Correcting SimpleALU

}

class SimpleALU extends Module {

  val io = IO(new Bundle {

    val a      = Input(UInt(4.W))

    val b      = Input(UInt(4.W))

    val opcode = Input(UInt(2.W))

    val out = Output(UInt(4.W))

  })

  io.out := 0.U

  when (io.opcode === 0.U) {

  val io = new Bundle {

    val a      = UInt(INPUT,  4)

    val b      = UInt(INPUT,  4)

    val opcode = UInt(INPUT,  2)

    val out = UInt(OUTPUT, 4)

  }

  io.out := UInt(0) 

  when (io.opcode === UInt(0)) {

    io.out := io.a + io.b //ADD

  } .elsewhen (io.opcode === 1.U) {

  } .elsewhen (io.opcode === UInt(1)) {

    io.out := io.a - io.b //SUB

  } .elsewhen (io.opcode === 2.U) {

  } .elsewhen (io.opcode === UInt(2)) {

    io.out := io.a  	     //PASS A

  } .otherwise {

    io.out := io.b        //PASS B