Chips › Processors › Fantasy & virtual CPUs › Uxn CPU
Uxn CPU
2021
A tiny stack-based virtual CPU by Hundred Rabbits, designed as a minimal, portable target for the Varvara computing ecosystem.
Uxn CPU Online Emulator
Play Uxn CPU using JavaScript directly in your browser.
Controls
Boots a small public-domain Uxn demo ROM that paints four colour fields and animates a sprite through the Varvara screen device. Add ?debug to the URL, or open the debugger, to single-step the Uxn stack machine one opcode at a time and set breakpoints on a PC. Arrow keys plus Z / X / Shift / Enter drive the Varvara controller; click the screen first so it captures the keyboard.
Configurations
| Configuration | Emulator | Machine | OS | Legal | |
|---|---|---|---|---|---|
| Varvara demo | Uxn | Uxn | open | Open ⛶ |
Downloads - ROMs & software
| Title | Type | Size (bytes) | Legal | |
|---|---|---|---|---|
| Varvara colour + sprite demo | demo | 98 | open | Download ↓ |
Machines
Emulators
| Emulator | Type | License | Site |
|---|---|---|---|
| Uxn | online | MIT | Website ↗ |
| Uxn32 | downloadable | MIT | Website ↗ |
| Uxn5 | online | MIT | Website ↗ |
| buxn | downloadable | BSD-2-Clause | Website ↗ |
| uxn11 | downloadable | MIT | Website ↗ |
| uxnemu | downloadable | MIT | Website ↗ |
Reference & documentation
External technical references for programming Uxn CPU and for writing emulators.
| Resource | Type | Notes |
|---|---|---|
| XXIIVV - Uxntal Opcodes ↗ | Instruction set | All 256 opcodes, stack effects, short/keep/return modes |
| XXIIVV - Varvara Devices ↗ | Interrupt list | Device vectors; CPU is non-interruptible model |
| XXIIVV - Varvara Devices ↗ | Memory map | Device page: 16 ports each at fixed addresses |
| compudanzas - Uxn Tutorial ↗ | Programming | Seven-day comprehensive Varvara/Uxntal programming guide |
| XXIIVV - Uxntal ↗ | Programming | Intro to the concatenative Uxntal assembly language |
| Uxn/Varvara Implementation Guide ↗ | Reference | How to implement the VM (note: dated 2022) |
| A WebAssembly Core for Uxn ↗ | Reference | Opcode codegen, dispatch, and coverage-based conformance |
| XXIIVV - Uxntal Stacking ↗ | Reference | Permutation lookup table for stack opcode combinations |
| Raven - a Uxn/Varvara emulator in Rust ↗ | Source | Fast safe-Rust CPU core; per-opcode dispatch design |
| Uxn Instruction Tests ↗ | Test suite | TAL opcode tests with expected reference hexdumps |
| awesome-uxn ↗ | Tool | Curated emulators, assemblers, disassemblers, and tools |