Adding saturating counter

Signed-off-by: Jason Lowe-Power <[email protected]>

src/test/scala/components/SaturatingCounterTest.scala

@@ -0,0 +1,69 @@
+// Unit tests for the saturating counter
+
+package dinocpu
+
+import chisel3._
+
+import chisel3.iotesters
+import chisel3.iotesters.{ChiselFlatSpec, Driver, PeekPokeTester}
+
+class Wrapper(width: Int) extends Module {
+  val io = IO(new Bundle {
+    val incr = Input(Bool())
+    val decr = Input(Bool())
+
+    val value = Output(UInt(width.W))
+    val up = Output(Bool())
+    val down = Output(Bool())
+  })
+  io := DontCare
+
+  val counter = RegInit(SaturatingCounter.initup(width))
+
+  when (io.incr) {
+    counter := SaturatingCounter.incr(counter)
+  }
+
+  when (io.decr) {
+    //counter.decr()
+  }
+
+  io.value := counter
+  //io.up := counter.up()
+  //io.down := counter.down()
+}
+
+class SaturatingCounterUnitTester(c: Wrapper, width: Int) extends PeekPokeTester(c) {
+  val max = 1 << width
+  val d = 1 << (width - 1)
+  expect(c.io.value, d)
+
+  step(1)
+  val v = d + 1
+  expect(c.io.value, if (v < max) v else max)
+
+}
+
+/**
+  * This is a trivial example of how to run this Specification
+  * From within sbt use:
+  * {{{
+  * testOnly dinocpu.SaturatingCounterTester
+  * }}}
+  * From a terminal shell use:
+  * {{{
+  * sbt 'testOnly dinocpu.SaturatingCounterTester'
+  * }}}
+  */
+class SaturatingCounterTester extends ChiselFlatSpec {
+  "SaturatingCounter" should s"match expectations for width 2" in {
+    Driver(() => new Wrapper(2)) {
+      c => new SaturatingCounterUnitTester(c, 2)
+    } should be (true)
+  }
+  "SaturatingCounter" should s"match expectations for width 4" in {
+    Driver(() => new Wrapper(4)) {
+      c => new SaturatingCounterUnitTester(c, 4)
+    } should be (true)
+  }
+}