BaseSubsystem: Move attachment function into trait

src/main/scala/subsystem/BaseSubsystem.scala

@@ -47,8 +47,28 @@ case object FBUS extends BaseSubsystemBusAttachment
 case object MBUS extends BaseSubsystemBusAttachment
 case object CBUS extends BaseSubsystemBusAttachment
 
+trait HasBusAttachmentFunction {
+  val sbus: SystemBus
+  val pbus: PeripheryBus
+  val fbus: FrontBus
+  val mbus: MemoryBus
+  val cbus: PeripheryBus
+
+  type BusAttachmentFunction = PartialFunction[BaseSubsystemBusAttachment, TLBusWrapper]
+  def baseBusAttachmentFunc: BusAttachmentFunction = {
+    case SBUS => sbus
+    case PBUS => pbus
+    case FBUS => fbus
+    case MBUS => mbus
+    case CBUS => cbus
+  }
+  def attach(where: BaseSubsystemBusAttachment): TLBusWrapper = baseBusAttachmentFunc(where)
+}
+
 /** Base Subsystem class with no peripheral devices or ports added */
-abstract class BaseSubsystem(implicit p: Parameters) extends BareSubsystem with HasLogicalTreeNode {
+abstract class BaseSubsystem(implicit p: Parameters) extends BareSubsystem 
+  with HasLogicalTreeNode with HasBusAttachmentFunction {
+
   override val module: BaseSubsystemModuleImp[BaseSubsystem]
 
   // These are wrappers around the standard buses available in all subsytems, where
@@ -60,16 +80,6 @@ abstract class BaseSubsystem(implicit p: Parameters) extends BareSubsystem with
   val mbus = LazyModule(new MemoryBus(p(MemoryBusKey)))
   val cbus = LazyModule(new PeripheryBus(p(ControlBusKey)))
 
-  type BusAttachmentFunction = PartialFunction[BaseSubsystemBusAttachment, TLBusWrapper]
-  protected def baseBusAttachmentFunc: BusAttachmentFunction = {
-    case SBUS => sbus
-    case PBUS => pbus
-    case FBUS => fbus
-    case MBUS => mbus
-    case CBUS => cbus
-  }
-  protected def attach(where: BaseSubsystemBusAttachment): TLBusWrapper = baseBusAttachmentFunc(where)
-
   // Collect information for use in DTS
   lazy val topManagers = sbus.unifyManagers
   ResourceBinding {