Additionally, in this header there is some data about the game its title, etc. We will need to ensure that the header is perfectly correct if we want our ROM to execute properly particularly if we're aiming to execute on an actual device rather than an emulator.
Thankfully, most of the details of ROM creation can be handled by a good toolchain. I use the devkitARM toolchain myself one of the devkitPro toolchains, based on the GCC toolchain , which makes the process extremely easy.
There are also some additional flags you might want to pass in for the first step the compilation — I'd recommend -fno-strict-aliasing , for example, as we'll be dealing with raw memory and pointers a lot and don't really want C's strict aliasing rule to bite us.
You might also find it beneficial to write a Makefile or shell script with these commands to make ROM compilation easier — these details seem a little unnecessary to include in this post though. With a process for ROM compilation from C established, let's try and test it out.
To throw a bone to any readers starting to drift off from all the theory, let's look at the code for our "Hello, World" GBA ROM first, and then discuss it afterwards. The code above is relatively simple, and should result in a horizontal set of three pixels being drawn in the middle of the GBA screen — one red, one green, and one blue:. Now, time to explain the code.
The first three bits of this register indicate the video mode, and the 11th bit indicates whether background 2 BG2 is enabled or not — thus, by writing the values we do, we set the video mode to mode 3, and enable BG2. Why do we need to do this? Well, first off the video mode.
It turns out that video mode 3 is a mode in which we can write bitmap data into VRAM, and BG2 will display this bitmap hence, why we also want to enable BG2. You might also be wondering why I've chosen to use video mode 3 rather than another video mode — the reason for this is that video modes 0 to 2 are much more difficult to explain though we'll be using them later. Therefore, we can express GBA colours using a bit long colour format — for data alignment reasons though, the GBA uses a bit colour format.
Specifically, the format is as follows:? So that's an unused bit, followed by five bits of blue, five bits of green, and then five bits of red. Using this format, and with knowledge of how video mode 3 treats VRAM as a x bitmap, our "Hello, World" ROM simply writes some colour values at specific pixel offsets e. Note, by the way, that all the memory accesses for interfacing with hardware in the code occur through volatile pointers — this prevents the compiler optimising out what it might think are useless memory operations.
Have you ever wondered how to program your own Gameboy, Gameboy Color, or Gameboy Advance game cartridges? Well, I certainly did at one point! Thinking tha.
Many third party game developers to create their own set of development libraries and even assemblers, emulators and debuggers to make Gameboy development easier. It is highly recommended to read the report to get a light introduction to Game Boy emulation.
About Contact Games Programming. Have you ever dreamed of becomming a game programmer? Today is your lucky day, becuase if you go through the following steps. I bet your can be making gameboy games in less than an hour, and that is if your modem is slow. By the time you finish reading this page you will have the basics that will enable you to build homebrewn games that will give give professional developers a run for their money. Note this tutorial is rather dated. It covers the original gameboy, and not gameboy advance.
For information about gameboy advance programming click here. You will definetly need to have a nice emulator for development. TheKnexChicken 5 years ago. Reply Upvote. Lowney 12 years ago on Introduction. Bartboy 13 years ago on Introduction. JshDav nerfer Reply 12 years ago on Introduction. That totally looked like "pedophile" for a second.
Anyway man, great instructable!
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