EnumeratedUInt.scala

package plan9

import Chisel._

object EnumeratedUInt {
  def apply(dir: IODirection = NODIR, enum: Map[Symbol, UInt]): EnumeratedUInt = {
    val res = new EnumeratedUInt()
    res.create(dir, enum)
    return res
  }
}

class EnumeratedUInt extends UInt {
  var enum: Map[Symbol, UInt] = _

  def create(dir: IODirection, enum: Map[Symbol, UInt]) {
    val width = log2Ceil(enum.size)
    this.enum = enum
    super.create(dir, width)
  }

  def :=(that: Symbol) = this colonEquals that

  protected def colonEquals(that: Symbol) {
    if (!enum.contains(that)) {
      ChiselError.error("Invalid assignment to EnumeratedUInt")
    } else {
      this := enum(that)
    }
  }
}

SomeModule.scala

package plan9

import Chisel._

class SomeModule extends Module {
  val io = new Bundle {
    val a = EnumeratedUInt(Enum(UInt(), List('a, 'b)))
  }
  a := 'c // Results in error
}