atari 2600 homebrew

Download Atari 2600 Homebrew

Post on 04-Feb-2016




2 download

Embed Size (px)


Atari 2600 Homebrew. Darrell Spice, Jr. What is Homebrew?. Games (or other software) made by hobbyists for platforms that are not typically end user programmable Over 100 have been released for the Atari 2600 - PowerPoint PPT Presentation


  • Atari 2600 HomebrewDarrell Spice, Jr.

  • What is Homebrew?Games (or other software) made by hobbyists for platforms that are not typically end user programmableOver 100 have been released for the Atari 2600AtariAge has 80+ homebrew 2600 titles available, only Atari had a larger catalog of 2600 games

    FranticTimmyMy Homebrew gamesMedieval MayhemSpace RocksStay FrostyStay Frosty 2FinishedWIP

    Medieval Mayhem

    Space Rocks

    Stay Frosty

    Stay Frosty 2

    WIP - Frantic

    WIP - TIMMY!

  • Challenges128 bytes of system RAM (1/8 KB) PS3 has 256 MB (262,144 KB)no video RAM PS3 has 256 MB4K cartridge space1 MHz CPU only 27% is available for game logic

  • 128 bytes of RAM1 KB cost $66 in 1975 when work began on Stella (code name for the Atari) 128 bytes = 1/8 KB, about $8.25

  • TIA - Television Interface Adaptor is scan line based2 players (sprites)2 missiles1 ballLow resolution playfieldNo video RAM

    2 Players8 x 1 imageSample patternIf not changed, pattern repeats down the screenShapes are created by changing pattern on each scan line

    Player FeaturesThree sizes:1x2x4xThree 1x duplicatesTwo 1x triplicates

  • 2 Missiles, 1 BallFour sizes:1x2x4x8x1 x 1 imageCan be used to create objects like this bell

  • Playfield20 x 1 imagePlayfield is repeatedor reflectedto fill width of screen

  • 4K Cartridgeoriginal games were 2K4K was believed to be large enough to last until the 2600's replacement hit the marketROM only, no Read/Write line for controlling access to RAM

  • 27% of 1 MHzCPU must update TIA ( scan line video chip) in real timePortion of program that drives TIA is known as the KernelCPU must also trigger sync signal for TV

    Program flowKernel(draw display)Game logicGame logicSync signal

  • What do you need?EditorDasmStellaHardware

  • EditorNotepad or TextEdit will do

  • A programmer's editor like jEdit is nicer

  • DasmAssembler that converts human readablecode into machine readable code

  • Integrated debugger makes coding easierTurns your computer into an AtariStella

  • HardwareAtari 2600SuperchargerKrokodile cartHarmony

    Atari 2600While Stella is great, it's not 100% accurate so you need to test your code on the real thing.

    32 character text on Atari

    32 character text on Stella

    Starpath Supercharger

    Starpath SuperchargerReleased in 1982 for $45Uses audio to load programs (games were sold on cassettes)6 K RAM, 2 K BIOSProgram MAKEWAV converts ROM image to sound file

    Starpath Supercharger

    Krokodile Cartridge

    Krokodile CartridgeReleased in 2005 for $99Uses serial port to load programs512 K Flash ROM, 32 K RAM

    Harmony Cartridge

    Harmony CartridgeReleased in 2009Still produced, sells for $59.99 and $79.99 http://harmony.atariage.comUses SD card or USB to load programs32 K Flash ROM, 8 K RAM70 MHz ARM processor Melody variation used by Atari Age to produce stand alone games

  • batari BasicProvides a simpler way to create Atari gamesUses a BASIC like language for game logicProvides a number of prebuilt Kernels

  • batari Basic games

  • How are the limited objects used to create complex games?

