Merge pull request #985 from freechipsproject/flop-interrupts

Add Parameters to diplomatic edges

src/main/scala/amba/ahb/ToTL.scala

@@ -139,7 +139,7 @@ object AHBToTL
 {
   def apply()(x: AHBOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val tl = LazyModule(new AHBToTL)
-    tl.node := x
+    tl.node :=? x
     tl.node
   }
 }

src/main/scala/amba/axi4/Buffer.scala

@@ -62,7 +62,7 @@ object AXI4Buffer
     ar: BufferParams,
     r:  BufferParams)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val buffer = LazyModule(new AXI4Buffer(aw, w, b, ar, r))
-    buffer.node := x
+    buffer.node :=? x
     buffer.node
   }
 }

src/main/scala/amba/axi4/Deinterleaver.scala

@@ -108,7 +108,7 @@ object AXI4Deinterleaver
   // applied to the AXI4 source node; y.node := AXI4Deinterleaver()(x.node)
   def apply(maxReadBytes: Int)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val deinterleaver = LazyModule(new AXI4Deinterleaver(maxReadBytes))
-    deinterleaver.node := x
+    deinterleaver.node :=? x
     deinterleaver.node
   }
 }

src/main/scala/amba/axi4/Fragmenter.scala

@@ -208,7 +208,7 @@ object AXI4Fragmenter
   // applied to the AXI4 source node; y.node := AXI4Fragmenter()(x.node)
   def apply()(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val fragmenter = LazyModule(new AXI4Fragmenter)
-    fragmenter.node := x
+    fragmenter.node :=? x
     fragmenter.node
   }
 }

src/main/scala/amba/axi4/IdIndexer.scala

@@ -84,7 +84,7 @@ object AXI4IdIndexer
   // applied to the AXI4 source node; y.node := AXI4IdIndexer(idBits)(x.node)
   def apply(idBits: Int)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val indexer = LazyModule(new AXI4IdIndexer(idBits))
-    indexer.node := x
+    indexer.node :=? x
     indexer.node
   }
 }

src/main/scala/amba/axi4/ToTL.scala

@@ -168,7 +168,7 @@ object AXI4ToTL
 {
   def apply()(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val tl = LazyModule(new AXI4ToTL)
-    tl.node := x
+    tl.node :=? x
     tl.node
   }
 }

src/main/scala/amba/axi4/UserYanker.scala

@@ -100,7 +100,7 @@ object AXI4UserYanker
   // applied to the AXI4 source node; y.node := AXI4UserYanker(idBits, maxFlight)(x.node)
   def apply(capMaxFlight: Option[Int] = None)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val yanker = LazyModule(new AXI4UserYanker(capMaxFlight))
-    yanker.node := x
+    yanker.node :=? x
     yanker.node
   }
 }

src/main/scala/config/Config.scala

@@ -2,13 +2,22 @@
 
 package freechips.rocketchip.config
 
-class Field[T]
+abstract class Field[T] private (val default: Option[T])
+{
+  def this() = this(None)
+  def this(x: T) = this(Some(x))
+}
 
 abstract class View {
   final def apply[T](pname: Field[T]): T = apply(pname, this)
-  final def apply[T](pname: Field[T], site: View): T = find(pname, site).asInstanceOf[T]
+  final def apply[T](pname: Field[T], site: View): T = find(pname, site) match {
+    case Some(x) => x.asInstanceOf[T]
+  }
 
-  protected[config] def find(pname: Any, site: View): Any
+  final def lift[T](pname: Field[T]): Option[T] = lift(pname, this)
+  final def lift[T](pname: Field[T], site: View): Option[T] = find(pname, site).map(_.asInstanceOf[T])
+
+  protected[config] def find[T](pname: Field[T], site: View): Option[T]
 }
 
 abstract class Parameters extends View {
@@ -16,8 +25,8 @@ abstract class Parameters extends View {
   final def alter(f: (View, View, View) => PartialFunction[Any,Any]): Parameters = Parameters(f) ++ this
   final def alterPartial(f: PartialFunction[Any,Any]):                Parameters = Parameters((_,_,_) => f) ++ this
 
-  protected[config] def chain(site: View, tail: View, pname: Any): Any
+  protected[config] def chain[T](site: View, tail: View, pname: Field[T]): Option[T]
-  protected[config] def find(pname: Any, site: View) = chain(site, new TerminalView, pname)
+  protected[config] def find[T](pname: Field[T], site: View) = chain(site, new TerminalView, pname)
 }
 
 object Parameters {
@@ -29,7 +38,7 @@ object Parameters {
 class Config(p: Parameters) extends Parameters {
   def this(f: (View, View, View) => PartialFunction[Any,Any]) = this(Parameters(f))
 
-  protected[config] def chain(site: View, tail: View, pname: Any) = p.chain(site, tail, pname)
+  protected[config] def chain[T](site: View, tail: View, pname: Field[T]) = p.chain(site, tail, pname)
   override def toString = this.getClass.getSimpleName
   def toInstance = this
 }
@@ -37,25 +46,24 @@ class Config(p: Parameters) extends Parameters {
 // Internal implementation:
 
 private class TerminalView extends View {
-  private class Unusable
+  def find[T](pname: Field[T], site: View): Option[T] = pname.default
-  def find(pname: Any, site: View): Any = pname match { case x: Unusable => () }
 }
 
 private class ChainView(head: Parameters, tail: View) extends View {
-  def find(pname: Any, site: View) = head.chain(site, tail, pname)
+  def find[T](pname: Field[T], site: View) = head.chain(site, tail, pname)
 }
 
 private class ChainParameters(x: Parameters, y: Parameters) extends Parameters {
-  def chain(site: View, tail: View, pname: Any) = x.chain(site, new ChainView(y, tail), pname)
+  def chain[T](site: View, tail: View, pname: Field[T]) = x.chain(site, new ChainView(y, tail), pname)
 }
 
 private class EmptyParameters extends Parameters {
-  def chain(site: View, tail: View, pname: Any) = tail.find(pname, site)
+  def chain[T](site: View, tail: View, pname: Field[T]) = tail.find(pname, site)
 }
 
 private class PartialParameters(f: (View, View, View) => PartialFunction[Any,Any]) extends Parameters {
-  protected[config] def chain(site: View, tail: View, pname: Any) = {
+  protected[config] def chain[T](site: View, tail: View, pname: Field[T]) = {
     val g = f(site, this, tail)
-    if (g.isDefinedAt(pname)) g.apply(pname) else tail.find(pname, site)
+    if (g.isDefinedAt(pname)) Some(g.apply(pname).asInstanceOf[T]) else tail.find(pname, site)
   }
 }

