3 files changed, 63 insertions, 1 deletions
diff --git a/src/main/scala/Chisel/testers/BasicTester.scala b/src/main/scala/Chisel/testers/BasicTester.scala
index 6807a30e..d3e9e7c8 100644
--- a/src/main/scala/Chisel/testers/BasicTester.scala
+++ b/src/main/scala/Chisel/testers/BasicTester.scala
@@ -24,4 +24,11 @@ class BasicTester extends Module {
       pushCommand(Stop(Node(clock), 0))
     }
   }
+
+  /** The finish method provides a hook that subclasses of BasicTester can use to
+    * alter a circuit after their constructor has been called.
+    * For example, a specialized tester subclassing BasicTester could override finish in order to
+    * add flow control logic for a decoupled io port of a device under test
+    */
+  def finish(): Unit = {}
 }
diff --git a/src/main/scala/Chisel/testers/TesterDriver.scala b/src/main/scala/Chisel/testers/TesterDriver.scala
index b25b160b..4547f48f 100644
--- a/src/main/scala/Chisel/testers/TesterDriver.scala
+++ b/src/main/scala/Chisel/testers/TesterDriver.scala
@@ -23,7 +23,7 @@ object TesterDriver extends BackendCompilationUtilities {
     * frontend, and which can be turned into executables with assertions. */
   def execute(t: () => BasicTester, additionalVResources: Seq[String] = Seq()): Boolean = {
     // Invoke the chisel compiler to get the circuit's IR
-    val circuit = Driver.elaborate(t)
+    val circuit = Driver.elaborate(finishWrapper(t))
 
     // Set up a bunch of file handlers based on a random temp filename,
     // plus the quirks of Verilator's naming conventions
@@ -55,4 +55,15 @@ object TesterDriver extends BackendCompilationUtilities {
       false
     }
   }
+  /**
+    * Calls the finish method of an BasicTester or a class that extends it.
+    * The finish method is a hook for code that augments the circuit built in the constructor.
+    */
+  def finishWrapper(test: () => BasicTester): () => BasicTester = {
+    () => {
+      val tester = test()
+      tester.finish()
+      tester
+    }
+  }
 }
diff --git a/src/test/scala/chiselTests/TesterDriverSpec.scala b/src/test/scala/chiselTests/TesterDriverSpec.scala
new file mode 100644
index 00000000..dfdd07cc
--- /dev/null
+++ b/src/test/scala/chiselTests/TesterDriverSpec.scala
@@ -0,0 +1,44 @@
+// See LICENSE for license details.
+
+package chiselTests
+
+import Chisel._
+import Chisel.testers.BasicTester
+
+/** Extend BasicTester with a simple circuit and finish method.  TesterDriver will call the
+  * finish method after the FinishTester's constructor has completed, which will alter the
+  * circuit after the constructor has finished.
+  */
+class FinishTester extends BasicTester {
+  val test_wire_width = 2
+  val test_wire_override_value = 3
+
+  val counter = Counter(1)
+
+  when(counter.inc()) {
+    stop()
+  }
+
+  val test_wire = Wire(UInt(1, width = test_wire_width))
+
+  // though we just set test_wire to 1, the assert below will pass because
+  // the finish will change it's value
+  assert(test_wire === UInt(test_wire_override_value))
+
+  /** In finish we use last connect semantics to alter the test_wire in the circuit
+    * with a new value
+    */
+  override def finish(): Unit = {
+    test_wire := UInt(test_wire_override_value)
+  }
+}
+
+class TesterDriverSpec extends ChiselFlatSpec {
+  "TesterDriver calls BasicTester's finish method which" should
+    "allow modifications of test circuit after the tester's constructor is done" in {
+    assertTesterPasses {
+      new FinishTester
+    }
+  }
+}
+