Homework 8 GBA Solution

1.1    Purpose

The goal of this assignment is to make a C program that will run on the GBA 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 speci c 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 resource-limited hardware device (such as DMA, integer math instead of oating 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 ll in code to do what your application speci cally does. You should have at least one .h header le and one .c le. 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.


1.3    Criteria

You will be evaluated on meeting all the feature requirements and technical requirements described below.

You will also demo this assignment to one of your TAs.

This assignment o ers an opportunity for you to be creative if you want to. However, creativity (and artistic ability) are NOT required. Your grade will be based on meeting all the requirements outlined below.

If you write a very creative program, but do not meet all the requirements, you will lose points. On the other hand, if you write a minimal program that works and meets all the requirements, but is not exciting, you will get full credit. So please do not feel pressure to be creative if that is not your personality, or if you do not have time to do so.



    • Before You Start

2.1    Resources

To tackle this homework, we’ve provided:

A gba.h  le that contains all of the necessary GBA declarations such as DMA, videoBu er, etc.

Several other les which contain more \starter" code to get you rolling. See Section 5.7 for details. A make le 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

Lecture Slides L17 and L18

TONC - full documentation of the GBA, including advanced features Lecture Demo Code: Canvas>Files>Source Code>GBAdemo

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 di erent from lecture code, since in this homework you will be creating your own program. But, you should keep the core setup with videoBu er, MODE 3, waitForVBlank, etc.

Additionally, we want to make one point very clear: please do not rehash lecture code in your program. This means that you are not allowed to just slightly modify lecture code and to call it a day. If we open your program and we see several boxes ying in random directions, that will be a very bad sign, and you will not receive a very pleasant grade.

2.2    Words of Warning

Do not use oats or doubles in your code. Doing so will slow your code down greatly. The ARM7 processor the GBA uses does not have a oating-point unit which means oating point operations are slow as they are done in software, not hardware. Anywhere you use oats, gcc has to insert assembly code to convert integers to that format. If you do need such things that you think requires oats or doubles, you should look into xed point math.

We strongly recommend that you do not use dynamic memory allocation in your program. Although malloc() will work on the emulator, it is not necessary. Instead just use arrays large enough to hold all possible 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

Keep your code e cient. If an O(1) solution exists to an algorithm and you are using an O(n2) algorithm then that’s bad (for larger values of n)! Contrary to this only worry about e ciency if your program is showing signs of 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.



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    • Requirements

There is no autograder for this assignment, so your grade entirely depends on the following requirements. These requirements will be checked by a TA during your demo, so be sure to cover them all!

3.1    Feature Requirements

Include a readme.txt le with your submission that brie y explains the program and the controls. You must use 3 distinct images in your program, all drawn with DMA.

{ Two full screened images sized 240x160. One of these images should be the rst screen displayed when launching your program.

{ A third image which will be used during the course of your program. The width of this image must be less than 240 pixels and the height of this image must be less than 160 pixels.

{ Note: all images should be included in your submission.

You must be able to reset the program to the title screen AT ANY TIME using the select key. This resets the ENTIRE program, including game state.

Button input should visibly and clearly a ect the  ow of the program

You must have 2-dimensional movement of at least one entity (an entity that moves both left/right and up/down). One entity moving up/down and another moving left/right alone does not count.

You should implement some form of object collision. For programs where application of this rule is more of a gray area (like Minesweeper), core functionality can take the place of this criteria, such as the numbers for Minesweeper tiles calculated correctly, accurate control, etc. When in doubt, ask a TA for clari cation.

Use text to show progression in your program. Use the example les from lecture as reference. You can also nd more information in Tonc:http://www.coranac.com/tonc/text/text.htm

There must be no tearing in your program. Make your code as e  cient as possible!


3.2    Technical Requirements

Your program must be in Mode 3! { Mode 3 should be the very  rst thing set in the main method. You must also implement drawImage with DMA. The prototype and explanation are later in the assignment.  Depending on when you are reading this, DMA may not have been covered in lecture yet. If this is the case, you should implement this function with setPixel  rst, and reimplement it with
DMA once it’s been covered in lecture.

You must implement waitforVBlank()! You must use at least one struct.

You can create your own header le or use the game.h header already available. You must move any #defines, function prototypes, and typedefs to this le from your code, along with your extern videoBu er statement if you wish to use videoBu er in other les. Remember that function and variable de nitions should not go in header les, just prototypes, extern variable declarations, and struct declarations.

{ As always, do not include .c les into other les. Only .h les should be included and .h les should contain no functional code.