src/main/scala/coreplex/Configs.scala

@@ -36,9 +36,6 @@ class BaseCoreplexConfig extends Config ((site, here, up) => {
   case PLICParams => PLICParams()
   case ClintParams => ClintParams()
   case DTSTimebase => BigInt(1000000) // 1 MHz
-  // TileLink connection global parameters
-  case TLMonitorBuilder => (args: TLMonitorArgs) => Some(LazyModule(new TLMonitor(args)))
-  case TLCombinationalCheck => false
   case TLBusDelayProbability => 0.0
 })
 

src/main/scala/coreplex/MemoryBus.scala

@@ -67,7 +67,7 @@ trait HasMemoryBus extends HasSystemBus with HasPeripheryBus with HasInterruptBu
     val mbus = new MemoryBus(mbusParams)
     for (bank <- 0 until nBanksPerChannel) {
       val offset = (bank * nMemoryChannels) + channel
-      in := sbus.toMemoryBus
+      ForceFanout(a = true) { implicit p => in := sbus.toMemoryBus }
       mbus.fromCoherenceManager := TLFilter(TLFilter.Mmask(AddressSet(offset * blockBytes, mask)))(out)
     }
     mbus

src/main/scala/coreplex/RocketCoreplex.scala

@@ -45,20 +45,20 @@ trait HasRocketTiles extends HasSystemBus
     val wrapper = crossing match {
       case SynchronousCrossing(params) => {
         val wrapper = LazyModule(new SyncRocketTile(tp, i)(pWithExtra))
-        sbus.fromSyncTiles(params, tp.externalBuffers, tp.name) :=* wrapper.masterNode
+        sbus.fromSyncTiles(params, tp.externalMasterBuffers, tp.name) :=* wrapper.masterNode
-        wrapper.slaveNode :*= pbus.bufferToSlaves
+        wrapper.slaveNode :*= pbus.toSyncSlaves(tp.name, tp.externalSlaveBuffers)
         wrapper
       }
       case AsynchronousCrossing(depth, sync) => {
         val wrapper = LazyModule(new AsyncRocketTile(tp, i)(pWithExtra))
-        sbus.fromAsyncTiles(depth, sync, tp.externalBuffers, tp.name) :=* wrapper.masterNode
+        sbus.fromAsyncTiles(depth, sync, tp.externalMasterBuffers, tp.name) :=* wrapper.masterNode
-        wrapper.slaveNode :*= pbus.toAsyncSlaves(sync, tp.name)
+        wrapper.slaveNode :*= pbus.toAsyncSlaves(sync, tp.name, tp.externalSlaveBuffers)
         wrapper
       }
       case RationalCrossing(direction) => {
         val wrapper = LazyModule(new RationalRocketTile(tp, i)(pWithExtra))
-        sbus.fromRationalTiles(direction, tp.externalBuffers, tp.name) :=* wrapper.masterNode
+        sbus.fromRationalTiles(direction, tp.externalMasterBuffers, tp.name) :=* wrapper.masterNode
-        wrapper.slaveNode :*= pbus.toRationalSlaves(tp.name)
+        wrapper.slaveNode :*= pbus.toRationalSlaves(tp.name, tp.externalSlaveBuffers)
         wrapper
       }
     }

src/main/scala/devices/tilelink/Clint.scala

@@ -25,7 +25,7 @@ object ClintConsts
   def ints = 2
 }
 
-case class ClintParams(baseAddress: BigInt = 0x02000000)
+case class ClintParams(baseAddress: BigInt = 0x02000000, intStages: Int = 0)
 {
   def address = AddressSet(baseAddress, ClintConsts.size-1)
 }
@@ -71,8 +71,8 @@ class CoreplexLocalInterrupter(params: ClintParams)(implicit p: Parameters) exte
     val ipi = Seq.fill(nTiles) { RegInit(UInt(0, width = 1)) }
 
     io.int.zipWithIndex.foreach { case (int, i) =>
-      int(0) := ipi(i)(0) // msip
+      int(0) := ShiftRegister(ipi(i)(0), params.intStages) // msip
-      int(1) := time.asUInt >= timecmp(i).asUInt // mtip
+      int(1) := ShiftRegister(time.asUInt >= timecmp(i).asUInt, params.intStages) // mtip
     }
 
     /* 0000 msip hart 0

src/main/scala/devices/tilelink/Plic.scala

@@ -52,7 +52,7 @@ object PLICConsts
   require(hartBase >= enableBase(maxHarts))
 }
 
-case class PLICParams(baseAddress: BigInt = 0xC000000, maxPriorities: Int = 7)
+case class PLICParams(baseAddress: BigInt = 0xC000000, maxPriorities: Int = 7, intStages: Int = 0)
 {
   require (maxPriorities >= 0)
   def address = AddressSet(baseAddress, PLICConsts.size-1)
@@ -166,7 +166,7 @@ class TLPLIC(params: PLICParams)(implicit p: Parameters) extends LazyModule
       val (maxPri, maxDev) = findMax(effectivePriority)
 
       maxDevs(hart) := maxDev
-      harts(hart) := Reg(next = maxPri) > Cat(UInt(1), threshold(hart))
+      harts(hart) := ShiftRegister(Reg(next = maxPri) > Cat(UInt(1), threshold(hart)), params.intStages)
     }
 
     def priorityRegField(x: UInt) = if (nPriorities > 0) RegField(32, x) else RegField.r(32, x)

src/main/scala/diplomacy/Nodes.scala

@@ -4,10 +4,30 @@ package freechips.rocketchip.diplomacy
 
 import Chisel._
 import chisel3.internal.sourceinfo.SourceInfo
-import freechips.rocketchip.config.Parameters
+import freechips.rocketchip.config.{Parameters,Field}
 import freechips.rocketchip.util.HeterogeneousBag
 import scala.collection.mutable.ListBuffer
 
