Create OneHotChiselEnum where elements have one-hot encoding IDs

Author: carlosedp

core/src/main/scala/chisel3/StrongEnum.scala

@@ -232,6 +232,9 @@ abstract class EnumType(private val factory: EnumFactory, selfAnnotating: Boolea
   def toPrintable: Printable = FullName(this) // TODO: Find a better pretty printer
 }
 
+trait OneHotEnumFactory extends EnumFactory{
+  override val oneHot: Boolean = true
+}
 
 abstract class EnumFactory {
   class Type extends EnumType(this)
@@ -241,6 +244,7 @@ abstract class EnumFactory {
 
   private var id: BigInt = 0
   private[chisel3] var width: Width = 0.W
+  val oneHot: Boolean = false
 
   private case class EnumRecord(inst: Type, name: String)
   private val enumRecords = mutable.ArrayBuffer.empty[EnumRecord]
@@ -274,13 +278,13 @@ abstract class EnumFactory {
   protected def do_Value(name: String): Type = {
     val result = new Type
 
-    // We have to use UnknownWidth here, because we don't actually know what the final width will be
-    result.bindToLiteral(id, UnknownWidth())
-
-    enumRecords.append(EnumRecord(result, name))
+    val resId = if (!oneHot) id else BigInt(1 << id.toInt)
 
-    width = (1 max id.bitLength).W
+    // We have to use UnknownWidth here, because we don't actually know what the final width will be
+    result.bindToLiteral(resId, UnknownWidth())
+    width = (1 max resId.bitLength).W
     id += 1
+    enumRecords.append(EnumRecord(result, name))
 
     result
   }
@@ -343,7 +347,6 @@ abstract class EnumFactory {
   }
 }
 
-
 private[chisel3] object EnumMacros {
   def ValImpl(c: Context) : c.Tree = {
     import c.universe._

core/src/main/scala/chisel3/experimental/package.scala

@@ -23,6 +23,13 @@ package object experimental {
 
   type ChiselEnum = EnumFactory
 
+  /**
+   * OneHotChiselEnum extends the ChiselEnum type for creating enums with
+   * one-hot encoding IDs.
+   * This enum type pairs well with [[Mux1H]] for parallel mux processing.
+   */
+  type OneHotChiselEnum = OneHotEnumFactory
+
   // Rocket Chip-style clonemodule
 
   /** A record containing the results of CloneModuleAsRecord

src/main/scala/chisel3/util/Mux.scala

@@ -9,6 +9,7 @@ import chisel3._
 
 /** Builds a Mux tree out of the input signal vector using a one hot encoded
   * select signal. Returns the output of the Mux tree.
+  * Pairs well with [[OneHotChiselEnum]] to create a one hot encoded select signal.
   *
   * @example {{{
   * val hotValue = chisel3.util.Mux1H(Seq(
@@ -17,6 +18,21 @@ import chisel3._
   *  io.selector(2) -> 8.U,
   *  io.selector(4) -> 11.U,
   * ))
+  *
+  * // or using OneHotChiselEnum
+  *
+  * object selector extends chisel3.experimental.OneHotChiselEnum {
+  *   val s0, s1, s2, s3 = Value
+  * }
+  * val selectorVal = Wire(UInt(selector.getWidth.W))
+  * selectorVal := selector.s1.asUInt
+  * val hotValue = chisel3.util.Mux1H(selectorVal.asUInt,
+      Seq(
+  *     2.U,
+  *     4.U,
+  *     8.U,
+  *     11.U,
+  *   ))
   * }}}
   *
   * @note results unspecified unless exactly one select signal is high