rocket-chip/rocket/src/main/scala/nbdcache.scala

// See LICENSE for license details.

package rocket

import Chisel._
import junctions._
import uncore.tilelink._
import uncore.coherence._
import uncore.agents._
import uncore.util._
import uncore.constants._
import cde.{Parameters, Field}
import Util._

case object WordBits extends Field[Int]
case object StoreDataQueueDepth extends Field[Int]
case object ReplayQueueDepth extends Field[Int]
case object NMSHRs extends Field[Int]
case object LRSCCycles extends Field[Int]

trait HasL1HellaCacheParameters extends HasL1CacheParameters {
  val wordBits = p(WordBits)
  val wordBytes = wordBits/8
  val wordOffBits = log2Up(wordBytes)
  val beatBytes = p(CacheBlockBytes) / outerDataBeats
  val beatWords = beatBytes / wordBytes
  val beatOffBits = log2Up(beatBytes)
  val idxMSB = untagBits-1
  val idxLSB = blockOffBits
  val offsetmsb = idxLSB-1
  val offsetlsb = wordOffBits
  val rowWords = rowBits/wordBits
  val doNarrowRead = coreDataBits * nWays % rowBits == 0
  val encDataBits = code.width(coreDataBits)
  val encRowBits = encDataBits*rowWords
  val sdqDepth = p(StoreDataQueueDepth)
  val nMSHRs = p(NMSHRs)
  val nIOMSHRs = 1
  val lrscCycles = p(LRSCCycles)

  require(lrscCycles >= 32) // ISA requires 16-insn LRSC sequences to succeed
  require(isPow2(nSets))
  require(rowBits <= outerDataBits)
  require(!usingVM || untagBits <= pgIdxBits)
}

abstract class L1HellaCacheModule(implicit val p: Parameters) extends Module
  with HasL1HellaCacheParameters
abstract class L1HellaCacheBundle(implicit val p: Parameters) extends junctions.ParameterizedBundle()(p)
  with HasL1HellaCacheParameters

trait HasCoreMemOp extends HasCoreParameters {
  val addr = UInt(width = coreMaxAddrBits)
  val tag  = Bits(width = coreDCacheReqTagBits)
  val cmd  = Bits(width = M_SZ)
  val typ  = Bits(width = MT_SZ)
}

trait HasCoreData extends HasCoreParameters {
  val data = Bits(width = coreDataBits)
}

trait HasSDQId extends HasL1HellaCacheParameters {
  val sdq_id = UInt(width = log2Up(sdqDepth))
}

trait HasMissInfo extends HasL1HellaCacheParameters {
  val tag_match = Bool()
  val old_meta = new L1Metadata
  val way_en = Bits(width = nWays)
}

class HellaCacheReqInternal(implicit p: Parameters) extends L1HellaCacheBundle()(p)
    with HasCoreMemOp {
  val phys = Bool()
}

class HellaCacheReq(implicit p: Parameters) extends HellaCacheReqInternal()(p) with HasCoreData

class HellaCacheResp(implicit p: Parameters) extends L1HellaCacheBundle()(p)
    with HasCoreMemOp
    with HasCoreData {
  val replay = Bool()
  val has_data = Bool()
  val data_word_bypass = Bits(width = coreDataBits)
  val store_data = Bits(width = coreDataBits)
}

class AlignmentExceptions extends Bundle {
  val ld = Bool()
  val st = Bool()
}

class HellaCacheExceptions extends Bundle {
  val ma = new AlignmentExceptions
  val pf = new AlignmentExceptions
}

// interface between D$ and processor/DTLB
class HellaCacheIO(implicit p: Parameters) extends CoreBundle()(p) {
  val req = Decoupled(new HellaCacheReq)
  val s1_kill = Bool(OUTPUT) // kill previous cycle's req
  val s1_data = Bits(OUTPUT, coreDataBits) // data for previous cycle's req
  val s2_nack = Bool(INPUT) // req from two cycles ago is rejected

  val resp = Valid(new HellaCacheResp).flip
  val replay_next = Bool(INPUT)
  val xcpt = (new HellaCacheExceptions).asInput
  val invalidate_lr = Bool(OUTPUT)
  val ordered = Bool(INPUT)
}

class L1DataReadReq(implicit p: Parameters) extends L1HellaCacheBundle()(p) {
  val way_en = Bits(width = nWays)
  val addr   = Bits(width = untagBits)
}