+object CardinalityInferenceDirection {
+  val cases = Seq(SOURCE_TO_SINK, SINK_TO_SOURCE, NO_INFERENCE)
+  sealed trait T {
+    def flip = this match {
+      case SOURCE_TO_SINK => SINK_TO_SOURCE
+      case SINK_TO_SOURCE => SOURCE_TO_SINK
+      case NO_INFERENCE   => NO_INFERENCE
+    }
+  }
+
+  case object SOURCE_TO_SINK extends T
+  case object SINK_TO_SOURCE extends T
+  case object NO_INFERENCE   extends T
+}
+
+private case object CardinalityInferenceDirectionKey extends
+  Field[CardinalityInferenceDirection.T](CardinalityInferenceDirection.NO_INFERENCE)
+
+private case object MonitorsEnabled extends Field[Boolean](true)
+
 // DI = Downwards flowing Parameters received on the inner side of the node
 // UI = Upwards   flowing Parameters generated by the inner side of the node
 // EI = Edge Parameters describing a connection on the inner side of the node
@@ -77,13 +97,15 @@ case class NodeHandle[DI, UI, BI <: Data, DO, UO, BO <: Data]
 
 trait InwardNodeHandle[DI, UI, BI <: Data]
 {
-  val inward: InwardNode[DI, UI, BI]
+  protected[diplomacy] val inward: InwardNode[DI, UI, BI]
   def := (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] =
     inward.:=(h)(p, sourceInfo)
   def :*= (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] =
     inward.:*=(h)(p, sourceInfo)
   def :=* (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] =
     inward.:=*(h)(p, sourceInfo)
+  def :=? (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] =
+    inward.:=?(h)(p, sourceInfo)
 }
 
 sealed trait NodeBinding
@@ -93,22 +115,22 @@ case object BIND_STAR  extends NodeBinding
 
 trait InwardNode[DI, UI, BI <: Data] extends BaseNode with InwardNodeHandle[DI, UI, BI]
 {
-  val inward = this
+  protected[diplomacy] val inward = this
 
   protected[diplomacy] val numPI: Range.Inclusive
   require (!numPI.isEmpty, s"No number of inputs would be acceptable to ${name}${lazyModule.line}")
   require (numPI.start >= 0, s"${name} accepts a negative number of inputs${lazyModule.line}")
 
-  private val accPI = ListBuffer[(Int, OutwardNode[DI, UI, BI], NodeBinding)]()
+  private val accPI = ListBuffer[(Int, OutwardNode[DI, UI, BI], NodeBinding, Parameters)]()
   private var iRealized = false
 
   protected[diplomacy] def iPushed = accPI.size
-  protected[diplomacy] def iPush(index: Int, node: OutwardNode[DI, UI, BI], binding: NodeBinding)(implicit sourceInfo: SourceInfo) {
+  protected[diplomacy] def iPush(index: Int, node: OutwardNode[DI, UI, BI], binding: NodeBinding)(implicit p: Parameters, sourceInfo: SourceInfo) {
     val info = sourceLine(sourceInfo, " at ", "")
     val noIs = numPI.size == 1 && numPI.contains(0)
     require (!noIs, s"${name}${lazyModule.line} was incorrectly connected as a sink" + info)
     require (!iRealized, s"${name}${lazyModule.line} was incorrectly connected as a sink after it's .module was used" + info)
-    accPI += ((index, node, binding))
+    accPI += ((index, node, binding, p))
   }
 
   protected[diplomacy] lazy val iBindings = { iRealized = true; accPI.result() }
@@ -116,32 +138,32 @@ trait InwardNode[DI, UI, BI <: Data] extends BaseNode with InwardNodeHandle[DI,
   protected[diplomacy] val iStar: Int
   protected[diplomacy] val iPortMapping: Seq[(Int, Int)]
   protected[diplomacy] val iParams: Seq[UI]
-  val bundleIn: HeterogeneousBag[BI]
+  protected[diplomacy] val bundleIn: HeterogeneousBag[BI]
 }
 
 trait OutwardNodeHandle[DO, UO, BO <: Data]
 {
-  val outward: OutwardNode[DO, UO, BO]
+  protected[diplomacy] val outward: OutwardNode[DO, UO, BO]
 }
 
 trait OutwardNode[DO, UO, BO <: Data] extends BaseNode with OutwardNodeHandle[DO, UO, BO]
 {
-  val outward = this
+  protected[diplomacy] val outward = this
 
   protected[diplomacy] val numPO: Range.Inclusive
   require (!numPO.isEmpty, s"No number of outputs would be acceptable to ${name}${lazyModule.line}")
   require (numPO.start >= 0, s"${name} accepts a negative number of outputs${lazyModule.line}")
 
-  private val accPO = ListBuffer[(Int, InwardNode [DO, UO, BO], NodeBinding)]()
+  private val accPO = ListBuffer[(Int, InwardNode [DO, UO, BO], NodeBinding, Parameters)]()
   private var oRealized = false
 
   protected[diplomacy] def oPushed = accPO.size
-  protected[diplomacy] def oPush(index: Int, node: InwardNode [DO, UO, BO], binding: NodeBinding)(implicit sourceInfo: SourceInfo) {
+  protected[diplomacy] def oPush(index: Int, node: InwardNode [DO, UO, BO], binding: NodeBinding)(implicit p: Parameters, sourceInfo: SourceInfo) {
     val info = sourceLine(sourceInfo, " at ", "")
     val noOs = numPO.size == 1 && numPO.contains(0)
     require (!noOs, s"${name}${lazyModule.line} was incorrectly connected as a source" + info)
     require (!oRealized, s"${name}${lazyModule.line} was incorrectly connected as a source after it's .module was used" + info)
-    accPO += ((index, node, binding))
+    accPO += ((index, node, binding, p))
   }
 
   protected[diplomacy] lazy val oBindings = { oRealized = true; accPO.result() }
@@ -149,7 +171,7 @@ trait OutwardNode[DO, UO, BO <: Data] extends BaseNode with OutwardNodeHandle[DO
   protected[diplomacy] val oStar: Int
   protected[diplomacy] val oPortMapping: Seq[(Int, Int)]
   protected[diplomacy] val oParams: Seq[DO]
-  val bundleOut: HeterogeneousBag[BO]
+  protected[diplomacy] val bundleOut: HeterogeneousBag[BO]
 }
 
 abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
@@ -164,22 +186,22 @@ abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
   protected[diplomacy] def mapParamsU(n: Int, p: Seq[UO]): Seq[UI]
 
