Retro Game Programming Copyright 2011 by brainycode com Retro Game Programming
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- Navigate this page:
- Setting up the 6502 simulator
- Testing 6502 simulator installation
- Testing DASM installation
- Chapter 9: Game Graphics
- Tools needed to get started
- Lab 12.1 – Testing Atari Programming Setup
- Chapter 13: Creating the game Pong on Atari 2600
- Chapter 16: Programming the Apple IIe
- Chapter 21: User Assignment: NES Sam’s World
Inside the 6502 CPU
Figure - 6505 Architecture Chapter 6: Learning Assembly Language – Part 3We will be using two tools for creating machine code for the 6502 machines we are studying:
Figure - 6502 Simulator The simulator allows us to watch a generic 6502 processor executing a program. We will be able to examine and watch the 6502 CPU internal registers and the contents of memory. We will use this simulator to learn 6502 programming. Setting up the 6502 simulator
Testing 6502 simulator installationSetting up DASMUnzip DASM zip file. I installed on my C drive, it automatically installed to C:\DASM. DASM is a cross-assembler that generates machine code (from assembler text) for many different microprocessors. There are binary versions for Amiga, DOS, Linux and Mac. For Windows I usually add a special file (setup.bat) when I have an application intended to be used in DOS. The setup.bat file contains lines to setup the path or any special environment variables. Place the following setup.bat into C:\DASM. 
Figure - Using Textpad to create setup.bat Testing DASM installation
Chapter 7: Learning Assembly Language – Part 4Chapter 8: The Video Mode and Video BufferChapter 9: Game GraphicsChapter 10: Player Input, Physics, and AIChapter 11: Sound EffectsChapter 12: Programming the Atari 2600The designers of the Atari 2600 wanted to build a machine that was easily extendable like the current machine at the time the Fairchild Channel F (see XXX) and inexpensive to build. They based the machine on a fairly new microprocessor that was rather cheap in comparison to competing CPUs and rather fast – the 6502. In fact, to reduce cost even further the Atari 2600 used a version of the 6502 – the 6507. The limitation of the 6507 was that it could only used 13 bits to address memory. The 6502 had a 16-bit address line that allows it to memory from 0-65536 (or 65KB) whereas the 6507 could only address addresses from 0-8192. The difference is considerable and the impact is that it affects the size and complexity of the programs you can create30. Tools needed to get startedYou only need three things to get started in building your own VCS games:
We will assume you can obtain, install and use a text editor. If you don’t have a favorite than try TextPad on your machine than just start using textpad.
For Atari 2600 programming you will need to obtain the Atari2600_1_10 zip files.
To test that it all works together do the next lab. We will explain the code in detail in subsequent sections: Lab 12.1 – Testing Atari Programming SetupStep 1: Obtain a command window. You can do this by simply by clicking on Start Windows icon and entering “cmd” (without the quotes) into “Start Search” input box. 
Figure - My Vista command window Step 2: Navigate to C:\DASM by entering “cd C:\DASM” Step 3: enter “setup” Step 4: Create a directory you will use to create you VCS programs. Enter “mkdir 2600” Step 5: Now navigate to that directory “cd 2600” Step 6: Copy of unzip the Atari 2600 macro files macro.h and VCS.h to the directory C:\DASM\2600. Step 6: Open your text editor and enter the following program:
Save the file under C:\DASM\2600 as kernel.asm Step 7: Return to the Command Prompt window and enter “dir” to see a listing of files in C:\DASM\2600 
Figure - Lising of files under C:\DASM\2600 Step 8: Assemble the program by entering the following command : Dasm kernel.asm –lkernel.txt –f3 –v5 –okernel.bin 
Figure - Assembling our first Atari program Step 9: Enter dir to see the new list of files: 
Figure - Files after assembling The kernel.txt contains the assembler listing. Take a look with your text editor. The output binary file kernel.bin is what you will execute. Step 10: Move the file kernel.bin to the location on your hard drive where you have you Atari ROM cartridges. In my case, I will move to C:\Stella-3.2.2\32-bit\ROMS directory: 
Figure - Moving kernel.bin to Atari ROM location Step 11: Start up your Atari emulator and locate the file kernel.bin. 
Figure - Starting kernel.bin You should see the following screen: 
Figure - Running kernel.bin on your emulator The program does not do much but now you know the steps to creating, assembling and executing a program for the VCS. Programming for a TVThe VCS programmer is not just concerned about the details of the game and its mechanics but must know how a television31 works! The mind is a wonderful tool. One of the ways it processes information is by fusing things together to create a clear and coherent whole. One example is how we a movie picture works Chapter 13: Creating the game Pong on Atari 2600Chapter 14: User Assignment: Atari TankChapter 15: Homebrew games for the Atari 2600Many programmers today enjoy the challenge of developing a game for a system like the 2600. Many of these new games are actually made available on cartridges so you can play them on your Atari 2600 VCS system. Many more are available to fun on the emulators z26 or Stella. You can find forums online where you can share and discuss ideas with fellow homebrew developers. In fact, the Atari enjoys the largest group of developers creating new programs for a systems long gone. One such game is Halo 2600 for the Atari 2600 developed by Ed Fries. Ed Fries is well-known as the vice president of game publishing at Microsoft during the development of the original Xbox game console. 
Figure - Title screen for Halo 2600 The game brings to the Atari 2600 Master Chief the lead character in the Microsoft Halo game. 
Figure - Screen shot from Halo 2600 I am assuming here that many of the readers are acquainted with the Xbox and Xbox 360 most popular series – Halo. On a modern day system master chief looks more impressive but the game developed and freely available for the VCS is as enjoyable. 
Figure - Master Chief in Halo 3 If you check out the Internet32 you will find a video clip from CNET detailing some home brew games you should check out, here they are: SCSIcideThis game was written by Joe Grand. This is a type only a real geek could love. In the game you are a hard drive controller that need to process the data bits in the correct color order. Chapter 16: Programming the Apple IIeChapter 17: Creating the game Crisis Mountain on the Apple IIeChapter 18: User Assignment: Apple Robot WarsChapter 19: Programming the NES |
