Dendy

Dendy is a NES/Famicom emulator written in Go and named after the soviet Famicom bootleg. It serves no practical purpose other than to be a toy project for me, so do not expect it to beat any of the existing emulators in terms of performance or accuracy. Yet, it is capable of running most of the games I tried, so it’s not completely useless, and it's still a great learning experience.

Try it

$ go install github.com/maxpoletaev/dendy/cmd/dendy@latest
$ dendy romfile.nes

You may need to install additional dependencies required by raylib. See https://github.com/gen2brain/raylib-go#requirements for more details.

Controls

Joystick

Player 1 joystick is emulated using the keyboard. The default mapping is as follows:

                   ┆┆
┌───────────────────────────────────────┐
│                                       │
│    [W]                                │
│ [A]   [D]                             │
│    [S]                       [J] [K]  │
│           [Enter] [RShift]            │
│                                       │
└───────────────────────────────────────┘

Zapper (Light Gun)

Zapper is emulated using the mouse and can be used in games like Duck Hunt. Point the mouse cursor at the right position on the screen and click to shoot.

Multiplayer

Dendy can be played over the network with another player. Run the emulator with the -listen=<host>:<port> flag to start a netplay server that will be waiting for the second player to connect via the -connect=<host>:<port> flag. Once the connection is established, the game will start for both sides. The player who started the server will be controlling the first joystick.

The feature works by synchronizing the state of the emulated NES and sending the controller input over the network to the other player. The algorithm allows slight drifts in the clock speed and network latency by generating fake input events for the other player if the state of the emulator is ahead of the other player’s state. Theoretically, this should keep the game playable for both players even if the network connection is not very stable (e.g. over the Internet), but it is not very well tested.

Most of the ideas for the netplay implementation were borrowed from RetroArch.

Status

CPU

Graphics

Input/Output

Graphics output
Controller 1
Zapper

Sound

TODO

Cartridges

The goal is to support top 7 mappers covering the majority of games. The percentage indicates the number of games that use the mapper according to nescartdb.com.

Test ROMs

The checked items are the ones that pass the tests completely or with minor inaccuracies (that might be caused by the test ROMs themselves).

Nestest CPU
Blargg’s CPU tests
Blargg’s PPU tests
Blargg’s APU tests

Resources

Although NES emulation is a pretty well-covered topic, It is still a very interesting and challenging project to work on. Here are some of the resources that I found particularly useful while writing this emulator. Big thanks to everyone who made them!

Documentation

MOS 6502 CPU Reference by Andrew Jabobs, 2009
Extra Instructions of the 65xx Series CPU by Adam Vardy, 1996
NES Rendering Overview by Austin Morlan, 2019
Making NES Games in Assembly by Kevin Zurawel, 2021
Retroarch Netplay README

Videos

The NES Emulator from Scratch series covers most of the topics from the CPU to the sound, but I found the two videos about the PPU to be the most useful for understanding the obscure details of the NES rendering pipeline: [1], [2].

Code

During bad times, it’s always nice to look at other people’s code to see how they solved the same problems. Here are some of the emulators written by other people that I often referred to when I was stuck:

maxpoletaev/dendy

maxpoletaev

Reviews

Repository Details