NES

This is my implementation of an NES emulator written in C.

TODO

• Rendering
  • 8x8 sprite rendering
  • 8x16 sprite rendering
  • Horizontal sprite flipping
  • Vertical sprite flipping
  • Background rendering
  • Sprite-background priority handling
  • Sprite overflow / sprite zero hit detection
• Audio support
  • Pulse Channels
  • Triange Channel
  • Noise Channel
  • DMC
• Mapper support
  • NROM / mapper 0

Project Structure

classDiagram-v2
direction LR

class Cpu6502 {
  +ppu : PPU*
  +apu_mmio : APU_MMIO*
  +PC : uint16_t
  +A, X, Y : uint8_t
}

class PPU {
  +v, t : uint16_t
  +frame_buffer : [240][256]
}

class APU_MMIO {
  +apu : APU*
  +registers : uint8_t[0x18]
}

class APU {
  +pulse1 : Pulse*
  +pulse2 : Pulse*
  +triangle : Triangle*
  +noise : Noise*
  +frame_counter : FrameCounter*
}

Cpu6502 --> PPU
Cpu6502 --> APU_MMIO
APU_MMIO --> APU

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classDiagram-v2
direction TB

class APU {
  +pulse1 : Pulse
  +pulse2 : Pulse
  +triangle : Triangle
  +noise : Noise
  +frame_counter : FrameCounter
}

class Pulse {
  +envelope : Envelope
  +sweep : Sweep
  +duty : uint8_t
  +timer : uint16_t
  +counter : uint16_t
  +length_counter : uint8_t
}

class Triangle {
  +linear_counter : Divider
  +timer : uint16_t
  +counter : uint16_t
  +length_counter : uint8_t
}

class Noise {
  +envelope : Envelope
  +timer : uint16_t
  +counter : uint16_t
  +lfsr : uint16_t
  +length_counter : uint8_t
}

class FrameCounter {
  +divider : Divider
  +mode : uint8_t
  +step : uint8_t
}

APU --> Pulse : pulse1/pulse2
APU --> Triangle
APU --> Noise
APU --> FrameCounter

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classDiagram-v2
direction TB

class Envelope {
  +divider : Divider
  +decay_level : uint8_t
  +volume : uint8_t
  +loop : bool
}

class Sweep {
  +divider : Divider
  +shift : uint8_t
  +negate : bool
  +enabled : bool
}

class Divider {
  +P : uint8_t
  +counter : uint8_t
}

Envelope --> Divider
Sweep --> Divider

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Usage

Requirements

The following items are required for this program to function:

• gcc/clang
• SDL2

Building

Git clone the repository with the following command:

git clone https://github.com/KavinTheG/chip8.git

Change directory to the NES project directory

cd NES

Enter the following command to build the project. Ensure a build directory exists.

make

This will create a binary file located in the bin/ folder. Currently, I am only testing on the nes-test.nes rom and donkey kong rom. Run the command below to execute.

./bin/emulator game-title.nes

Progress

Able to run Donkey Kong.

References

• https://www.nesdev.org/wiki/Nesdev_Wiki