Robin from 8-Bit Show and Tell takes a deep dive into a fascinating C64 project. This is not a clone. It’s not a port. Instead, it’s a near-true version of the original 1979 Asteroids arcade game—running on a Commodore 64.
In 2013, Norbert Kehrer created this impressive version. Rather than recreating Asteroids from scratch, he used Atari’s actual 6502 machine code. However, to make it run on the C64, he had to patch the code.
This adaptation converts vector graphics into raster bitmaps. It swaps arcade sound for SID-compatible audio and remaps control inputs. Surprisingly, 95% of the original code remains untouched. Robin proves this with real-time binary comparisons.
SuperCPU: Unlocking Full Performance
What really sets this version apart is its support for the SuperCPU. This rare 20 MHz accelerator boosts the C64’s performance dramatically.
Robin shows the game running slowly at 1 MHz (around 15 FPS). But once the SuperCPU kicks in, the game runs at a smooth 60 FPS. That’s unheard of for a raster-based C64 game.
Performance Boosts for C128 Users
If you don’t have a SuperCPU, don’t worry. The program includes special raster interrupts for the Commodore 128’s 2 MHz mode. These offer a decent performance boost. Unfortunately, NTSC C128 systems may crash. Robin is working on a fix and promises an update.
How the ROM Is Patched
Robin also breaks down the technical details. Using ROM disassembly, he shows how Atari’s ROM segments are loaded into RAM. Over 300 patch instructions are applied to redirect functions like graphics rendering, sound, and input handling.
For example, the fire button input is mapped from the joystick port to the arcade’s original RAM address. This action triggers bullets, sound effects, and visual updates.
Why This Version Stands Out
This project is more than emulation. It’s a hybrid of simulation, adaptation, and original code reuse. While not a textbook emulator, it delivers one of the most authentic Asteroids experiences ever on a C64.
Especially with a SuperCPU, this version brings near-arcade gameplay to a system never designed for it.
Final Thoughts
Robin’s technical breakdown is clear, fun, and informative. More importantly, it showcases the C64 doing something truly unexpected. Thanks to brilliant programming—and just a 5% patch—Asteroids lives again, almost exactly as it did in 1979.