class L1DataWriteReq(implicit p: Parameters) extends L1DataReadReq()(p) {
  val wmask  = Bits(width = rowWords)
  val data   = Bits(width = encRowBits)
}

class L1RefillReq(implicit p: Parameters) extends L1DataReadReq()(p)

class L1MetaReadReq(implicit p: Parameters) extends MetaReadReq {
  val tag = Bits(width = tagBits)
  override def cloneType = new L1MetaReadReq()(p).asInstanceOf[this.type] //TODO remove
}

class L1MetaWriteReq(implicit p: Parameters) extends 
  MetaWriteReq[L1Metadata](new L1Metadata)

object L1Metadata {
  def apply(tag: Bits, coh: ClientMetadata)(implicit p: Parameters) = {
    val meta = Wire(new L1Metadata)
    meta.tag := tag
    meta.coh := coh
    meta
  }
}
class L1Metadata(implicit p: Parameters) extends Metadata()(p) with HasL1HellaCacheParameters {
  val coh = new ClientMetadata
}

class Replay(implicit p: Parameters) extends HellaCacheReqInternal()(p) with HasCoreData
class ReplayInternal(implicit p: Parameters) extends HellaCacheReqInternal()(p) with HasSDQId

class MSHRReq(implicit p: Parameters) extends Replay()(p) with HasMissInfo
class MSHRReqInternal(implicit p: Parameters) extends ReplayInternal()(p) with HasMissInfo

class ProbeInternal(implicit p: Parameters) extends Probe()(p) with HasClientTransactionId

class WritebackReq(implicit p: Parameters) extends Release()(p) with HasCacheParameters {
  val way_en = Bits(width = nWays)
}

class IOMSHR(id: Int)(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val req = Decoupled(new HellaCacheReq).flip
    val acquire = Decoupled(new Acquire)
    val grant = Valid(new GrantFromSrc).flip
    val finish = Decoupled(new FinishToDst)
    val resp = Decoupled(new HellaCacheResp)
    val replay_next = Bool(OUTPUT)
  }

  def beatOffset(addr: UInt) = addr.extract(beatOffBits - 1, wordOffBits)

  def wordFromBeat(addr: UInt, dat: UInt) = {
    val shift = Cat(beatOffset(addr), UInt(0, wordOffBits + log2Up(wordBytes)))
    (dat >> shift)(wordBits - 1, 0)
  }

  val req = Reg(new HellaCacheReq)
  val req_cmd_sc = req.cmd === M_XSC
  val grant_word = Reg(UInt(width = wordBits))
  val fq = Module(new FinishQueue(1))

  val s_idle :: s_acquire :: s_grant :: s_resp :: s_finish :: Nil = Enum(Bits(), 5)
  val state = Reg(init = s_idle)
  io.req.ready := (state === s_idle)

  fq.io.enq.valid := io.grant.valid && io.grant.bits.requiresAck()
  fq.io.enq.bits := io.grant.bits.makeFinish()
  io.finish.valid := fq.io.deq.valid && (state === s_finish)
  io.finish.bits := fq.io.deq.bits
  fq.io.deq.ready := io.finish.ready && (state === s_finish)

  val storegen = new StoreGen(req.typ, req.addr, req.data, wordBytes)
  val loadgen = new LoadGen(req.typ, req.addr, grant_word, req_cmd_sc, wordBytes)

  val beat_mask = (storegen.mask << Cat(beatOffset(req.addr), UInt(0, wordOffBits)))
  val beat_data = Fill(beatWords, storegen.data)

  val addr_block = req.addr(paddrBits - 1, blockOffBits)
  val addr_beat  = req.addr(blockOffBits - 1, beatOffBits)
  val addr_byte  = req.addr(beatOffBits - 1, 0)

  val get_acquire = Get(
    client_xact_id = UInt(id),
    addr_block = addr_block,
    addr_beat = addr_beat,
    addr_byte = addr_byte,
    operand_size = req.typ,
    alloc = Bool(false))

  val put_acquire = Put(
    client_xact_id = UInt(id),
    addr_block = addr_block,
    addr_beat = addr_beat,
    data = beat_data,
    wmask = Some(beat_mask),
    alloc = Bool(false))

  val putAtomic_acquire = PutAtomic(
    client_xact_id = UInt(id),
    addr_block = addr_block,
    addr_beat = addr_beat,
    addr_byte = addr_byte,
    atomic_opcode = req.cmd,
    operand_size = req.typ,
    data = beat_data)

