Amiga ROM Toolkit

A browser-based tool for analysing, patching, and validating Amiga Kickstart ROM images.

Features

• ROM Parser – Detects ROM size, base address, entry point, version/revision
• RomTag Scanner – Finds all Resident modules via $4AFC magic + self-reference validation
• Module Editor – Replace or remove individual modules; optional same-size padding
• ROM Assembler – Rebuilds a complete ROM with corrected RomTag pointers and checksum
• Validator – 8-stage validation pipeline (size, alignment, checksum, entry point, RomTags, required modules, pointer sanity, overlap check)
• Export – Download the assembled .rom file; export is gated behind a passing validator

Supported ROMs

Kickstart	Size	Base Address
1.2 / 1.3	256 KB	$FC0000
2.x / 3.x / 3.2	512 KB	$F80000

Setup

npm install
npm run dev

Then open http://localhost:5173 in your browser.

Architecture

src/
├── engine/
│   ├── RomParser.js       # ArrayBuffer → ROM descriptor
│   ├── RomTagScanner.js   # Resident structure scanner
│   ├── RomPatcher.js      # Pointer patching + checksum
│   ├── RomAssembler.js    # Module list → ROM binary
│   └── RomValidator.js    # 8-stage validation pipeline
├── hooks/
│   └── useRomToolkit.js   # Central application state
└── components/
    ├── FileLoader.jsx      # Drop zone
    ├── RomOverview.jsx     # Header metadata display
    ├── ModuleList.jsx      # RomTag table with actions
    ├── AssemblerView.jsx   # Layout preview + build trigger
    └── ValidatorPanel.jsx  # Stage-by-stage validation display

Validator Stages

#	Stage	Description
1	Size Check	Must be exactly 256 KB or 512 KB
2	Alignment	Length must be a multiple of 4
3	Checksum	Sum of all 32-bit words must equal 0xFFFFFFFF
4	Entry Point	Byte 0/1 must be 4E F9 (JMP); target within ROM
5	RomTag Scan	Each $4AFC candidate validated via rt_MatchTag self-reference
6	Required Modules	exec, dos, graphics, intuition, expansion must be present
7	Pointer Sanity	rt_Init and rt_Name must point within ROM address space
8	Overlap Check	No two module boundaries may overlap

Checksum Algorithm

1. Zero the last 4 bytes (checksum slot)
2. Sum all 32-bit big-endian longwords (mod 2³²)
3. checksum = (0x1_0000_0000 - sum) & 0xFFFFFFFF
4. Write checksum into last 4 bytes
→ Verification: sum of all longs including checksum == 0xFFFFFFFF

Important Notes

• Internal pointer relocation: Only the 6 RomTag header fields are patched when a module moves. Code-internal absolute pointers within module bodies are not adjusted. Use same-size padding (checkbox in Module Editor) to avoid this entirely.
• The assembler fills unused ROM space with 0x00.
• Export is only enabled when the assembled ROM passes all validation stages without errors.

License

MIT