Space Invaders Compatible Gateware Core for Analogue Pocket

This repo contains a gateware core compatible with the original 1978 Space Invaders arcade hardware written in SystemVerilog, optimized for the Analogue Pocket.

Features

• Cycle-accurate i8080: New, custom i8080 (i8085) core implementation in SystemVerilog, developed using a custom AI-assisted test-driven-development approach.
• High-Resolution Backdrops: Supports a 24-bit RGB backdrop image (at 512x448) with transparency for authentic mirror/overlay effects.
• Simulated Color Overlays: Translucent color overlay effects used in original arcade cabinets (White, Red, and Green bands).
• Discrete Audio Engine: High-resolution audio synthesis, using a combination of direct hardware simulation, and synthesized effects derived from spectral/temporal analysis of reference samples.
• Analogizer Support: Support for the Analogizer, enabling CRT output (RGB, Component) and SNAC controller support. See Analogizer Support for details.

Analogizer Support Details

The core includes integration for the Analogizer adapter, but users should be aware of the following technical constraints:

• 31 kHz / VGA Output Only: The core's video pipeline is natively upscaled to 2x (512x448) at a 20 MHz pixel clock to support high-resolution backdrops. This results in a horizontal frequency of approximately 31.25 kHz.
• CRT Compatibility: Due to the 31 kHz output, the Analogizer will only work with VGA monitors, PC CRTs, or multi-sync professional monitors (PVM/BVM) capable of handling 31 kHz signals.
• Unsupported Modes: Standard 15 kHz televisions using Y/C (S-Video/Composite) or standard Component connections are not compatible with this core in its current 2x scaled configuration.
• SNAC Support: Full support for SNAC controllers (NES, SNES, PSX, etc.) is provided and operates at the 20 MHz master clock rate.
• CRT Scanlines: A specialized scanline effect is available in the menu. This effect is applied exclusively to the CRT game layer (simulating the reflection from the CRT in the original cabinet mirror assembly) and does not affect the high-resolution background backdrop, ensuring authentic visual fidelity.

• DIP Switches: Adjustable settings for starting lives, bonus life thresholds, and coinage through the interact menu.

Architecture Overview

The core is built on a modular, performance-oriented architecture:

• CPU: A cycle-accurate Intel i8080 core running at 2MHz.
• Graphics Subsystem:
  • Core Timing: Strictly follows the original arcade hardware timings (5MHz pixel clock).
  • SDRAM Arbiter: A custom CDC-safe SDRAM arbiter manages high-bandwidth access between the 20MHz video pipeline and 100MHz SDRAM for background assets.
  • Video Effects Pipeline: A pipelined architecture handles real-time blending of monochrome game pixels, color overlays, and high-resolution SDRAM backdrops with alpha-blending support.
• Audio Engine: A parallel synthesis engine that uses digital logic to emulate the original hardware's analog sound circuits (SN76477, NE555, op-amp filters), featuring a 44.1kHz high-pass filter and anti-aliasing logic.

Installation

1. Copy the Cores, Platforms, and Assets directories from the dist folder to the root of your Pocket's SD card.
2. Generate the required invaders.rom file (see below) and place it in Assets/spaceinvaders/common/.

ROM Generation

This core requires a merged ROM file generated from original arcade assets. No ROMs are provided with this core. You must provide your own legally-obtained ROM files.

Requirements

• mratool (available on GitHub or as part of MiSTer utility suites)
• invaders.mra (located in the mra/ directory of this repo)
• Original Space Invaders ROM set (compatible with the MAME invaders romset)

Instructions

1. Place your invaders.zip in the same directory as invaders.mra.
2. Run the following command:

   mratool invaders.mra

3. The tool will output a file (typically invaders.rom).
4. Copy invaders.rom to Assets/spaceinvaders/common/ on your SD card.

Legal Disclaimer

No ROMs or copyrighted assets are provided.

Users are responsible for providing their own legally-obtained arcade ROM files. Space Invaders is a trademark of Taito / Midway. This project is not affiliated with, endorsed by, or sponsored by Taito or Midway.

AI Disclaimer

Significant portions of core IP, tooling, and other assets were developed with the assistance of generative AI. Do not use this codebase if this is incompatible with your use-case or principles.

License

• All IP modules originating with this project are licensed under the terms of the MIT license, and are labeled as follows:

  // SPDX-License-Identifier: MIT
  // Copyright (c) 2026, Obsidian.dev

• For all other modules, see the respective source-code headers.

Credits

• The MAME project for serving as a reference for Space Invaders technical reference documentation.
• The SingleStepTests project, which inspired the work to create the i8080 core.
• RndMnkIII for developing the Analogizer and supporting its integration into Analogue Pocket cores.
• Agg23 for providing various miscellaneous IP blocks used in this core.