A retro‑hardware hacker group has published a reverse‑engineering of the TI‑84 Plus operating system. The team dumped the 1 MiB flash ROM, identified the OS version as 2.55MP, and built a Ghidra project that maps every address, system call and paging scheme. Their notes detail the Z80 CPU core, the 64 KiB logical window and the four‑slot flash/RAM paging that powers the calculator.

Internally the OS runs as a single‑tasking monitor. Page 0 holds the boot kernel, while the remaining flash pages host routines accessed via the “bcall” mechanism. RAM holds system state, floating‑point registers, display buffers and the Variable Allocation Table. The notes also unpack the floating‑point engine, TI‑BASIC tokenizer and the interrupt‑driven I/O subsystems. The bcall table spans both retail and USB boot routines, exposing entry points.

All documentation is organized into sub‑documents that dive into memory maps, paging logic, system calls and each user‑facing feature such as graphing, statistics and USB link protocol. Builders can regenerate the ROM image with the provided script, enabling emulators or custom firmware experiments. The project offers the most granular view yet of a classic educational calculator.