  io.acquire.valid := (state === s_acquire)
  io.acquire.bits := Mux(isAMO(req.cmd), putAtomic_acquire, Mux(isRead(req.cmd), get_acquire, put_acquire))

  io.replay_next := (state === s_grant) || io.resp.valid && !io.resp.ready
  io.resp.valid := (state === s_resp)
  io.resp.bits := req
  io.resp.bits.has_data := isRead(req.cmd)
  io.resp.bits.data := loadgen.data | req_cmd_sc
  io.resp.bits.store_data := req.data
  io.resp.bits.replay := Bool(true)

  when (io.req.fire()) {
    req := io.req.bits
    state := s_acquire
  }

  when (io.acquire.fire()) {
    state := s_grant
  }

  when (state === s_grant && io.grant.valid) {
    state := s_resp
    when (isRead(req.cmd)) {
      grant_word := wordFromBeat(req.addr, io.grant.bits.data)
    }
  }

  when (io.resp.fire()) {
    state := s_finish
  }

  when (io.finish.fire()) {
    state := s_idle
  }
}

class MSHR(id: Int)(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val req_pri_val    = Bool(INPUT)
    val req_pri_rdy    = Bool(OUTPUT)
    val req_sec_val    = Bool(INPUT)
    val req_sec_rdy    = Bool(OUTPUT)
    val req_bits       = new MSHRReqInternal().asInput

    val idx_match       = Bool(OUTPUT)
    val tag             = Bits(OUTPUT, tagBits)

    val mem_req  = Decoupled(new Acquire)
    val refill = new L1RefillReq().asOutput // Data is bypassed
    val meta_read = Decoupled(new L1MetaReadReq)
    val meta_write = Decoupled(new L1MetaWriteReq)
    val replay = Decoupled(new ReplayInternal)
    val mem_grant = Valid(new GrantFromSrc).flip
    val mem_finish = Decoupled(new FinishToDst)
    val wb_req = Decoupled(new WritebackReq)
    val probe_rdy = Bool(OUTPUT)
  }

  val s_invalid :: s_wb_req :: s_wb_resp :: s_meta_clear :: s_refill_req :: s_refill_resp :: s_meta_write_req :: s_meta_write_resp :: s_drain_rpq :: Nil = Enum(UInt(), 9)
  val state = Reg(init=s_invalid)

  def stateIsOneOf(check_states: Seq[UInt]): Bool =
    check_states.map(state === _).reduce(_ || _)

  def stateIsOneOf(st1: UInt, st2: UInt*): Bool =
    stateIsOneOf(st1 +: st2)

  val new_coh_state = Reg(init=ClientMetadata.onReset)
  val req = Reg(new MSHRReqInternal())
  val req_idx = req.addr(untagBits-1,blockOffBits)
  val idx_match = req_idx === io.req_bits.addr(untagBits-1,blockOffBits)
  // We only accept secondary misses if we haven't yet sent an Acquire to outer memory
  // or if the Acquire that was sent will obtain a Grant with sufficient permissions
  // to let us replay this new request. I.e. we don't handle multiple outstanding
  // Acquires on the same block for now.
  val cmd_requires_second_acquire = 
    req.old_meta.coh.requiresAcquireOnSecondaryMiss(req.cmd, io.req_bits.cmd)
  // Track whether or not a secondary acquire will cause the coherence state
  // to go from clean to dirty.
  val dirties_coh = Reg(Bool())
  val states_before_refill = Seq(s_wb_req, s_wb_resp, s_meta_clear)
  val gnt_multi_data = io.mem_grant.bits.hasMultibeatData()
  val (refill_cnt, refill_count_done) = Counter(io.mem_grant.valid && gnt_multi_data, refillCycles)
  val refill_done = io.mem_grant.valid && (!gnt_multi_data || refill_count_done)
  val sec_rdy = idx_match &&
                  (stateIsOneOf(states_before_refill) ||
                    (stateIsOneOf(s_refill_req, s_refill_resp) &&
                      !cmd_requires_second_acquire && !refill_done))

  val rpq = Module(new Queue(new ReplayInternal, p(ReplayQueueDepth)))
  rpq.io.enq.valid := (io.req_pri_val && io.req_pri_rdy || io.req_sec_val && sec_rdy) && !isPrefetch(io.req_bits.cmd)
  rpq.io.enq.bits := io.req_bits
  rpq.io.deq.ready := io.replay.ready && state === s_drain_rpq || state === s_invalid

