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bigspicy

bigspicy is a tool for merging circuit descriptions (netlists), generating Spice decks modeling those circuits, generating Spice tests to measure those models, and analyzing the results of running Spice on those tests.

bigspicy allows you to combine structural Verilog from a PDK, Spice models of standard cells, a structural Verilog model of some circuit implemented in that PDK, and parasitics extracted into SPEF format. You can then reason about the electrical structure of the design however you want.

bigspicy generates Spice decks in Xyce format, though this can (and should) be extended to other Spice dialects. (That is why we recommend setting up Xyce below.)

Prerequisites

You need:

• The protocol buffer compiler protoc
• Icarus Verilog
• Xyce
  • Note this one is special, and takes some more care.
• python3 (see requirements.txt)
  • pyverilog
  • numpy
  • matplotlib
  • protobuf

On debian-family Linuxes, several of the system-installed dependencies can be installed with

sudo apt install -y protobuf-compiler iverilog

Given a python installation and environment, all other Python dependencies can be installed with

pip install -e ".[dev]"
pip install -r requirements.txt

Set up Xyce

Install the 'Serial' or 'Parallel' versions of Xyce. Follow the Xyce Building Guide.

Set up XDM

XDM is needed to prepare Spice netlists generated for common proprietary Spice engines for use with Xyce. It is only needed to prepare the input libraries used by bigspicy, and only once for each corner in the PDK.

Follow the XDM installation instructions on their GitHub clone. If existing XDM-translated libraries are available, you can skip this step.

XDM 2.5.0/Debian 11.4 build cheat-sheet

sudo apt install libboost-dev libboost-python-dev
sudo pip3 install pyinstaller  # 'sudo' needed to be install in site packages dir
wget https://github.com/Xyce/XDM/archive/refs/tags/Release-2.5.0.tar.gz
tar xf XDM-Release-2.5.0.tar.gz
cd XDM-Release-2.5.0/
mkdir build && cd build
cmake -DBOOST_ROOT=/usr/include/boost ../
make -j $(nproc)
sudo make install

Compile protos and prepare PDK models

Generating SPICE library files

Spice files fed to bigspicy should be in Xyce format because bigspicy does minimal internal processing of the files and will include them almost verbatim. These files are in turn read directly into Xyce. That means that any PDK Spice files you receive should be converted to Xyce's spice dialect. The xdm_bdl tool (XDM) can usually do this for you, though in some cases you will need to interfere by hand :(

e.g. Convert ASAP7 models using xdm_bdl

For example, for the TT corner and RVT ASAP7 cells:

xdm_bdl -s hspice ${HOME}/src/asap7PDK_r1p7/models/hspice/7nm_TT.pm -d lib
xdm_bdl -s hspice ${HOME}/src/asap7sc7p5t_27/CDL/xAct3D_extracted/asap7sc7p5t_27_R.sp -d lib

These can then be included as Spice headers (blackboxes) or full Spice modules using the --spice_header/--spice arguments, e.g:

[...]
    --spice_header lib/7nm_TT.pm \
    --spice_header lib/asap7sc7p5t_27_R.sp \
[...]

Compile protobufs

git submodule update --init   # Make sure we pull from Vlsir/schema-proto the
                              # first time.
protoc --proto_path vlsir vlsir/*.proto vlsir/*/*.proto --python_out=.
protoc proto/*.proto --python_out=.

Usage

Merge SPEF, Verilog and Spice information into Circuit protobuf

In addition to some circuit definition, in order to generate a Spice deck the order of ports for each instantiated module are also required. When relying on PDK cells, that usually means providing the PDK spice models as a header.

In the example below, lib/sky130_fd_sc_hd.spice is copied from ${PDK_ROOT}/share/pdk/sky130A/libs.ref/sky130_fd_sc_hd/spice/sky130_fd_sc_hd.spice as it is produced by open_pdks.

