README

Atari TOS ROM Splitter

Overview

A Lazarus/Free Pascal tool to split Atari TOS ROM files into smaller parts for backup, modification, or flashing. Supports Atari ST, STe, and TT ROMs with 2, 4, or 6 output files.

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Features

• Split ROMs into 2 parts (Atari STe), 4 parts (Atari TT), or 6 parts (Atari ST).
• Simple GUI for loading and splitting ROMs.
• Outputs files with standard extensions (.HI, .LO, .TT0, etc.).

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Requirements

• Lazarus 4 (or Free Pascal with LCL).
• Tested on Windows.

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Usage

1. Load a ROM

• Click "Load ROM" and select your TOS ROM file (e.g., tos206se.img).
• The filename and size will appear in the GUI.

2. Split the ROM

Choose the split option based on your Atari model:

Option	Typical Use Case	Output Files
Split into 2	Atari STe	.HI (even bytes), .LO (odd bytes)
Split into 4	Atari TT	.TT0, .TT1, .TT2, .TT3
Split into 6	Atari ST	.HI0, .HI1, .HI2, .LO0, .LO1, .LO2

How Splitting Works

• 2 parts: Even bytes → .HI, odd bytes → .LO.
• 4 parts: Every 4th byte → .TT0 (bytes 0,4,8,...), .TT1 (bytes 1,5,9,...), etc.
• 6 parts: Even bytes split into 3 → .HI0, .HI1, .HI2; odd bytes split into 3 → .LO0, .LO1, .LO2.

3. Verify Output

Use a hex editor (e.g., HxD) to check the split files:

• For 2 parts, .HI should contain bytes at offsets 0, 2, 4, ... and .LO should contain bytes at offsets 1, 3, 5, ...
• For 4 parts, .TT0 contains bytes 0, 4, 8, ..., .TT1 contains bytes 1, 5, 9, ..., etc.
• For 6 parts, .HI0/.HI1/.HI2 contain even bytes split into 3, and .LO0/.LO1/.LO2 contain odd bytes split into 3.

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Code Logic

Splitting

• 2 parts: Separates even/odd bytes.
• 4 parts: Treats the ROM as 512KB (pads with zeros if smaller) and splits into 4 interleaved chunks.
• 6 parts: Splits even/odd bytes, then splits each half into 3 parts.

Merging (Not Yet Implemented)

To merge split files back into a ROM:

1. Read all split files.
2. Interleave bytes in the correct order.
3. Save as a new ROM file.

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Example Workflow

Splitting for Atari STe (2 parts)

1. Load tos104.img (256KB).
2. Click "Split into 2".
3. Output: .HI, .LO.

Splitting for Atari ST (6 parts)

1. Load tos104.img (192KB).
2. Click "Split into 6".
3. Output: .HI0, .HI1, .HI2, .LO0, .LO1, .LO2.

Splitting for Atari TT (4 parts)

1. Load tos306.img (512KB).
2. Click "Split into 4".
3. Output: .TT0, .TT1, .TT2, .TT3.

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Notes

• Backup your ROM before splitting/modifying.
• If the ROM is <512KB, the tool pads it with zeros for 4-part splits.
• Merge functionality is not yet implemented in the GUI.

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Troubleshooting

• "File not loaded": Check file permissions and validity.
• Incorrect output: Verify the input ROM size and type (ST/STe/TT).
• Missing files: Ensure write permissions in the output directory.

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Future Improvements

• [ ] Implement merge functionality in the GUI.
• [ ] Add CRC checking for TOS 2.06.
• [ ] Support drag-and-drop for ROM loading.

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License

MIT