m68kasm

A compact, table-driven Motorola 68k assembler written in Go, targeting the full 68000–68060 family plus CPU32, an optional FPU, and a PMMU.

Current version: v1.4.0

The goal of this project is to provide a clean, maintainable, and easily extensible assembler for the 68k family — focusing on clarity, modularity, and full control over binary output. It is particularly well suited for educational use, embedded projects, and retro computing enthusiasts who prefer a minimal toolchain.

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🚀 Features

• Two-pass macro assembler with deterministic binary output
• Targets the full 68000/68008/68010/68012/68020/68030/68040/68060 family and CPU32, plus an optional FPU (68881/68882 or integrated) and PMMU (68851/68030+), selected via --cpu/--fpu/--mmu
• Embeddable directly into Go programs via a public API
• Output formats: flat binary, Motorola S-record, and ELF32 (m68k)
• Table-driven instruction encoding (InstrDef/FormDef/EmitStep), so adding an instruction is a data change, not new control flow

See docs/user-manual.md for the full CLI reference, what each --cpu/--fpu/--mmu flag unlocks, output-format details, and the complete Go API.

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🛠️ Installation

go install github.com/jenska/m68kasm/cmd/m68kasm@latest

Or build locally:

git clone https://github.com/jenska/m68kasm.git
cd m68kasm
go build -o m68kasm ./cmd/m68kasm

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⚙️ Quick Start

cat > hello.s <<'EOF'
        MOVEQ   #1,D0
        LEA     $2000,A0
        BRA     start
start:
EOF
m68kasm -i hello.s -o hello.bin
hexdump -C hello.bin

For every CLI flag, output-format details, and the Go API (go get github.com/jenska/m68kasm), see docs/user-manual.md.

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📁 Project Structure

cmd/m68kasm/              # Command-line frontend
internal/asm/             # Assembler pipeline (lexer, parser, evaluation, encoding)
internal/asm/instructions # Declarative instruction tables and helpers
docs/                     # Reference material: syntax, grammar, design history, opcode tables

• docs/user-manual.md — full CLI and Go API guide, start to finish
• docs/syntax.md — accepted assembly syntax and directives
• docs/design/cpu-family-support.md — full CPU/FPU/PMMU design history, scope decisions, and open items

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💡 Contributing

1. Fork the repository.
2. Create a feature branch.
3. Add or update tests for any change.
4. Run go fmt ./... && go vet ./... && go test ./... before submitting.
5. Submit a pull request — CI must pass.

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📄 License

Released under the MIT License. You are free to use, modify, and distribute the project with attribution.

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❤️ Acknowledgments

• Motorola M68000 Programmer's Reference Manual (3rd Ed.)
• Easy68k and vasm project maintainers for inspiration on encoding tables
• GNU binutils' GAS m68k backend, used throughout to cross-check encodings