A ChiselTest question

[Martin Schoeberl]

HI all,

I want to have some test functions as part of a Bundle definition. E.g., having a bus interface and providing read and write functions. I am able to do it on a Module, e.g.,

class CpuInterface(addrWidth: Int) extends Module {
  val io = IO(new Bundle {
    val cpuPort = new MemoryMappedIO(addrWidth)
  })

  def read(addr: Int): BigInt = {
    io.cpuPort.address.poke(addr.U)
    io.cpuPort.wr.poke(false.B)
    io.cpuPort.rd.poke(true.B)
    clock.step()
    // Ignore waiting for a moment
    io.cpuPort.rdData.peekInt()
  }

However, MemoryMappedIO might be used on other classes that are not a CpuInterface. Therefore, I would like to add it to the Bundle (interface definition). But I need a reference to the Module. I can only do it like this:

class MemoryMappedIO(private val addrWidth: Int) extends Bundle {
  val address = Input(UInt(addrWidth.W))
  val rd = Input(Bool())
  val wr = Input(Bool())
  val rdData = Output(UInt(32.W))
  val wrData = Input(UInt(32.W))
  val ack = Output(Bool())

  // TODO: it would fit better here than in CpuInterface, but without a reference to a CpuInterface
  def readX(addr: Int, d: CpuInterface): BigInt = {
    d.io.cpuPort.address.poke(addr.U)
    d.io.cpuPort.wr.poke(false.B)
    d.io.cpuPort.rd.poke(true.B)
    d.clock.step()
    // Ignore waiting for a moment
    d.io.cpuPort.rdData.peekInt()
  }
}

which is worse, as it contains now a reference to a CpuInterface.

Any good idea to solve this elegantly?

Cheers,

Martin

[Albert Magyar]

Have you considered making it a free function that takes a MemoryMappedIO argument, along with a separate argument of either a clock or “clock-having module” type? Cleanly capturing behavioral effects within instance methods can be a bit tricky.

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[Martin Schoeberl]

My current solution is to have a helper class (in test, as this should not be in the main design part) that takes a CpuInterface object as parameter: https://github.com/t-crest/soc-comm/blob/master/src/test/scala/soc/MemoryMappedIOHelper.scala

But using just the MemoryMappedIO plus a clock is probably the better way. I will try this out.

Thanks,

Martin

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