  val coh_on_grant = req.old_meta.coh.onGrant(
                          incoming = io.mem_grant.bits,
                          pending = Mux(dirties_coh, M_XWR, req.cmd))
  val coh_on_hit =  io.req_bits.old_meta.coh.onHit(io.req_bits.cmd)

  when (state === s_drain_rpq && !rpq.io.deq.valid) {
    state := s_invalid
  }
  when (state === s_meta_write_resp) {
    // this wait state allows us to catch RAW hazards on the tags via nack_victim
    state := s_drain_rpq
  }
  when (state === s_meta_write_req && io.meta_write.ready) {
    state := s_meta_write_resp
  }
  when (state === s_refill_resp && refill_done) {
    state := s_meta_write_req
    new_coh_state := coh_on_grant
  }
  when (io.mem_req.fire()) { // s_refill_req
    state := s_refill_resp
  }
  when (state === s_meta_clear && io.meta_write.ready) {
    state := s_refill_req
  }
  when (state === s_wb_resp && io.mem_grant.valid) {
    state := s_meta_clear
  }
  when (io.wb_req.fire()) { // s_wb_req
    state := Mux(io.wb_req.bits.requiresAck(), s_wb_resp, s_meta_clear)
  }
  when (io.req_sec_val && io.req_sec_rdy) { // s_wb_req, s_wb_resp, s_refill_req
    //If we get a secondary miss that needs more permissions before we've sent
    //  out the primary miss's Acquire, we can upgrade the permissions we're 
    //  going to ask for in s_refill_req
    when(cmd_requires_second_acquire) {
      req.cmd := io.req_bits.cmd
    }
    dirties_coh := dirties_coh || isWrite(io.req_bits.cmd)
  }
  when (io.req_pri_val && io.req_pri_rdy) {
    val coh = io.req_bits.old_meta.coh
    req := io.req_bits
    dirties_coh := isWrite(io.req_bits.cmd)
    when (io.req_bits.tag_match) {
      when(coh.isHit(io.req_bits.cmd)) { // set dirty bit
        state := s_meta_write_req
        new_coh_state := coh_on_hit
      }.otherwise { // upgrade permissions
        state := s_refill_req
      }
    }.otherwise { // writback if necessary and refill
      state := Mux(coh.requiresVoluntaryWriteback(), s_wb_req, s_meta_clear)
    }
  }

  val fq = Module(new FinishQueue(1))
  val g = io.mem_grant.bits
  val can_finish = state === s_invalid || state === s_refill_req
  fq.io.enq.valid := io.mem_grant.valid && g.requiresAck() && refill_done
  fq.io.enq.bits := g.makeFinish()
  io.mem_finish.valid := fq.io.deq.valid && can_finish
  fq.io.deq.ready := io.mem_finish.ready && can_finish
  io.mem_finish.bits := fq.io.deq.bits

  io.idx_match := (state =/= s_invalid) && idx_match
  io.refill.way_en := req.way_en
  io.refill.addr := ((req_idx << log2Ceil(refillCycles)) | refill_cnt) << rowOffBits
  io.tag := req.addr >> untagBits
  io.req_pri_rdy := state === s_invalid
  io.req_sec_rdy := sec_rdy && rpq.io.enq.ready

  val meta_hazard = Reg(init=UInt(0,2))
  when (meta_hazard =/= UInt(0)) { meta_hazard := meta_hazard + 1 }
  when (io.meta_write.fire()) { meta_hazard := 1 }
  io.probe_rdy := !idx_match || (!stateIsOneOf(states_before_refill) && meta_hazard === 0) 

  io.meta_write.valid := state === s_meta_write_req || state === s_meta_clear
  io.meta_write.bits.idx := req_idx
  io.meta_write.bits.data.coh := Mux(state === s_meta_clear,
                                      req.old_meta.coh.onCacheControl(M_FLUSH),
                                      new_coh_state)
  io.meta_write.bits.data.tag := io.tag
  io.meta_write.bits.way_en := req.way_en

  io.wb_req.valid := state === s_wb_req
  io.wb_req.bits := req.old_meta.coh.makeVoluntaryWriteback(
                      client_xact_id = UInt(id),
                      addr_block = Cat(req.old_meta.tag, req_idx))
  io.wb_req.bits.way_en := req.way_en

