-----
code: xyw
sourcehut: xyw
home: /xyw/
site: "https://xyw.2c.fyi"
title: "xyw"
subtitle: "A minimal virtual machine and assembler targeting terminals, inspired by Uxn."
summary: "xyw is a simple and minimal virtual machine and assembler inspured by Uxn, that aims at providing a low-level, future-proof way to create terminal applications."
content-type: project
active: true
version: 320-1
conver: true
branch: master
changelog: true
stage: prototype
license: MIT
-----

xyw is a specification for a minimalist virtual machine programmable via a concatenative, assembly-like language. It is implemented primarily as a [stack machine](https://en.wikipedia.org/wiki/Stack_machine), but it also provides four "registers" that can be used by most instructions by specifying dedicated modes, to reduce the need of stack juggling operations common to languages like Forth.

### Rationale

xyw is heavily inspired by [Uxn](https://100r.co/site/uxn.html) and its fork [Bedrock](https://benbridle.com/projects/bedrock Bedrock), but aims at being even simpler and easier to learn. In particular, it differs from Uxn because:

- its syntax is more minimalist: no runes or sigils except for . for directives, $ for hex numbers and % for binary numbers (all these are inspired by 6502 assembly syntax).
- it includes specific modes to operate on registers.
- it exposes more basic and simpler devices by default.
- it only exposes a single stack to the user (corresponding to Uxn's working stack).
- it has a concept of relocatable zero page (direct page), partly borrowed from 6809 assembly.
- it maps devices to addressable memory.

In a nutshell, if Uxn can be used to create small multimedia programs that could be running on low-end laptops and small gaming handhelds, xyw can create programs that could hypothetically run on the equivalent of a 1980s [pocket computer](https://en.wikipedia.org/wiki/Pocket_computer) or early terminal.

### Key Features

- up to 64KiB of addressable memory.
- two stacks, one used internally by the system to manage subroutines, and one accessible to the user.
- 32 instructions, each with up to three different modes to operate on registers and on 16bit values.
- Two 8bit registers called x and y, and two 16bit registers accessible via the w mode.
- Up to a maximum of 16 memory-mapped devices, each with up to 16 reserved bytes (like Uxn).
- Event-based operation, similar to Uxn.
- Direct page accessible via a single byte, set by default to the device page, that can be moved to different locations in memory.
- A few assembly-inspired directives, which are also used to implement labels.
- Support for integers expressed in hexadecimal or binary notation.