SHDL – A minimal hardware description language built from logic gates
Hi, everyone! I built SHDL (Simple Hardware Description Language) as an experiment in stripping hardware description down to its absolute fundamentals. In SHDL, there are no arithmetic operators, no implicit bit widths, and no high-level constructs. You build everything explicitly from logic gates and wires, and then compose larger components hierarchically. The goal is not synthesis or performance, but understanding: what digital systems actually look like when abstractions are removed. SHDL is accompanied by PySHDL, a Python interface that lets you load circuits, poke inputs, step the…
In plain words
SHDL is a minimal hardware description language that removes abstractions and requires builders to construct digital circuits explicitly from logic gates and wires. Designed for learning and experimentation rather than production synthesis, it offers no arithmetic operators, implicit bit widths, or high-level constructs. Users compose circuits hierarchically and test them through PySHDL, a Python interface for simulation. The language compiles to C for execution while maintaining transparency and simplicity, making it suitable for engineers and students studying digital logic from foundational principles.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Hi, everyone! I built SHDL (Simple Hardware Description Language) as an experiment in stripping hardware description down to its absolute fundamentals. In SHDL, there are no arithmetic operators, no implicit bit widths, and no high-level constructs. You build everything explicitly from logic gates and wires, and then compose larger components hierarchically. The goal is not synthesis or performance, but understanding: what digital systems actually look like when abstractions are removed. SHDL is accompanied by PySHDL, a Python interface that lets you load circuits, poke inputs, step the simulation, and observe outputs. Under the hood, SHDL compiles circuits to C for fast execution, but the language itself remains intentionally small and transparent. This is not meant to replace Verilog or VHDL. It’s aimed at: - learning digital logic from first principles - experimenting with HDL and language design - teaching or visualizing how complex hardware emerges from simple gates. I would especially appreciate feedback on: - the language design choices - what feels unnecessarily restrictive vs. educationally valuable - whether this kind of “anti-abstraction” HDL is useful to you. Repo: https://github.com/rafa-rrayes/SHDL Python package: PySHDL on PyPI To make this concrete, here are a few small working examples written in SHDL: 1. Full Adder component FullAdder(A, B, Cin) -> (Sum, Cout) { x1: XOR; a1: AND; x2: XOR; a2: AND; o1: OR; connect { A -> x1.A; B -> x1.B; A -> a1.A; B -> a1.B; x1.O -> x2.A; Cin -> x2.B; x1.O -> a2.A; Cin -> a2.B; a1.O -> o1.A; a2.O -> o1.B; x2.O -> Sum; o1.O -> Cout; } } 2. 16 bit register # clk must be high for two cycles to store a value component Register16(In[16], clk) -> (Out[16]) { >i[16]{ a1{i}: AND; a2{i}: AND; not1{i}: NOT; nor1{i}: NOR; nor2{i}: NOR; } connect { >i[16]{ # Capture on clk In[{i}] -> a1{i}.A; In[{i}] -> not1{i}.A; not1{i}.O -> a2{i}.A; clk -> a1{i}.B; clk -> a2{i}.B; a1{i}.O -> nor1{i}.A; a2{i}.O -> nor2{i}.A; nor1{i}.O -> nor2{i}.B; nor2{i}.O -> nor1{i}.B; nor2{i}.O -> Out[{i}]; } } } 3. 16-bit Ripple-Carry Adder use fullAdder::{FullAdder}; component Adder16(A[16], B[16], Cin) -> (Sum[16], Cout) { >i[16]{ fa{i}: FullAdder; } connect { A[1] -> fa1.A; B[1] -> fa1.B; Cin -> fa1.Cin; fa1.Sum -> Sum[1]; >i[2,16]{ A[{i}] -> fa{i}.A; B[{i}] -> fa{i}.B; fa{i-1}.Cout -> fa{i}.Cin; fa{i}.Sum -> Sum[{i}]; } fa16.Cout -> Cout; } }
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