Break out Utils.scala into smaller portions

14 files changed, 808 insertions, 0 deletions

diff --git a/src/main/scala/Chisel/util/Arbiter.scala b/src/main/scala/Chisel/util/Arbiter.scala
new file mode 100644
index 00000000..119b9f5a
--- /dev/null
+++ b/src/main/scala/Chisel/util/Arbiter.scala
@@ -0,0 +1,107 @@
+// See LICENSE for license details.
+
+/** Arbiters in all shapes and sizes.
+  */
+
+package Chisel
+
+/** An I/O bundle for the Arbiter */
+class ArbiterIO[T <: Data](gen: T, n: Int) extends Bundle {
+  val in  = Vec(Decoupled(gen), n).flip
+  val out = Decoupled(gen)
+  val chosen = UInt(OUTPUT, log2Up(n))
+}
+
+/** Arbiter Control determining which producer has access */
+object ArbiterCtrl
+{
+  def apply(request: Seq[Bool]): Seq[Bool] = {
+    Bool(true) +: (1 until request.length).map(i => !request.slice(0, i).foldLeft(Bool(false))(_ || _))
+  }
+}
+
+abstract class LockingArbiterLike[T <: Data](gen: T, n: Int, count: Int, needsLock: Option[T => Bool] = None)
+    extends Module {
+  require(isPow2(count))
+  def grant: Seq[Bool]
+  val io = new ArbiterIO(gen, n)
+  val locked  = if(count > 1) Reg(init=Bool(false)) else Bool(false)
+  val lockIdx = if(count > 1) Reg(init=UInt(n-1)) else UInt(n-1)
+  val chosen = Wire(UInt(width = log2Up(n)))
+
+  io.out.valid := io.in(chosen).valid
+  io.out.bits := io.in(chosen).bits
+  io.chosen := chosen
+
+  io.in(chosen).ready := Bool(false) // XXX FIRRTL workaround
+  for ((g, i) <- grant.zipWithIndex)
+    io.in(i).ready := Mux(locked, lockIdx === UInt(i), g) && io.out.ready
+
+  if(count > 1){
+    val cnt = Reg(init=UInt(0, width = log2Up(count)))
+    val cnt_next = cnt + UInt(1)
+    when(io.out.fire()) {
+      when(needsLock.map(_(io.out.bits)).getOrElse(Bool(true))) {
+        cnt := cnt_next
+        when(!locked) {
+          locked := Bool(true)
+          lockIdx := Vec(io.in.map{ in => in.fire()}).indexWhere{i: Bool => i}
+        }
+      }
+      when(cnt_next === UInt(0)) {
+        locked := Bool(false)
+      }
+    }
+  }
+}
+
+class LockingRRArbiter[T <: Data](gen: T, n: Int, count: Int, needsLock: Option[T => Bool] = None)
+    extends LockingArbiterLike[T](gen, n, count, needsLock) {
+  lazy val last_grant = Reg(init=UInt(0, log2Up(n)))
+  override def grant: Seq[Bool] = {
+    val ctrl = ArbiterCtrl((0 until n).map(i => io.in(i).valid && UInt(i) > last_grant) ++ io.in.map(_.valid))
+    (0 until n).map(i => ctrl(i) && UInt(i) > last_grant || ctrl(i + n))
+  }
+
+  var choose = UInt(n-1)
+  for (i <- n-2 to 0 by -1)
+    choose = Mux(io.in(i).valid, UInt(i), choose)
+  for (i <- n-1 to 1 by -1)
+    choose = Mux(io.in(i).valid && UInt(i) > last_grant, UInt(i), choose)
+  chosen := Mux(locked, lockIdx, choose)
+
+  when (io.out.fire()) { last_grant := chosen }
+}
+
+class LockingArbiter[T <: Data](gen: T, n: Int, count: Int, needsLock: Option[T => Bool] = None)
+    extends LockingArbiterLike[T](gen, n, count, needsLock) {
+  def grant: Seq[Bool] = ArbiterCtrl(io.in.map(_.valid))
+
+  var choose = UInt(n-1)
+  for (i <- n-2 to 0 by -1) {
+    choose = Mux(io.in(i).valid, UInt(i), choose)
+  }
+  chosen := Mux(locked, lockIdx, choose)
+}
+
+/** Hardware module that is used to sequence n producers into 1 consumer.
+  Producers are chosen in round robin order.
