Last week a friend shared the existence of hlorenzi’s customasm, a tool that can serve as the assembler for arbitrary CPU architectures just by defining a mapping of instructions to encodings.

Hey, I made a CPU once! How hard would it be to make a customasm definition for ROSE-8? Turns out…not very! I played around with it for about two hours, and by the end of it I’d translated an entire ROSE-8 program to customasm, with most of the definition file looking basically the same as the text reference for the ISA encoding.

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When designing ROSE-8, I realized that the last 8-bit CPU architecture I had learned about was the Nintendo Game Boy, via Eevee’s Cheezball Rising series. That gave me a goal for ROSE-8: implement a system that could display graphics and receive real-time button presses, and thus play games. As I hinted last time, I did indeed manage to achieve this! Introducing the Game ’by Color (pronounced like “Game B Color”).

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