{ It is optional for you to use other .c/.h les to organize your logic if you wish. Just make sure you include them in your submission and Make le.


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    • Deliverables

Please archive all of your source code les as a zip or a tar and upload to Gradescope under the Homework 8 assignment. This includes all .c and .h les needed for your program to compile and run. Do not submit any compiled les. You can use make clean to remove any compiled les, or make submit to remove compiled les and create the tar archive!



























































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    • Appendix

5.1    Appendix A: What to Make?

You may either create your own program the way you wish it to be as long as it ful lls the requirements, or you can make programs that have been made before with you own code. However, your assignment must be yours entirely and not based on anyone else’s code. This also means that you are not allowed to base your program o the code posted from lecture. Programs that are lecture code that have been slightly modi ed are subject to heavy penalties. Below are some previous programs that you can create or use as inspiration:

5.1.1    Example Programs

Interactive Storybook:

Recreate a story from a movie or a book using the GBA

Use text to narrate what is currently happening in the scene

Use the controls to advance to the next scene or control a character within the scene Smooth movement (for any moving characters or objects)

Start o with a full screen title image and end with a full screen credits image Characters represented by structs

Galaga:

Use text to show lives

Game ends when all lives are lost. Level ends when all aliens are gone.

Di erent types of aliens: there should be one type of alien that rushes towards the ship and attacks it Smooth movement (aliens and player)

Aliens and the ship represented by structs

The World’s Hardest Game:

Smooth motion for enemies and player (no jumping around) Con ned to the boundaries of the level

Enemies moving at di erent speeds and in di erent directions Sensible, repeating patterns of enemy motion

Enemies and the player represented by structs

Flyswatter:

Images of ies moving smoothly across the screen Player controlled yswatter to swat the ies

Score counter to keep track of how many ies have been swatted Fullscreen image for title screen and game background

Enemies and the player represented by structs


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5.2    Appendix B: GBA Coding Guidelines

5.2.1    Building and Running your Code

To build your code and run the emulator, run

$ make med

5.2.2    Images

As a requirement, you must use at least 3 images in your program. To use images in GBA, you will rst have to convert them into the suitable format. We recommend using a tool called nin10kit, which is pre-installed on the Docker image, or you just installed using the command above.

You can read about nin10kit in the nin10kit documentation (there are pictures!):

https://github.com/TricksterGuy/nin10kit/raw/master/readme.pdf

nin10kit reads in, converts, and exports image les into C arrays in .c/.h les ready to be copied to the GBA video bu er by your implementation of drawImageDMA()! It also supports resizing images before they are exported.

You want to use Mode 3 since this assignment requires it, so to convert a picture of smelly festering garbage into GBA pixel format in garbage.c and garbage.h, resizing it to 50 horizontal by 37 vertical pixels, you would run nin10kit like

$ nin10kit --mode=3 --resize=50x37 garbage garbage.png

This creates a garbage.h    le containing

extern const unsigned short garbage[1850];

#define GARBAGE_SIZE 3700

#define GARBAGE_LENGTH 1850

#define GARBAGE_WIDTH 50

#define GARBAGE_HEIGHT 37

which you can use in your program by saying #include "garbage.h".

The garbage.c generated, which you should add to the Make le under OFILES as garbage.o if you plan to use it, contains all of the pixel data in a huge array:

const unsigned short garbage[1850] =

{

0x7fff,0x7fff,0x7fff,0x7fff,0x7fff, // ...

0x7fff,0x7fff,0x7fff,0x7fff,0x7fff, // ...

    • ...

0x7fff,0x7fff,0x7fff,0x7fff,0x7fff, // ...

0x7fff,0x7fff,0x7fff,0x7fff,0x7fff, // ...

};

We’ve included garbage.png, garbage.c, and garbage.h in the homework zip so you can check them out yourself. To draw the garbage in your own game, you can pass the array, width, height to your drawImageDMA() like drawImageDMA(10, 20, GARBAGE WIDTH, GARBAGE HEIGHT, garbage) (to draw at row 10 and col 20). The next section will cover drawImageDMA() in more detail.





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5.2.3    DMA / drawImageDMA

In your program, you must use DMA to code drawImageDMA.

The GBA screen is represented with a short pointer declared as videoBuffer in the gba.h le. The pointer represents the rst pixel in a 240 by 160 screen that has been attened into a one dimensional array. Each pixel is a short and has red, green, and blue channels.

DMA stands for Direct Memory Access and should be used to make your rendering code run much faster.

