xsil

Reference CLI for the .xsil RISC-V ISA extension package format.

xsil lets you describe a custom RISC-V instruction set extension, scaffold a runnable package (with Spike extension skeleton, opcodes, tests and examples), run it locally, and publish it to a registry — without waiting for silicon.

TL;DR

cargo install xsil
xsil new            # interactive wizard
xsil run ./my-ext   # build + run inside the generated package

Install

cargo install xsil

Or grab a prebuilt binary from GitHub Releases.

xsil new — interactive wizard

The fastest way to start. The wizard asks for:

• package name, version, ISA base (e.g. RV64GC), license
• repository URL (mandatory)
• honest classification: standardStatus (ratified | draft | vendor | research | custom) and free-text authority (e.g. RISC-V International, T-Head / XuanTie, University of Michigan). Both are mandatory. Don't label a package ratified unless RISC-V International has actually frozen the spec — the registry checks.
• one or more custom instructions: mnemonic, format (R/I/S/B/U/J), opcode, funct3, funct7, operands, summary

It then generates a ready-to-build .xsil tree:

• manifest.json — package metadata + instruction list
• opcodes.json — machine-readable encoding table
• opcodes.h — C header with .insn-based inline-assembly macros
• examples/<mnemonic>.S — one runnable example per instruction
• tests/instructions.S — combined regression test
• sim/spike-extension/ — Spike extension_t C++ skeleton + Makefile + README
• toolchain/, LICENSE (full SPDX text), CHANGELOG.md, README.md

Prefer non-interactive? Use xsil init <name> for a minimal scaffold, or pass xsil new the same fields as flags:

xsil new my-ext \
  --description "What it does, in one line." \
  --isa     "RV64G_Zbkb" \
  --license "Apache-2.0" \
  --repository      "https://github.com/you/my-ext" \
  --standard-status "vendor" \
  --authority       "ACME Corp."

What xsil does not touch

A package's provenance on a registry — whether it was auto-seeded from upstream, ported by the community, claimed by the maintainer, or admin-verified as official — is tracked server-side in a separate portStatus field. The CLI does not read or write it; the registry sets it for you (see spec §4.8). This is intentional: it prevents publishers from misrepresenting themselves as the official upstream maintainer.

What is .xsil?

A .xsil is a reproducible, gzipped tarball with SHA-256 payload checksums that bundles everything needed to describe and exercise a custom RISC-V extension. The format spec lives at https://github.com/ExtenSilica/xsil/blob/main/spec/xsil.md.

Common commands

The hosted registry, web UI, and an equivalent web wizard are at https://extensilica.com.

License

ISC — see LICENSE.