First cut at refactoring unittests into a top-level utility. Individual tests co-located with their DUT. No functional changes.

src/main/scala/util/Timer.scala

@@ -0,0 +1,74 @@
+/// See LICENSE for license details.
+package util
+
+import Chisel._
+
+/** Timer with a statically-specified period.
+  * Can take multiple inflight start-stop events with ID
+  * Will continue to count down as long as at least one event is inflight
+  */
+class Timer(initCount: Int, maxInflight: Int) extends Module {
+  val io = new Bundle {
+    val start = Valid(UInt(width = log2Up(maxInflight))).flip
+    val stop = Valid(UInt(width = log2Up(maxInflight))).flip
+    val timeout = Valid(UInt(width = log2Up(maxInflight)))
+  }
+
+  val inflight = Reg(init = Vec.fill(maxInflight) { Bool(false) })
+  val countdown = Reg(UInt(width = log2Up(initCount)))
+  val active = inflight.reduce(_ || _)
+
+  when (active) {
+    countdown := countdown - UInt(1)
+  }
+
+  when (io.start.valid) {
+    inflight(io.start.bits) := Bool(true)
+    countdown := UInt(initCount - 1)
+  }
+  when (io.stop.valid) {
+    inflight(io.stop.bits) := Bool(false)
+  }
+
+  io.timeout.valid := countdown === UInt(0) && active
+  io.timeout.bits := PriorityEncoder(inflight)
+
+  assert(!io.stop.valid || inflight(io.stop.bits),
+         "Timer stop for transaction that's not inflight")
+}
+
+object Timer {
+  def apply(initCount: Int, start: Bool, stop: Bool): Bool = {
+    val timer = Module(new Timer(initCount, 1))
+    timer.io.start.valid := start
+    timer.io.start.bits  := UInt(0)
+    timer.io.stop.valid  := stop
+    timer.io.stop.bits   := UInt(0)
+    timer.io.timeout.valid
+  }
+}
+
+/** Timer with a statically-specified period.  */
+class DynamicTimer(w: Int) extends Module {
+  val io = new Bundle {
+    val start   = Bool(INPUT)
+    val period  = UInt(INPUT, w)
+    val stop    = Bool(INPUT)
+    val timeout = Bool(OUTPUT)
+  }
+
+  val countdown = Reg(init = UInt(0, w))
+  val active = Reg(init = Bool(false))
+
+  when (io.start) {
+    countdown := io.period
+    active := Bool(true)
+  } .elsewhen (io.stop || countdown === UInt(0)) {
+    active := Bool(false)
+  } .elsewhen (active) {
+    countdown := countdown - UInt(1)
+  }
+
+  io.timeout := countdown === UInt(0) && active
+}
+