+
+  Example usage:
+    val arb = new RRArbiter(2, UInt())
+    arb.io.in(0) <> producer0.io.out
+    arb.io.in(1) <> producer1.io.out
+    consumer.io.in <> arb.io.out
+  */
+class RRArbiter[T <: Data](gen:T, n: Int) extends LockingRRArbiter[T](gen, n, 1)
+
+/** Hardware module that is used to sequence n producers into 1 consumer.
+ Priority is given to lower producer
+
+ Example usage:
+   val arb = Module(new Arbiter(2, UInt()))
+   arb.io.in(0) <> producer0.io.out
+   arb.io.in(1) <> producer1.io.out
+   consumer.io.in <> arb.io.out
+ */
+class Arbiter[T <: Data](gen: T, n: Int) extends LockingArbiter[T](gen, n, 1)
diff --git a/src/main/scala/Chisel/util/Bitwise.scala b/src/main/scala/Chisel/util/Bitwise.scala
new file mode 100644
index 00000000..7188ec32
--- /dev/null
+++ b/src/main/scala/Chisel/util/Bitwise.scala
@@ -0,0 +1,79 @@
+// See LICENSE for license details.
+
+/** Miscellaneous circuit generators operating on bits.
+  */
+
+package Chisel
+
+object FillInterleaved
+{
+  def apply(n: Int, in: UInt): UInt = apply(n, in.toBools)
+  def apply(n: Int, in: Seq[Bool]): UInt = Vec(in.map(Fill(n, _))).toBits
+}
+
+/** Returns the number of bits set (i.e value is 1) in the input signal.
+  */
+object PopCount
+{
+  def apply(in: Iterable[Bool]): UInt = {
+    if (in.size == 0) {
+      UInt(0)
+    } else if (in.size == 1) {
+      in.head
+    } else {
+      apply(in.slice(0, in.size/2)) + Cat(UInt(0), apply(in.slice(in.size/2, in.size)))
+    }
+  }
+  def apply(in: Bits): UInt = apply((0 until in.getWidth).map(in(_)))
+}
+
+/** Fill fans out a UInt to multiple copies */
+object Fill {
+  /** Fan out x n times */
+  def apply(n: Int, x: UInt): UInt = {
+    n match {
+      case 0 => UInt(width=0)
+      case 1 => x
+      case y if n > 1 =>
+        val p2 = Array.ofDim[UInt](log2Up(n + 1))
+        p2(0) = x
+        for (i <- 1 until p2.length)
+          p2(i) = Cat(p2(i-1), p2(i-1))
+        Cat((0 until log2Up(y + 1)).filter(i => (y & (1 << i)) != 0).map(p2(_)))
+      case _ => throw new IllegalArgumentException(s"n (=$n) must be nonnegative integer.")
+    }
+  }
+  /** Fan out x n times */
+  def apply(n: Int, x: Bool): UInt =
+    if (n > 1) {
+      UInt(0,n) - x
+    } else {
+      apply(n, x: UInt)
+    }
+}
+
+/** Litte/big bit endian convertion: reverse the order of the bits in a UInt.
+*/
+object Reverse
+{
+  private def doit(in: UInt, length: Int): UInt = {
+    if (length == 1) {
+      in
+    } else if (isPow2(length) && length >= 8 && length <= 64) {
+      // This esoterica improves simulation performance
+      var res = in
+      var shift = length >> 1
+      var mask = UInt((BigInt(1) << length) - 1, length)
+      do {
+        mask = mask ^ (mask(length-shift-1,0) << shift)
+        res = ((res >> shift) & mask) | ((res(length-shift-1,0) << shift) & ~mask)
+        shift = shift >> 1
+      } while (shift > 0)
+      res
+    } else {
+      val half = (1 << log2Up(length))/2
+      Cat(doit(in(half-1,0), half), doit(in(length-1,half), length-half))
+    }
+  }
+  def apply(in: UInt): UInt = doit(in, in.getWidth)
+}
diff --git a/src/main/scala/Chisel/util/CircuitMath.scala b/src/main/scala/Chisel/util/CircuitMath.scala
new file mode 100644
index 00000000..06cab903
--- /dev/null
+++ b/src/main/scala/Chisel/util/CircuitMath.scala
@@ -0,0 +1,26 @@
+// See LICENSE for license details.
+
+/** Circuit-land math operations.
