rocket-chip/uncore/src/main/scala/cache.scala

// See LICENSE for license details.

package uncore
import Chisel._

case object CacheName extends Field[String]
case object NSets extends Field[Int]
case object NWays extends Field[Int]
case object BlockOffBits extends Field[Int]
case object RowBits extends Field[Int]
case object WordBits extends Field[Int]
case object Replacer extends Field[() => ReplacementPolicy]

abstract trait CacheParameters extends UsesParameters {
  val paddrBits = params(PAddrBits)
  val vaddrBits = params(VAddrBits)
  val pgIdxBits = params(PgIdxBits) 
  val nSets = params(NSets)
  val blockOffBits = params(BlockOffBits)
  val idxBits = log2Up(nSets)
  val untagBits = blockOffBits + idxBits
  val tagBits = paddrBits - untagBits
  val nWays = params(NWays)
  val wayBits = log2Up(nWays)
  val isDM = nWays == 1
  val wordBits = params(WordBits)
  val wordBytes = wordBits/8
  val wordOffBits = log2Up(wordBytes)
  val rowBits = params(RowBits)
  val rowWords = rowBits/wordBits 
  val rowBytes = rowBits/8
  val rowOffBits = log2Up(rowBytes)
  val refillCycles = params(TLDataBits)/rowBits
}

abstract class CacheBundle extends Bundle with CacheParameters
abstract class CacheModule extends Module with CacheParameters

abstract class ReplacementPolicy {
  def way: UInt
  def miss: Unit
  def hit: Unit
}

class RandomReplacement(ways: Int) extends ReplacementPolicy {
  private val replace = Bool()
  replace := Bool(false)
  val lfsr = LFSR16(replace)

  def way = if(ways == 1) UInt(0) else lfsr(log2Up(ways)-1,0)
  def miss = replace := Bool(true)
  def hit = {}
}

abstract class Metadata extends CacheBundle {
  val tag = Bits(width = tagBits)
  val coh: CoherenceMetadata
}

class MetaReadReq extends CacheBundle {
  val idx  = Bits(width = idxBits)
}

class MetaWriteReq[T <: Metadata](gen: T) extends MetaReadReq {
  val way_en = Bits(width = nWays)
  val data = gen.clone
  override def clone = new MetaWriteReq(gen).asInstanceOf[this.type]
}

class MetadataArray[T <: Metadata](makeRstVal: () => T) extends CacheModule {
  val rstVal = makeRstVal()
  val io = new Bundle {
    val read = Decoupled(new MetaReadReq).flip
    val write = Decoupled(new MetaWriteReq(rstVal.clone)).flip
    val resp = Vec.fill(nWays){rstVal.clone.asOutput}
  }
  val metabits = rstVal.getWidth
  val rst_cnt = Reg(init=UInt(0, log2Up(nSets+1)))
  val rst = rst_cnt < UInt(nSets)
  val waddr = Mux(rst, rst_cnt, io.write.bits.idx)
  val wdata = Mux(rst, rstVal, io.write.bits.data).toBits
  val wmask = Mux(rst, SInt(-1), io.write.bits.way_en)
  when (rst) { rst_cnt := rst_cnt+UInt(1) }

  val tag_arr = Mem(UInt(width = metabits*nWays), nSets, seqRead = true)
  when (rst || io.write.valid) {
    tag_arr.write(waddr, Fill(nWays, wdata), FillInterleaved(metabits, wmask))
  }

  val tags = tag_arr(RegEnable(io.read.bits.idx, io.read.valid))
  for (w <- 0 until nWays) {
    val m = tags(metabits*(w+1)-1, metabits*w)
    io.resp(w) := rstVal.clone.fromBits(m)
  }

  io.read.ready := !rst && !io.write.valid // so really this could be a 6T RAM
  io.write.ready := !rst
}