If you want to read up on DMA before it is covered in lecture, you may read these pages from Tonc.

http://www.coranac.com/tonc/text/dma.htm (Up until 14.3.2).

If you want to wait, then you can choose to implement drawImageDMA without DMA and then when you learn DMA rewrite it using DMA. Your nal answer for drawImageDMA must use DMA.

You must not use DMA to do one pixel copies (Doing this defeats the purpose of DMA and is actually slower than just using setPixel!). Solutions that do this will receive no credit for that function. The prototype and parameters for drawImageDMA are as follows.

/* drawImageDMA

    • A function that will draw an arbitrary sized image

    • onto the screen (with DMA).

    • @param row the row coordinate to start drawing the image at

    • @param col the col coordinate to start drawing the image at

    • @param width width of the image

    • @param height height of the image

    • @param image pointer to the first element of the image

*/

void drawImageDMA (int row, int col, int width, int height, const u16* image)

{

// Todo implement :)

}

Protip: if your implementation of this function does not use all the parameters that are passed in then you are not implementing the function correctly. You should know that DMA acts as a for loop, but it is done in hardware.

5.2.4    GBA Controls

Here are the inputs from the GameBoy based on the keyboard for the default emulator vbam:

Gameboy
Keyboard


Start
Enter


Select
Backspace


A
Z


B
X


L
A


R
S



The directional arrows are mapped to the same directional arrows on the keyboard.

5.2.5    C Coding Conventions

Do not jam all your code into one function (i.e. the main function)



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Split your code into multiple les (for example, you can have your main logic in your game les, but other helper functions for drawing or assessing the game state in external les)

Do not include .c les into other les. Only .h les should be included. .h les should contain no functional code.

Comment your code, and comment what each function does.

5.2.6    Making Sense of the Files

As mentioned in the C Coding Conventions section, it’s often a good idea to split up functionality into multiple les. In fact, this is exactly what we’ve done with the \starter" code we’ve given you. The pure volume of les may be a bit daunting, so here’s a brief breakdown of what each le is used for.

Makefile

This Make le contains all of the tasks you can run to build and test your program. You’ll need to modify it to include the .o le for any image you’d like to use. However, you should not modify the bottom portion of this le, as bad things may happen. Feel free to look through it in order to see all of the tasks at your disposal.

game.c

This le contains a state machine which ultimately calls all other functionality in the program. It is also the main entry point to the entire application.

game.h

This  le should contain any function prototypes and structs that you create.

gba.h

This le contains a large collection of useful macros and constants which will help primarily with GBA-speci c tasks. These include macros for handling GBA input, DMA graphics, and general GBA graphics.

The le also contains an extern declaration of the font data found in font.c, which is necessary for drawing text.

This  le also contains some prototypes for functions in gba.c.

gba.c

The functions you will write in this le do the \dirty" work, executing graphics updates with both DMA and non-DMA strategies. All of this code will be very speci c to the GBA platform and the way it handles graphics.

The  le also comes with some prepackaged functions for drawing text.

font.c

Simply exists to store a large amount of font data. No real need to mess around with this  le.

Various Image Files

When you create your own image les, you will need to include the relevant header les in any le you’d like to reference these images from. The data stored in each of these les (and how to create them) is pretty well explained in section 5.3.







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Personal .c  les and .h  les

You are heavily encouraged to split your code up into separate .c and .h les! Do not put everything in your main method. Keep your code organized and readable.

NOTE: For any .c les you create please place its respective .o le in the OFILES variable in the Make le. For example, if you create newFile.c you will need to update the Make le to reference the newFile object le.

OFILES = gba.o font.o game.o images/garbage.o newFile.o

5.2.7    Submit

To submit your code:

    1. Make sure your code compiles by running make med

    2. Clean the code by running make clean

    3. Create the submission tar by running make submit

    4. Turn in submission.tar.gz on gradescope!

5.2.8    Installing Dependencies

If you are not using Docker, you will have to install some dependencies before you are able to begin using GBA. Run the following commands (don’t worry about these if you are using Docker).

$ sudo apt update

$ sudo apt install gcc-arm-none-eabi cs2110-vbam-sdl mednafen cs2110-gba-linker-script nin10kit

Note that this requires Brandon \The Machine" Whitehead’s CS 2110 PPA, which you should’ve added earlier in the class for complx. If you didn’t (or this is a new VM/dual boot or something), run the following and then run the two commands above again:

$ sudo add-apt-repository ppa:tricksterguy87/ppa-gt-cs2110

























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5.3    Appendix C: Rules and Regulations

5.3.1    General Rules

    1. Starting with the assembly homeworks, any code you write must be meaningfully commented. You should comment your code in terms of the algorithm you are implementing; we all know what each line of code does.