+  */
+
+package Chisel
+
+/** Compute Log2 with truncation of a UInt in hardware using a Mux Tree
+  * An alternative interpretation is it computes the minimum number of bits needed to represent x
+  * @example
+  * {{{ data_out := Log2(data_in) }}}
+  * @note Truncation is used so Log2(UInt(12412)) = 13*/
+object Log2 {
+  /** Compute the Log2 on the least significant n bits of x */
+  def apply(x: Bits, width: Int): UInt = {
+    if (width < 2) {
+      UInt(0)
+    } else if (width == 2) {
+      x(1)
+    } else {
+      Mux(x(width-1), UInt(width-1), apply(x, width-1))
+    }
+  }
+
+  def apply(x: Bits): UInt = apply(x, x.getWidth)
+}
diff --git a/src/main/scala/Chisel/util/Conditional.scala b/src/main/scala/Chisel/util/Conditional.scala
new file mode 100644
index 00000000..b0ac4491
--- /dev/null
+++ b/src/main/scala/Chisel/util/Conditional.scala
@@ -0,0 +1,69 @@
+// See LICENSE for license details.
+
+/** Conditional blocks.
+  */
+
+package Chisel
+
+import scala.language.reflectiveCalls
+import scala.language.experimental.macros
+import scala.reflect.runtime.universe._
+import scala.reflect.macros.blackbox._
+
+/** This is identical to [[Chisel.when when]] with the condition inverted */
+object unless {  // scalastyle:ignore object.name
+  def apply(c: Bool)(block: => Unit) {
+    when (!c) { block }
+  }
+}
+
+class SwitchContext[T <: Bits](cond: T) {
+  def is(v: Iterable[T])(block: => Unit) {
+    if (!v.isEmpty) when (v.map(_.asUInt === cond.asUInt).reduce(_||_)) { block }
+  }
+  def is(v: T)(block: => Unit) { is(Seq(v))(block) }
+  def is(v: T, vr: T*)(block: => Unit) { is(v :: vr.toList)(block) }
+}
+
+/** An object for separate cases in [[Chisel.switch switch]]
+  * It is equivalent to a [[Chisel.when$ when]] block comparing to the condition
+  * Use outside of a switch statement is illegal */
+object is {   // scalastyle:ignore object.name
+  // Begin deprecation of non-type-parameterized is statements.
+  def apply(v: Iterable[Bits])(block: => Unit) {
+    Builder.error("The 'is' keyword may not be used outside of a switch.")
+  }
+
+  def apply(v: Bits)(block: => Unit) {
+    Builder.error("The 'is' keyword may not be used outside of a switch.")
+  }
+
+  def apply(v: Bits, vr: Bits*)(block: => Unit) {
+    Builder.error("The 'is' keyword may not be used outside of a switch.")
+  }
+}
+
+/** Conditional logic to form a switch block
+  * @example
+  * {{{ ... // default values here
+  * switch ( myState ) {
+  *   is( state1 ) {
+  *     ... // some logic here
+  *   }
+  *   is( state2 ) {
+  *     ... // some logic here
+  *   }
+  * } }}}*/
+object switch {  // scalastyle:ignore object.name
+  def apply[T <: Bits](cond: T)(x: => Unit): Unit = macro impl
+  def impl(c: Context)(cond: c.Tree)(x: c.Tree): c.Tree = { import c.universe._
+    val sc = c.universe.internal.reificationSupport.freshTermName("sc")
+    def extractIsStatement(tree: Tree): List[c.universe.Tree] = tree match {
+      case q"Chisel.is.apply( ..$params )( ..$body )" => List(q"$sc.is( ..$params )( ..$body )")
+      case b => throw new Exception(s"Cannot include blocks that do not begin with is() in switch.")
+    }
+    val q"..$body" = x
+    val ises = body.flatMap(extractIsStatement(_))
+    q"""{ val $sc = new SwitchContext($cond); ..$ises }"""
+  }
+}
diff --git a/src/main/scala/Chisel/util/Counter.scala b/src/main/scala/Chisel/util/Counter.scala
new file mode 100644
index 00000000..e4a8e95b
--- /dev/null
+++ b/src/main/scala/Chisel/util/Counter.scala
@@ -0,0 +1,35 @@
+// See LICENSE for license details.
+
+package Chisel
+
+/** A counter module
+  * @param n The maximum value of the counter, does not have to be power of 2
+  */
+class Counter(val n: Int) {
+  val value = if (n == 1) UInt(0) else Reg(init=UInt(0, log2Up(n)))
+  def inc(): Bool = {
+    if (n == 1) {
+      Bool(true)
+    } else {
+      val wrap = value === UInt(n-1)
+      value := Mux(Bool(!isPow2(n)) && wrap, UInt(0), value + UInt(1))
+      wrap
+    }
+  }
+}
+
+/** Counter Object
+  * Example Usage:
+  * {{{ val countOn = Bool(true) // increment counter every clock cycle
+  * val myCounter = Counter(countOn, n)
+  * when ( myCounter.value === UInt(3) ) { ... } }}}*/
+object Counter
+{
+  def apply(n: Int): Counter = new Counter(n)
+  def apply(cond: Bool, n: Int): (UInt, Bool) = {
+    val c = new Counter(n)
+    var wrap: Bool = null
+    when (cond) { wrap = c.inc() }
+    (c.value, cond && wrap)
+  }
+}
diff --git a/src/main/scala/Chisel/util/Decoupled.scala b/src/main/scala/Chisel/util/Decoupled.scala
new file mode 100644
index 00000000..b1505887
--- /dev/null
+++ b/src/main/scala/Chisel/util/Decoupled.scala
@@ -0,0 +1,143 @@
+// See LICENSE for license details.
+
+/** Wrappers for ready-valid (Decoupled) interfaces and associated circuit generators using them.
+  */
+
+package Chisel
+
+/** An I/O Bundle with simple handshaking using valid and ready signals for data 'bits'*/
+class DecoupledIO[+T <: Data](gen: T) extends Bundle
+{
+  val ready = Bool(INPUT)
+  val valid = Bool(OUTPUT)
+  val bits  = gen.cloneType.asOutput
+  def fire(dummy: Int = 0): Bool = ready && valid
+  override def cloneType: this.type = new DecoupledIO(gen).asInstanceOf[this.type]
+}
+
+/** Adds a ready-valid handshaking protocol to any interface.
+  * The standard used is that the consumer uses the flipped interface.
+  */
+object Decoupled {
+  def apply[T <: Data](gen: T): DecoupledIO[T] = new DecoupledIO(gen)
+}
+
+/** An I/O bundle for enqueuing data with valid/ready handshaking */
+class EnqIO[T <: Data](gen: T) extends DecoupledIO(gen)
+{
+  def enq(dat: T): T = { valid := Bool(true); bits := dat; dat }
+  valid := Bool(false)
+  for (io <- bits.flatten)
+    io := UInt(0)
+  override def cloneType: this.type = { new EnqIO(gen).asInstanceOf[this.type]; }
+}
+
+/** An I/O bundle for dequeuing data with valid/ready handshaking */
+class DeqIO[T <: Data](gen: T) extends DecoupledIO(gen)
+{
+  flip()
+  ready := Bool(false)
+  def deq(b: Boolean = false): T = { ready := Bool(true); bits }
+  override def cloneType: this.type = { new DeqIO(gen).asInstanceOf[this.type]; }
+}
+
+/** An I/O bundle for dequeuing data with valid/ready handshaking */
+class DecoupledIOC[+T <: Data](gen: T) extends Bundle
+{
+  val ready = Bool(INPUT)
+  val valid = Bool(OUTPUT)
+  val bits  = gen.cloneType.asOutput
+}
+
+/** An I/O Bundle for Queues
+  * @param gen The type of data to queue
+  * @param entries The max number of entries in the queue */
+class QueueIO[T <: Data](gen: T, entries: Int) extends Bundle
+{
+  /** I/O to enqueue data, is [[Chisel.DecoupledIO]] flipped */
+  val enq   = Decoupled(gen.cloneType).flip
+  /** I/O to enqueue data, is [[Chisel.DecoupledIO]]*/
+  val deq   = Decoupled(gen.cloneType)
+  /** The current amount of data in the queue */
+  val count = UInt(OUTPUT, log2Up(entries + 1))
+}
+
+/** A hardware module implementing a Queue
+  * @param gen The type of data to queue
+  * @param entries The max number of entries in the queue
+  * @param pipe True if a single entry queue can run at full throughput (like a pipeline). The ''ready'' signals are
+  * combinationally coupled.
+  * @param flow True if the inputs can be consumed on the same cycle (the inputs "flow" through the queue immediately).
+  * The ''valid'' signals are coupled.
