Interested in learning more about the the original Game Boy or Game Boy Color? Excellent! This section will guide you through the basics, starting from basic assembly language all the way to reverse engineering your first game!
Main specs of the original GameBoy:
When it comes to finding a game to reverse engineer, it can be helpful to look at games that are cross-platform to compare builds. But the most valuable reverse engineering projects tend to be the platform exclusives, as these are the games people can no longer play on modern consoles.
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List of Original DMG Game Boy exclusives
Wikipedia has compiled an excellent list of games that have never been re-released and thus need a Game Boy to be able to play
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List of Game Boy Color exclusives
Wikipedia has compiled an excellent list of games that have never been re-released and thus need a Game Boy Color to be able to play
The 8-bit Game Boy was sold between 1989 and 2003, but its architecture more closely resembles machines from the early 1980s, like the Commodore 64 or the NES.
This talk attempts to communicate “everything about the Game Boy” to the listener, including its internals and quirks, as well as the tricks that have been used by games and modern demos, reviving once more the spirit of times when programmers counted clock cycles and hardware limitations were seen as a challenge.
The Game Boy has a variant of the Zilog Z80 processor, well technically it is a CPU between the i8080 and the Z80, it is not binary compatible with either but there are similarities. You need a assembler that can handle the Game Boy specific opcodes in order to write functional code for the Game Boy in assembly language.
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gbZ80 Assembly programming for the Gameboy and Gameboy Color
ChibiAkumas has an excellent page with tutorials and information to get started with Game Boy assembly language
Every game produced for the Game Boy required a little piece of code known as the “bootloader” or boot code to initialise the state of the console. You don’t have to know anything about this, but it can be fascinating to find out what the Game Boy does as soon as you hit that power button.
A Look At The Game Boy Bootstrap: Let The Fun Begin!
RealBoy has an excellent page that gives you an in-depth look at how the Game Boy's bootloader works
There have been a few very successful reverse engineering projects for the Game Boy, one of the most successful is the Pokemon dissassembly which managed to reverse engineer the entire game into a rebuildable ROM!
The Pokemon Reverse Engineering Team (PRET) have managed to pull off a marvellous achievement, they have fully reverse engineered Pokemon Red and Blue back into retail-matching assembly code.
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Reversing Pokemon Red and Blue (Game Boy)
For more information about the project check out this post.
In August 2016 the website KZone started a full disassembly of the classic Game Boy game Link’s Awakening, along the way they have written some excellent in-depth articles about how the game works. Check it out!
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Reverse Engineering Carrot Crazy
Find out how to reverse engineer Looney Tunes: Carrot Crazy for the GBC
Special hardware was sold directly from Nintendo in order to make it easy for third party developers to get started making their own games for the new handheld.
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Gameboy (DMG & GBC) Development Kit Hardware
For more information about the development hardware used for Game Boy projects check out this post.
Along with the hardware, Nintendo also provided a fairly limited software development kit, which contained tools such as z80 assemblers and linkers.
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Game Boy Software Development Kits
For more information about the SDK used to make Game Boy games check out this post.
We used to have a post on the hardware architecture of the Game Boy, but now we have replaced it for a link to the far superior page on copetti.org, it is a must read for any reverse engineer or beginner emulator developer.
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Game boy Architecture - A Practical Analysis
This page on copetti.org has everything you need to know about the Game Boy Hardware, it is a must read!
If you want to go really low level into the Game Boy hardware, you can view a re-creation of the Gameboy Circuit Schematics over on Github: gb-schematics/MGB-xCPU.pdf at master · Gekkio/gb-schematics · GitHub
In Japan an adapter was released that allowed you to connect your GameBoy Color to a mobile phone called The Mobile Adapter GB. Only a few Japanese games supported this adapter, one of which was Pokemon Crystal.
TheXcellerator has written an excellent article on not only how the adapter works but also how he managed to create an exploit to run custom code through the adapter!
