Allow a counter to be instantiated using a Scala range (#1515)

* Add positive range generator

* Allow the Counter module to be instantiated with a Scala range

* Use head/last to determine counter width

Co-authored-by: Jack Koenig <jack.koenig3@gmail.com>

* Let counter overflow naturally when appropriate

We only need to explicitly wrap counters that don't start at zero, or end on a power of two. Otherwise we just let the counter overflow naturally to avoid wasting an extra mux.

* Require counter range to be non-empty

Co-authored-by: Jack Koenig <jack.koenig3@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

2 files changed, 33 insertions, 0 deletions

diff --git a/src/test/scala/chiselTests/ChiselSpec.scala b/src/test/scala/chiselTests/ChiselSpec.scala
index 7980e772..9518fb5c 100644
--- a/src/test/scala/chiselTests/ChiselSpec.scala
+++ b/src/test/scala/chiselTests/ChiselSpec.scala
@@ -150,6 +150,20 @@ class ChiselPropSpec extends PropSpec with ChiselRunners with ScalaCheckProperty
   // Generator for small positive integers.
   val smallPosInts = Gen.choose(1, 4)
 
+  // Generator for positive (ascending or descending) ranges.
+  def posRange: Gen[Range] = for {
+    dir <- Gen.oneOf(true, false)
+    step <- Gen.choose(1, 3)
+    m <- Gen.choose(1, 10)
+    n <- Gen.choose(1, 10)
+  } yield {
+    if (dir) {
+      Range(m, (m+n)*step, step)
+    } else {
+      Range((m+n)*step, m, -step)
+    }
+  }
+
   // Generator for widths considered "safe".
   val safeUIntWidth = Gen.choose(1, 30)
 
diff --git a/src/test/scala/chiselTests/Counter.scala b/src/test/scala/chiselTests/Counter.scala
index 34fdec8e..31bfe7eb 100644
--- a/src/test/scala/chiselTests/Counter.scala
+++ b/src/test/scala/chiselTests/Counter.scala
@@ -35,6 +35,19 @@ class WrapTester(max: Int) extends BasicTester {
   }
 }
 
+class RangeTester(r: Range) extends BasicTester {
+  val (cnt, wrap) = Counter(r)
+  val checkWrap = RegInit(false.B)
+
+  when(checkWrap) {
+    assert(cnt === r.head.U)
+    stop()
+  }.elsewhen(wrap) {
+    assert(cnt === r.last.U)
+    checkWrap := true.B
+  }
+}
+
 class CounterSpec extends ChiselPropSpec {
   property("Counter should count up") {
     forAll(smallPosInts) { (max: Int) => assertTesterPasses{ new CountTester(max) } }
@@ -47,4 +60,10 @@ class CounterSpec extends ChiselPropSpec {
   property("Counter should wrap") {
     forAll(smallPosInts) { (max: Int) => assertTesterPasses{ new WrapTester(max) } }
   }
+
+  property("Counter should handle a range") {
+    forAll(posRange) { (r: Range) =>
+      assertTesterPasses{ new RangeTester(r) }
+    }
+  }
 }