In this article we will prepare the necessary development environment to program games in C using GBDK . For this, we will use the Linux binary compatibility layer since GBDK requires a patched version of SDCC and compiling it on FreeBSD is very complicated, believe me, I’ve tried. We will also install the Emulicious emulator/debugger which will help us visualize the state of the microprocessor, the system memory, and the video memory graphically.

The manual is divided into several sections:

• Linuxulator
• GBDK
• Example
• Debugger/Emulator

Linuxulator

We enable linuxulator, the easiest way is to use mrclksr’s script.

First, we make sure that generic compatibility is not enabled:

Now we clone mrclksr’s script and install the chroot:

We enable the chroot at boot:

Now every time we run a Linux binary, it will run with the Linux compatibility layer.

GBDK

In reality, GBDK is a set of C libraries for programming in GameBoy, the compiler itself is SDCC, and when we download GBDK, a patched version of SDCC is already included.

We install the compiler/libraries:

Example

A simple example could be this, it shows a text on the screen and waits for us to press START:

#include <gb/gb.h>
#include <stdio.h>

void main()
{
        printf("Welcome to GAMEBOY\nProgramming");
        printf("\nPress Start");
        waitpad(J_START);  // other keys are J_A, J_UP, J_SELECT, etc.
        printf("\nIsn't it easy!");
}

We compile the example:

NOTE: We can find all the documentation about GBDK functions in this link .

Debugger Emulator

Emulicious is written in Java so we will have to download the JAR file and run it.
We download the emulator/debugger:
https://emulicious.net/downloads/

We run it:

We tweak some parameters, in my case I prefer to see the display with colors that remind me of the gameboy pocket:

Options -> Emulation -> Game boy -> Color scheme -> Green

A little problem I had with Emulicious is that it doesn’t recognize the USB controller, but with a software called antimicro we can map the controller to keys:

We just check the keys of Emulicious:

Options -> Configure Input

Now we go to antimicro:

And we map each of the keys, for example the up/down arrows:

As we can see there are predefined presets, normal buttons are mapped in the same way by selecting the key to simulate:

We leave antimicro in the systray and open the ROM from Emulicious:

/compat/ubuntu/gbdk_code/00.gb

It will load the ROM and if we press the Start key the message will appear:

The most interesting thing about Emulicious is that it is also a debugger, very useful for detecting and debugging bugs:

Another option is to use bgb through wine, this emulator is well known as it appears in most videos and tutorials: