Add optional PLRU replacement to the L2

uncore/src/main/scala/cache.scala

@@ -11,6 +11,7 @@ case object NSets extends Field[Int]
 case object NWays extends Field[Int]
 case object RowBits extends Field[Int]
 case object Replacer extends Field[() => ReplacementPolicy]
+case object L2Replacer extends Field[() => SeqReplacementPolicy]
 case object AmoAluOperandBits extends Field[Int]
 case object NPrimaryMisses extends Field[Int]
 case object NSecondaryMisses extends Field[Int]
@@ -58,6 +59,68 @@ class RandomReplacement(ways: Int) extends ReplacementPolicy {
   def hit = {}
 }
 
+abstract class SeqReplacementPolicy {
+  def access(set: UInt): Unit
+  def update(valid: Bool, hit: Bool, set: UInt, way: UInt): Unit
+  def way: UInt
+}
+
+class SeqRandom(n_ways: Int) extends SeqReplacementPolicy {
+  val logic = new RandomReplacement(n_ways)
+  def access(set: UInt) = { }
+  def update(valid: Bool, hit: Bool, set: UInt, way: UInt) = {
+    when (valid && !hit) { logic.miss }
+  }
+  def way = logic.way
+}
+
+class PseudoLRU(n: Int)
+{
+  val state_reg = Reg(Bits(width = n))
+  def access(way: UInt) {
+    state_reg := get_next_state(state_reg,way)
+  }
+  def get_next_state(state: Bits, way: UInt) = {
+    var next_state = state
+    var idx = UInt(1,1)
+    for (i <- log2Up(n)-1 to 0 by -1) {
+      val bit = way(i)
+      val mask = (UInt(1,n) << idx)(n-1,0)
+      next_state = next_state & ~mask | Mux(bit, UInt(0), mask)
+      //next_state.bitSet(idx, !bit)
+      idx = Cat(idx, bit)
+    }
+    next_state
+  }
+  def replace = get_replace_way(state_reg)
+  def get_replace_way(state: Bits) = {
+    var idx = UInt(1,1)
+    for (i <- 0 until log2Up(n))
+      idx = Cat(idx, state(idx))
+    idx(log2Up(n)-1,0)
+  }
+}
+
+class SeqPLRU(n_sets: Int, n_ways: Int) extends SeqReplacementPolicy {
+  val state = SeqMem(Bits(width = n_ways-1), n_sets)
+  val logic = new PseudoLRU(n_ways)
+  val current_state = Wire(Bits())
+  val plru_way = logic.get_replace_way(current_state)
+  val next_state = Wire(Bits())
+
+  def access(set: UInt) = {
+    current_state := Cat(state.read(set), Bits(0, width = 1))
+  }
+
+  def update(valid: Bool, hit: Bool, set: UInt, way: UInt) = {
+    val update_way = Mux(hit, way, plru_way)
+    next_state := logic.get_next_state(current_state, update_way)
+    when (valid) { state.write(set, next_state(n_ways-1,1)) }
+  }
+
+  def way = plru_way
+}
+
 abstract class Metadata(implicit p: Parameters) extends CacheBundle()(p) {
   val tag = Bits(width = tagBits)
   val coh: CoherenceMetadata
@@ -212,16 +275,22 @@ class L2MetadataArray(implicit p: Parameters) extends L2HellaCacheModule()(p) {
   val s1_clk_en = Reg(next = io.read.fire())
   val s1_tag_eq_way = wayMap((w: Int) => meta.io.resp(w).tag === s1_tag)
   val s1_tag_match_way = wayMap((w: Int) => s1_tag_eq_way(w) && meta.io.resp(w).coh.outer.isValid()).toBits
+  val s1_idx = RegEnable(io.read.bits.idx, io.read.valid) // deal with stalls?
   val s2_tag_match_way = RegEnable(s1_tag_match_way, s1_clk_en)
   val s2_tag_match = s2_tag_match_way.orR
   val s2_hit_coh = Mux1H(s2_tag_match_way, wayMap((w: Int) => RegEnable(meta.io.resp(w).coh, s1_clk_en)))
 
-  val replacer = p(Replacer)()
+  val replacer = p(L2Replacer)()
+  val s1_hit_way = Wire(Bits())
+  s1_hit_way := Bits(0)
+  (0 until nWays).foreach(i => when (s1_tag_match_way(i)) { s1_hit_way := Bits(i) })
+  replacer.access(io.read.bits.idx)
+  replacer.update(s1_clk_en, s1_tag_match_way.orR, s1_idx, s1_hit_way)
+
   val s1_replaced_way_en = UIntToOH(replacer.way)
   val s2_replaced_way_en = UIntToOH(RegEnable(replacer.way, s1_clk_en))
   val s2_repl_meta = Mux1H(s2_replaced_way_en, wayMap((w: Int) => 
     RegEnable(meta.io.resp(w), s1_clk_en && s1_replaced_way_en(w))).toSeq)
-  when(!s2_tag_match) { replacer.miss }
 
   io.resp.valid := Reg(next = s1_clk_en)
   io.resp.bits.id := RegEnable(s1_id, s1_clk_en)