Simulation Backends

Use Verilator by default. Use Icarus Verilog for lightweight smoke tests, or where installing Verilator is impractical.

Choose a backend

Capability	Verilator	Icarus 12
SystemVerilog procedural code	Yes	Yes
Concurrent SVA and cover property	Yes	No
interface class frameworks	Yes	No
RTL Buddy line/toggle coverage	Yes	No
cocotb through VPI	Yes	Yes
Default waveform	FST	VCD

Verilator compiles a cycle-based simv binary. Icarus compiles a .vvp snapshot and runs it with vvp; RTL Buddy generates a simv wrapper so the rest of the flow is the same.

If a suite must run on Icarus, gate unsupported constructs. Use expected failures only when the failure mode is understood.

Select a builder

The builder comes from, in order: --builder <name>, the test's builder:, the suite's builder:, the platform default.

Set simulator-family on the cfg-rtl-builder entry, or use an executable name RTL Buddy can infer it from. See Selecting the simulator builder.

Open waveforms

Verilator writes dump.fst and Icarus writes dump.vcd. rb wave opens the newest supported dump under artefacts/<test>/.

To convert an Icarus dump to FST after simulation, set wave-format: fst-postproc on the builder. If vcd2fst is missing, the VCD is kept.

Collect coverage

RTL Buddy coverage supports Verilator only and follows the platform-selected builder. Pass --builder verilator or make Verilator the platform default; a suite- or test-level override alone is not enough. See Coverage uses the platform builder.