5 files changed, 10 insertions, 19 deletions
diff --git a/src/main/scala/Chisel/Data.scala b/src/main/scala/Chisel/Data.scala
index 1011fe47..0ac3ee32 100644
--- a/src/main/scala/Chisel/Data.scala
+++ b/src/main/scala/Chisel/Data.scala
@@ -119,7 +119,7 @@ object Wire {
     if (init != null) {
       x := init
     } else {
-      x.flatten.foreach(e => e := e.fromInt(0))
+      pushCommand(DefInvalid(x.ref))
     }
     x
   }
@@ -141,11 +141,3 @@ sealed class Clock(dirArg: Direction) extends Element(dirArg, Width(1)) {
     case _ => this badConnect that
   }
 }
-
-// TODO: check with FIRRTL specs, how much official implementation flexibility
-// is there?
-/** A source of garbage data, used to initialize Wires to a don't-care value. */
-private object Poison extends Command {
-  def apply[T <: Data](t: T): T =
-    pushCommand(DefPoison(t.cloneType)).id
-}
diff --git a/src/main/scala/Chisel/Mem.scala b/src/main/scala/Chisel/Mem.scala
index 3bbb1151..21284607 100644
--- a/src/main/scala/Chisel/Mem.scala
+++ b/src/main/scala/Chisel/Mem.scala
@@ -113,6 +113,9 @@ object SeqMem {
   * result is undefined (unlike Vec, where the last assignment wins)
   */
 sealed class SeqMem[T <: Data](t: T, n: Int) extends MemBase[T](t, n) {
-  def read(addr: UInt, enable: Bool): T =
-    read(Mux(enable, addr, Poison(addr)))
+  def read(addr: UInt, enable: Bool): T = {
+    val a = Wire(UInt())
+    when (enable) { a := addr }
+    read(a)
+  }
 }
diff --git a/src/main/scala/Chisel/Module.scala b/src/main/scala/Chisel/Module.scala
index 2a0f29db..463c2f81 100644
--- a/src/main/scala/Chisel/Module.scala
+++ b/src/main/scala/Chisel/Module.scala
@@ -20,16 +20,12 @@ object Module {
   def apply[T <: Module](bc: => T): T = {
     val parent = dynamicContext.currentModule
     val m = bc.setRefs()
-    // init module outputs
-    m._commands prependAll (for (p <- m.io.flatten; if p.dir == OUTPUT)
-      yield Connect(p.lref, p.fromInt(0).ref))
+    m._commands.prepend(DefInvalid(m.io.ref)) // init module outputs
     dynamicContext.currentModule = parent
     val ports = m.computePorts
     Builder.components += Component(m, m.name, ports, m._commands)
     pushCommand(DefInstance(m, ports))
-    // init instance inputs
-    for (p <- m.io.flatten; if p.dir == INPUT)
-      p := p.fromInt(0)
+    pushCommand(DefInvalid(m.io.ref)) // init instance inputs
     m.connectImplicitIOs()
   }
 }
diff --git a/src/main/scala/Chisel/internal/firrtl/Emitter.scala b/src/main/scala/Chisel/internal/firrtl/Emitter.scala
index 2765efa8..13d9fa8f 100644
--- a/src/main/scala/Chisel/internal/firrtl/Emitter.scala
+++ b/src/main/scala/Chisel/internal/firrtl/Emitter.scala
@@ -11,7 +11,6 @@ private class Emitter(circuit: Circuit) {
   private def emit(e: Command, ctx: Component): String = e match {
     case e: DefPrim[_] => s"node ${e.name} = ${e.op.name}(${e.args.map(_.fullName(ctx)).reduce(_ + ", " + _)})"
     case e: DefWire => s"wire ${e.name} : ${e.id.toType}"
-    case e: DefPoison[_] => s"poison ${e.name} : ${e.id.toType}"
     case e: DefReg => s"reg ${e.name} : ${e.id.toType}, ${e.clock.fullName(ctx)}"
     case e: DefRegInit => s"reg ${e.name} : ${e.id.toType}, ${e.clock.fullName(ctx)} with : (reset => (${e.reset.fullName(ctx)}, ${e.init.fullName(ctx)}))"
     case e: DefMemory => s"cmem ${e.name} : ${e.t.toType}[${e.size}]"
@@ -21,6 +20,7 @@ private class Emitter(circuit: Circuit) {
     case e: BulkConnect => s"${e.loc1.fullName(ctx)} <- ${e.loc2.fullName(ctx)}"
     case e: Stop => s"stop(${e.clk.fullName(ctx)}, UInt<1>(1), ${e.ret})"
     case e: Printf => s"""printf(${e.clk.fullName(ctx)}, UInt<1>(1), "${e.format}"${e.ids.map(_.fullName(ctx)).fold(""){_ + ", " + _}})"""
+    case e: DefInvalid => s"${e.arg.fullName(ctx)} is invalid"
     case e: DefInstance => {
       val modName = moduleMap.getOrElse(e.id.name, e.id.name)
       s"inst ${e.name} of $modName"
diff --git a/src/main/scala/Chisel/internal/firrtl/IR.scala b/src/main/scala/Chisel/internal/firrtl/IR.scala
index 3e923366..7bb273c0 100644
--- a/src/main/scala/Chisel/internal/firrtl/IR.scala
+++ b/src/main/scala/Chisel/internal/firrtl/IR.scala
@@ -147,6 +147,7 @@ abstract class Definition extends Command {
   def name: String = id.getRef.name
 }
 case class DefPrim[T <: Data](id: T, op: PrimOp, args: Arg*) extends Definition
+case class DefInvalid(arg: Arg) extends Command
 case class DefWire(id: Data) extends Definition
 case class DefReg(id: Data, clock: Arg) extends Definition
 case class DefRegInit(id: Data, clock: Arg, reset: Arg, init: Arg) extends Definition
@@ -154,7 +155,6 @@ case class DefMemory(id: HasId, t: Data, size: Int) extends Definition
 case class DefSeqMemory(id: HasId, t: Data, size: Int) extends Definition
 case class DefMemPort[T <: Data](id: T, source: Node, dir: MemPortDirection, index: Arg, clock: Arg) extends Definition
 case class DefInstance(id: Module, ports: Seq[Port]) extends Definition
-case class DefPoison[T <: Data](id: T) extends Definition
 case class WhenBegin(pred: Arg) extends Command
 case class WhenEnd() extends Command
 case class Connect(loc: Node, exp: Arg) extends Command