Add a Smi to TileLink converter (#59)

I'm trying to get someone to attach their stuff to Rocket Chip for the
upcoming tapout.  TileLink sounded too complicated, but Smi went over
well.  Since the mmioNetwork in Rocket Chip is based on TileLink, it
seemed like the easiest thing to do was to write a TileLink to Smi
converter so people could use it.

It turns out there was already one inside the groundtest unit tests, so
I just moved that into uncore (it was inlined into a test case so you
couldn't actually use it before).  Internally the converter uses Nasti,
but I figured that's good enough for now.

uncore/src/main/scala/smi.scala

@@ -0,0 +1,31 @@
+// See LICENSE for details
+
+package uncore
+
+import Chisel._
+import junctions._
+import cde.Parameters
+
+/** Convert TileLink protocol to Smi protocol */
+class SmiIOTileLinkIOConverter(val dataWidth: Int, val addrWidth: Int)
+                              (implicit p: Parameters) extends Module {
+  val io = new Bundle {
+    val tl = (new ClientUncachedTileLinkIO).flip
+    val smi = new SmiIO(dataWidth, addrWidth)
+  }
+
+  def decoupledNastiConnect(outer: NastiIO, inner: NastiIO) {
+    outer.ar <> Queue(inner.ar)
+    outer.aw <> Queue(inner.aw)
+    outer.w  <> Queue(inner.w)
+    inner.r  <> Queue(outer.r)
+    inner.b  <> Queue(outer.b)
+  }
+
+  val tl2nasti  = Module(new NastiIOTileLinkIOConverter())
+  val nasti2smi = Module(new SmiIONastiIOConverter(dataWidth, addrWidth))
+
+  tl2nasti.io.tl <> io.tl
+  decoupledNastiConnect(nasti2smi.io.nasti, tl2nasti.io.nasti)
+  io.smi <> nasti2smi.io.smi
+}