lsim and ldraw

Huh. I've never really talked about lsim here. Strange since I'm fairly pleased with it. I made an allusion to it here, but didn't really talk about it.

Hmm ... maybe it's because it's a pretty niche project - of no particular use to anybody except me.

HAH! Like that's ever stopped me!

LSIM

Lsim is a hardware logic simulator. You specify a set of devices, like NAND gates, latches, LEDs, and switches, and specify how they connect. Lsim then simulates the circuit. The non-NAND logic devices are simply composites of NAND gates; my goal is to design a simple CPU using only NANDs.

It's a tool that only I could love. There's no GUI. No blinking lights. No wave forms. It's pure text, both input and output. It's a pain to describe the circuit with the little language I devised, and it's a bigger pain to interpret the output to see if it does what it is supposed to. I'm so proud.

Some day I might make a blog post about its internals - it has a few interesting aspects - but let's skip that for now.

Anyway, my biggest problem has been interpreting the output of LSIM. I find I need to look at a properly-drawn circuit diagram so that I can visually trace signals and verify that the printout is doing what I want. But drawing logic circuits is hard, and it's even harder to ensure that the diagram matches the circuit given to lsim.

LDRAW

So I started the ldraw project. This is a GUI drawing tool that is interesting (or boring - you decide) for these reasons:

• It only lets you use the devices that lsim supports.
• It's Javascript that lives inside a single html file and runs in the chrome browser.
• It was written by Claude.ai. I used the chat interface (Opus 4.6 in extended mode).
• I don't know Javascript, and I've never learned the libraries or environment of a browser. Sure, I could have learned it - what, maybe a week or two? - but I also have no interest in GUI work. I.e. it would be a chore. And this is my hobby; I avoid chore work whenever possible.
• So I "vibe coded" it, a term I don't like, but I don't like "hallucination" either. Coiners of new lingo don't come to me for advice.

I have not reviewed Claude's code, but Claude has. And, of course, I've tested it. Given the nature of the program, most bugs show up pretty quickly. After every major phase of development, I ask Claude to: "Perform a deep review for bugs, paying special attention to state management and potential opportunities to make the code more maintainable." Even though it just finished coding, it always finds a few things. One time it decreased code length by about 400 lines by replacing identical repeated code with a few helper functions.

I'll post a few interesting details about the methodology we used in a different post.

WHY NOT CLAUDE CODE?

I tried CC for a different project. It failed. I had asked it to take my lsim language and convert it to a netlist that lcapy could use. Seemed like an easy enough project. CC cranked for an hour or two (with me having to be there the whole time to tell it to keep going). It kept getting errors from lcapy, and having to reverse-engineer the lcapy code to understand why. At the end it declared success. I fired up lcapy with the resulting .sch file, and it was complete garbage.

Now maybe this was just a fundamentally hard problem, and the web interface could not have done any better. Or maybe I didn't use it well (it was my first time trying it). But I can tell you this: using CC wasn't particularly fun. I enjoy the back-and-forth that the chatbot gives me. At the risk of over-anthropomorphizing a chatbot, it feels collaborative instead of directive. It even sort of laughs at my jokes.