    Space Invaders





    Player 0

    Player 1

    Missile 0

    Missile 1

    Hunchy II





    Player 0

    Player 1

    Missile 0

    Missile 1

    Keystone Kapers





    Player 0

    Player 1

    Missile 0

    Missile 1

    (graphic by Nathan Strum)Supercharging games

    BankswitchingExtra RAMCoprocessorBus StuffingSupercharging your game

  • BankswitchingGame split into 4K banksAtari can only see 1 bank at a timeCartridge has hardware to present different banks upon requestCompanies came up with various "modes" of making the requestKrokodile Cartridge supports up to 512K using mode 3F

    Game Selection Matrices were used due to limited ROM

    Extra ROM with bankswitching allows for in game menus

  • Extra RAMExtra RAM allows for more complex gamesAddress line used to work around the lack of a R/W line. This makes the RAM appear twice in memory, one address range for reading and the second for writing.Not compatible with INCrement or DECrement instructions. Krokodile Cartridge supports up to 32K using mode 3E

  • CoprocessorDPC in Pitfall 2DPC+ in Harmony/Melody

  • DPCDisplay Processor Chip designed by David Crane8K ROM2K Display Data (holds graphics and other data)Data Fetchers return Display Data for fast updates to TIAData Fetcher Window mode greatly speeds up player processing3 voice music using square waves (4 bit digital sound)

  • DPC+Enhanced version of DPC designed for Harmony/Melody by Fred Quimby, Chris Walton and Darrell Spice, Jr.24K ROM4K ROM/RAM based Display DataFast Fetch mode for even faster Data Fetchers3 voice music using custom waveforms (4 bit digital sound)Can offload non-Kernel processing to 70 MHz ARM

    DPC+ Games

  • Bus StuffingCommodore(!) developed The Graduate, a computer keyboard add-on for the 2600Processors in the keyboard overdrive the data bus (aka bus stuffing) for fastest possible TIA updatesHarmony/Melody support bus stuffing

    Display Sprite RoutinesDoDrawDPCDPC+Bus Stuffing

    LDA #SPRITEHEIGHT DCP SpriteTemp BCS DoDraw LDA #0 .BYTE $2CDoDraw LDA (GfxPtr),Y STA GRP0 LDA (ColorPtr),y STA COLUP0Display Sprite RoutinesDoDraw, 26 cyclesDPCDPC+Bus StuffingUpdate ImageUpdate Color

    LDA DF0DATAWSTA GRP0LDA DF1DATASTA COLUP0Display Sprite RoutinesDoDraw, 26 cyclesDPC, 14 cyclesDPC+Bus StuffingUpdate ColorUpdate Image

    LDA #

  • Resources

    Atari Age dig 2600 Programming Programming for Newbies

  • batari Basic

    batari Basic Age forum Terrain bB

  • Presentation will be made available at


    Best selling home brew at AtariAge is Synthcart, used by musicians Part of Stella's Stocking128 bytes0 VRAM4K cartridge1 MHz CPU, 27%1K $390, 128 bytes $50 Players are sprites in modern terms8x1 imagepattern repeats on every scan line unless it's changed3 sizes: 1x, 2x or 4x1x can be duplicated with 3 spacing options1x can be tripled with 2 spacing options 1x1Can be horizontally stretchedObjects can be created by changing size & positionNote - if a player is in duplicate or triplicate, the corresponding missile will be as well20x1 background imageBackground is 40 pixels wide, so the 20 are repeated or mirrored Television Interface AdaptorGenerates display, sound & reads paddles and joystick fire buttonsThis is your gameThis is what the TV seesThis is what your program doesColor coding in a programmer's editor makes it easy to see typosSam Thomas (eshu on AtariAge) figured out the TIA tricks for 32 character text in 2011Garbage on left

    Stella is also more forgiving on TV sync timing, so it's best to test on a real Atari to make sure the picture is stableAvailable here at ??boothGingerbread man, Elf DashCave-in, Seaweed AssaultWe can use Stella's Fixed Color mode to seePlayers are used in triplicate to create 6 invaders per rowPlayers are reused multiple times down the screenMissile 0used to draw all the bellschanging the color of the background creates most of the game screen Nathan came up with the concept for Stay Frosty, and created all the graphics for it. Heaven forbid you should lose your manual!Medieval Mayhem's menu uses 6K. Original Warlords is 4kDouble DunkSpace RocksStay Frosty 2Evil Magician Returns II (batari BASIC)Eggventure (batari BASIC)

    Mini dig has Atari documentation

View more