Illustrates toUInt conversion and Cat behavior

BitExamples.scala

package bit_examples

import chisel3._
import chisel3.experimental.MultiIOModule
import chisel3.iotesters.PeekPokeTester
import chisel3.util.Cat

import org.scalatest.{FreeSpec, Matchers}

//scalastyle:off magic.number

// Class and companion Object to support instantiation and initialization of
// state due to the need to have subword assignment for vectors > 64-bits
//
// Fields in the bundle enumerate from to low.  When converting this bundle
// to UInt it is equivalent to Cat(Word1, Word0) or if subword assignment
// was supported:
//
//      state(127,64) := word1
//      state(63,0)   := word0
//

class State_Class extends Bundle {
  val word1 = UInt(64.W)
  val word0 = UInt(64.W)
}

object State_Class {
  def init: State_Class = {
    val wire = Wire(new State_Class)
    wire.word1 := BigInt("a"*16, 16).U
    wire.word0 := BigInt("b"*16, 16).U
    wire
  }
}

// Class and companion Object to support instantiation and initialization of
// key due to the need to have subword assignment for vectors > 64-bits
//
class Key_Class extends Bundle {
  val word2 = UInt(64.W)
  val word1 = UInt(64.W)
  val word0 = UInt(64.W)
}

object Key_Class {
  def init: Key_Class = {
    val wire = Wire(new Key_Class)
    wire.word2 := BigInt("c"*16, 16).U
    wire.word1 := BigInt("d"*16, 16).U
    wire.word0 := BigInt("e"*16, 16).U
    wire
  }
}

class Example extends MultiIOModule {
  val stateOut    = IO(Output((UInt((new State_Class).getWidth.W))))
  val keyOut      = IO(Output((UInt((new Key_Class).getWidth.W))))
  val combinedOut = IO(Output((UInt((stateOut.getWidth + keyOut.getWidth).W))))

  val state = RegInit(State_Class.init)
  val key   = RegInit(Key_Class.init)

  stateOut := state.asUInt
  keyOut   := key.asUInt

  combinedOut := Cat(stateOut, keyOut)
}

class BitTests extends FreeSpec with Matchers {
  "example of uint conversion and and ordering of cat" in {
    iotesters.Driver.execute(Array(), () => new Example) { c =>
      new PeekPokeTester(c) {
        step(1)

        peek(c.stateOut).toString(16)    should be ("a"*16 + "b"*16)
        peek(c.keyOut).toString(16)      should be ("c"*16 + "d"*16 + "e"*16)
        peek(c.combinedOut).toString(16) should be ("a"*16 + "b"*16 + "c"*16 + "d"*16 + "e"*16)

        println(s"stateOut       ${peek(c.stateOut).toString(16)}")
        println(s"keyOut         ${peek(c.keyOut).toString(16)}")
        println(s"combined       ${peek(c.combinedOut).toString(16)}")
      }
    }
  }
}