   protected[diplomacy] lazy val (oPortMapping, iPortMapping, oStar, iStar) = {
-    val oStars = oBindings.filter { case (_,_,b) => b == BIND_STAR }.size
+    val oStars = oBindings.filter { case (_,_,b,_) => b == BIND_STAR }.size
-    val iStars = iBindings.filter { case (_,_,b) => b == BIND_STAR }.size
+    val iStars = iBindings.filter { case (_,_,b,_) => b == BIND_STAR }.size
-    val oKnown = oBindings.map { case (_, n, b) => b match {
+    val oKnown = oBindings.map { case (_, n, b, _) => b match {
       case BIND_ONCE  => 1
       case BIND_QUERY => n.iStar
       case BIND_STAR  => 0 }}.foldLeft(0)(_+_)
-    val iKnown = iBindings.map { case (_, n, b) => b match {
+    val iKnown = iBindings.map { case (_, n, b, _) => b match {
       case BIND_ONCE  => 1
       case BIND_QUERY => n.oStar
       case BIND_STAR  => 0 }}.foldLeft(0)(_+_)
     val (iStar, oStar) = resolveStar(iKnown, oKnown, iStars, oStars)
-    val oSum = oBindings.map { case (_, n, b) => b match {
+    val oSum = oBindings.map { case (_, n, b, _) => b match {
       case BIND_ONCE  => 1
       case BIND_QUERY => n.iStar
       case BIND_STAR  => oStar }}.scanLeft(0)(_+_)
-    val iSum = iBindings.map { case (_, n, b) => b match {
+    val iSum = iBindings.map { case (_, n, b, _) => b match {
       case BIND_ONCE  => 1
       case BIND_QUERY => n.oStar
       case BIND_STAR  => iStar }}.scanLeft(0)(_+_)
@@ -190,11 +212,11 @@ abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
     (oSum.init zip oSum.tail, iSum.init zip iSum.tail, oStar, iStar)
   }
 
-  lazy val oPorts = oBindings.flatMap { case (i, n, _) =>
+  lazy val oPorts = oBindings.flatMap { case (i, n, _, _) =>
     val (start, end) = n.iPortMapping(i)
     (start until end) map { j => (j, n) }
   }
-  lazy val iPorts = iBindings.flatMap { case (i, n, _) =>
+  lazy val iPorts = iBindings.flatMap { case (i, n, _, _) =>
     val (start, end) = n.oPortMapping(i)
     (start until end) map { j => (j, n) }
   }
@@ -218,6 +240,9 @@ abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
   lazy val externalEdgesOut = if (externalOut) {edgesOut} else { Seq() }
   lazy val externalEdgesIn = if (externalIn) {edgesIn} else { Seq() }
 
+  lazy val paramsOut: Seq[Parameters] = (oPortMapping zip oBindings).flatMap { case ((s, e), b) => Seq.fill(e-s) { b._4 } }
+  lazy val paramsIn:  Seq[Parameters] = (iPortMapping zip iBindings).flatMap { case ((s, e), b) => Seq.fill(e-s) { b._4 } }
+
   val flip = false // needed for blind nodes
   private def flipO(b: HeterogeneousBag[BO]) = if (flip) b.flip else b
   private def flipI(b: HeterogeneousBag[BI]) = if (flip) b      else b.flip
@@ -229,7 +254,7 @@ abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
   lazy val bundleIn  = wireI(flipI(HeterogeneousBag(edgesIn .map(inner.bundleI(_)))))
 
   // connects the outward part of a node with the inward part of this node
-  private def bind(h: OutwardNodeHandle[DI, UI, BI], binding: NodeBinding, enableMonitoring: Boolean)
+  private def bind(h: OutwardNodeHandle[DI, UI, BI], binding: NodeBinding)
                   (implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = {
     val x = this // x := y
     val y = h.outward
@@ -256,18 +281,21 @@ abstract class MixedNode[DI, UI, EI, BI <: Data, DO, UO, EO, BO <: Data](
         (x.bundleIn(iStart+j), y.bundleOut(oStart+j))
       }
     }
-    val (out, newbinding) = inner.connect(edges _, bundles _, enableMonitoring)
+    val (out, newbinding) = inner.connect(edges _, bundles _, p(MonitorsEnabled))
     LazyModule.stack.head.bindings = newbinding :: LazyModule.stack.head.bindings
     out
   }
 
-  override def :=  (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_ONCE, true)
+  override def :=  (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_ONCE)
-  override def :*= (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_STAR, true)
+  override def :*= (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_STAR)
-  override def :=* (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_QUERY, true)
+  override def :=* (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_QUERY)
-
+  override def :=? (h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = {
-  def connectButDontMonitor(h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_ONCE, false)
+    p(CardinalityInferenceDirectionKey) match {
-  def connectButDontMonitorSlaves(h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_STAR, false)
+      case CardinalityInferenceDirection.SOURCE_TO_SINK => this :=* h
-  def connectButDontMonitorMasters(h: OutwardNodeHandle[DI, UI, BI])(implicit p: Parameters, sourceInfo: SourceInfo): Option[MonitorBase] = bind(h, BIND_QUERY, false)
+      case CardinalityInferenceDirection.SINK_TO_SOURCE => this :*= h
+      case CardinalityInferenceDirection.NO_INFERENCE   => this :=  h
+    }
+  }
 
   // meta-data for printing the node graph
   protected[diplomacy] def colour  = inner.colour

src/main/scala/diplomacy/Parameters.scala

@@ -293,3 +293,14 @@ object BufferParams
   val flow    = BufferParams(1, true, false)
   val pipe    = BufferParams(1, false, true)
 }
+
+case class TriStateValue(value: Boolean, set: Boolean)
+{
+  def update(orig: Boolean) = if (set) value else orig
+}
+
+object TriStateValue
+{
+  implicit def apply(value: Boolean): TriStateValue = TriStateValue(value, true)
+  def unset = TriStateValue(false, false)
+}

src/main/scala/diplomacy/package.scala

@@ -3,6 +3,7 @@
 package freechips.rocketchip
 
 import chisel3.internal.sourceinfo.{SourceInfo, SourceLine, UnlocatableSourceInfo}
+import freechips.rocketchip.config.Parameters
 
 package object diplomacy
 {
@@ -20,4 +21,23 @@ package object diplomacy
       bitIndexes(x.clearBit(lowest), lowest +: tail)
     }
   }
+
+  def SinkCardinality[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case CardinalityInferenceDirectionKey => CardinalityInferenceDirection.SINK_TO_SOURCE
+  })
+  def SourceCardinality[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case CardinalityInferenceDirectionKey => CardinalityInferenceDirection.SOURCE_TO_SINK
+  })
+  def UnaryCardinality[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case CardinalityInferenceDirectionKey => CardinalityInferenceDirection.NO_INFERENCE
+  })
+  def FlipCardinality[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case CardinalityInferenceDirectionKey => p(CardinalityInferenceDirectionKey).flip
+  })
+  def EnableMonitors[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case MonitorsEnabled => true
+  })
+  def DisableMonitors[T](body: Parameters => T)(implicit p: Parameters) = body(p.alterPartial {
+    case MonitorsEnabled => false
+  })
 }

