnes. hnes is a NES emulator written in Haskell.


Mapper support

The following mappers are supported:

  • NROM (0)
  • UNROM (2)
  • AOROM (7)

Lots of games run, but more don't. You can see which roms are compatible here: http://tuxnes.sourceforge.net/nesmapper.txt The best games seem to be MMC3, so that is a priority.

Mappers are basically custom memory modules that exist on the cartridges themselves, that allow referencing more memory than the NES originally shipped with. Sometimes they even do computation. A very clever idea, but a nightmare to emulate, since each mapper has to be emulated as well


Nintendo Emulator
Up, Down, Left, Right Arrow Keys
Start Enter
Select Space


Get Stack for building Haskell projects.

Windows instructions:

$ stack exec -- pacman -Sy mingw-w64-x86_64-pkg-config mingw-w64-x86_64-SDL2
$ stack build

OS X instructions:

$ brew install sdl2
$ stack build

Ubuntu Linux instructions:

$ sudo apt-get install libsdl2-dev
$ stack build

FreeBSD instructions:

$ pkg install sdl2
$ stack build


To run:

stack exec -- hnes roms/tests/cpu/nestest/nestest.nes

Task list

  • Basic structure
  • Mappers
    • Loading roms
    • Mappers
      • UNROM
      • NROM
      • AOROM
      • CNROM
      • MMC1
      • MMC3
  • CPU
    • All official opcodes
    • All illegal opcodes
    • Nestest passing
    • Blarggs CPU test roms passing
  • PPU
    • SDL integration
    • Background rendering
    • Scrolling
    • Sprite rendering
    • VBlank timing for Battletoads edge case
  • APU
  • Controller input handled
  • Performance tuning
  • Command line interface
    • Parse args
    • Use optparse-applicative
    • Some debug params?


There's a small test suite that is used to check for CPU and PPU accuracy. They use test roms rather than hand coding tests.

Just run stack test:

Known issues.

There are so many, where do I even begin.

  • Performance is pretty average still. I get around 80 fps on my 2015 i5 MacBook.
  • VBlank timing is off. I don't know the exact reasons, but it causes scrolling issues.