Simulation Backends

Use Verilator by default. Use Icarus Verilog for lightweight smoke tests or environments 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 and provides RTL Buddy's coverage path. Icarus compiles a .vvp snapshot and runs it through vvp; RTL Buddy generates a simv wrapper so the surrounding flow stays the same.

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

Select a builder

Builder precedence is --builder <name>, per-test builder:, suite-level builder:, then the platform default.

The selected cfg-rtl-builder entry should set simulator-family, or use an executable name from which RTL Buddy can infer it. See Selecting the simulator builder.

Open waveforms

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

Set wave-format: fst-postproc on an Icarus builder to run vcd2fst after simulation. If vcd2fst is unavailable, the VCD remains usable.

Collect coverage

RTL Buddy coverage is currently Verilator-only and follows the platform-selected builder. Use --builder verilator, or make Verilator the platform default, instead of relying only on a suite- or test-level override. See Coverage uses the platform builder.