[siraben]

This was made collaboratively by me directing coding agents at the binary, using Ghidra MCP extensively, disassembly and also dynamic analysis with an emulator. I don't have a writeup of the process but it was definitely not fully automatable (I wish though). I might prepare a blog post with transcripts and session history and things I learned along the way.

Broad takeaways:

- Ghidra MCP is not a silver bullet. Lots of opportunities for mis-decoding especially on older instruction sets (e.g. conflating code + data), which requires user input to flag data layout/structs.

- Agents still need a lot of user direction otherwise the RE production is just kind of a random walk. With Z80 it's decent at reading code but I expect that it has much worse performance than reading x86 or ARM for instance. The TI-84+ has a bunch of hardware quirks as well.

- GPT 5.5 is better than Opus 4.8 at RE. Opus 4.8 loves plausible-sounding RE'd logic without any checking. The gold standard is actually dynamically executing the binary and comparing the logic against the prose.

- Maintaining consistency in style and prose is a PITA across the wiki. Hard to reconcile prose <-> code. Can be somewhat mitigated by agent loops.

Was also in discussions with people in the TI calculator programming space who helped provide guidance as well. We previously did not have a catalogue of every subsystem in TI-OS yet alone most subroutines in the OS.

[RgrTheShrubbr]

Having just recently heard about Ghidra and started using it with Claude. I am absolutely blown away how little resistance it has decompiling old Win95/98 binaries. It's turning into a bit of a hobby of mine to take old software, decompile and find hidden treasures like images or messages.

[Chu4eeno]

There's this unfortunate common misconception (that LLMs luckily don't tend to share) that reverse engineering is illegal or immoral, when it's both a great source of learning, a necessity for things like interop/preservation, and even has explicit carve-outs in the copyright laws of many/sane countries.

I know my government has a good amount of reverse engineers on the payroll (mostly in the security services).

[hedgehog]

Do you have plans to generate a buildable version of the sources, and do you know the original implementation language (C?).

[siraben]

It's highly likely that the original implementation language was assembly. The code is very idiomatic.

Regarding source build, I think reverse engineering it to the point where you can reconstruct the source is possibly legally problematic, so I don't plan to do this, but maybe for certain subsystems like MathPrint (equation display) which was especially fun to RE. I have a PR up for it and it will be live at

https://siraben.github.io/ti84p-re/mathprint

[ndiddy]

Typically the approach taken by people who are concerned about legal issues regarding disassemblies is that they distribute a script file that contains all the code/data annotations, comments, variable names, and labels, and then the user can feed this file and a copy of the original binary into the disassembler to reproduce the disassembly. Here's a random example for a 6502 codebase: https://github.com/TakuikaNinja/FDS-disksys . IDA Pro has this functionality built in, you can export a .idc script file that will reproduce the .idb file if you load the original binary into a fresh instance of IDA Pro and then run the script. Maybe Ghidra has something similar, if not I bet you can get your AI to write export/import scripts for Ghidra.

[jamesfinlayson]

> It's highly likely that the original implementation language was assembly.

Agreed. I did a bit of development on a TI-84+ years ago and I was not a skilled programmer back then so only used TI-BASIC, but the fact you could only write apps in assembly makes me think the operating system was the same. ticalc.org had a gcc fork from memory though I don't recall which calculators it targetted.

[analogpixel]

how much have you spent so far on this (for tokens)?

[siraben]

The plans are heavily subsidized by the AI companies so I didn't end up needing to do API usage or buy another subscription. I have ChatGPT Pro and Claude Code Max.