Use def instead of var Option for ref frequency

generators/chipyard/src/main/scala/ChipTop.scala

@@ -16,7 +16,7 @@ import barstools.iocell.chisel._
 case object BuildSystem extends Field[Parameters => LazyModule]((p: Parameters) => new DigitalTop()(p))
 
 trait HasReferenceClockFreq {
-  var refClockFreqMHz: Option[Double] = None
+  def refClockFreqMHz: Double
 }
 
 /**
@@ -35,7 +35,8 @@ class ChipTop(implicit p: Parameters) extends LazyModule with BindingScope
   val implicitClockSinkNode = ClockSinkNode(Seq(ClockSinkParameters(name = Some("implicit_clock"))))
 
   // Generate Clocks and Reset
-  p(ClockingSchemeKey)(this)
+  val mvRefClkFreq = p(ClockingSchemeKey)(this)
+  def refClockFreqMHz: Double = mvRefClkFreq.getWrappedValue
 
   // NOTE: Making this a LazyRawModule is moderately dangerous, as anonymous children
   // of ChipTop (ex: ClockGroup) do not receive clock or reset.

generators/chipyard/src/main/scala/Clocks.scala

@@ -7,7 +7,7 @@ import scala.collection.mutable.{ArrayBuffer}
 import freechips.rocketchip.prci._
 import freechips.rocketchip.subsystem.{BaseSubsystem, SubsystemDriveAsyncClockGroupsKey, InstantiatesTiles}
 import freechips.rocketchip.config.{Parameters, Field, Config}
-import freechips.rocketchip.diplomacy.{OutwardNodeHandle, InModuleBody, LazyModule}
+import freechips.rocketchip.diplomacy.{ModuleValue, OutwardNodeHandle, InModuleBody, LazyModule}
 import freechips.rocketchip.util.{ResetCatchAndSync}
 
 import barstools.iocell.chisel._
@@ -38,7 +38,7 @@ object GenerateReset {
 }
 
 
-case object ClockingSchemeKey extends Field[ChipTop => Unit](ClockingSchemeGenerators.dividerOnlyClockGenerator)
+case object ClockingSchemeKey extends Field[ChipTop => ModuleValue[Double]](ClockingSchemeGenerators.dividerOnlyClockGenerator)
 /*
   * This is a Seq of assignment functions, that accept a clock name and return an optional frequency.
   * Functions that appear later in this seq have higher precedence that earlier ones.
@@ -59,7 +59,7 @@ class ClockNameContainsAssignment(name: String, fMHz: Double) extends Config((si
 })
 
 object ClockingSchemeGenerators {
-  val dividerOnlyClockGenerator: ChipTop => Unit = { chiptop =>
+  val dividerOnlyClockGenerator: ChipTop => ModuleValue[Double] = { chiptop =>
     implicit val p = chiptop.p
 
     // Requires existence of undriven asyncClockGroups in subsystem
@@ -100,9 +100,6 @@ object ClockingSchemeGenerators {
       val (clock_io, clockIOCell) = IOCell.generateIOFromSignal(clock_wire, "clock")
       chiptop.iocells ++= clockIOCell
 
-      // set the reference clock used
-      chiptop.refClockFreqMHz = Some(dividerOnlyClkGenerator.module.referenceFreq)
-
       referenceClockSource.out.unzip._1.map { o =>
         o.clock := clock_wire
         o.reset := reset_wire
@@ -111,6 +108,9 @@ object ClockingSchemeGenerators {
       chiptop.harnessFunctions += ((th: HasHarnessSignalReferences) => {
         clock_io := th.harnessClock
         Nil })
+
+      // return the reference frequency
+      dividerOnlyClkGenerator.module.referenceFreq
     }
   }
 }

generators/chipyard/src/main/scala/TestHarness.scala

@@ -91,7 +91,7 @@ class TestHarness(implicit val p: Parameters) extends Module with HasHarnessSign
   io.success := false.B
 
   val freqMHz = lazyDut match {
-    case d: HasReferenceClockFreq => d.refClockFreqMHz.getOrElse(p(DefaultClockFrequencyKey))
+    case d: HasReferenceClockFreq => d.refClockFreqMHz
     case _ => p(DefaultClockFrequencyKey)
   }
   val refClkBundle = p(HarnessClockInstantiatorKey).requestClockBundle("buildtop_reference_clock", freqMHz * (1000 * 1000))

generators/firechip/src/main/scala/FireSim.scala

@@ -194,14 +194,14 @@ class WithFireSimSimpleClocks extends Config((site, here, up) => {
         RationalClock(sinkP.name.get, 1, division)
       }
 
-      // Set the reference frequency used
-      chiptop.refClockFreqMHz = Some(pllConfig.referenceFreqMHz)
-
       chiptop.harnessFunctions += ((th: HasHarnessSignalReferences) => {
         reset := th.harnessReset
         input_clocks := p(ClockBridgeInstantiatorKey)
           .requestClockRecordMap(rationalClockSpecs.toSeq, p(FireSimBaseClockNameKey), pllConfig.referenceFreqMHz * (1000 * 1000))
         Nil })
+
+      // return the reference frequency
+      pllConfig.referenceFreqMHz
     }
   }
 })
@@ -230,7 +230,7 @@ class FireSim(implicit val p: Parameters) extends RawModule with HasHarnessSigna
     val module = Module(lazyModule.module)
 
     btFreqMHz = Some(lazyModule match {
-      case d: HasReferenceClockFreq => d.refClockFreqMHz.getOrElse(p(DefaultClockFrequencyKey))
+      case d: HasReferenceClockFreq => d.refClockFreqMHz
       case _ => p(DefaultClockFrequencyKey)
     })