LibreCell

LibreCell aims to be a toolbox for automated synthesis of CMOS logic cells.

LibreCell is structured in multiple sub-projects:

• librecell-layout: Automated layout generator for CMOS standard cells.
• lctime: Characterization kit for CMOS cells and tool for handling liberty files.

The project is in a very early stage and might not yet be ready for productive use. Project structure and API might change heavily in near future.

Getting started

LibreCell can be installed using the Python package manager pip or directly from the git repository.

Dependencies

The following dependencies must be installed manually:

• python3
• z3 https://github.com/Z3Prover/z3 : SMT solver.

Optional dependencies (not required for default configuration):

• GLPK https://www.gnu.org/software/glpk : ILP/MIP solver

Depending on your linux distribution this packages can be installed using the package manager.

Installing from git

It is recommended to use a Python 'virtual environment' for installing all Python dependencies:

# Create a new virtual environment
python3 -m venv my-librecell-env
# Activate the virtual environment
source ./my-librecell-env/bin/activate

Install from git:

git clone https://codeberg.org/tok/librecell.git
cd librecell
./install.sh

# Alternatively use ./install_develop.sh to install symlinks.
# This allows to edit the code with immediate effect on the installed program.

Now, check if the command-line scripts are in the current search path:

lclayout --help

If this shows the documentation of the lclayout command, then things are fine. Otherwise, the PATH environment variable needs to be updated to include $HOME/.local/bin.

# Instead of executing this line each time it can be added to ~/.bashrc
export PATH=$PATH:$HOME/.local/bin

Installing with pip

Note: The version PyPI is often not the most recent one. Consider installing from git to get the most recent version.

It is recommended to use a Python 'virtual environment' for installing all Python dependencies:

# Create a new virtual environment
python3 -m venv my-librecell-env
# Activate the virtual environment
source ./my-librecell-env/bin/activate

pip3 install lclayout

Generate a layout

Generate a layout from a SPICE netlist which includes the transistor sizes:

• --output-dir: Directory which will be used to store GDS and LEF of the cell
• --tech: Python script file containing design rules and technology related data
• --netlist: A SPICE netlist containing the netlist of the cell as a sub circuit (.subckt).
• --cell: Name of the cell. Must match the name of the sub circuit in the SPICE netlist.

mkdir mylibrary
lclayout --output-dir mylibrary --tech examples/dummy_tech.py --netlist examples/cells.sp --cell AND2X1

Adapting design rules

Design rulesi and technology related data need to be encoded in a Python script file as shown in examples/dummy_tech.py.

Known issues

Reproducibility

You may want to generate standard cells in a fully reproducable manner. Right now there is some non-determinism in LibreCell that has not been investigated yet. The current workaround is to set the PYTHONHASHSEED environment variable.

export PYTHONHASHSEED=42
lclayout ...

Contact

"codextkramerych".replace("x", "@").replace("y", ".")