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3 Generations of Game Machine Architecture


Original product conception: generate cartoon-quality video games. ... luck matters: the collapse of the video game business in 1984 poisoned the well ... – PowerPoint PPT presentation

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Title: 3 Generations of Game Machine Architecture

3 Generations of Game Machine Architecture
  • Joe Decuir
  • jdecuir_at_nwlink.com
  • alumnus of Atari Amiga

  • My background
  • Atari Stella system (2600)
  • Atari Colleen system (400/800, 5200, etc)
  • Amiga Lorraine system (1000, 2000, etc)
  • looking ahead

My background, pre-Atari
  • Clearly an engineer from my first Erector set
    (age 6)
  • BS MS degrees from Berkeley, in EECS and
    pre-med, including Intel 4004 design
  • A couple years spent in medical instrument design
    and in medical research that leveraged those
  • Bought my one 6502 at Wescon in 1975.

Stella Architecture
  • Product requirements
  • Design choices
  • Hardware/firmware tradeoffs
  • Results
  • Lessons

Stella Requirements
  • Atari management had a clear vision for the
    product provide a means to bring successful
    Arcade games home.
  • We had to hit a 200 max retail price for the
    console, for Christmas of 1977.
  • Expected product life 3 years (e.g. to 1979)
  • Non-goals be an expandable personal computer.

Stella System
  • TIA video chip (see below)
  • 6502-based processor, 6507
  • 13 bit address, no interrupts, RDY line
  • 1.2 MHz
  • 6532 combo
  • 128 bytes of RAM (all mapped into zero page)
  • 16 bits of parallel I/O (joysticks and panel)
  • timer (interrupt not used)
  • cartridge slot for 2K or 4K ROMs (24 pins)
  • 2 game control ports

Stella Implementation
  • From coin-op games, there were two obvious ways
    to architect the system
  • non-programmable random logic
  • programmable (uP) with screen bit-map
  • Fatal flaws in both
  • random logic would be slow development, and not
  • bit maps were expensive

Bit maps and games
  • Games traditionally contain a background of some
    kind (playfield) and foreground active objects
    (players, sprites, etc).
  • If only a bit map is used for everything
  • sprite graphics and motion resolution are the
    same as the playfield resolution, forcing
  • a hard choice between high cost or clunkiness

The breakthrough soft video
  • Mayer and Milner proposed using a fast enough
    processor to reload video on a line-by-line
    basis. The processor replaces logic.
  • They had to wait for the right chip
  • Intel 8080 was expensive, needed 3 supplies.
  • Motorola 6800 was too slow
  • Fairchild F8 was even slower
  • MOS 6502 was perfect fast and cheap

Why was the 6502 so good?
  • Process speed depletion load pullup transistors
    were much faster and smaller than enhancement
    pullups (e.g. 6800).
  • Architecture speed
  • little-endian addresses pipelined instructions
  • indexed-indirect and indirect-indexed
    instructions allowed use of zero page as an array
    of fast memory pointers.

Design decisions
  • Our target coin op games were two player action
    (Tank - Combat), sports (Basketball) and paddle
    (Pong -Video Olympics) .
  • We decided that we needed
  • 2 8-bit motion objects (P0, P1)
  • 3 1-bit motion objects (M0, M1, Ball)
  • 20 or 40 bits of low resolution playfield

Hardware Software tradeoffs Motion control
  • The easy way to make these motion objects would
    require a binary horizontal counter, and 5 8-bit
    position registers and comparators. We thought
    this would be huge.
  • The cheap way was to use dynamic polynomial
    counters, running in parallel. Motion in
    implemented with resets and motion vectors.

Motion control, continued
  • To appease the programmers, I generated a
    Compute Horizontal Reset CHRST utility.
  • Called with object index in X, position in A
  • computes a loop count (15 clocks)
  • computes a residual motion vector (/-7)
  • waits for sync, loops, resets and writes motion
  • For the programmers, this was good enough

Motion control, epilog
  • An alternative that we considered too late
  • keep the polynomial horizontal counter
  • replace the separate object counters and motion
    registers with simple position latches and
  • use a 160-byte look up table in cartridge ROM to
    map binary horizontal positions to polynomial
    counter values.

Other TIA chip features
  • 4 7-bit palette registers
  • 15 collision detection latches
  • 2 channel sound system
  • variable prescaler
  • 45 bit polynomial counters
  • volume registers
  • trigger and potentiometer input ports
  • trigger input could be used for light pens or
    light guns.

