[clocks] Use the periphery frequency as the default

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

@@ -88,7 +88,7 @@ case object ClockingSchemeKey extends Field[ChipTop => Unit](ClockingSchemeGener
   * [[DefaultClockFrequencyKey]] will be used -- DFU.
   */
 case object ClockFrequencyAssignersKey extends Field[Seq[(String) => Option[Double]]](Seq.empty)
-case object DefaultClockFrequencyKey extends Field[Double](100.0)
+case object DefaultClockFrequencyKey extends Field[Double]()
 
 class ClockNameMatchesAssignment(name: String, fMHz: Double) extends Config((site, here, up) => {
   case ClockFrequencyAssignersKey => up(ClockFrequencyAssignersKey, site) ++

generators/chipyard/src/main/scala/ConfigFragments.scala

@@ -169,4 +169,10 @@ class WithNoDebug extends Config((site, here, up) => {
   case DebugModuleKey => None
 
 })
+
 class WithTileFrequency(fMHz: Double) extends ClockNameContainsAssignment("core", fMHz)
+
+class WithPeripheryBusFrequencyAsDefault extends Config((site, here, up) => {
+  case DefaultClockFrequencyKey => (site(PeripheryBusKey).dtsFrequency.get / (1000 * 1000)).toDouble
+})
+

generators/chipyard/src/main/scala/config/AbstractConfig.scala

@@ -44,6 +44,7 @@ class AbstractConfig extends Config(
   new chipyard.config.WithUART ++                                // add a UART
   new chipyard.config.WithL2TLBs(1024) ++                        // use L2 TLBs
   new chipyard.config.WithNoSubsystemDrivenClocks ++             // drive the subsystem diplomatic clocks from ChipTop instead of using implicit clocks
+  new chipyard.config.WithPeripheryBusFrequencyAsDefault ++      // Unspecified clocks will match the frequency specified by the pbus dtsFrequency parameter
   new freechips.rocketchip.subsystem.WithJtagDTM ++              // set the debug module to expose a JTAG port
   new freechips.rocketchip.subsystem.WithNoMMIOPort ++           // no top-level MMIO master port (overrides default set in rocketchip)
   new freechips.rocketchip.subsystem.WithNoSlavePort ++          // no top-level MMIO slave port (overrides default set in rocketchip)