POLYBIUS — Reproduction Project Specifications

A period-authentic reproduction arcade cabinet inspired by the Polybius urban legend. Designed as a conversation piece and functional game unit for hackerspace/makerspace environments. Not intended as a forgery — a loving, technically accurate homage to the golden age of arcade hardware.

• Standard Midway/Atari upright cabinet style, common 1981 form factor
• Slightly worn finish — chipped paint, faded marquee, authentic patina
• Cabinet door: glass window panel to expose internal hardware for viewing
• Worn joystick surround and button bezel
• Coin mechanism (functional or non-functional)
• Slightly faded/flickering fluorescent marquee backlight
• Period correct speaker grille cloth
• Subtle 60Hz hum from power supply — a feature, not a bug

• Wells-Gardner or equivalent CRT raster scan monitor
• Period correct curved glass face
• Authentic phosphor glow and visible scan lines
• Slight screen burn-in pattern (simulated or natural)
• No LCD substitutes — CRT only for authenticity

• Green PCB, no copper fills — bare, utilitarian government look
• 100% THT (through-hole) components — no SMD
• Lead solder — 60/40 tin-lead, period correct
• Components socketed where appropriate (EPROMs especially)
• Edge finger connectors for board interconnects
• Molex connectors for power and larger harnesses
• JST connectors for smaller signal harnesses
• Flat ribbon cables between boards
• Test points placed at natural locations:
  • CPU clock line
  • Reset line
  • Sound chip output before amplifier
  • Video sync signals (H-sync, V-sync)
  • Power rails (+5V, +12V, GND)
  • EPROM chip select lines
  • Audio amplifier input/output
• Silkscreen: SRI International logo
• Silkscreen: "PROPERTY OF US GOVERNMENT"
• Government-style serial number format (e.g. SRI-GOV-1981-XXXX)
• Slight oxidation on edge connectors — period authentic

• Zilog Z80 or Motorola 6809
• 6809 preferred for its clean architecture and West Coast developer familiarity
• Period correct clock speed (1-4 MHz)

• Intel 2732 EPROMs (4KB each)
• Approximately 10 chips for ~40KB total
• Chips in DIP-24 sockets — swappable, mysterious looking
• UV-erasable quartz windows visible on chips
• Hand-labeled chips with government-style markings

• Period correct 4116 or 4164 DRAM chips
• Or 6116 SRAM for simpler design
• Fully socketed

Primary sound chip (choose one or combine):

• GI AY-3-8910 — period perfect, built-in noise generator, flexible
• Yamaha YM2149 — AY-3-8910 compatible, excellent quality
• TI SN76489 — dead-on period correct
• Namco 54XX — late 1982, acceptable within reproduction window

Secondary/supplemental:

• HC-55516 (CVSD) — for distorted, unsettling voice/speech elements
• Adds genuine psychological unease — period correct (Williams hardware)

Audio output:

• Period correct small speaker
• Slightly tinny cabinet acoustics
• Simple transistor or LM386 amplifier circuit
• Test point at amplifier input and output

Sound palette (not strictly locked, period appropriate):

• Square waves
• Sawtooth approximations
• Sine-like tones via DAC or filtered output
• White/pink noise
• Occasional distorted CVSD voice fragments

Language: C — West Coast / K&R Dialect

West Coast C grew from UC Berkeley's BSD Unix culture, geographically and culturally close to SRI International in the San Francisco Bay Area. It contrasts with Bell Labs (East Coast/AT&T) C in attitude: terse, clever, slightly cavalier, and deeply Unix-influenced. Code was expected to be read by people who already knew what they were doing. Comments were considered a sign of weakness.

Key influences:

• Bill Joy (vi, csh, BSD) — terse, fast, ship it
• Ken Arnold (curses library) — clean but minimal
• Unix philosophy — do one thing, do it well, use pipes
• SRI hacker culture — adjacent to Stanford, ARPA funded, brilliant and secretive

K&R function declarations, named after Brian Kernighan and Dennis Ritchie, represent an older style of defining functions in C. This method does not specify parameter types in the function declaration itself, which can lead to potential issues in type checking.

K&R Function Declarations — not ANSI prototypes:

/* update player position and state -- sn 1982 */
update_player(x, y, flg)
int x, y, flg;
{
    register int d;
    d = flg & 0x1 ? -1 : 1;   /* inversion active? */
    px += d * x;
    py += d * y;
}

Implicit int, terse names, no ceremony:

/* no return type = implicit int, West Coast standard */
chk_bounds(x, y)
int x, y;
{
    return (x < 0 || x >= XMAX || y < 0 || y >= YMAX);
}

Bitwise tricks instead of multiply/divide:

/* multiply by 8 -- never use * on this hardware */
#define TILE(x)   ((x) << 3)

/* fast modulo power of 2 */
#define WRAP(x,n) ((x) & ((n)-1))

/* check if level is odd -- controls inversion phase */
#define ODD(n)    ((n) & 1)

Register keyword used liberally:

render_tunnel(lvl, frame)
int lvl, frame;
{
    register int i, j, d;
    register char *p;

    p = vram_base;
    d = inv_active ? -1 : 1;   /* direction flipped? */
    for (i = 0; i < ROWS; i++) {
        for (j = 0; j < COLS; j++) {
            *p++ = tunnel_lut[lvl][WRAP(i + frame, 16)];
        }
    }
}

Terse, almost hostile comments:

/* invert ctl -- per spec */
inv_ctl(flg)
int flg;
{
    ctl_state ^= flg;   /* xor flip bits */
}

/* dont call this twice -- sn */
init_hw()
{
    *(char *)0xC000 = 0;   /* reset sound latch */
    *(char *)0xC001 = 0xFF; /* enable all channels */
}

