71 lines
2.3 KiB
Markdown
71 lines
2.3 KiB
Markdown
# Circus Charlie
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## Status
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**Pass 1.** The project builds and verifies byte-identical to the
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original ROM (with branch-over-data adjustments). `prg.s` is a traced
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disassembly classifying bytes as reachable code or data, with every
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instruction carrying a trailing audit comment. Unreached bytes remain
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as explicit `.byte` blocks; no ROM byte is deleted or reformatted.
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`make` assembles `header.s`, `prg.s`, `chr.s`, links them with `ld65` and compares the
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result against `rom.nes`:
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```
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Byte-identical ROM verified.
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```
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## ROM
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| Property | Value |
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|----------|-------|
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| Format | iNES |
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| Mapper | 0 |
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| Board | NROM-128 |
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| Mirroring | Horizontal |
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| Four-screen VRAM | no |
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| Battery | no |
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| PRG | 16 KB (1 x 16 KB), mapped at CPU $C000-$FFFF |
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| CHR | 8 KB (1 x 8 KB) |
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| Trainer | none |
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| Footer | 127 bytes past the CHR |
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| NMI vector | $C05A |
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| RESET vector | $C000 |
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| IRQ vector | $C007 |
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| ROM file | `Circus Charlie.nes` |
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| SHA-256 | `e7925b67d577b8d05da01d935d9fe74b66f6487e18922f6c065647c5b13aa252` |
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### Header notes
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- 127 bytes follow the CHR; they are reproduced by the TRAILER memory area
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## Open work
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- **Pass 1** - run `nesdis.py` over `prg.bin` to produce the code/data
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split. The tracer reads the vectors from the last six bytes of the PRG
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image, so the split seeds correctly.
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- **Pass 1** must emit the canonical audit comment
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`; CPU:$C123 PRG:0123 AD 21 03` at column 35 for every instruction.
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- **Pass 2** - replace the address-derived `Label_XXXX` names and the raw
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`$XXXX` call operands.
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- **Pass 3** - semantic zero-page aliases (applied only at the sites where
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their role is proven) and named data tables.
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- **Promotion** to `NROM/<name>/` once Pass 3 is done, as `git mv`.
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## Files
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| File | Purpose |
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|------|---------|
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| `prg.s` | Pass 0 PRG include (replaced by the Pass 1 disassembly) |
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| `header.s` | iNES header include |
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| `chr.s` | CHR include |
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| `trailer.s` | footer include |
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| `prg.bin` | 16384 bytes (16 KB) PRG image |
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| `chr.bin` | 8192 bytes (8 KB) CHR image |
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| `trailer.bin` | 127 footer bytes |
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| `rom.nes` | byte-identical copy of the original ROM |
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| `linker.cfg` | HEADER / PRG / CHR / TRAILER memory areas |
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| `symbols.inc` | NES hardware register names |
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| `locals.inc` | zero-page aliases (empty at Pass 0) |
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| `Makefile` | build and byte-identity check |
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