src/main/scala/rocket/Frontend.scala

@@ -8,7 +8,7 @@ import Chisel.ImplicitConversions._
 import chisel3.core.withReset
 import freechips.rocketchip.config._
 import freechips.rocketchip.coreplex._
-import freechips.rocketchip.diplomacy.{LazyModule, LazyModuleImp}
+import freechips.rocketchip.diplomacy._
 import freechips.rocketchip.tilelink._
 import freechips.rocketchip.tile._
 import freechips.rocketchip.util._
@@ -61,7 +61,7 @@ class Frontend(val icacheParams: ICacheParams, hartid: Int)(implicit p: Paramete
 
   masterNode := icache.masterNode
   // Avoid breaking tile dedup due to address constants in the monitor
-  icache.slaveNode.map { _ connectButDontMonitor slaveNode }
+  DisableMonitors { implicit p => icache.slaveNode.map { _ := slaveNode } }
 }
 
 class FrontendBundle(outer: Frontend) extends CoreBundle()(outer.p) {

src/main/scala/rocket/ScratchpadSlavePort.scala

@@ -103,16 +103,18 @@ trait CanHaveScratchpad extends HasHellaCache with HasICacheFrontend with HasCor
   val slaveNode = TLInputNode() // Up to two uses for this input node:
 
   // 1) Frontend always exists, but may or may not have a scratchpad node
+  // 2) ScratchpadSlavePort always has a node, but only exists when the HellaCache has a scratchpad
   val fg = LazyModule(new TLFragmenter(fetchWidth*coreInstBytes, p(CacheBlockBytes), earlyAck=true))
   val ww = LazyModule(new TLWidthWidget(xLen/8))
-  frontend.slaveNode connectButDontMonitorSlaves fg.node
-  fg.node connectButDontMonitorSlaves ww.node
-  ww.node connectButDontMonitorSlaves slaveNode
-
-  // 2) ScratchpadSlavePort always has a node, but only exists when the HellaCache has a scratchpad
   val scratch = tileParams.dcache.flatMap(d => d.scratch.map(s =>
     LazyModule(new ScratchpadSlavePort(AddressSet(s, d.dataScratchpadBytes-1)))))
-  scratch foreach { lm => lm.node connectButDontMonitor TLFragmenter(xLen/8, p(CacheBlockBytes), earlyAck=true)(slaveNode) }
+
+  DisableMonitors { implicit p =>
+    frontend.slaveNode :*= fg.node
+    fg.node :*= ww.node
+    ww.node :*= slaveNode
+    scratch foreach { lm => lm.node := TLFragmenter(xLen/8, p(CacheBlockBytes), earlyAck=true)(slaveNode) }
+  }
 
   def findScratchpadFromICache: Option[AddressSet] = scratch.map { s =>
     val finalNode = frontend.masterNode.edgesOut.head.manager.managers.find(_.nodePath.last == s.node)

src/main/scala/tile/RocketTile.scala

@@ -20,7 +20,8 @@ case class RocketTileParams(
     dataScratchpadBytes: Int = 0,
     boundaryBuffers: Boolean = false,
     name: Option[String] = Some("tile"),
-    externalBuffers: Int = 0) extends TileParams {
+    externalMasterBuffers: Int = 0,
+    externalSlaveBuffers: Int = 0) extends TileParams {
   require(icache.isDefined)
   require(dcache.isDefined)
 }
@@ -190,7 +191,7 @@ abstract class RocketTileWrapper(rtp: RocketTileParams, hartid: Int)(implicit p:
   def optionalSlaveBuffer(in: TLOutwardNode): TLOutwardNode = {
     if (rtp.boundaryBuffers) {
       val sbuf = LazyModule(new TLBuffer(BufferParams.flow, BufferParams.none, BufferParams.none, BufferParams.none, BufferParams.none))
-      sbuf.node connectButDontMonitorSlaves in
+      DisableMonitors { implicit p => sbuf.node :*= in }
       sbuf.node
     } else {
       in
@@ -216,7 +217,7 @@ class SyncRocketTile(rtp: RocketTileParams, hartid: Int)(implicit p: Parameters)
   masterNode :=* optionalMasterBuffer(rocket.masterNode)
 
   val slaveNode = new TLInputNode() { override def reverse = true }
-  rocket.slaveNode connectButDontMonitorSlaves optionalSlaveBuffer(slaveNode)
+  DisableMonitors { implicit p => rocket.slaveNode :*= optionalSlaveBuffer(slaveNode) }
 
   // Fully async interrupts need synchronizers.
   // Others need no synchronization.
@@ -236,8 +237,11 @@ class AsyncRocketTile(rtp: RocketTileParams, hartid: Int)(implicit p: Parameters
 
   val slaveNode = new TLAsyncInputNode() { override def reverse = true }
   val sink = LazyModule(new TLAsyncCrossingSink)
-  rocket.slaveNode connectButDontMonitorSlaves sink.node
+
-  sink.node connectButDontMonitorSlaves slaveNode
+  DisableMonitors { implicit p =>
+    rocket.slaveNode :*= sink.node
+    sink.node :*= slaveNode
+  }
 
   // Fully async interrupts need synchronizers,
   // as do those coming from the periphery clock.
@@ -260,8 +264,11 @@ class RationalRocketTile(rtp: RocketTileParams, hartid: Int)(implicit p: Paramet
 
   val slaveNode = new TLRationalInputNode() { override def reverse = true }
   val sink = LazyModule(new TLRationalCrossingSink(SlowToFast))
-  sink.node connectButDontMonitorSlaves slaveNode
+
-  rocket.slaveNode connectButDontMonitorSlaves optionalSlaveBuffer(sink.node)
+  DisableMonitors { implicit p =>
+    sink.node :*= slaveNode
+    rocket.slaveNode :*= optionalSlaveBuffer(sink.node)
+  }
 
