PETProject

A Commodore 64–native IDE for BASIC and 6502 assembly.

PETProject is a full-featured integrated development environment that runs directly on a stock Commodore 64 with a 1541 disk drive. Write, edit, assemble, disassemble, and renumber code without ever leaving your C64 — no cross-assembler, no modern PC, no special hardware required.

🕹️ Download a ready-to-run disk image: https://gopherbrokesoftware.com/petproject

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Table of Contents

• Features
• Quick Start
• Keyboard Reference
• Modules
• Building From Source
• Source Layout
• Documentation
• Tips
• License & Credits

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Features

• 🖊️ Full-screen PETSCII editor backed by gap-buffer storage (up to ~24 KB of source)
• 🌈 Syntax highlighting for both BASIC 2.0 and 6502 assembly
• ⚙️ Built-in two-pass assembler — turn your source into runnable machine language
• 🔍 Built-in disassembler with full illegal-opcode support; runs automatically when you open an ML file
• 🔢 Line renumbering that also fixes GOTO/GOSUB targets
• 💾 Disk utility — browse the directory, load files, delete, rename, format, and send raw drive commands
• 🔎 Search & replace with toggleable case sensitivity
• ⌨️ Keyword completion — press TAB to cycle through completions
• 📜 BASIC scripting engine with extended keywords to automate the IDE (REU required)
• 🧰 Many quality-of-life touches that make coding on a real C64 pleasant
• 📦 Fully self-contained — runs perfectly on a stock C64; an REU is optional and used only by the scripting subsystem

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Quick Start

1. Grab the disk image (petproject.d64) from the download page, or build it yourself.

2. Insert it into drive 8 (in VICE or on real hardware).

3. Load and run:

   LOAD"*",8
   RUN

   (Or use your emulator's autostart feature.)

That's it — you're in the editor. Press F8 to open the module picker, or start typing to write some BASIC.

💡 Tip: Your experience will be much smoother with a fastloader cartridge.

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Keyboard Reference

Key	Action
F1	Settings — colors, data-drive number, cursor blink
F2	Page Up
F3	Load a file (BASIC, assembly, or compiled ML)
F4	Page Down
F5	Save the current file
F6	Load a SEQ (plain text / source) file
F7	Quit to BASIC
F8	Open the module picker (see Modules)
CTRL+F	Find / replace
CTRL+L	Force a full screen redraw
CTRL+N	New file (clears the buffer)
CTRL+R	Run Script (shortcut for F8 → Run Script)
TAB	Cycle keyword completions
Cursor keys	Navigate
INST/DEL	Delete the character left of the cursor

ℹ️ The program disk must stay in drive 8; the data drive is configurable in Settings (F1). If you try to do something destructive (new file, load, quit) with unsaved changes, the IDE prompts you to save first. During long-running tasks it flashes the top-left character so you know it's working, not frozen.

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Modules

Reach these from the module picker (F8):

Module	Purpose
Assemble (MODASM)	Two-pass 6502 assembler — compiles the current buffer to ML
Disassemble (MODDIS)	6502 disassembler; runs automatically when loading an ML file
Renumber (MODREN)	Renumbers BASIC lines and updates GOTO/GOSUB targets
Disk Utility (MODDSK)	Directory browser, delete, rename, format, raw commands
Run Script (MODSCT/MODSCR/MODSCRH)	Run BASIC automation scripts with extended keywords (REU required)

Search & replace (MODSFR) is available directly via CTRL+F.

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Building From Source

Requirements: the cc65 toolchain (ca65 + ld65, v2.19 or newer) and Python 3.

# Build the editor, all modules, and the .d64 disk image
bash make_petproject.sh

To build only the modules:

bash build_modules.sh

To (re)create the disk image manually:

python3 make_disk.py --build-dir build --name petproject --id pp petproject.d64

⚠️ make_petproject.sh ends with an optional line that launches VICE (x64sc). Edit or comment out that path to match your setup. See the script's comments for the full ca65/ld65 invocations, which you can override with the CA65 and LD65 environment variables.

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Source Layout

Editor core

File	Description
editor.asm	Main editor: entry point, main loop, rendering, input
colorize.asm	Syntax colorizer (included by editor.asm)
loadsave.asm	File I/O (included by editor.asm)
modules.asm	Module-loader framework (included by editor.asm)
petproject.cfg	Linker config for the editor PRG

Modules

File	Loads at	Description
modasm.asm	$A000	Assembler
moddis.asm	$A000	Disassembler
modren.asm	$C000	Renumber
moddsk.asm	$C000	Disk utility
modsfr.asm	$C000	Search / replace
moddet.asm	—	Detokenizer (hidden; runs on BASIC load)
modtok.asm	—	Tokenizer (hidden; runs on BASIC save)
modsct.asm	—	Script tokenizer (hidden; runs on Run Script)
modscr.asm	$A000	Script runner stub
modscrh.asm	$C000	Script handler (stays resident during scripts)

Linker configs: module.cfg (default $C000), modasm.cfg ($A000), moddis.cfg, modsfr.cfg, modscr.cfg, modsct.cfg.

Build tooling: make_petproject.sh (full build), build_modules.sh (modules only), make_disk.py (creates the .d64 image).

Reference: Resources/basic.asm and Resources/kernal.asm are annotated ROM disassemblies kept for reference.

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Documentation

In-depth manuals live in the docs/ directory:

• Editor manual
• Assembler manual
• Renumber manual
• Script runner manual

Security policy: SECURITY.md.

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Tips

• Use a fastloader cartridge for a much snappier experience.
• Keep the program disk in drive 8; point Settings (F1) at a separate data drive if you have one.
• The scripting engine needs an REU for script tokenization and IDE snapshots.

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License & Credits

Released under the MIT License — see LICENSE.txt.

PETProject was designed and built by Thomas Knox / Gopher Broke Software.