Aonic brings the magic of Sonic to Amiga: Green Hill Zone demo now available

In 1991, Sonic the Hedgehog was released for the Mega Drive, Sega's answer to Nintendo's Super Mario. Unlike the game starring the world's most famous Italian plumber, Sonic was a platformer built around speed and visual spectacle.

As an Amiga owner, I could not help feeling a little jealous of those who owned Sega's 16-bit console, and one question came almost automatically: could my beloved computer ever run something like that?

At one point, it looked as if an answer might actually arrive. In an issue of TGM, The Games Machine, that I can no longer identify today, I remember reading a rumour that Virgin was trying to strike a deal with Sega to bring some of the Japanese company's classics to Commodore's machine. Games such as Streets of Rage and, of course, Sonic.

I never heard anything about it again, and that dream slowly ended up in a drawer.

In November 2025, REASSEMBLER, already known for OutRun: Amiga Edition, announced that he was working on a port of Sega's mascot. Thirty-four years had passed since the first time I saw the blue hedgehog at a friend's house. That announcement immediately took me back to those days and to the endless arguments about which system was better. Suddenly, that old desire to prove that the Amiga was not necessarily inferior started to take shape again.

Just one month later, RetroRic released his own version of Sonic's first level, recreated with the well-known Scorpion Engine. At the same time, he explained that he was already busy with several projects and that continuing his Sonic experiment would make little sense, since REASSEMBLER was taking a completely different approach: a dedicated port of the original Mega Drive code, adapted directly to Amiga hardware without using the Scorpion Engine.

RetroRic's demo was already a tasty preview of what we would see only a few months later and, as REASSEMBLER himself explained, his contribution would remain valuable, especially in the complicated work of adapting the graphics and reduced colour palette for the Amiga version.

REASSEMBLER'S PROJECT

Unlike his previous project, OutRun: Amiga Edition, REASSEMBLER made it clear from the beginning that Sonic's target machine would be a vanilla Amiga 1200.

No accelerator cards, no Fast RAM. That would have made things too easy.

Sonic had to run on AGA with just 2 MB of Chip RAM.

The Amiga 1200 was released in 1992 and, unlike the Amiga 500 and Mega Drive, used a Motorola 68EC020, a more advanced processor from the same 68k family. The AGA chipset could also handle far more colours on screen.

So, would porting Sonic be easy?

Not at all.

Sega's console was designed specifically around 2D graphics, with an architecture based heavily on tiles and hardware sprites. The Amiga instead used bitmap graphics organised into bitplanes, with the Blitter and Copper playing an active role in handling and composing the image.

Chip RAM, however, was also shared with the processor and the other custom chips, creating constant competition for memory access. One of the main bottlenecks of the Amiga architecture.

Two completely different philosophies.

To bring Sonic to Amiga, REASSEMBLER also had to modify some of the tools used to work with the original game's data. A modified version of SonicLVL can convert Mega Drive tiles and levels into the format used by the Amiga engine.

The foreground uses five bitplanes which, combined, allow a total of 32 colours shared between scenery and sprites. The background uses another 16 colours and linked AGA sprites to reproduce the parallax effect.

Everything moving around the screen creates another major challenge. On Mega Drive, Sonic himself is built from several hardware sprites. On Amiga, many equivalent elements have to be handled through the Blitter, with completely different hardware costs.

There is also the need to restore whatever sits behind an object after drawing it, otherwise the BOBs would simply remain printed on screen.

These problems gave the programmer more than a few headaches and started a long process of experiments, optimisations and compromises.

THE NON-NEGOTIABLE TARGET OF 50 FRAMES PER SECOND

The reference system for the entire project is PAL which, as we all know, runs at a refresh rate of 50 Hz. REASSEMBLER developed a profiler capable of measuring Chip RAM bus usage through the so-called "colour clocks".

The biggest problem is not the individual frame itself, but the resources needed to keep everything moving when the scene becomes busy. If the required workload exceeds the time and bandwidth available to complete the frame, the game can immediately drop from 50 to 25 fps.

And for Sonic, a character whose defining feature is speed, that is like cutting his legs off.

One of the most significant optimisations involved the main sprite itself. On Mega Drive, the character is built from three or four hardware sprites. Initially REASSEMBLER preserved this structure, but on Amiga it proved too expensive.

He therefore precomposed Sonic's animation frames, sacrificing around 167 kB of Chip RAM. The measured result was a 38% improvement in sprite rendering, a 4% reduction in overall frame time and, most importantly, 13% fewer dropped frames.

Other solutions make much more aggressive use of the Amiga's peculiarities. Static elements of the scenery, such as rocks, spikes and parts of the bridge, can be incorporated directly into the playfield when they enter the visible area, avoiding the need to erase and redraw them constantly.

A revision of the Copper list reduced frame time by 8.4%, while selective use of the mode known to Amiga developers as Blitter Nasty reduced dropped frames by another 11% in REASSEMBLER's tests.

Those numbers describe the nature of the project very well. There is no single trick capable of magically turning an A1200 into a Mega Drive.

The port moves forward by accumulating small and large gains, reducing unnecessary transfers, precalculating data, using Chip RAM where it makes sense and changing some of the architectural choices of the original game whenever they become too expensive on the Amiga.

SO, CAN THE AMIGA RUN SONIC OR NOT?

The answer comes directly from the playable demo released by REASSEMBLER on his official itch.io page.

Aonic, the name eventually given to the project, lets us run Sonic through Green Hill Zone Act 1 directly on our Amiga 1200s.

You read that correctly.

The downloadable ZIP file weighs just 286 kB and contains an ADF that can be loaded on original Commodore hardware through a Gotek drive, not just through emulation in WinUAE.

And I have to admit, seeing it running makes quite an impression.

Of course, some compromises are immediately visible. The transparent HUD of the Mega Drive version has been moved to the top of the screen inside a bar that takes up part of the visible area. The game also loses a few pixels horizontally.

But Sonic the Hedgehog is there, right in front of our eyes, faithfully reproduced by the Commodore machine that thirty-four years ago could only dream of having a game like this.

Without wanting to spoil the party, however, I also have to point out that this is still a demo. For now, it makes no claim that the entire game could be converted while maintaining the same quality.

REASSEMBLER himself urges caution and reminds us that the project is still in development. Many elements still need to be implemented, first of all music and sound effects. The current demo is completely silent.

But after months of video updates, discussions about working around limitations and finding ways to make the most of the Blitter and Copper, Sonic has finally arrived on our Amiga 1200s.

And that may not be the end of it.

Perhaps one day it could even reach ECS and OCS machines. The Amiga community is free to dream again, but this time we have something more than speculation.

The answer to the question I asked at the beginning is all there, inside those 286 kB.