./bigspicy.py \
    --import \
    --verilog example_inputs/fp_multiplier/fp_multiplier.synth.v \
    --spef /path/to/fp_multiplier/fp_multiplier.spef \
    --spice_header lib/sky130_fd_sc_hd.spice \
    --top fp_multiplier \
    --save final.pb \
    --working_dir /tmp/bigspicy

Generate whole-module Spice model

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice_header lib/sky130_fd_sc_hd.spice \
    --top fp_multiplier \
    --dump_spice fp_multiplier.sp

Generate whole-module Spice model with transistors

Requires models for the PDK standard cells (included as full-fat netlists with --spice) and also black-box models for the transistors (included with --spice_header). Then pass the --flatten_spice argument.

If you had started with a gate-level netlist for an ASAP7 design, for example, you could do this:

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice_header lib/7nm_TT.pm \
    --spice lib/asap7sc7p5t_27_R.sp \
    --top fp_multiplier_asap7 \
    --flatten_spice \
    --dump_spice fp_multiplier_asap7.sp

Generate tests to measure input capacitance

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice_header lib/7nm_TT.pm \
    --spice_header lib/asap7sc7p5t_27_R.sp \
    --top fp_multiplier_asap7 \
    --working_dir /tmp/bigspicy \
    --generate_input_capacitance_tests

This will generate all necessary test files in /tmp/bigspicy. It will also generate a test manifest, test_manifest.pb, and an analysis file circuit_analysis.pb, which you must specify as paths to subsequent analysis steps.

Run Xyce to perform tests

cd /tmp/bigspicy
for test in *.linearZ.sp *.transient_*.sp; do
  ~/XyceInstall/Serial/bin/Xyce "${test}" &
done

Generate wire and whole-module tests

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice lib/7nm_TT.pm \
    --spice lib/asap7sc7p5t_27_R.sp \
    --top fp_multiplier_asap7 \
    --working_dir /tmp/bigspicy \
    --generate_module_tests \
    --test_manifest /tmp/bigspicy/test_manifest.pb \
    --test_analysis /tmp/bigspicy/analysis.pb

Include results of external module measurements

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice lib/7nm_TT.pm \
    --spice lib/asap7sc7p5t_27_R.sp \
    --top fp_multiplier_asap7 \
    --working_dir /tmp/bigspicy \
    --generate_module_tests \
    --test_manifest /tmp/bigspicy/test_manifest.pb \
    --test_analysis /tmp/bigspicy/analysis.pb \
    --analyze_input_capacitance_tests

Run Xyce to perform tests

cd /tmp/bigspicy
for test in *.linearY.sp *.transient.sp; do
  ~/XyceInstall/Serial/bin/Xyce "${test}" &
done

Perform analysis on wire and whole-module tests

./bigspicy.py \
    --load /tmp/bigspicy/final.pb \
    --spice lib/7nm_TT.pm \
    --spice lib/asap7sc7p5t_27_R.sp \
    --top fp_multiplier_asap7 \
    --working_dir /tmp/bigspicy \
    --test_manifest /tmp/bigspicy/test_manifest.pb \
    --test_analysis /tmp/bigspicy/analysis.pb \
    --analyze_module_tests \
    --input_caps_csv=input_caps.csv \
    --delays_csv=delays.csv

Import all Skywater 130 sky130_fd_sc_hd standard cells into circuit proto

./bigspicy.py \
    --import \
    --spice ${PDK_ROOT}/share/pdk/sky130A/libs.ref/sky130_fd_sc_hd/spice/sky130_fd_sc_hd.spice
    --save sky130hd.pb
    --working_dir /tmp/bigspicy

Import all Skywater 130 primitives too

Caution! Globbing every spice file as in this example is not a good idea. You will likely end up with multiple definitions for the same circuit. But you can do it if you want.

./bigspicy.py \
    --import \
    --spice ${PDK_ROOT}/share/pdk/sky130A/libs.ref/sky130_fd_pr/spice/sky130_fd_pr__\* \
    --spice ${PDK_ROOT}/share/pdk/sky130A/libs.ref/sky130_fd_sc_hd/spice/sky130_fd_sc_hd.spice \
    --save sky130hd.pb \
    --working_dir /tmp/bigspicy

Likely:

warning: multiple definitions for subckt sky130_fd_pr__rf_nfet_01v8_bM04W3p00, overwriting previous