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Testing Cookbook

How do I change the default testing directory?​

Override the buildDir method.

The example below changes the testing directory to test/:

import chisel3._
import chisel3.simulator.scalatest.ChiselSim
import java.nio.file.Paths
import org.scalatest.funspec.AnyFunSpec

class FooSpec extends FunSpec with ChiselSim {

  override def buildDir: Path = Paths.get("test")

}

How do I enable waveforms for a simulation?​

If using Scalatest and ChiselSim, pass the -DemitVcd=1 argument to Scalatest, e.g.:

./mill 'chisel[].test.testOnly' chiselTests.ShiftRegistersSpec -- -DemitVcd=1

How do I enable Verilator coverage in svsim?​

If you are configuring svsim directly, set Verilator backend coverage settings at compile time:

import svsim.verilator

val backend = verilator.Backend.initializeFromProcessEnvironment()
val settings = verilator.Backend.CompilationSettings.default
  .withCoverageSettings(
    new verilator.Backend.CompilationSettings.CoverageSettings(
      line = true,
      toggle = true,
      user = true
    )
  )

This enables Verilator coverage instrumentation and writes coverage.dat at the end of simulation. You can convert it to LCOV info with verilator_coverage for downstream reporting tools.

How do I see what options a ChiselSim Scalatest test supports?​

Pass -Dhelp=1 to Scalatest, e.g.:

./mill 'chisel[].test.testOnly' chiselTests.ShiftRegistersSpec -- -Dhelp=1