miniHDL: A Python Hardware Description Language DSL

2025-07-31 · Source: Nicholas Carlini · Field: Technology & Digital — Software Development & Engineering, Computer Architecture · Depth: Intermediate, long

Summary

Nicholas Carlini introduces miniHDL, a Python domain-specific language (DSL) designed for hardware description. This DSL simplifies circuit generation for deterministic simulators, abstracting away complexities like clock domain crossing and unknown X/Z states found in traditional HDLs like Verilog or VHDL. miniHDL, comprising 212 lines of Python, defines `Bit` and `Bits` classes to represent single bits and collections of bits, respectively, allowing for natural Pythonic operations like bitwise AND (`&`) and XOR (`^`). The DSL includes a compiler that converts these Pythonic circuit descriptions into a text file detailing gate connections, which is then processed by an efficient simulator. The article demonstrates miniHDL's capability by implementing a ripple-carry full-adder and a simple 32-bit RISC CPU in approximately 170 lines of code, featuring a register file, ALU, program counter, and instruction ROM.

Key takeaway

For hardware engineers or software developers exploring digital circuit design, miniHDL offers a Python-centric approach that significantly lowers the barrier to entry compared to traditional HDLs. You should consider using miniHDL for rapid prototyping and simulation of deterministic circuits, especially if you prefer Python's syntax and abstractions. This could accelerate your learning curve and development cycles for custom CPU architectures or logic designs.

Key insights

miniHDL simplifies hardware description using Python, enabling intuitive circuit design and efficient simulation.

Principles

• Abstract complex HDL concepts for simpler circuit design.
• Represent circuit elements as Python objects for natural operations.
• Optimize simulation by only updating changed gate inputs.

Method

miniHDL defines `Bit` and `Bits` classes to model circuit components. A compiler translates Pythonic circuit definitions into gate connection descriptions for a deterministic simulator, which uses a caching mechanism for efficient updates.

In practice

• Build a 32-bit RISC CPU in ~170 lines of Python.
• Implement D flip-flops using cyclic dependencies.
• Simulate circuits with 100x-500x performance boost via caching.

Topics

• miniHDL
• Hardware Description Languages
• Python DSL
• Circuit Simulation
• RISC CPU Architecture

Code references

• carlini/miniHDL

Best for: AI Hardware Engineer, Software Engineer, Research Scientist

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Editorial summary, takeaway, and curation by AIssential. Original article published by Nicholas Carlini.