+  *
+  * Example usage:
+  *    {{{ val q = new Queue(UInt(), 16)
+  *    q.io.enq <> producer.io.out
+  *    consumer.io.in <> q.io.deq }}}
+  */
+class Queue[T <: Data](gen: T, val entries: Int,
+                       pipe: Boolean = false,
+                       flow: Boolean = false,
+                       _reset: Bool = null) extends Module(_reset=_reset)
+{
+  val io = new QueueIO(gen, entries)
+
+  val ram = Mem(gen, entries)
+  val enq_ptr = Counter(entries)
+  val deq_ptr = Counter(entries)
+  val maybe_full = Reg(init=Bool(false))
+
+  val ptr_match = enq_ptr.value === deq_ptr.value
+  val empty = ptr_match && !maybe_full
+  val full = ptr_match && maybe_full
+  val maybe_flow = Bool(flow) && empty
+  val do_flow = maybe_flow && io.deq.ready
+
+  val do_enq = io.enq.ready && io.enq.valid && !do_flow
+  val do_deq = io.deq.ready && io.deq.valid && !do_flow
+  when (do_enq) {
+    ram(enq_ptr.value) := io.enq.bits
+    enq_ptr.inc()
+  }
+  when (do_deq) {
+    deq_ptr.inc()
+  }
+  when (do_enq != do_deq) {
+    maybe_full := do_enq
+  }
+
+  io.deq.valid := !empty || Bool(flow) && io.enq.valid
+  io.enq.ready := !full || Bool(pipe) && io.deq.ready
+  io.deq.bits := Mux(maybe_flow, io.enq.bits, ram(deq_ptr.value))
+
+  val ptr_diff = enq_ptr.value - deq_ptr.value
+  if (isPow2(entries)) {
+    io.count := Cat(maybe_full && ptr_match, ptr_diff)
+  } else {
+    io.count := Mux(ptr_match,
+                    Mux(maybe_full,
+                      UInt(entries), UInt(0)),
+                    Mux(deq_ptr.value > enq_ptr.value,
+                      UInt(entries) + ptr_diff, ptr_diff))
+  }
+}
+
+/** Generic hardware queue. Required parameter entries controls
+  the depth of the queues. The width of the queue is determined
+  from the inputs.
+
+  Example usage:
+     {{{ val q = Queue(Decoupled(UInt()), 16)
+     q.io.enq <> producer.io.out
+     consumer.io.in <> q.io.deq }}}
+  */
+object Queue
+{
+  def apply[T <: Data](enq: DecoupledIO[T], entries: Int = 2, pipe: Boolean = false): DecoupledIO[T]  = {
+    val q = Module(new Queue(enq.bits.cloneType, entries, pipe))
+    q.io.enq.valid := enq.valid // not using <> so that override is allowed
+    q.io.enq.bits := enq.bits
+    enq.ready := q.io.enq.ready
+    q.io.deq
+  }
+}
diff --git a/src/main/scala/Chisel/util/Enum.scala b/src/main/scala/Chisel/util/Enum.scala
new file mode 100644
index 00000000..3e2b038f
--- /dev/null
+++ b/src/main/scala/Chisel/util/Enum.scala
@@ -0,0 +1,20 @@
+// See LICENSE for license details.
+
+/** Enum generators, allowing circuit constants to have more meaningful names.
+  */
+
+package Chisel
+
+object Enum {
+  /** Returns a sequence of Bits subtypes with values from 0 until n. Helper method. */
+  private def createValues[T <: Bits](nodeType: T, n: Int): Seq[T] = (0 until n).map(x => nodeType.fromInt(x))
+
+  /** create n enum values of given type */
+  def apply[T <: Bits](nodeType: T, n: Int): List[T] = createValues(nodeType, n).toList
+
+  /** create enum values of given type and names */
+  def apply[T <: Bits](nodeType: T, l: Symbol *): Map[Symbol, T] = (l zip createValues(nodeType, l.length)).toMap
+
+  /** create enum values of given type and names */
+  def apply[T <: Bits](nodeType: T, l: List[Symbol]): Map[Symbol, T] = (l zip createValues(nodeType, l.length)).toMap
+}
diff --git a/src/main/scala/Chisel/util/LFSR.scala b/src/main/scala/Chisel/util/LFSR.scala
new file mode 100644
index 00000000..839b1d1f
--- /dev/null
+++ b/src/main/scala/Chisel/util/LFSR.scala
@@ -0,0 +1,22 @@
+// See LICENSE for license details.
