AVL - Apheleia Verification Library

AVL has been developed by experienced, industry professional verification engineers to provide a methodology
and library of base classes for developing functional verification environments in Python.

AVL is built on the CocoTB framework, but aims to combine the best elements of
UVM in a more engineer friendly and efficient way.

CocoTB 2.0

AVL now supports CocoTB2.0 https://docs.cocotb.org/en/development/upgrade-2.0.html. This was introduced in v0.3.0.

All older versions support v1.9.1 and will fail if run with CocoTB 2.0.

To upgrade follow the instructions given on the link above.

🧬 Mutation Testing

Coverage tells you the testbench ran a line. It does not tell you the testbench would have noticed had that line been wrong.

Mutation testing — known in hardware as functional qualification — answers the second question. avl-mutation-testing takes your golden RTL, writes out a set of copies each carrying exactly one deliberate defect, and re-runs your existing tests against every one. A mutant the tests still pass is a hole in the verification environment: a class of bug that could ship unnoticed. The testbench needs no knowledge of any of this — a mutant is ordinary RTL that happens to be wrong.

avl-mutation-testing --source rtl/*.sv --top my_module --types arith,compare --count 10

Supported mutations

Classes are selected with --types, and avl-mutation-testing --list-types prints them with the syntax each one matches.

Every line a mutation changes carries an /* AVL MUTATION - ... */ comment, so a mutant that turns up in an editor, a debugger or a waveform cannot be mistaken for the golden source. Generation also writes mutations.html, a report explaining each mutation in its source context.

Equivalent mutants

Some defects cannot change behaviour — flipping the + in a + 0 to a - is still a. No testbench can ever catch those, so scoring them as survivors reports verification holes that are not there. Where Yosys is installed each mutation is proved to change the design before any simulation time is spent on it, and the ones that do not are reported as equivalent and left out of the score. Yosys is optional; without it the stage is skipped.

Background and tools

Nineteen worked examples live under examples/mutation_testing, one per mutation class plus a hierarchical ALU, a synchronous FIFO, and a design with a provably equivalent mutant. See its README for the full walkthrough, and the documentation for the complete option reference.

📦 Installation

Using pip

# Standard build
pip install avl-core

# Development build
pip install avl-core[dev]

Install from Source

git clone https://github.com/projectapheleia/avl.git
cd avl

# Standard build
pip install .

# Development build
pip install .[dev]

Alternatively if you want to create a virtual environment rather than install globally a script is provided. This will install, with edit privileges to local virtual environment.

This script assumes you have Verilator, GTKWave and Graphviz installed, so all examples and documentation will build out of the box. Yosys is optional; the mutation testing examples use it to prove each mutation changes the design, and skip that stage without it. The script warns about anything it cannot find.

git clone https://github.com/projectapheleia/avl.git
cd avl
source avl.sh

📖 Documentation

In order to build the documentation you must have installed the development build.

Build from Source

cd docs
make html
<browser> build/html/index.html

🏃 Examples

In order to run all the examples you must have installed the development build.

To run all examples:

cd examples

# To run
make -j 8 sim

# To clean
make -j 8 clean

To run an individual example:

cd examples/THE EXAMPLE YOU WANT

# To run
make sim

# To clean
make clean

The examples use the CocoTB Makefile and default to Verilator with all waveforms generated. This can be modified using the standard CocoTB build system.

WARNING: Due to GNU Make not exporting variables not already in env the user must ensure PYTHONPATH is set in the environment. If you have sourced the avl.sh this is done for you.

🧹 Code Style & Linting

This project uses Ruff for linting and formatting.

Check code for issues:

ruff check .

Automatically fix common issues:

ruff check . --fix

Additional Libraries / UVCs

📧 Contact

• Email: avl@projectapheleia.net
• GitHub: projectapheleia