    2. Although you may ask TAs for clari cation, you are ultimately responsible for what you submit. This means that (in the case of demos) you should come prepared to explain to the TA how any piece of code you submitted works, even if you copied it from the book or read about it on the internet.

    3. Please read the assignment in its entirety before asking questions.

    4. Please start assignments early, and ask for help early. Do not email us the night the assignment is due with questions.

    5. If you nd any problems with the assignment it would be greatly appreciated if you reported them to the author (which can be found at the top of the assignment). Announcements will be posted if the assignment changes.

5.3.2    Submission Conventions

    1. All les you submit for assignments in this course should have your name at the top of the le as a comment for any source code le, and somewhere in the le, near the top, for other les unless otherwise noted.

    2. When preparing your submission you may either submit the les individually to Canvas/Gradescope or you may submit an archive (zip or tar.gz only please) of the les. You can create an archive by right clicking on les and selecting the appropriate compress option on your system. Both ways (uploading raw les or an archive) are exactly equivalent, so choose whichever is most convenient for you.

    3. Do not submit compiled les, that is .class les for Java code and .o les for C code. Only submit the les we ask for in the assignment.

    4. Do not submit links to les. The autograder does not understand it, and we will not manually grade assignments submitted this way as it is easy to change the les after the submission period ends.

5.3.3    Submission Guidelines

    1. You are responsible for turning in assignments on time. This includes allowing for unforeseen circum-stances. If you have an emergency let us know IN ADVANCE of the due time supplying documenta-tion (i.e. note from the dean, doctor’s note, etc). Extensions will only be granted to those who contact us in advance of the deadline and no extensions will be made after the due date.

    2. You are also responsible for ensuring that what you turned in is what you meant to turn in. After submitting you should be sure to download your submission into a brand new folder and test if it works. No excuses if you submit the wrong les, what you turn in is what we grade. In addition, your assignment must be turned in via Canvas/Gradescope. Under no circumstances whatsoever we will accept any email submission of an assignment. Note: if you were granted an extension you will still turn in the assignment over Canvas/Gradescope.

    3. There is a 6-hour grace period added to all assignments. You may submit your assignment without penalty up until 11:55PM, or with 25% penalty up until 5:55AM. So what you should take from this is not to start assignments on the last day and plan to submit right at 11:54AM. You alone are responsible for submitting your homework before the grace period begins or ends; neither Canvas/Gradescope, nor


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your aky internet are to blame if you are unable to submit because you banked on your computer working up until 11:54PM. The penalty for submitting during the grace period (25%) or after (no credit) is non-negotiable.

5.3.4    Syllabus Excerpt on Academic Misconduct

Academic misconduct is taken very seriously in this class. Quizzes, timed labs and the nal examination are individual work.

Homework assignments are collaborative, In addition many if not all homework assignments will be evaluated via demo or code review. During this evaluation, you will be expected to be able to explain every aspect of your submission. Homework assignments will also be examined using computer programs to nd evidence of unauthorized collaboration.

What is unauthorized collaboration? Each individual programming assignment should be coded by you. You may work with others, but each student should be turning in their own version of the assignment. Submissions that are essentially identical will receive a zero and will be sent to the Dean of Students’ O ce of Academic Integrity. Submissions that are copies that have been super cially modi ed to conceal that they are copies are also considered unauthorized collaboration.

You are expressly forbidden to supply a copy of your homework to another student via elec-tronic means. This includes simply e-mailing it to them so they can look at it. If you supply an electronic copy of your homework to another student and they are charged with copying, you will also be charged. This includes storing your code on any site which would allow other parties to obtain your code such as but not limited to public repositories (Github), pastebin, etc. If you would like to use version control, use github.gatech.edu

5.3.5    Is collaboration allowed?

Collaboration is allowed on a high level, meaning that you may discuss design points and concepts relevant to the homework with your peers, share algorithms and pseudo-code, as well as help each other debug code. What you shouldn’t be doing, however, is pair programming where you collaborate with each other on a single instance of the code. Furthermore, sending an electronic copy of your homework to another student for them to look at and gure out what is wrong with their code is not an acceptable way to help them, because it is frequently the case that the recipient will simply modify the code and submit it as their own.

























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Figure 1: Collaboration rules, explained colorfully









































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