A few weeks ago I got sucked into designing a toy 8-bit CPU, ROSE-8, and got as far as writing an emulator for the machine that you could manually feed instructions to. At the end, I listed some future projects, the first of which was

• An assembler/interpreter, i.e. running from a text file (and outputting to a binary file, I guess). Writing arrays of instructions by hand (as shown above) isn’t so bad except for manually computing addresses and offsets, so I still want to get to this at some point.

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In my last post I talked about how I was disappointed I wouldn’t be able to post my toy projects on GitHub, since GitHub supports ICE. I did get a few recommendations for other places to host Git repositories, but—at least partly inspired by Tom Ryder’s “Why Not GitHub?”—I decided to take the plunge and set up my own hosting. After all, these aren’t big collaborative projects; they’re “just” projects whose revision history I’m willing to share. In all cases so far, I’m the only author, even.

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or, “How I put too much time into making an 8-bit ISA and accompanying virtual machine”

It all started with my colleague Cassie having fun designing a toy 8-bit ISA (“instruction set architecture”). I love encoding tables (I helped out a little with the one for Swift’s String struct representation), and I did assignments in college involving simplified CPUs. So I started thinking about what it would be like to write a program in Cassie’s ISA…and decided its four registers were too limited for me. How could I get up to 8 registers while still keeping most of the instructions in a single byte?

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