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.
• librecell-lib: Characterization kit for CMOS cells and tool for handling liberty files.
• librecell-common: Code that is used across different LibreCell projects such as a netlist parser.
• librecell-meta: Convinience Python package for easier installation.

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
• ngspice http://ngspice.sourceforge.net/ : SPICE simulator used for cell characterization.
• 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.

Example for Arch Linux:

sudo pacman -S python ngspice z3

Installing with pip

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 librecell

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 librecell-common
cd librecell-common
python3 setup.py develop
cd ..

# Install lclayout
cd librecell-layout
python3 setup.py develop
cd ..

# Install lclib
cd librecell-lib
python3 setup.py develop
cd ..

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

Generate a layout

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

cd librecell-layout
mkdir /tmp/mylibrary
lclayout --output-dir /tmp/mylibrary --tech examples/dummy_tech.py --netlist examples/cells.sp --cell AND2X1
# Use a GDS viewer such as KLayout to inspect the generated layout file `/tmp/mylibrary/*.gds`

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", ".")