   // Fully async interrupts need synchronizers.
   // Those coming from periphery clock need a

src/main/scala/tilelink/AsyncCrossing.scala

@@ -80,7 +80,7 @@ object TLAsyncCrossingSource
   // applied to the TL source node; y.node := TLAsyncCrossingSource()(x.node)
   def apply(sync: Int = 3)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLAsyncOutwardNode = {
     val source = LazyModule(new TLAsyncCrossingSource(sync))
-    source.node := x
+    source.node :=? x
     source.node
   }
 }
@@ -90,7 +90,7 @@ object TLAsyncCrossingSink
   // applied to the TL source node; y.node := TLAsyncCrossingSink()(x.node)
   def apply(depth: Int = 8, sync: Int = 3)(x: TLAsyncOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val sink = LazyModule(new TLAsyncCrossingSink(depth, sync))
-    sink.node := x
+    sink.node :=? x
     sink.node
   }
 }

src/main/scala/tilelink/AtomicAutomata.scala

@@ -265,7 +265,7 @@ object TLAtomicAutomata
   // applied to the TL source node; y.node := TLAtomicAutomata(x.node)
   def apply(logical: Boolean = true, arithmetic: Boolean = true, concurrency: Int = 1, passthrough: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val atomics = LazyModule(new TLAtomicAutomata(logical, arithmetic, concurrency, passthrough))
-    atomics.node := x
+    atomics.node :=? x
     atomics.node
   }
 

src/main/scala/tilelink/Buffer.scala

@@ -73,7 +73,7 @@ object TLBuffer
       d: BufferParams,
       e: BufferParams)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val buffer = LazyModule(new TLBuffer(a, b, c, d, e))
-    buffer.node := x
+    buffer.node :=? x
     buffer.node
   }
 }
@@ -82,18 +82,19 @@ class TLBufferChain(depth: Int)(implicit p: Parameters) extends LazyModule {
 
   val nodeIn = TLInputNode()
   val nodeOut = TLOutputNode()
+  val node = NodeHandle(nodeIn, nodeOut)
 
   val buf_chain = if (depth > 0) {
     val chain = List.fill(depth)(LazyModule(new TLBuffer(BufferParams.default)))
 
-    (chain.init zip chain.tail) foreach { case(prev, next) => next.node :=* prev.node }
+    (chain.init zip chain.tail) foreach { case(prev, next) => next.node :=? prev.node }
     chain
   } else {
     List(LazyModule(new TLBuffer(BufferParams.none)))
   }
 
-  buf_chain.head.node :=* nodeIn
+  buf_chain.head.node :=? nodeIn
-  nodeOut :=* buf_chain.last.node
+  nodeOut :=? buf_chain.last.node
 
   lazy val module = new LazyModuleImp(this) {
     val io = new Bundle {
@@ -102,3 +103,12 @@ class TLBufferChain(depth: Int)(implicit p: Parameters) extends LazyModule {
     }
   }
 }
+
+object TLBufferChain
+{
+  def apply(depth: Int)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
+    val buffer = LazyModule(new TLBufferChain(depth))
+    buffer.node :=? x
+    buffer.node
+  }
+}

src/main/scala/tilelink/Bus.scala

@@ -68,26 +68,32 @@ abstract class TLBusWrapper(params: TLBusParams, val busName: String)(implicit p
   protected def inwardBufNode: TLInwardNode = master_buffer.node
 
   protected def bufferChain(depth: Int, name: Option[String] = None): (TLInwardNode, TLOutwardNode) = {
+    SourceCardinality { implicit p =>
       val chain = LazyModule(new TLBufferChain(depth))
       name.foreach { n => chain.suggestName(s"${busName}_${n}_TLBufferChain")}
       (chain.nodeIn, chain.nodeOut)
     }
+  }
 
   def bufferFromMasters: TLInwardNode = inwardBufNode
 
   def bufferToSlaves: TLOutwardNode = outwardBufNode 
 
-  def toAsyncSlaves(sync: Int = 3, name: Option[String] = None): TLAsyncOutwardNode = {
+  def toSyncSlaves(name: Option[String] = None, addBuffers: Int = 0): TLOutwardNode = SinkCardinality { implicit p =>
+    TLBufferChain(addBuffers)(outwardBufNode)
+  }
+
+  def toAsyncSlaves(sync: Int = 3, name: Option[String] = None, addBuffers: Int = 0): TLAsyncOutwardNode = SinkCardinality { implicit p =>
     val source = LazyModule(new TLAsyncCrossingSource(sync))
     name.foreach{ n => source.suggestName(s"${busName}_${n}_TLAsyncCrossingSource")}
-    source.node :*= outwardNode
+    source.node :=? TLBufferChain(addBuffers)(outwardNode)
     source.node
   }
 
-  def toRationalSlaves(name: Option[String] = None): TLRationalOutwardNode = {
+  def toRationalSlaves(name: Option[String] = None, addBuffers: Int = 0): TLRationalOutwardNode = SinkCardinality { implicit p =>
     val source = LazyModule(new TLRationalCrossingSource())
     name.foreach{ n => source.suggestName(s"${busName}_${n}_TLRationalCrossingSource")}
-    source.node :*= outwardNode
+    source.node :=? TLBufferChain(addBuffers)(outwardNode)
     source.node
   }
 

src/main/scala/tilelink/CacheCork.scala

@@ -131,7 +131,7 @@ object TLCacheCork
   // applied to the TL source node; y.node := TLCacheCork()(x.node)
   def apply(unsafe: Boolean = false)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val cork = LazyModule(new TLCacheCork(unsafe))
-    cork.node := x
+    cork.node :=? x
     cork.node
   }
 }

src/main/scala/tilelink/Delayer.scala

@@ -81,7 +81,7 @@ object TLDelayer
   // applied to the TL source node; y.node := TLDelayer(0.01)(x.node)
   def apply(q: Double)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val delayer = LazyModule(new TLDelayer(q))
-    delayer.node := x
+    delayer.node :=? x
     delayer.node
   }
 }

src/main/scala/tilelink/FIFOFixer.scala

@@ -122,7 +122,7 @@ object TLFIFOFixer
   // applied to the TL source node; y.node := TLFIFOFixer()(x.node)
   def apply(policy: Policy = all)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val fixer = LazyModule(new TLFIFOFixer(policy))
-    fixer.node := x
+    fixer.node :=? x
     fixer.node
   }
 }

src/main/scala/tilelink/Fragmenter.scala

@@ -292,7 +292,7 @@ object TLFragmenter
   // applied to the TL source node; y.node := TLFragmenter(x.node, 256, 4)
   def apply(minSize: Int, maxSize: Int, alwaysMin: Boolean = false, earlyAck: Boolean = false)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val fragmenter = LazyModule(new TLFragmenter(minSize, maxSize, alwaysMin, earlyAck))
-    fragmenter.node := x
+    fragmenter.node :=? x
     fragmenter.node
   }
 }

src/main/scala/tilelink/HintHandler.scala

@@ -100,7 +100,7 @@ object TLHintHandler
   // applied to the TL source node; y.node := TLHintHandler(x.node)
   def apply(supportManagers: Boolean = true, supportClients: Boolean = false, passthrough: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val hints = LazyModule(new TLHintHandler(supportManagers, supportClients, passthrough))
-    hints.node := x
+    hints.node :=? x
     hints.node
   }
 }