Inline assembly for critical loop (6809 example):

/* too slow in C -- asm for scanline fill */
fill_line(addr, val, cnt)
char *addr;
int val, cnt;
{
#asm
    LDX  addr
    LDA  val
    LDB  cnt
LOOP:
    STA  ,X+
    DECB
    BNE  LOOP
#endasm
}

Pointer arithmetic showing off:

/* blast sprite to vram -- no memcpy on this target */
blt(dst, src, n)
char *dst, *src;
int n;
{
    while (n--)
        *dst++ = *src++;
}

Global state, minimal structure:

/* globals -- West Coast didn't believe in hiding state */
int  px, py;        /* player pos */
int  plives;        /* lives remaining */
int  lvl;           /* current level */
int  score;
int  ctl_state;     /* bitmask: bit0=inv_x, bit1=inv_y */
int  inv_tmr;       /* inversion countdown */
char inv_active;    /* nonzero if controls flipped */

The Polybius inversion logic — West Coast style:

/*
 * ctl -- read joystick, apply inversion if active
 * returns dx,dy via pointers -- sn/jb 1982
 */
ctl(dx, dy)
int *dx, *dy;
{
    register int raw, d;
    raw = *(char *)JOY_PORT;
    d   = inv_active ? -1 : 1;
    *dx = d * ((raw & JOY_R) ? 1 : (raw & JOY_L) ? -1 : 0);
    *dy = d * ((raw & JOY_D) ? 1 : (raw & JOY_U) ? -1 : 0);
}

Additional West Coast style notes:

• No function prototypes — declaration order matters, caller beware
• char used freely as small integer to save RAM
• Manual memory layout — developer knows exactly where every byte lives
• No standard library — roll your own strlen, memset etc.
• Magic numbers preferred over named constants in hot paths
• Occasional unexplained /* ?? */ comment left in deliberately
• One or two intentionally cryptic variable names — authenticity detail

Target size: ~40KB across EPROMs ~12,000 lines of C code

Single player only

Influences:

• Cube Quest (1983) — vector/polygon style 3D
• Tempest (1980) — tube shooter, edge-of-screen movement
• Tron (1982) — grid aesthetics, geometric environments

Core Mechanic:

• 11 levels of increasing psychological intensity
• Geometric tunnel/grid environments
• Enemy patterns become increasingly erratic and unpredictable

The Polybius Twist — Control Inversion:

• At unpredictable moments controls flip:
  • Up becomes Down
  • Left becomes Right
  • Fire may reverse or misdirect
• Player must adapt or fail
• Frequency of inversion increases with level progression
• Designed to disorient — faithful to the legend

Visual Style:

• Psychedelic color palette shifts between and during levels
• Color cycling inspired by:
  • Moebius (Jean Giraud) — geometric, clean, cosmic
  • H.R. Giger — biomechanical undertones, dark geometry
  • Roger Dean — flowing, surreal environmental shapes
• Strobing and pulse effects (consider photosensitivity disclaimer on cabinet)
• Grid warping effects
• Tunnel/vortex perspective shifts

Audio Design:

• Tangerine Dream / John Carpenter influenced atmosphere
• Dissonant tones during control inversion moments
• HC-55516 voice fragments — barely intelligible
• White noise bursts at key stress moments
• Sound deliberately designed to be slightly unsettling

Cabinet exterior:

• Minimal, stark side art — geometric, Moebius-influenced
• No cheerful arcade colors — dark, governmental
• Small, slightly cryptic marquee

PCB markings:

• SRI International logo (silkscreen)
• "PROPERTY OF US GOVERNMENT"
• "UNAUTHORIZED DUPLICATION PROHIBITED"
• Date code: 1981 or 1982
• Government contract number format

Documentation (for display):

• Laminated "technical manual" pages in period typewriter font
• Fictional government memo referencing the project
• Adds to the narrative for hackerspace visitors

• Period correct linear power supply (no switching supply)
• +5V, +12V rails
• Contributes to authentic 60Hz hum
• Proper fusing, period correct

• Period correct Panasonic capacitors throughout
• Source vintage NOS components where possible for authenticity
• New Nichicon/Panasonic acceptable where NOS unavailable
• EPROM burner required for programming 2732 chips
• Cabinet can be sourced from a donor 1981-era cabinet and repainted
• Glass door panel retrofitted to standard cabinet door opening
• This is a novelty/showpiece — not a forgery — enjoy the craft!

The glass door shows the beautiful period correct PCB to visitors. What visitors don't see depends entirely on how the PCB is mounted.

The Approach:

• Period correct green PCB mounted face-forward, fully visible through glass
• PCB can be non-functional — purely decorative display board
• Behind the PCB, hidden from view, the actual game hardware runs

Hidden Modern Options:

The Sneaky Details:

• PCB mounted on standoffs — enough gap behind for a Pi or FPGA board
• Modern board powered from same supply, wiring hidden behind PCB
• USB from modern board connects to original-looking joystick/button harness
• CRT driven via GBS-8200 or similar scan converter from HDMI
• Audio from modern board through period correct amplifier circuit on display PCB

MiSTer FPGA Note: For the most authentic feel without full deception, MiSTer running a 6809/Z80 core is genuinely cycle-accurate — the hidden hardware is actually behaving like 1981 hardware, just on modern silicon.

Mounting Suggestion:

• PCB on 25-30mm standoffs from rear panel
• Modern board velcro or screwed to rear panel behind PCB
• Cable management with period-looking braided sleeving on visible runs

"What you are about to experience may cause dizziness, altered perception, and an inexplicable urge to play again."

Project Type: Hackerspace/Makerspace Showpiece Period: 1981–1982 Reproduction Status: Specification Document v1.0