CIRCT

Why Ruby for Hardware Design

2 min read

Hardware description languages like Verilog and VHDL were designed decades ago. They get the job done, but they lack the expressiveness and tooling that modern software developers expect. Ruby offers a compelling alternative as a host language for hardware DSLs.

The Case for Ruby

Ruby’s metaprogramming capabilities make it uniquely suited for building domain-specific languages. With RHDL, hardware designers get:

  • Expressive syntax — Ruby reads like pseudocode, reducing boilerplate
  • Metaprogramming — generate parameterized designs programmatically
  • Testing with RSpec — use a mature test framework for hardware verification
  • Package management — leverage RubyGems for reusable component libraries
  • REPL-driven development — explore designs interactively with IRB

Comparison with Traditional HDLs

# RHDL — a 4-bit counter
class Counter < RHDL::Component
  input  :clk, :reset, :enable
  output :count, width: 4
 
  sequential(clk: :posedge, reset: :sync) do
    if reset
      count <= 0
    elsif enable
      count <= count + 1
    end
  end
end

Compare with the equivalent Verilog — the RHDL version eliminates sensitivity lists, explicit always blocks, and repetitive type declarations while remaining clear about the hardware intent.

Standing on CIRCT

The Ruby DSL is a frontend to the CIRCT compiler. Your Ruby code is lowered through multiple stages — RTL model, gate-level netlist, and finally CIRCT IR — before being handed off to backends for simulation, synthesis, or export. This means you get the productivity of Ruby with the rigor of a real compiler infrastructure.

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