src/main/scala/tilelink/Isolation.scala

@@ -79,7 +79,7 @@ object TLIsolation
   // **** WARNING: the isolation functions must bring the values to 0 ****
   def apply(fOut: (Bool, UInt) => UInt, fIn: (Bool, UInt) => UInt)(x: TLAsyncOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): (TLAsyncOutwardNode, () => (Bool, Bool)) = {
     val iso = LazyModule(new TLIsolation(fOut, fIn))
-    iso.node := x
+    iso.node :=? x
     (iso.node, () => (iso.module.io.iso_out, iso.module.io.iso_in))
   }
 }

src/main/scala/tilelink/Map.scala

@@ -48,7 +48,7 @@ object TLMap
   // applied to the TL source node; y.node := TLMap(fn)(x.node)
   def apply(fn: AddressSet => BigInt)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val map = LazyModule(new TLMap(fn))
-    map.node := x
+    map.node :=? x
     map.node
   }
 }

src/main/scala/tilelink/NodeNumberer.scala

@@ -67,7 +67,7 @@ object TLNodeNumberer
   // applied to the TL source node; y.node := TLBuffer(x.node)
   def apply(nodeAddressOffset: Option[Int] = None)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val numberer = LazyModule(new TLNodeNumberer(nodeAddressOffset))
-    numberer.node := x
+    numberer.node :=? x
     numberer.node
   }
 }

src/main/scala/tilelink/Nodes.scala

@@ -9,8 +9,8 @@ import freechips.rocketchip.diplomacy._
 import freechips.rocketchip.util.RationalDirection
 import scala.collection.mutable.ListBuffer
 
-case object TLMonitorBuilder extends Field[TLMonitorArgs => Option[TLMonitorBase]]
+case object TLMonitorBuilder extends Field[TLMonitorArgs => TLMonitorBase](args => LazyModule(new TLMonitor(args)))
-case object TLCombinationalCheck extends Field[Boolean]
+case object TLCombinationalCheck extends Field[Boolean](false)
 
 object TLImp extends NodeImp[TLClientPortParameters, TLManagerPortParameters, TLEdgeOut, TLEdgeIn, TLBundle]
 {
@@ -26,7 +26,7 @@ object TLImp extends NodeImp[TLClientPortParameters, TLManagerPortParameters, TL
 
   override def connect(edges: () => Seq[TLEdgeIn], bundles: () => Seq[(TLBundle, TLBundle)], enableMonitoring: Boolean)
                       (implicit p: Parameters, sourceInfo: SourceInfo): (Option[TLMonitorBase], () => Unit) = {
-    val monitor = if (enableMonitoring) p(TLMonitorBuilder)(TLMonitorArgs(edges, sourceInfo, p)) else None
+    val monitor = if (enableMonitoring) Some(p(TLMonitorBuilder)(TLMonitorArgs(edges, sourceInfo, p))) else None
     (monitor, () => {
       val eval = bundles ()
       monitor.foreach { m => (eval zip m.module.io.in) foreach { case ((i,o), m) => m := TLBundleSnoop(o,i) } }

src/main/scala/tilelink/RationalCrossing.scala

@@ -92,7 +92,7 @@ object TLRationalCrossingSource
   // applied to the TL source node; y.node := TLRationalCrossingSource()(x.node)
   def apply()(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLRationalOutwardNode = {
     val source = LazyModule(new TLRationalCrossingSource)
-    source.node := x
+    source.node :=? x
     source.node
   }
 }
@@ -102,7 +102,7 @@ object TLRationalCrossingSink
   // applied to the TL source node; y.node := TLRationalCrossingSink()(x.node)
   def apply(direction: RationalDirection = Symmetric)(x: TLRationalOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val sink = LazyModule(new TLRationalCrossingSink(direction))
-    sink.node := x
+    sink.node :=? x
     sink.node
   }
 }

src/main/scala/tilelink/SourceShrinker.scala

@@ -83,7 +83,7 @@ object TLSourceShrinker
   // applied to the TL source node; y.node := TLSourceShrinker(n)(x.node)
   def apply(maxInFlight: Int)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val shrinker = LazyModule(new TLSourceShrinker(maxInFlight))
-    shrinker.node := x
+    shrinker.node :=? x
     shrinker.node
   }
 }

src/main/scala/tilelink/ToAHB.scala

@@ -195,7 +195,7 @@ object TLToAHB
   // applied to the TL source node; y.node := TLToAHB()(x.node)
   def apply(aFlow: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AHBOutwardNode = {
     val ahb = LazyModule(new TLToAHB(aFlow))
-    ahb.node := x
+    ahb.node :=? x
     ahb.node
   }
 }

src/main/scala/tilelink/ToAPB.scala

@@ -94,7 +94,7 @@ object TLToAPB
   // applied to the TL source node; y.node := TLToAPB()(x.node)
   def apply(aFlow: Boolean = true)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): APBOutwardNode = {
     val apb = LazyModule(new TLToAPB(aFlow))
-    apb.node := x
+    apb.node :=? x
     apb.node
   }
 }

src/main/scala/tilelink/ToAXI4.scala

@@ -223,7 +223,7 @@ object TLToAXI4
   // applied to the TL source node; y.node := TLToAXI4(beatBytes)(x.node)
   def apply(beatBytes: Int, combinational: Boolean = true, adapterName: Option[String] = None, stripBits: Int = 0)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
     val axi4 = LazyModule(new TLToAXI4(beatBytes, combinational, adapterName, stripBits))
-    axi4.node := x
+    axi4.node :=? x
     axi4.node
   }
 

src/main/scala/tilelink/WidthWidget.scala

@@ -200,7 +200,7 @@ object TLWidthWidget
   // applied to the TL source node; y.node := WidthWidget(x.node, 16)
   def apply(innerBeatBytes: Int)(x: TLOutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): TLOutwardNode = {
     val widget = LazyModule(new TLWidthWidget(innerBeatBytes))
-    widget.node := x
+    widget.node :=? x
     widget.node
   }
 }

src/main/scala/tilelink/Xbar.scala

@@ -3,9 +3,31 @@
 package freechips.rocketchip.tilelink
 
 import Chisel._
-import freechips.rocketchip.config.Parameters
+import freechips.rocketchip.config._
 import freechips.rocketchip.diplomacy._
 
