tm20

ESC/POS for Epson TM-T20 printers, proven on the TM-T20III (04b8:0e28). Protocol, typesetter, markdown. There is no printer builder and no CUPS.

Pinned to nightly-2026-08-15 (rust-toolchain.toml), same dated nightly as bumbledb. Edition 2024. cargo clippy --workspace --all-targets -- -D warnings is the lint gate (all + pedantic, unsafe_code = deny).

Three library crates and a CLI, 0BSD, one workspace. Nothing is published; the repo is the distribution.

The tm20-set binary lives in tm20-cli so markdown can depend on the typesetter without a crate cycle.

• tm20 — protocol. A Document of Command values encodes to bytes; a Transport writes them. USB, serial, TCP. Command::Text is CP437. The printer never sees a font. cargo run -p tm20 is the protocol CLI.
• tm20-set — typesetter. A Sheet of Frames (flush left, Vignelli sizes, leading on an 8-dot grid) compiles to one or more tm20::Graphics (each GS ( L) payload is at most 910 dots tall at tape width). OpenType lives here as bytes. Which face those bytes came from is the program that prints, not the library.
• tm20-md — CommonMark 0.31.2 plus pipe tables, task lists, autolinks, footnotes, and LaTeX math (\(inline\), \[display\]), walked into a Sheet. Dollars stay currency. comrak and RaTeX live here. This crate does not depend on tm20.

tm20-set depends on tm20. Never the reverse.

use tm20::{encode, Command, Document, Transport, Usb};

let doc = Document::new(vec![
    Command::Init,
    Command::Text("SYSTEM ONLINE".into()),
    Command::Feed { lines: 3 },
    Command::Cut,
]);
Usb::open(None)?.write(&encode(&doc)?)?;

This is one encoding per job. Commands the T20 firmware ignores or that have a newer replacement stay unrepresentable. Other 80 mm Epson TMs that speak the same modern subset (GS ( L, function-B barcodes) should work; USB open is hardcoded to the T20III product id until someone adds another.

cargo run -p tm20 -- hello
cargo run -p tm20 -- test all          # skip --wait if bulk IN is dirty
cargo run --bin tm20-set -- print ticket
cargo run --bin tm20-set -- print helvetica
cargo run --bin tm20-set -- print md path.md
cargo run --bin tm20-set -- print md crates/tm20-md/fixtures