A few months ago I was thinking again about Pavel Panchenka’s (LLM-assisted) “We’d be Better Off with 9-bit Bytes”, which posits that standardizing on nine-bit bytes would have saved us from a number of encodings running out of space while not having much of a downside. They’re even historically plausible given the PDP machines from DEC with 18-bit and 36-bit words. But what would the impact have been on small systems, those that got the most out of every byte, if not necessarily every bit?

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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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