+
+/** LFSRs in all shapes and sizes.
+  */
+
+package Chisel
+
+// scalastyle:off magic.number
+/** linear feedback shift register
+  */
+object LFSR16
+{
+  def apply(increment: Bool = Bool(true)): UInt =
+  {
+    val width = 16
+    val lfsr = Reg(init=UInt(1, width))
+    when (increment) { lfsr := Cat(lfsr(0)^lfsr(2)^lfsr(3)^lfsr(5), lfsr(width-1,1)) }
+    lfsr
+  }
+}
+// scalastyle:on magic.number
+
diff --git a/src/main/scala/Chisel/util/Lookup.scala b/src/main/scala/Chisel/util/Lookup.scala
new file mode 100644
index 00000000..54922fc4
--- /dev/null
+++ b/src/main/scala/Chisel/util/Lookup.scala
@@ -0,0 +1,17 @@
+// See LICENSE for license details.
+
+package Chisel
+
+object ListLookup {
+  def apply[T <: Data](addr: UInt, default: List[T], mapping: Array[(BitPat, List[T])]): List[T] = {
+    val map = mapping.map(m => (m._1 === addr, m._2))
+    default.zipWithIndex map { case (d, i) =>
+      map.foldRight(d)((m, n) => Mux(m._1, m._2(i), n))
+    }
+  }
+}
+
+object Lookup {
+  def apply[T <: Bits](addr: UInt, default: T, mapping: Seq[(BitPat, T)]): T =
+    ListLookup(addr, List(default), mapping.map(m => (m._1, List(m._2))).toArray).head
+}
diff --git a/src/main/scala/Chisel/util/Math.scala b/src/main/scala/Chisel/util/Math.scala
new file mode 100644
index 00000000..270301f0
--- /dev/null
+++ b/src/main/scala/Chisel/util/Math.scala
@@ -0,0 +1,39 @@
+// See LICENSE for license details.
+
+/** Scala-land math helper functions, like logs.
+  */
+
+package Chisel
+
+/** Compute the log2 rounded up with min value of 1 */
+object log2Up {
+  def apply(in: BigInt): Int = 1 max (in-1).bitLength
+  def apply(in: Int): Int = apply(BigInt(in))
+}
+
+/** Compute the log2 rounded up */
+object log2Ceil {
+  def apply(in: BigInt): Int = {
+    require(in > 0)
+    (in-1).bitLength
+  }
+  def apply(in: Int): Int = apply(BigInt(in))
+}
+
+/** Compute the log2 rounded down with min value of 1 */
+object log2Down {
+  def apply(in: BigInt): Int = log2Up(in) - (if (isPow2(in)) 0 else 1)
+  def apply(in: Int): Int = apply(BigInt(in))
+}
+
+/** Compute the log2 rounded down */
+object log2Floor {
+  def apply(in: BigInt): Int = log2Ceil(in) - (if (isPow2(in)) 0 else 1)
+  def apply(in: Int): Int = apply(BigInt(in))
+}
+
+/** Check if an Integer is a power of 2 */
+object isPow2 {
+  def apply(in: BigInt): Boolean = in > 0 && ((in & (in-1)) == 0)
+  def apply(in: Int): Boolean = apply(BigInt(in))
+}
diff --git a/src/main/scala/Chisel/util/Mux.scala b/src/main/scala/Chisel/util/Mux.scala
new file mode 100644
index 00000000..18b5dd53
--- /dev/null
+++ b/src/main/scala/Chisel/util/Mux.scala
@@ -0,0 +1,75 @@
+// See LICENSE for license details.
+
+/** Mux circuit generators.
+  */
+
+package Chisel
+
+/** Builds a Mux tree out of the input signal vector using a one hot encoded
+  select signal. Returns the output of the Mux tree.
+  */
+object Mux1H
+{
+  def apply[T <: Data](sel: Seq[Bool], in: Seq[T]): T =
+    apply(sel zip in)
+  def apply[T <: Data](in: Iterable[(Bool, T)]): T = {
+    if (in.tail.isEmpty) {
+      in.head._2
+    } else {
+      val masked = in map {case (s, i) => Mux(s, i.toBits, Bits(0))}
+      val width = in.map(_._2.width).reduce(_ max _)
+      in.head._2.cloneTypeWidth(width).fromBits(masked.reduceLeft(_|_))
+    }
+  }
+  def apply[T <: Data](sel: UInt, in: Seq[T]): T =
+    apply((0 until in.size).map(sel(_)), in)
+  def apply(sel: UInt, in: UInt): Bool = (sel & in).orR
+}
+
+/** Builds a Mux tree under the assumption that multiple select signals
+  can be enabled. Priority is given to the first select signal.