Stella Graphics
  • Fundamental pixel resolution is 1 color burst
    clock (280nsec, 160/line) by 1 line.
  • Motion objects are 1, 2, 4 or 8 clocks/bit.
  • Motion objects may be replicated in hardware.
  • Playfield is 4 clocks per bit.
  • Playfield bits are either repeated or reflected
    in hardware.

Example Stella Game structure
  • In Vertical Blank
  • detect collisions and control inputs
  • decide new game conditions
  • computer new game graphics pointers
  • In Display, for each line or two
  • step graphics pointers
  • fetch graphics
  • wait for horizontal blank, and write graphics

Atari 2600 market history
  • 1st shown at June 1977 CES show
  • 250,000 sold in 1977, with 6 cartridges
  • 550,000 sold in 1978, but big unsold inventory
    (800,000 made that year).
  • Sales continued to double annually until the
    market collapse in 1983.
  • Est. sales over 50 million by late 1980s.

Atari 2600 Lessons
  • Make the hardware a flexible platform for clever
    developers. (Bill Joys theorem)
  • Good hardware-software tradeoffs make the product
    economically viable.
  • Real marketing is essential. This means that
    somebody has a clear vision of
  • who will buy the product
  • why they buy the product at all
  • why they buy the product from us

Colleen System Architecture (Atari 400/800, 5200,
65XE, etc)
  • Product requirements
  • Design choices
  • Hardware/firmware tradeoffs
  • Results
  • Lessons

Colleen requirements
  • Split requirements
  • support 1978 vintage arcade games. We knew we
    would need to leapfrog the 2600 before somebody
    else did.
  • support home computer character and bit map
    graphics. We saw the Apple II, Commodore and
    Radio Shack appliance machines coming.
  • Result
  • Atari 800 was full computer
  • Atari 400 was a game machine w/flat keyboard

Colleen computer requirements
  • Keyboard
  • Character graphics
  • Enough memory to run large programs.
  • Means to load programs from tape or disk.
  • Means for memory expansion
  • Means for peripheral expansion

Colleen game Requirements
  • Hardware drives the graphics, so that the CPU has
    time to do other things.
  • More moving objects.
  • Multi-colored character maps, so that complex
    playfields can be generated without large amounts
    of memory.
  • Playfield motion vertical and horizontal

Colleen System Architecture
  • 5 LSI parts
  • 6502 at 1.8 MHz, all address and interrupts
  • ANTIC Video address generator, etc
  • CTIA/GTIA video output
  • POKEY pots, keyboard, audio, serial bus
  • 6520 PIA simple 16 bits of parallel I/O
  • at least 4KB of DRAM (1st shipped w/8K)
  • 1-2 ROM cartridge slots
  • 4 game controller ports

Colleen Video architecture
  • 5 motion object generators
  • Display list processor generates playfield or
    character displays, on line-by-line basis.
  • Both graphics generators get DMA access, so they
    share memory with the 6502.
  • Maximum resolutions 320x240x1 in monochrome or
    160x240x2 in color
  • 8-bit palette registers 4 color, 4 luminance

ANTIC Display list modes
  • 8-bit instructions
  • 4-bit display mode
  • 2-bits scroll control
  • 1-bit interrupt request
  • 1-bit load new address
  • bit map modes 40x8x2 to 320x1x1
  • text modes 20x(8x8)x2 and 40x(8x8)x1
  • color characters 40x(4x8)x2

ANTIC player graphics
  • DMA from 5 fixed strips of 120 or 240 bytes of
  • Horizontal motion by writing a binary register
    (the way the programmers wanted Stella to work).
  • Vertical motion by erasing and rewriting the
  • Vertical reuse possible use Display list
    interrupts to rewrite horizontal positions.

More about playfield motion
  • Complex games may have a huge virtual playfield,
    windowed on the screen.
  • For each display instruction with horizontal
    scrolling enabled, ANTIC will load 192 pixels
    worth of data, and clip, controlled by the
    horizontal scrolling register.
  • For each display instruction with vertical
    scrolling enabled, ANTIC will clip that line,
    controlled by the vertical scrolling register.

Non-video I/O
  • Pokey supported 4 audio channels
  • Pokey supported 8 potentiometer inputs, sampled
    in hardware
  • Pokey scanned a keyboards, using commodity CMOS
    external muxes.