  io.mem_req.valid := state === s_refill_req && fq.io.enq.ready
  io.mem_req.bits := req.old_meta.coh.makeAcquire(
                       addr_block = Cat(io.tag, req_idx).toUInt,
                       client_xact_id = Bits(id),
                       op_code = req.cmd)

  io.meta_read.valid := state === s_drain_rpq
  io.meta_read.bits.idx := req_idx
  io.meta_read.bits.tag := io.tag

  io.replay.valid := state === s_drain_rpq && rpq.io.deq.valid
  io.replay.bits := rpq.io.deq.bits
  io.replay.bits.phys := Bool(true)
  io.replay.bits.addr := Cat(io.tag, req_idx, rpq.io.deq.bits.addr(blockOffBits-1,0)).toUInt

  when (!io.meta_read.ready) {
    rpq.io.deq.ready := Bool(false)
    io.replay.bits.cmd := M_FLUSH_ALL /* nop */
  }
}

class MSHRFile(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val req = Decoupled(new MSHRReq).flip
    val resp = Decoupled(new HellaCacheResp)
    val secondary_miss = Bool(OUTPUT)

    val mem_req  = Decoupled(new Acquire)
    val refill = new L1RefillReq().asOutput
    val meta_read = Decoupled(new L1MetaReadReq)
    val meta_write = Decoupled(new L1MetaWriteReq)
    val replay = Decoupled(new Replay)
    val mem_grant = Valid(new GrantFromSrc).flip
    val mem_finish = Decoupled(new FinishToDst)
    val wb_req = Decoupled(new WritebackReq)

    val probe_rdy = Bool(OUTPUT)
    val fence_rdy = Bool(OUTPUT)
    val replay_next = Bool(OUTPUT)
  }

  // determine if the request is cacheable or not
  val cacheable = addrMap.isCacheable(io.req.bits.addr)

  val sdq_val = Reg(init=Bits(0, sdqDepth))
  val sdq_alloc_id = PriorityEncoder(~sdq_val(sdqDepth-1,0))
  val sdq_rdy = !sdq_val.andR
  val sdq_enq = io.req.valid && io.req.ready && cacheable && isWrite(io.req.bits.cmd)
  val sdq = Mem(sdqDepth, io.req.bits.data)
  when (sdq_enq) { sdq(sdq_alloc_id) := io.req.bits.data }

  val idxMatch = Wire(Vec(nMSHRs, Bool()))
  val tagList = Wire(Vec(nMSHRs, Bits(width = tagBits)))
  val tag_match = Mux1H(idxMatch, tagList) === io.req.bits.addr >> untagBits

  val wbTagList = Wire(Vec(nMSHRs, Bits()))
  val refillMux = Wire(Vec(nMSHRs, new L1RefillReq))
  val meta_read_arb = Module(new Arbiter(new L1MetaReadReq, nMSHRs))
  val meta_write_arb = Module(new Arbiter(new L1MetaWriteReq, nMSHRs))
  val mem_req_arb = Module(new LockingArbiter(
                                new Acquire,
                                nMSHRs + nIOMSHRs,
                                outerDataBeats,
                                Some((a: Acquire) => a.hasMultibeatData())))
  val mem_finish_arb = Module(new Arbiter(new FinishToDst, nMSHRs + nIOMSHRs))
  val wb_req_arb = Module(new Arbiter(new WritebackReq, nMSHRs))
  val replay_arb = Module(new Arbiter(new ReplayInternal, nMSHRs))
  val alloc_arb = Module(new Arbiter(Bool(), nMSHRs))

  var idx_match = Bool(false)
  var pri_rdy = Bool(false)
  var sec_rdy = Bool(false)

  io.fence_rdy := true
  io.probe_rdy := true

  for (i <- 0 until nMSHRs) {
    val mshr = Module(new MSHR(i))

    idxMatch(i) := mshr.io.idx_match
    tagList(i) := mshr.io.tag
    wbTagList(i) := mshr.io.wb_req.bits.addr_block >> idxBits

    alloc_arb.io.in(i).valid := mshr.io.req_pri_rdy
    mshr.io.req_pri_val := alloc_arb.io.in(i).ready

    mshr.io.req_sec_val := io.req.valid && sdq_rdy && tag_match
    mshr.io.req_bits := io.req.bits
    mshr.io.req_bits.sdq_id := sdq_alloc_id