+
+  Returns the output of the Mux tree.
+  */
+object PriorityMux
+{
+  def apply[T <: Bits](in: Seq[(Bool, T)]): T = {
+    if (in.size == 1) {
+      in.head._2
+    } else {
+      Mux(in.head._1, in.head._2, apply(in.tail))
+    }
+  }
+  def apply[T <: Bits](sel: Seq[Bool], in: Seq[T]): T = apply(sel zip in)
+  def apply[T <: Bits](sel: Bits, in: Seq[T]): T = apply((0 until in.size).map(sel(_)), in)
+}
+
+/** MuxLookup creates a cascade of n Muxs to search for a key value */
+object MuxLookup {
+  /** @param key a key to search for
+    * @param default a default value if nothing is found
+    * @param mapping a sequence to search of keys and values
+    * @return the value found or the default if not
+    */
+  def apply[S <: UInt, T <: Bits] (key: S, default: T, mapping: Seq[(S, T)]): T = {
+    var res = default;
+    for ((k, v) <- mapping.reverse)
+      res = Mux(k === key, v, res);
+    res
+  }
+
+}
+
+/** MuxCase returns the first value that is enabled in a map of values */
+object MuxCase {
+  /** @param default the default value if none are enabled
+    * @param mapping a set of data values with associated enables
+    * @return the first value in mapping that is enabled */
+  def apply[T <: Bits] (default: T, mapping: Seq[(Bool, T)]): T = {
+    var res = default;
+    for ((t, v) <- mapping.reverse){
+      res = Mux(t, v, res);
+    }
+    res
+  }
+}
diff --git a/src/main/scala/Chisel/util/OneHot.scala b/src/main/scala/Chisel/util/OneHot.scala
new file mode 100644
index 00000000..38b96511
--- /dev/null
+++ b/src/main/scala/Chisel/util/OneHot.scala
@@ -0,0 +1,62 @@
+// See LICENSE for license details.
+
+/** Circuit generators for working with one-hot representations.
+  */
+
+package Chisel
+
+/** Converts from One Hot Encoding to a UInt indicating which bit is active
+  * This is the inverse of [[Chisel.UIntToOH UIntToOH]]*/
+object OHToUInt {
+  def apply(in: Seq[Bool]): UInt = apply(Vec(in))
+  def apply(in: Vec[Bool]): UInt = apply(in.toBits, in.size)
+  def apply(in: Bits): UInt = apply(in, in.getWidth)
+
+  def apply(in: Bits, width: Int): UInt = {
+    if (width <= 2) {
+      Log2(in, width)
+    } else {
+      val mid = 1 << (log2Up(width)-1)
+      val hi = in(width-1, mid)
+      val lo = in(mid-1, 0)
+      Cat(hi.orR, apply(hi | lo, mid))
+    }
+  }
+}
+
+/** @return the bit position of the trailing 1 in the input vector
+  * with the assumption that multiple bits of the input bit vector can be set
+  * @example {{{ data_out := PriorityEncoder(data_in) }}}
+  */
+object PriorityEncoder {
+  def apply(in: Seq[Bool]): UInt = PriorityMux(in, (0 until in.size).map(UInt(_)))
+  def apply(in: Bits): UInt = apply(in.toBools)
+}
+
+/** Returns the one hot encoding of the input UInt.
+  */
+object UIntToOH
+{
+  def apply(in: UInt, width: Int = -1): UInt =
+    if (width == -1) {
+      UInt(1) << in
+    } else {
+      (UInt(1) << in(log2Up(width)-1,0))(width-1,0)
+    }
+}
+
+/** Returns a bit vector in which only the least-significant 1 bit in
+  the input vector, if any, is set.