+// Trades off slave port proximity against routing resource cost
+object ForceFanout
+{
+  def apply[T](
+    a: TriStateValue = TriStateValue.unset,
+    b: TriStateValue = TriStateValue.unset,
+    c: TriStateValue = TriStateValue.unset,
+    d: TriStateValue = TriStateValue.unset,
+    e: TriStateValue = TriStateValue.unset)(body: Parameters => T)(implicit p: Parameters) =
+  {
+    body(p.alterPartial {
+      case ForceFanoutKey => p(ForceFanoutKey) match {
+        case ForceFanoutParams(pa, pb, pc, pd, pe) =>
+          ForceFanoutParams(a.update(pa), b.update(pb), c.update(pc), d.update(pd), e.update(pe))
+      }
+    })
+  }
+}
+
+private case class ForceFanoutParams(a: Boolean, b: Boolean, c: Boolean, d: Boolean, e: Boolean)
+private case object ForceFanoutKey extends Field(ForceFanoutParams(false, false, false, false, false))
+
 class TLXbar(policy: TLArbiter.Policy = TLArbiter.roundRobin)(implicit p: Parameters) extends LazyModule
 {
   val node = TLNexusNode(
@@ -157,11 +179,11 @@ class TLXbar(policy: TLArbiter.Policy = TLArbiter.roundRobin)(implicit p: Parame
     def filter[T](data: Seq[T], mask: Seq[Boolean]) = (data zip mask).filter(_._2).map(_._1)
 
     // Fanout the input sources to the output sinks
-    val portsAOI = transpose((in  zip requestAIO) map { case (i, r) => TLXbar.fanout(i.a, r) })
+    val portsAOI = transpose((in  zip requestAIO) map { case (i, r) => TLXbar.fanout(i.a, r, node.paramsOut.map(_(ForceFanoutKey).a)) })
-    val portsBIO = transpose((out zip requestBOI) map { case (o, r) => TLXbar.fanout(o.b, r) })
+    val portsBIO = transpose((out zip requestBOI) map { case (o, r) => TLXbar.fanout(o.b, r, node.paramsIn .map(_(ForceFanoutKey).b)) })
-    val portsCOI = transpose((in  zip requestCIO) map { case (i, r) => TLXbar.fanout(i.c, r) })
+    val portsCOI = transpose((in  zip requestCIO) map { case (i, r) => TLXbar.fanout(i.c, r, node.paramsOut.map(_(ForceFanoutKey).c)) })
-    val portsDIO = transpose((out zip requestDOI) map { case (o, r) => TLXbar.fanout(o.d, r) })
+    val portsDIO = transpose((out zip requestDOI) map { case (o, r) => TLXbar.fanout(o.d, r, node.paramsIn .map(_(ForceFanoutKey).d)) })
-    val portsEOI = transpose((in  zip requestEIO) map { case (i, r) => TLXbar.fanout(i.e, r) })
+    val portsEOI = transpose((in  zip requestEIO) map { case (i, r) => TLXbar.fanout(i.e, r, node.paramsOut.map(_(ForceFanoutKey).e)) })
 
     // Arbitrate amongst the sources
     for (o <- 0 until out.size) {
@@ -216,10 +238,10 @@ object TLXbar
   }
 
   // Replicate an input port to each output port
-  def fanout[T <: TLChannel](input: DecoupledIO[T], select: Seq[Bool]) = {
+  def fanout[T <: TLChannel](input: DecoupledIO[T], select: Seq[Bool], force: Seq[Boolean] = Nil) = {
     val filtered = Wire(Vec(select.size, input))
     for (i <- 0 until select.size) {
-      filtered(i).bits := input.bits
+      filtered(i).bits := (if (force.lift(i).getOrElse(false)) IdentityModule(input.bits) else input.bits)
       filtered(i).valid := input.valid && select(i)
     }
     input.ready := Mux1H(select, filtered.map(_.ready))

src/main/scala/util/IdentityModule.scala

@@ -0,0 +1,24 @@
+// See LICENSE.SiFive for license details.
+
+package freechips.rocketchip.tilelink
+
+import Chisel._
+
+class IdentityModule[T <: Data](gen: T) extends Module
+{
+  val io = new Bundle {
+    val in = gen.cloneType.flip
+    val out = gen.cloneType
+  }
+
+  io.out := io.in
+}
+
+object IdentityModule
+{
+  def apply[T <: Data](x: T): T = {
+    val identity = Module(new IdentityModule(x))
+    identity.io.in := x
+    identity.io.out
+  }
+}

src/main/scala/util/RationalCrossing.scala

@@ -73,10 +73,10 @@ class RationalCrossingSource[T <: Data](gen: T, direction: RationalDirection = S
 
   val deq = io.deq
   val enq = direction match {
-    case Symmetric  => Queue(io.enq, 1, flow=true)
+    case Symmetric  => ShiftQueue(io.enq, 1, flow=true)
-    case Flexible => Queue(io.enq, 2)
+    case Flexible => ShiftQueue(io.enq, 2)
     case FastToSlow => io.enq
-    case SlowToFast => Queue(io.enq, 2)
+    case SlowToFast => ShiftQueue(io.enq, 2)
   }
 
   val count = RegInit(UInt(0, width = 2))
@@ -109,9 +109,9 @@ class RationalCrossingSink[T <: Data](gen: T, direction: RationalDirection = Sym
   val enq = io.enq
   val deq = Wire(io.deq)
   direction match {
-    case Symmetric  => io.deq <> Queue(deq, 1, pipe=true)
+    case Symmetric  => io.deq <> ShiftQueue(deq, 1, pipe=true)
-    case Flexible   => io.deq <> Queue(deq, 2)
+    case Flexible   => io.deq <> ShiftQueue(deq, 2)
-    case FastToSlow => io.deq <> Queue(deq, 2)
+    case FastToSlow => io.deq <> ShiftQueue(deq, 2)
     case SlowToFast => io.deq <> deq
   }
 

src/main/scala/util/ShiftQueue.scala

@@ -26,7 +26,7 @@ class ShiftQueue[T <: Data](gen: T,
     val wdata = if (i == entries-1) io.enq.bits else Mux(valid(i+1), elts(i+1), io.enq.bits)
     val wen =
       Mux(io.deq.ready,
-          paddedValid(i+1) || io.enq.fire() && valid(i),
+          paddedValid(i+1) || io.enq.fire() && (Bool(i == 0 && !flow) || valid(i)),
           io.enq.fire() && paddedValid(i-1) && !valid(i))
     when (wen) { elts(i) := wdata }
 
@@ -52,3 +52,12 @@ class ShiftQueue[T <: Data](gen: T,
   io.mask := valid.asUInt
   io.count := PopCount(io.mask)
 }
+
+object ShiftQueue
+{
+  def apply[T <: Data](enq: DecoupledIO[T], entries: Int = 2, pipe: Boolean = false, flow: Boolean = false): DecoupledIO[T] = {
+    val q = Module(new ShiftQueue(enq.bits.cloneType, entries, pipe, flow))
+    q.io.enq <> enq
+    q.io.deq
+  }
+}