asm816

A simple WDC 65C816 / 6502 assembler written in Rust.

Canonical syntax: ca65 (source of truth) https://cc65.github.io/doc/ca65.html

Goals

• Assemble 65C816 and 6502 source code into a raw .bin output.
• Stay close to ca65 syntax while accepting a practical subset of common 6502/65816 conventions.
• Provide clear, source-spanned error messages.
• Keep assembly readable by supporting a canonical, formatter-friendly style.

Non-goals (v1):

• No optimization.
• No object files or linking (raw .bin only).

Install

Requires a recent Rust toolchain.

git clone <repo-url>
cd asm816
cargo build --release -p asm816_cli

Usage

Assemble to a raw binary:

cargo run --release -p asm816_cli -- assemble path/to/main.s -o out.bin

Add include directories:

cargo run --release -p asm816_cli -- assemble path/to/main.s -o out.bin -I include -I vendor

Use module imports instead of .include:

; main.asm
import libs::constants
.org $8000
LDA #libs::constants::ONE

; libs/constants.asm
pub ONE = 1

Notes:

• module files map from roots as foo/bar.asm -> foo::bar
• pub controls cross-module visibility
• selective imports are supported: use foo::bar::{ONE, TWO as T}
• inner modules are supported: mod util { ... } -> <current>::util
• public macros are supported and expand at call site:
  • define: pub macro emit { LDA #ONE }
  • invoke: foo::macros::emit or via use ...::{emit} then emit
  • macro-local labels: %%loop
• .include is deprecated and now reported as an error

Set default 65816 register widths (used to size immediate operands):

cargo run --release -p asm816_cli -- assemble path/to/main.s -o out.bin --a16 --i16

Validate input without writing output:

cargo run --release -p asm816_cli -- check path/to/main.s

Format to canonical style (if available in your build):

cargo run --release -p asm816_cli -- fmt path/to/main.s

Exit codes

• 0 on success
• non-zero if any errors were reported