NES

A Nintendo Entertainment System emulator written in C.

This is an implementation of the NES console developed and manufactured by Nintendo. The UI is built with Dear ImGui (via cimgui) and rendered through OpenGL 3.3, using SDL2 for windowing, input, and audio.

Features

• Accurate emulation of the 6502 CPU, PPU, and APU
• Audio output with individual channel control (Pulse 1, Pulse 2, Triangle, Noise, DMC)
• Save states written automatically alongside the loaded ROM (.nsave format)
• Keyboard and gamepad (SDL GameController) input support
• Integrated debugger with:
  • Step-by-step CPU execution and single-cycle stepping
  • Breakpoint support
  • CPU register viewer
  • Memory viewer
  • Pattern table, palette, sprite (OAM), and nametable viewers
  • Audio channel waveform inspection

Supported Mappers

Mapper	Name
000	NROM
001	MMC1 / SxROM
002	UxROM
003	CNROM
066	GxROM / MxROM

Libraries

Library	Description
SDL2	Windowing, input, audio
cimgui	C bindings for Dear ImGui (immediate-mode UI)

Build

The build system uses nob (a single-header C build tool).

Prerequisites:

• A GCC toolchain for Windows (e.g. MinGW-w64) with g++ available on PATH.

Steps:

1. Compile the build tool (only needed once, or after nob.c changes):

   g++ -o nob.exe nob.c
   

2. Run the build:

   nob.exe
   

The output binary is build/nes.exe. SDL2.dll is copied next to it automatically.

Controls

Keyboard

Key	NES Button
Arrow keys	D-Pad
A	B
S	A
Space	Select
Enter	Start

Gamepad input is also supported via SDL's GameController API.

Run

build\nes.exe path\to\game.nes

• You can also drag and drop a .nes or .nsave file onto the emulator window.
• Save states are written automatically next to the loaded ROM using the same base name with a .nsave extension and loaded automatically on the next run.

Screenshots