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A Hardware Construct Language

Project description


Build Status codecov PyPI

PyHCL is a hardware construct language like Chisel but more lightweight and more relaxed to use. As a novel hardware construction framework embedded in Python, PyHCL supports several useful features include object-oriented, functional programming, and dynamically typed objects.

The goal of PyHCL is providing a complete design and verification tool flow for heterogeneous computing systems flexibly using the same design methodology.

PyHCL is powered by FIRRTL, an intermediate representation for digital circuit design. With the FIRRTL compiler framework, PyHCL-generated circuits can be compiled to the widely-used HDL Verilog.

Getting Started

Installing PyHCL

$ pip install py-hcl

Writing A Full Adder

PyHCL defines modules using only simple Python syntax that looks like this:

from py_hcl import *

class FullAdder(Module):
    io = IO(

    # Generate the sum
    io.sum <<= io.a ^ io.b ^ io.cin

    # Generate the carry
    io.cout <<= io.a & io.b | io.b & io.cin | io.a & io.cin

Compiling To FIRRTL

Compiling module by calling compile_to_firrtl:

compile_to_firrtl(FullAdder, 'full_adder.fir')

Will generate the following FIRRTL codes:

circuit FullAdder :
  module FullAdder :
    input clock : Clock
    input reset : UInt<1>
    input FullAdder_io_a : UInt<1>
    input FullAdder_io_b : UInt<1>
    input FullAdder_io_cin : UInt<1>
    output FullAdder_io_sum : UInt<1>
    output FullAdder_io_cout : UInt<1>

    node _T_0 = xor(FullAdder_io_a, FullAdder_io_b)
    node _T_1 = xor(_T_0, FullAdder_io_cin)
    FullAdder_io_sum <= _T_1
    node _T_2 = and(FullAdder_io_a, FullAdder_io_b)
    node _T_3 = and(FullAdder_io_b, FullAdder_io_cin)
    node _T_4 = or(_T_2, _T_3)
    node _T_5 = and(FullAdder_io_a, FullAdder_io_cin)
    node _T_6 = or(_T_4, _T_5)
    FullAdder_io_cout <= _T_6

Compiling To Verilog

While FIRRTL is generated, PyHCL's job is complete. To further compile to Verilog, the FIRRTL compiler framework is required:

$ firrtl -i full_adder.fir

Then FullAdder.v will be generated:

module FullAdder(
  input   clock,
  input   reset,
  input   FullAdder_io_a,
  input   FullAdder_io_b,
  input   FullAdder_io_cin,
  output  FullAdder_io_sum,
  output  FullAdder_io_cout
  wire  _T_0;
  wire  _T_2;
  wire  _T_3;
  wire  _T_4;
  wire  _T_5;
  assign _T_0 = FullAdder_io_a ^ FullAdder_io_b;
  assign _T_2 = FullAdder_io_a & FullAdder_io_b;
  assign _T_3 = FullAdder_io_b & FullAdder_io_cin;
  assign _T_4 = _T_2 | _T_3;
  assign _T_5 = FullAdder_io_a & FullAdder_io_cin;
  assign FullAdder_io_sum = _T_0 ^ FullAdder_io_cin;
  assign FullAdder_io_cout = _T_4 | _T_5;


  • Supports multiple data types: UInt, SInt, Vector, Bundle, Clock, Memory, and casual combination between them.
  • Supports object-oriented inheritance, can compose modules by writing fewer codes.
  • Supports a bunch of convenient operations, such as the addition of UInts, SInts, Vectors and Bundles.
  • Supports the parameterization of variables, such as bit width, with the syntax facilities of the host language Python.


  • Supports more operations
  • PyHCL's verification facility

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