+  */
+object PriorityEncoderOH
+{
+  private def encode(in: Seq[Bool]): UInt = {
+    val outs = Vec.tabulate(in.size)(i => UInt(BigInt(1) << i, in.size))
+    PriorityMux(in :+ Bool(true), outs :+ UInt(0, in.size))
+  }
+  def apply(in: Seq[Bool]): Vec[Bool] = {
+    val enc = encode(in)
+    Vec.tabulate(in.size)(enc(_))
+  }
+  def apply(in: Bits): UInt = encode((0 until in.getWidth).map(i => in(i)))
+}
diff --git a/src/main/scala/Chisel/util/Reg.scala b/src/main/scala/Chisel/util/Reg.scala
new file mode 100644
index 00000000..44593dfd
--- /dev/null
+++ b/src/main/scala/Chisel/util/Reg.scala
@@ -0,0 +1,55 @@
+// See LICENSE for license details.
+
+/** Variations and helpers for registers.
+  */
+
+package Chisel
+
+object RegNext {
+
+  def apply[T <: Data](next: T): T = Reg[T](next, next, null.asInstanceOf[T])
+
+  def apply[T <: Data](next: T, init: T): T = Reg[T](next, next, init)
+
+}
+
+object RegInit {
+
+  def apply[T <: Data](init: T): T = Reg[T](init, null.asInstanceOf[T], init)
+
+}
+
+/** A register with an Enable signal */
+object RegEnable
+{
+  def apply[T <: Data](updateData: T, enable: Bool): T = {
+    val r = Reg(updateData)
+    when (enable) { r := updateData }
+    r
+  }
+  def apply[T <: Data](updateData: T, resetData: T, enable: Bool): T = {
+    val r = RegInit(resetData)
+    when (enable) { r := updateData }
+    r
+  }
+}
+
+/** Returns the n-cycle delayed version of the input signal.
+  */
+object ShiftRegister
+{
+  /** @param in input to delay
+    * @param n number of cycles to delay
+    * @param en enable the shift */
+  def apply[T <: Data](in: T, n: Int, en: Bool = Bool(true)): T =
+  {
+    // The order of tests reflects the expected use cases.
+    if (n == 1) {
+      RegEnable(in, en)
+    } else if (n != 0) {
+      RegNext(apply(in, n-1, en))
+    } else {
+      in
+    }
+  }
+}
diff --git a/src/main/scala/Chisel/util/Valid.scala b/src/main/scala/Chisel/util/Valid.scala
new file mode 100644
index 00000000..9e2202bb
--- /dev/null
+++ b/src/main/scala/Chisel/util/Valid.scala
@@ -0,0 +1,59 @@
+// See LICENSE for license details.
+
+/** Wrappers for valid interfaces and associated circuit generators using them.
+  */
+
+package Chisel
+
+/** An I/O Bundle containing data and a signal determining if it is valid */
+class ValidIO[+T <: Data](gen2: T) extends Bundle
+{
+  val valid = Bool(OUTPUT)
+  val bits = gen2.cloneType.asOutput
+  def fire(dummy: Int = 0): Bool = valid
+  override def cloneType: this.type = new ValidIO(gen2).asInstanceOf[this.type]
+}
+
+/** Adds a valid protocol to any interface. The standard used is
+  that the consumer uses the flipped interface.
+*/
+object Valid {
+  def apply[T <: Data](gen: T): ValidIO[T] = new ValidIO(gen)
+}
+
+/** A hardware module that delays data coming down the pipeline
+  by the number of cycles set by the latency parameter. Functionality
+  is similar to ShiftRegister but this exposes a Pipe interface.
+
+  Example usage:
+    val pipe = new Pipe(UInt())
+    pipe.io.enq <> produce.io.out
+    consumer.io.in <> pipe.io.deq
+  */
+object Pipe
+{
+  def apply[T <: Data](enqValid: Bool, enqBits: T, latency: Int): ValidIO[T] = {
+    if (latency == 0) {
+      val out = Wire(Valid(enqBits))
+      out.valid <> enqValid
+      out.bits <> enqBits
+      out
+    } else {
+      val v = Reg(Bool(), next=enqValid, init=Bool(false))
+      val b = RegEnable(enqBits, enqValid)
+      apply(v, b, latency-1)
+    }
+  }
+  def apply[T <: Data](enqValid: Bool, enqBits: T): ValidIO[T] = apply(enqValid, enqBits, 1)
+  def apply[T <: Data](enq: ValidIO[T], latency: Int = 1): ValidIO[T] = apply(enq.valid, enq.bits, latency)
+}
+
+class Pipe[T <: Data](gen: T, latency: Int = 1) extends Module
+{
+  val io = new Bundle {
+    val enq = Valid(gen).flip
+    val deq = Valid(gen)
+  }
+
+  io.deq <> Pipe(io.enq, latency)
+}