# CIRCUS — Skeleton Project

ROM: `_wip/CIRCUS/CIRCUS.NES` (24,592 bytes, iNES). Status: **SKELETON — not yet disassembled.** The entire 16 KB PRG bank is a single unclassified block; `copilot/prg.s` is the default-project skeleton (`default_project.tar.gz`) that reproduces it as one `.incbin`. The skeleton build is **byte-identical** at the PRG level.


## ROM Facts

| Property | Value |
|----------|-------|
| Mapper | 0 (NROM) — from the iNES header |
| PRG | 16 KB (header claims map at CPU $C000–$FFFF) |
| CHR | 8 KB |
| Mirroring | Horizontal |
| Battery-backed flag | clear |
| ROM SHA-256 | `608a8c542e49d5fa500634aa49ee96921d52c49c6e1646db7ca21ac7682ce4ba` |
| PRG SHA-256 | `e707fddce05efeb064b644b91b36969e4f4d7723db9965a1a1a85021a6a3da57` |

## Interrupt Vectors (taken from PRG $3FFA–$3FFF)

| Vector | Target | Note |
|--------|--------|------|
| NMI | `$C05A` | per-frame heartbeat |
| RESET | `$C000` | cold start at $C000 — the usual pattern in this repo |
| IRQ | `$4CB7` | $4CB7 is outside the mapped address space — effectively unused |

## `copilot/` Contents

| File | Purpose |
|------|---------|
| `CIRCUS.NES` | original ROM image (reference) |
| `prg.bin` / `header.bin` / `chr.bin` | split image, produced by `_tools/splitnes.py` |
| `prg.s` | Pass-1 skeleton: `.incbin "prg.bin", $0000, $4000` (whole PRG) |
| `symbols.inc` | shared NES hardware constants (PPU/APU/controller, from the skeleton) |
| `locals.inc` | project-local zero-page aliases — empty for now (filled in Pass 2) |
| `linker.cfg` | PRG at $C000, 16 KB, `fill = yes` |
| `Makefile` | links `reconstructed_prg.bin` and `cmp`s it against `prg.bin` |
| `reconstructed_prg.bin` | build output from the last verified build |

Header/CHR are reproduced verbatim from `header.bin`/`chr.bin` (not linked): `make` verifies **PRG bytes only** at this stage, which is exactly what a skeleton proves. When this project is promoted to a full disassembly, `header.s` / `chr.s` (as e.g. `Burger Time (U)`) and a full-ROM `make` target get added.

## Build

```bash
cd "_wip/CIRCUS/copilot"
make        # → cmp reconstructed_prg.bin prg.bin → "BYTE-IDENTICAL"
```

## Next Steps (per `PROMPTS.md`)

1. **Pass 1** — replace the blanket `.incbin` with classified code/data: trace reachability from RESET ($C000) and NMI ($C05A), emit per-instruction `; PRG:$xxxx AA BB` annotations, keep unreached bytes as explicit `.byte` blocks.
2. **Pass 2** — replace `Label_`/`Sub_` names with semantic routine names; fill `locals.inc`.
3. **Pass 3** — name data tables/structures; release provisional flags.
4. **Promotion** — move to a top-level `<name>/copilot/` folder, add full-ROM build (header.s + chr.s + vectors), and write the power-on flow `OVERVIEW.md` in the established style; then it joins the root index's numbered inventory.