Of the machines from the 16-bit era, the Commodore Amiga arguably has the most active community decades later, and it’s a space which still has the power to surprise. Today we have a story which perhaps pushes the hardware farther than ever before: a demo challenge for the Amiga custom chips only, no CPU involved.
The Amiga was for a time around the end of the 1980s the most exciting multimedia platform, not because of the 68000 CPU it shared with other platforms, but because of its set of custom co-processors that handled tasks such as graphics manipulation, audio, and memory. Each one is a very powerful piece of silicon capable of many functions, but traditionally it would have been given its tasks by the CPU. The competition aims to find how possible it is to run an Amiga demo entirely on these chips, by using the CPU only for a loader application, with the custom chip programming coming entirely from a pre-configured memory map which forms the demo.
The demoscene is a part of our community known for pushing hardware to its limits, and we look forward to seeing just what they do with this one. If you have never been to a demo party before, you should, after all everyone should go to a demo party!
Amiga CD32 motherboard: Evan-Amos, Public domain.
This was actually copied from arcade machines and other game consoles, when the company first intended to make the machine into a game console. The chipset would have been the “CPU” of the machine and where the 68000 CPU sits would have been a ROM chip in a game cartridge, with the optional extra CPU with its own memory.
The designers pivoted it into a personal computer by doing exactly that: instead of a cartridge, a 68000 CPU and memory. That’s why there’s two memory buses and two different types of RAM. and the custom chipset sits in the midde of it.
If they had made it into a personal computer to begin with, they would have gone PC style with a common backplane bus between memory, CPU, and additional hardware, with the chipset present as an “accelerator” card.
The way it was originally supposed to work. The boot ROM initializes the chipset to read off the game ROM and then Bob’s your uncle. They’re just starting with the data in chip RAM.