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Many kids remember the GameBoy Advance (GBA)as their favorite gaming console. Nintendo developed this handheld console, and it offered gamers a wide variety of enjoyable video games. The console was discontinued, but many gamers would still want to play its nostalgic games.
Today you can only achieve that by using a GameBoy Advance emulator and GameBoy Advance ROMs.
Interestingly, did you know that writing your own GBA emulator is possible? Some may do it out of curiosity, for fun, for the challenge, while the nostalgia sparks some. But how do you get started? Find out below.
A Brief Look at Emulators
When it comes to emulating gaming consoles, an emulator is a program that imitates the hardware components of the targeted system so as to enable games to run on your chosen host platform or computer.
Emulators come in handy as they help preserve classic games exclusively on hardware that can’t be easily acquired currently. They also have improved features that are not present on the actual hardware and more.
Essential Requirements and Concepts for GBA Programming
Research
Do simple research about the GameBoy Advance console. This will help you discover things like its complexity, instruction sets, memory size, quantity and type of registers, and more.You can always decipher GBA architecture using the information on the internet.
A Programming Language
You need to choose a programming language to use. There are many options like C, Rust, Python, JavaScripte.t.c. Pick a language but ensure you are comfortable using it.
Loading ROMs
To write, you will need to get GBA ROMs into memory. To get these, search the web for Romspedia.com GBA ROMs to download ROMs that will work. These ROMs are what you will use to implement CPU instructions.
CPU Emulation
Consoles work because of the CPU. In the context of emulation, two key CPU aspects are essential; CPU registers and Instructions. The two are primarily defined by Instruction Set Architecture (ISA), which is the CPU architecture.
CPU registers are small pieces of fast memory contained in the CPU. On the other hand, CPU instructions are simply the CPU operations to be implemented. Every instruction contains a particular bit pattern for understanding by the CPU.
The first bits help you determine what instructions do, while the last ones have the data to be used. To properly use instructions and make them work, you have to understand what they mean and also execute the right actions.
GameBoy Advance uses the ARM CPU. ARM lacks anMMU( Memory Management Unit);therefore, it has no virtual memory. GBA programs,hence directly access physical memory and communicate with the hardware through Memory Mapped IO (MMIO).GBA programs are precisely written for GBA hardware and do not depend on the operating system.
Implementing all GBA instructions should make GBA ROMs playable, assuming no mistakes are made. Printing them as they execute can help you debug in case of errors.
The BIOS file
The BIOS file is like the key that gives you emulator access. It is the first code that runs once ARM boots as it contains the instructions that tell your emulator how to start.GBA doesn’t have an operating system but has a BIOS that you need to obtain.
The BIOS belongs to Nintendo, and distribution is not allowed. However, you can dump it yourself.
Have the Necessary Emulator and Action scripts
Emulator scripts handle initialization, help with loading the bios, pausing and resuming the emulator, etc. Some scripts are used internally by other critical functions, while others depend on user clicks. Action scripts load ROMs, and they, therefore, need to be loaded with regards to where GBA exists.
Additional Details
During instruction implementation, you will discover things like timers, keyboard, sound, display, and sprites which you can implement as deemed appropriate.
GBA display modes include tile modes and bitmap modes. The former are faster but more challenging to design and use for programming.
To draw GBA graphics,you use sprites. Sprites mean small memory stored images drawable to the screen at provided coordinates.
Testing
It is always crucialthat you give proper attention to your project by testing to deal with bugs. You can use the GBA ROMs to test if your emulator works. But, this is not always a guarantee that you have perfect emulation. You can also test the sprites, CPU, PPU (Picture Processing Unit), DMA(Direct Memory Access), buttons, and so on.
Final Thoughts
We have provided you with a general overview of programming a GBA emulator. However, creating a fully functional one from scratch requires more detailed instructions, commands, and debugging.
With this guide, as a beginner, you can help yourself understand the issues and requirements behind building a GBA emulator. The critical thing to remember is that programming an emulator is a cumulative progress. Everything does not have to be implemented at once.
