Util: Add ResetCatchAndSync for synchronous deassert of Async Reset (#615)

src/main/scala/util/ResetCatchAndSync.scala

@@ -0,0 +1,41 @@
+// See LICENSE.SiFive for license details.
+package util
+
+import Chisel._
+
+/** Reset: asynchronous assert,
+  *  synchronous de-assert
+  *
+  */
+
+class ResetCatchAndSync (sync: Int = 3) extends Module {
+
+  val io = new Bundle {
+    val sync_reset = Bool(OUTPUT)
+  }
+
+  val reset_n_catch_reg = Module (new AsyncResetRegVec(sync, 0))
+
+  reset_n_catch_reg.io.en := Bool(true)
+  reset_n_catch_reg.io.d  := Cat(Bool(true), reset_n_catch_reg.io.q >> 1)
+
+  io.sync_reset := ~reset_n_catch_reg.io.q(0)
+
+}
+
+object ResetCatchAndSync {
+
+  def apply(clk: Clock, rst: Bool, sync: Int = 3, name: Option[String] = None): Bool = {
+
+    val catcher = Module (new ResetCatchAndSync(sync))
+    if (name.isDefined) {catcher.suggestName(name.get)}
+    catcher.clock := clk
+    catcher.reset := rst
+
+    catcher.io.sync_reset
+  }
+
+  def apply(clk: Clock, rst: Bool, sync: Int, name: String): Bool = apply(clk, rst, sync, Some(name))
+  def apply(clk: Clock, rst: Bool, name: String): Bool = apply(clk, rst, name = Some(name))
+
+}