From 9a7077b70cd527c9ae50fd4817459a32db2af68b Mon Sep 17 00:00:00 2001
From: Jerry Zhao <jerryz123@berkeley.edu>
Date: Thu, 8 Aug 2024 15:46:30 -0700
Subject: [PATCH] Add reset pipeline support

---
 .../main/scala/clocking/HasChipyardPRCI.scala |  3 ++
 .../main/scala/clocking/ResetPipeline.scala   | 34 +++++++++++++++++++
 .../config/fragments/ClockingFragments.scala  |  8 +++++
 3 files changed, 45 insertions(+)
 create mode 100644 generators/chipyard/src/main/scala/clocking/ResetPipeline.scala

diff --git a/generators/chipyard/src/main/scala/clocking/HasChipyardPRCI.scala b/generators/chipyard/src/main/scala/clocking/HasChipyardPRCI.scala
index f1936d487c..bb261e250d 100644
--- a/generators/chipyard/src/main/scala/clocking/HasChipyardPRCI.scala
+++ b/generators/chipyard/src/main/scala/clocking/HasChipyardPRCI.scala
@@ -20,6 +20,7 @@ import testchipip.clocking.{ClockGroupFakeResetSynchronizer}
 case class ChipyardPRCIControlParams(
   slaveWhere: TLBusWrapperLocation = CBUS,
   baseAddress: BigInt = 0x100000,
+  resetPipeStages: Int = 0,
   enableTileClockGating: Boolean = true,
   enableTileResetSetting: Boolean = true,
   enableResetSynchronizers: Boolean = true // this should only be disabled to work around verilator async-reset initialization problems
@@ -66,6 +67,7 @@ trait HasChipyardPRCI { this: BaseSubsystem with InstantiatesHierarchicalElement
   // diplomatic IOBinder should drive
   val frequencySpecifier = ClockGroupFrequencySpecifier(p(ClockFrequencyAssignersKey))
   val clockGroupCombiner = ClockGroupCombiner()
+  val resetPipeline      = prci_ctrl_domain { LazyModule(new ResetPipeline(prciParams.resetPipeStages)) }
   val resetSynchronizer  = prci_ctrl_domain {
     if (prciParams.enableResetSynchronizers) ClockGroupResetSynchronizer() else ClockGroupFakeResetSynchronizer()
   }
@@ -105,6 +107,7 @@ RTL SIMULATORS, NAMELY VERILATOR.
 
   (aggregator
     := frequencySpecifier
+    := resetPipeline.node
     := clockGroupCombiner
     := resetSynchronizer
     := tileClockGater.map(_.clockNode).getOrElse(ClockGroupEphemeralNode()(ValName("temp")))
diff --git a/generators/chipyard/src/main/scala/clocking/ResetPipeline.scala b/generators/chipyard/src/main/scala/clocking/ResetPipeline.scala
new file mode 100644
index 0000000000..1933c428db
--- /dev/null
+++ b/generators/chipyard/src/main/scala/clocking/ResetPipeline.scala
@@ -0,0 +1,34 @@
+package chipyard.clocking
+
+import chisel3._
+import chisel3.util._
+import org.chipsalliance.cde.config._
+import org.chipsalliance.diplomacy._
+import org.chipsalliance.diplomacy.lazymodule._
+import freechips.rocketchip.prci.{ClockGroupAdapterNode}
+
+/** This adapter takes input synchronous resets and stretch them via a reset pipeline
+  *  This is useful for distributing a synchronous reset across the chip
+  */
+class ResetPipeline(stages: Int)(implicit p: Parameters) extends LazyModule {
+  val node = ClockGroupAdapterNode()(ValName(s"reset_pipeline_$stages"))
+  override lazy val desiredName = s"ResetPipeline$stages"
+  lazy val module = new Impl
+  class Impl extends LazyRawModuleImp(this) {
+    (node.in zip node.out).foreach { case ((iG, _), (oG, _)) =>
+      (oG.member.data zip iG.member.data).foreach { case (out, in) =>
+        out.clock := in.clock
+        withClock (in.clock) {
+          if (stages == 0) {
+            out.reset := in.reset
+          } else {
+            val regs = Seq.fill(stages)(Reg(Bool()))
+            regs.head := in.reset
+            out.reset := regs.last
+              (regs.init zip regs.tail).foreach(t => t._2 := t._1)
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/generators/chipyard/src/main/scala/config/fragments/ClockingFragments.scala b/generators/chipyard/src/main/scala/config/fragments/ClockingFragments.scala
index 83a42146ae..f98a3f5dcd 100644
--- a/generators/chipyard/src/main/scala/config/fragments/ClockingFragments.scala
+++ b/generators/chipyard/src/main/scala/config/fragments/ClockingFragments.scala
@@ -133,3 +133,11 @@ class WithNoResetSynchronizers extends Config((site, here, up) => {
 class WithNoClockTap extends Config((site, here, up) => {
   case ClockTapKey => false
 })
+
+// Adds a reset pipeline after the ResetSynchronizer in chipyard's clock/reset path
+// This assists with PD and timing of sync reset
+// NOTE: This will likely result in spurious early assertions when reset-assertion
+// is propagating through the pipeline. You may ignore these in RTL simulators
+class WithSyncResetPipeStages(stages: Int) extends Config((site, here, up) => {
+  case ChipyardPRCIControlKey => up(ChipyardPRCIControlKey).copy(resetPipeStages = stages)
+})