SHDL

SHDL (Simple Hardware Description Language) is an educational, gate-level hardware description language. You describe hardware out of AND, OR, NOT and XOR gates and watch signals ripple through it. Circuits simulate gate by gate, one propagation level per cycle (the unit-delay model), and no tool in the chain is allowed to collapse or shortcut that structure.

Get started

• SHDL Studio: the desktop app, with the editor, simulator, schematic, waveforms and tests in one window. Download the DMG for macOS (Apple Silicon and Intel). It needs no Python and no command line.
• PySHDL: the toolchain as a Python package, with the shdl command for projects and packages. uv tool install --python 3.14 PySHDL (or pip install PySHDL).
• Documentation: a guided tour, the language reference and the tools.

A taste of SHDL

component HalfAdder(A, B) -> (Sum, Carry) {
    x1: XOR;  a1: AND;

    connect {
        A -> x1.A;  B -> x1.B;  x1.O -> Sum;
        A -> a1.A;  B -> a1.B;  a1.O -> Carry;
    }
}

top component FullAdder(A, B, Cin) -> (Sum, Cout) {
    ha1: HalfAdder;     # A + B
    ha2: HalfAdder;     # (A + B) + Cin
    o1:  OR;            # carry out if either stage carried

    connect {
        A       -> ha1.A;   B   -> ha1.B;
        ha1.Sum -> ha2.A;   Cin -> ha2.B;
        ha2.Sum -> Sum;

        ha1.Carry -> o1.A;  ha2.Carry -> o1.B;
        o1.O -> Cout;
    }
}

examples/ is a graded tour, from a single gate to a parameterized ALU, followed by SR16 (a 16-bit CPU built from primitive gates) and Conway's Game of Life.

In this repository

Path	What it is
pyshdl/	The toolchain: the flattener (SHDL → Base SHDL), the shdlc compiler (Base SHDL → C), the Circuit Python driver, the shdl CLI, the conformance suite and the tests
examples/	The learning path, the SR16 CPU and Game of Life
docs/	The normative specs and the verification map, and the documentation site

SHDL Studio's installers are published on this repository's releases, and packages for the shdl CLI come from Circuit Circus, the SHDL package index.

License

GPL-3.0-or-later.