Description
1.1 Purpose
The goal of this assignment is to make a C program that will run on a Game Boy Advance emulator. Your program will be an interactive graphical application. Your program can be a game, or any other interactive program that meets the requirements outlined below.
While completing this program, you will learn about low level hardware programming in C. This program is similar to how you would write device drivers or parts of an operating system, which are typically written in C. The GBA devices (screen, buttons, DMA controller, etc.) are accessed via memory-mapped I/O. You will access specific hard-coded memory addresses in your C code. You will gain experience with bit masks and bitwise operators to set bits in the device registers.
The GBA is also a very slow computer. You will learn tricks to optimize the performance on a resourcelimited hardware device (such as DMA, integer math instead of floating point, and so forth).
1.2 Tasks
You will write an interactive graphical application in C that runs on the GBA emulator. This application can be a game, or any application that meets the feature and technical requirements below. For ideas on what you could do, please see What to Make in the Appendix. This is an open-ended assignment. Just be sure that your program meets all the requirements.
We have provided some resources to help you get started. You can use the outline structure of a program, and fill in code to do what your application specifically does. You should have at least one .h header file and one .c file. You can have more if you wish.
Your program must use DMA and waitForVblank(), and Mode 3 video. You must have a title screen, in addition to the other screen(s) in your program. You must use button input and include some text on the screen, as well as other images (a background image, and small image, e.g. a character that can move up, down, left, and right). You must detect collisions between two objects on the screen. You must not have any tearing (visual distortion, due to drawing too many things in each screen frame on a slow computer). Please see the full list of requirements below.
2.1 Resources
To tackle this homework, we’ve provided:
- A h file that contains all of the necessary GBA declarations such as DMA, videoBuffer, etc.
- Several other files which contain more “starter” code to get you rolling. See Section 5.7 for details.
- A Makefile that you can use to compile and run your program by typing or make med In addition, here are some other helpful resources:
- Lab Guides/Slides
- Lecture Slides 17 and 18
- TONC – full documentation of the GBA, including advanced features
- Lecture Demo Code: Canvas > Files > Source Code > gba demo
- The Appendix, including GBA Coding Guidelines
Feel free to use code from class resources as you need to, but as always, not from your friends or random sketchy Internet sites.
Your main.c should be something different from lecture code, since in this homework you will be creating your own program. You should keep the core setup with videoBuffer, MODE 3, waitForVBlank, etc., though.
Additionally, please do not rehash lecture code in your program; programs that are merely slightly modified lecture code are subject to heavy penalties. You may borrow some idea and structure from lecture code, but your code should be your own, and your idea should be distinct from lecture code in some way. For example, you are allowed to create games or programs that include bouncing squares, like Pong; however, you should attempt to add new features, like drawing an image instead of a square, or making the square change velocity whenever it bounces. If you have concerns over whether or not your idea is different enough from the demos in lecture, feel free to ask a TA in office hours or on Piazza.
2.2 Words of Warning
- Do not use floats or doubles in your code. Doing so will slow your code down greatly. The ARM7 processor the GBA uses does not have a floating-point unit which means floating point operations are slow as they are done in software, not hardware. Anywhere you use floats, gcc has to insert assembly code to convert integers to that format. If you do need such things that you think requires floats or doubles, you should look into fixed point math.
- We strongly recommend that you do not use malloc() in your program. Instead, use arrays large enough to hold all possible elements (images, game characters, etc.) that you could possibly have at one time. You can use an array of structs, as in the lecture code example.
- Only call waitForVBlank once per iteration of your main loop. Each waitForVBlank call will stall your program for about one sixtieth of a second, so excessive calls will make your program feel slower. Keep your code efficient; particularly, try to do as little drawing per frame as possible. See the guide on Reducing Tearing for tips on how to make your drawing more efficient.
- If your program does have tearing, keep in mind that it will affect the top of the screen first. So, if text or images drawn at the top of the screen are disappearing for some unknown reason, it is likely that your program is attempting to draw during the VDraw period, which is often leads to tearing.
- If you choose to use more advanced GBA features like sprites or sound, making them work is your responsibility; we (the TAs) do not really know how they work, so we sadly can’t help you. (TONC is useful to reference when implementing these features, if you do choose to add them.) Note that sound support is currently unstable and is unlikely to work in the current version of the Docker container.