Here is the link: Tetsuji: Remote Code Execution on a GameBoy Colour 22 Years Later :: TheXcellerator
The Super GameBoy was a Super Nintendo Cartridge that allowed you to play Original GameBoy (DMG) games on the big screen (TV Monitor). It did this by including all the hardware a normal GameBoy has (a z80 cpu etc) minus the screen and the buttons:
Similar to the Super GameBoy but this is for the Nintendo 64 and not licenced by Nintendo, I first saw this for sale in issue X of the UK Nintendo Official Magazine.
For more information:
Official device to play gameboy (including GBA) games on the N64, but was not sold to the general public. You had to be a game developer or press in order to buy one from Intelligent Systems.
Similar to the Super GameBoy but this is for the Sony Playstation!
The source code for the Game Boy classic Mr Do! has been kindly released by two of the original game developers and can provide an excellent reference for how retail Game Boy games were developed in 1990!
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Mr Do! Source Code (Game Boy)
For more information about the source code check out this post.
The Game Boy game Alien 3 was written in only 5 weeks by legendary game programmer Jas Austin:
Fastest commercial game I've ever written? That would have been Alien3 on Gameboy. Done in about 5 weeks :) with @recluse_games #gamedev
— Jas Austin (@IamXERO) February 1, 2013
The Game Boy classic R-Type was programmed by Jas Austin completely from Memory as he didn’t have any code or assets from any other version of the game!
I agree, it's amazing some of the lengths we have to go to when we didn't have code or assets. For R-Type I did most of it from memory after visits to the Trocadero in London. And I didn't live in London.
— Jas Austin (@IamXERO) April 18, 2020
The company B.I.T.S obtained the license to develop the Game Boy version of the game but required a programmer to work on the title. Jas Austin heard about this through his agency and travelled to London to meet up, he impressed them so much that he was given a development kit and a deadline of a week to come up with a demo! He did such a good job he got a permanent job at B.I.T.S 1.
One cool easter egg he added to the game was an implementation of John Conway’s game of Life!
I hid a version of John Conway’s game of Life in R-Type on the Game Boy.
— Jas Austin (@IamXERO) April 5, 2021
Source graphics for Gameboy R-Type Lv3 ship. By Mark Jones... #ScreenshotSaturday24YearsAgo pic.twitter.com/RsKlc0rQOE
— Jas Austin (@IamXERO) April 25, 2015
I reverse-engineered the audio chip in the #Nintendo Game Boy Color. It contains three power op-amps for the speaker and headphone channels. This 1998 chip is built from about 100 NPN and PNP transistors. Die photo from @johndmcmaster. Article & schematic:https://t.co/EhsVogAJPl pic.twitter.com/J6CYPsOdaz
— Ken Shirriff (@kenshirriff) May 2, 2020
If you are interested in low-level hardware details about the Game Boy then this is a must read article: Reverse-engineering the audio amplifier chip in the Nintendo Game Boy Color
This is a very interesting project that played a large set of gameboy games in a custom headless emulator and tracked the audio registers into a text format. They then trained a Machine Learning algorithm on that audio data and used it to generate completely new Gameboy Music! Check it out here: jawline/Synthic: Automatically generate gameboy music using machine learning
There are a few different file formats that you will find relating to the GameBoy which are listed below:
If you backup your own games they will be created with a .GB or .GBC file extension along with most of the ROMS that can be found online. If the ROM was leaked from a first party developer such as Nintendo then they will likely be in .ISX format, this can easily be converted to .GBC with the tool CVTISX included in the Official GameBoy SDK.
The emulator SameBoy recently added support to play ISX files due to the 2020 Nintendo Leaks:
Following the... uh... recent events, I've added ISX file format support to SameBoy, including symbol support pic.twitter.com/Ba28bA2ARu
— Lior Halphon (@LIJI32) April 25, 2020
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