Colleen system issues
  • The most direct competitor was the Apple II
  • The Apple II was not bundled with a TV RF
    modulator, so it was not regulated by FCC.
  • It could have slots! Peripherals were easy.
  • The 800 was cased in cast aluminum
  • The 800 had internal memory slots.
  • The 800 used a serial bus for external expansion,
    19,200 b/s. The peripherals had intelligence, so
    they were expensive.

Colleen in the market
  • First debut in 1979. Sold respectably but not
    near as well as the Apple.
  • FCC changed the rules in 1979 Class B
  • Commodore C64 jumped in with lower cost and more
  • Atari answered with 800XL, etc, but trailed Apple
    and Commodore (and Radio Shack)
  • Repackaged as pure game machine, 5200, competed
    with wealth of 2600 games.

Colleen Lessons
  • A personal computer has to have easy expansion,
    with lots of room for 3rd parties to add value
    (e.g. Apple II and IBM PC/AT family)
  • It appears to confuse things to sell a hybrid
    game console and crippled PC (e.g. Atari 400).
  • It was bad luck that the FCC didnt change the
    rules until after the Atari 800 shipped.
    Something like the 1200XL might have flown.

Amiga Lorraine System
  • Company founded by Dave Morse (Mattel marketing)
    and Jay Miner. I was badge 3.
  • Original product conception generate
    cartoon-quality video games.
  • Also a computer, with a built-in floppy driver
    for distributing games.
  • Commodore turned it into a color multi-media
    MAC in 1984, shipped in 1986.

Amiga System Architecture (Amiga 1000, Amiga
2000, etc)
  • Product requirements
  • Design choices
  • Hardware/firmware tradeoffs
  • Results
  • Lessons

Amiga computer requirements
  • Use a modern processor 68000 (w/o memory
    management unit)
  • Built in floppy drive, not built in hard drive.
  • 40 or more characters/line on TV, 80 or better on
    a monitor
  • GUI OS requirement added after Commodore purchase
    in 1984.

Amiga gaming requirements
  • Hardware assist for
  • common graphics operations
  • changing the hardware synchronous with the video
  • Foreground and background bit maps
  • Multiple motion objects
  • Multi-channel DMA audio
  • Loading games from floppy drive.
  • Interact with external video (disk, VCR, etc)

Amiga system design
  • 4 LSI chips
  • 68000 CPU, at 7.2 MHz
  • AGNUS address generator/DMA engine
  • DENISE video output chip
  • PAULA I/O chip
  • 256K DRAM minimum, 512K common
  • 2 game ports
  • Floppy drive

Amiga video design
  • Primary display is a set of bit plane engines.
  • Bit planes can be used as a set of 4, for
    16-color displays, or in two sets of 3 and 3, for
    an 8-color foreground (or motion objects) and an
    8-color background.
  • 8 identical sprite engines.
  • Palette registers are 12 bit 4 each RGB, or 4
    each color, saturation and luminance

Amiga bit blitter detail
  • Automates common graphics operations
  • line draw
  • area fill
  • splicing and manipulating images
  • Bit blitter
  • 3 input images, 1 output image
  • 2 input images can be barrel shifted
  • any arbitrary operation can be performed,
    selected by 8-bit mask.

Amiga sprite engines
  • Each engine reads a string of 16-bit words in
  • The first words specify top left corner and size.
  • Subsequent words are data (16 x 2 bits/line)
  • Sprites can be reused to the end of the screen.

Amiga Audio
  • 4 DMA channels
  • 8 bits/sample
  • adjustable sample rate
  • sample table in memory can be from 2 bytes
    (square wave) to 8192 bytes.
  • Separate pointers each chunk of audio can come
    from anywhere in memory.

Amiga System Issues
  • The first version would have looked like the
    Amiga 500, with 128K of DRAM and no GUI OS, and
    shipped in 1984.
  • Amiga ran out of money, which slowed development.
  • Commodore bought it in June of 1984.
  • Commodore repositioned it as a color multimedia
    MAC-like PC

Amiga in the market
  • The Amiga 1000, loaded with computer options,
    shipped in 1986. Competitors
  • IBM PC/AT and clones
  • Mac, with color
  • Atari ST
  • It was the best multi-media computer of its time,
    but it had a distinct market only for video
    production (with the Video Toaster)
  • It became a cult favorite, but a market failure.

Amiga lessons
  • Again, clear product focus matters a lot
    competent marketing people working with engineers
    who listen.
  • Bad luck matters the collapse of the video game
    business in 1984 poisoned the well financially
    and prospectively. Otherwise, we would play
    Amiga consoles instead of the NES in the
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