ChiselEnum: cannot use .asUInt.litValue to get the litValue

[edwardcwang]

Type of issue: bug report / feature request

Impact: API addition (no impact on existing code)

Development Phase: request

Other information:

When using ChiselEnum, one should be able to take enum literals and use asUInt followed by litValue. This pattern is notably useful when trying to turn enum literals into BitPats.

object ExampleEnum extends ChiselEnum {
  val Foo, Bar = Value
}

// Does not work since BitPat() internally calls .litValue which crashes with None.get
val simple = BitPat(ExampleEnum.Foo.asUInt)

// Instead we have to use a clumsy workaround
val complicated = BitPat(ExampleEnum.Foo.litValue.U(ExampleEnum.getWidth.W))

[ekiwi]

This sounds like a good idea. Would you be interested in making a PR?

[carlosedp]

Related to https://github.com/chipsalliance/chisel3/pull/2327