SubXPAT

This work presents a novel iterative approach to achieve effective and scalable approximate logic synthesis (ALS). The core idea is to perform circuit rewriting in a way that is both local, i.e., is applied piece-wise to selected subcircuits, and extensive, i.e., systematically explores the design space for good solutions.

Prerequisits

• Install the following tools:

1. Python
2. Linux
3. Yosys: link (https://github.com/YosysHQ/yosys) Note: add the binaries of Yosys to your PATH

Setup

To prepare the system for execution you will need to follow a few steps:

1. Initial system setup:

   # bulk commands
   make setup-all # everything
   make setup     # everything except package dependencies
   
   # individual commands
   make sftw_dep    # install package dependencies
   make py_init     # create python environment
   make py_dep      # install/update requirements
   make folders_dep # create folders (WIP)
   make local_dep   # create input folders and local files

2. Activate the python environment:

   . venv/bin/activate

Other useful commands

• To remove temporary files and the virtual python environment:

  # all together
  make clean
  
  # individually
  make rm_cache # remove the pycache folders
  make rm_temp  # remove temporary files
  make rm_pyenv # remove the virtual python environment

• To display the program help:

  make help

Usage

You use the system by running the following command

python3 main.py exact-benchmark [options]

Here are all the arguments with their types and descriptions

Argument	type	description
exact-benchmark	file in input/ver/	Circuit to approximate.
--current-benchmark --curr	file in input/ver/	Approximated circuit to continue from.
--min-labeling		Nodes are weighted using their minimum error, instead of maximum error
--partial-labeling		Assign weight only to relevant nodes
--extraction-mode --mode	{ 1, 2, 3, 4, 5, 55, 11, 12 }	Subgraph extraction algorithm to use
--input-max --imax	int > 0	Maximum allowed number of inputs to the subgraph
--output-max --omax	int > 0	Maximum allowed number of outputs from the subgraph
--max-sensitivity	int > 0	Maximum partitioning sensitivity
--min-subgraph-size	int	Minimum valid size for the subgraph
--num-subgraphs	int > 0	The number of attempts for subgraph extraction
--subxpat		Run the system as SubXPAT instead of XPat
--constants	{ never, always }	The way constants are used
--template	{ nonshared, shared }	Select template logic
--max-lpp --literals-per-product	int > 0	The max number of literals per product to use
--max-ppo --products-per-output	int > 0	The max number of products per output to use
--max-pit --products-in-total	int > 0	The max number of products to use in total
--wanted-models	int > 0	Wanted number of models to generate for each step
--max-error -e	int > 0	The maximum allowable error
--error-partitioning --epar	{ asc, desc, smart_asc, smart_desc }	The error partitioning algorithm to use
--encoding	{ z3int, z3bvec, qbf }	The encoding to use in solving the approximation
--timeout	float > 0 (default: 3h)	The maximum time each cell is given to run in seconds
--parallel		Run in parallel what is possilbe
--clean		Reset the output folder before running
--help -h		Show the help message and exit

Examples

To run XPAT with the Non-Shared template with Integer logic encoding

python3 main.py adder_i8_o5 --max-lpp=8 --max-ppo=32 --max-error=16

To run SubXPAT with the Shared template with BitVector logic encoding, using Subgraph Extraction 5 (all sub-outputs weight must be less than the error threshold) with Minimum Labeling.

python3 main.py adder_i8_o5 --subxpat --extraction-mode=5 --min-labeling --max-lpp=8 --max-ppo=10 --max-error=16

Once the command is finished executing, you can find the outputs in the following directories:

output/csv/ Contains the log of execution and every information at each it.
output/ver/ Contains all the Verilog descriptions of all the approximate circuits found.
output/gv/ Contains the information about all the subgraphs that have been detected in a visual form.

Known limitations

• On Apple devices running M# architecture, you will have problems with some packages.
  No support is given at the moment for this situation.