Chisel test - internal signals

Question

I would like to test my code, so I'm doing a testbench. I wanted to know if it was possible to check the internal signals -like the value of the state register in this example- or if the peek was available only for the I/O

class MatrixMultiplier(matrixSize : UInt, cellSize : Int) extends Module {
  val io = IO(new Bundle {
    val writeEnable = Input(Bool())
    val bufferSel = Input(Bool())
    val writeAddress = Input(UInt(14.W)) //(matrixSize * matrixSize)
    val writeData = Input(SInt(cellSize.W))
    val readEnable = Input(Bool())
    val readAddress = Input(UInt(14.W)) //(matrixSize * matrixSize)
    val readReady = Output(Bool())
    val readData = Output(SInt((2 * cellSize).W))
  })

  val s_idle :: s_writeMemA :: s_writeMemB :: s_multiplier :: s_ready :: s_readResult :: Nil = Enum(6)
  val state = RegInit(s_idle)
...

and for the testbench :

class MatrixUnitTester(matrixMultiplier: MatrixMultiplier) extends PeekPokeTester(matrixMultiplier) { //(5.asUInt(), 32.asSInt())

    println("State is: " + peek(matrixMultiplier.state).toString) // is it possible to have access to state ?
    poke(matrixMultiplier.io.writeEnable, true.B)
    poke(matrixMultiplier.io.bufferSel, false.B)
    step(1)
...

EDIT : Ok, with VCD + GTKWave it is possible to graphically see these variables ;)

Answer 1

Good question. There's several parts to this answer

1. The Chisel supplied unit testing frameworks older chisel-testers and the newer chiseltest. Do not provide a mechanism to look into the wires directly. Currently the chisel team is looking into ways of doing that.

2. Both provide indirect ways of doing it. Writing VCD output and using printf to see internal values

3. The Treadle firrtl simulator, which can directly simulate a firrtl (the direct output of the Chisel compiler) does allow for peek, and poking any signal directly. There are lots of examples of how its use in Treadle's unit tests. Treadle also provides a REPL shell which can be useful for exploring a circuit with manual peeks and pokes