    meta_read_arb.io.in(i) <> mshr.io.meta_read
    meta_write_arb.io.in(i) <> mshr.io.meta_write
    mem_req_arb.io.in(i) <> mshr.io.mem_req
    mem_finish_arb.io.in(i) <> mshr.io.mem_finish
    wb_req_arb.io.in(i) <> mshr.io.wb_req
    replay_arb.io.in(i) <> mshr.io.replay

    mshr.io.mem_grant.valid := io.mem_grant.valid &&
                                 io.mem_grant.bits.client_xact_id === UInt(i)
    mshr.io.mem_grant.bits := io.mem_grant.bits
    refillMux(i) := mshr.io.refill

    pri_rdy = pri_rdy || mshr.io.req_pri_rdy
    sec_rdy = sec_rdy || mshr.io.req_sec_rdy
    idx_match = idx_match || mshr.io.idx_match

    when (!mshr.io.req_pri_rdy) { io.fence_rdy := false }
    when (!mshr.io.probe_rdy) { io.probe_rdy := false }
  }

  alloc_arb.io.out.ready := io.req.valid && sdq_rdy && cacheable && !idx_match

  io.meta_read <> meta_read_arb.io.out
  io.meta_write <> meta_write_arb.io.out
  io.mem_req <> mem_req_arb.io.out
  io.mem_finish <> mem_finish_arb.io.out
  io.wb_req <> wb_req_arb.io.out

  val mmio_alloc_arb = Module(new Arbiter(Bool(), nIOMSHRs))
  val resp_arb = Module(new Arbiter(new HellaCacheResp, nIOMSHRs))

  var mmio_rdy = Bool(false)
  io.replay_next := Bool(false)

  for (i <- 0 until nIOMSHRs) {
    val id = nMSHRs + i
    val mshr = Module(new IOMSHR(id))

    mmio_alloc_arb.io.in(i).valid := mshr.io.req.ready
    mshr.io.req.valid := mmio_alloc_arb.io.in(i).ready
    mshr.io.req.bits := io.req.bits

    mmio_rdy = mmio_rdy || mshr.io.req.ready

    mem_req_arb.io.in(id) <> mshr.io.acquire
    mem_finish_arb.io.in(id) <> mshr.io.finish

    mshr.io.grant.bits := io.mem_grant.bits
    mshr.io.grant.valid := io.mem_grant.valid &&
        io.mem_grant.bits.client_xact_id === UInt(id)

    resp_arb.io.in(i) <> mshr.io.resp

    when (!mshr.io.req.ready) { io.fence_rdy := Bool(false) }
    when (mshr.io.replay_next) { io.replay_next := Bool(true) }
  }

  mmio_alloc_arb.io.out.ready := io.req.valid && !cacheable

  io.resp <> resp_arb.io.out
  io.req.ready := Mux(!cacheable, mmio_rdy,
    Mux(idx_match, tag_match && sec_rdy, pri_rdy) && sdq_rdy)
  io.secondary_miss := idx_match
  io.refill := refillMux(io.mem_grant.bits.client_xact_id)

  val free_sdq = io.replay.fire() && isWrite(io.replay.bits.cmd)
  io.replay.bits.data := sdq(RegEnable(replay_arb.io.out.bits.sdq_id, free_sdq))
  io.replay <> replay_arb.io.out

  when (io.replay.valid || sdq_enq) {
    sdq_val := sdq_val & ~(UIntToOH(replay_arb.io.out.bits.sdq_id) & Fill(sdqDepth, free_sdq)) | 
               PriorityEncoderOH(~sdq_val(sdqDepth-1,0)) & Fill(sdqDepth, sdq_enq)
  }
}

class WritebackUnit(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val req = Decoupled(new WritebackReq).flip
    val meta_read = Decoupled(new L1MetaReadReq)
    val data_req = Decoupled(new L1DataReadReq)
    val data_resp = Bits(INPUT, encRowBits)
    val release = Decoupled(new Release)
  }

  val active = Reg(init=Bool(false))
  val r1_data_req_fired = Reg(init=Bool(false))
  val r2_data_req_fired = Reg(init=Bool(false))
  val data_req_cnt = Reg(init = UInt(0, width = log2Up(refillCycles+1))) //TODO Zero width
  val buf_v = (if(refillCyclesPerBeat > 1) Reg(init=Bits(0, width = refillCyclesPerBeat-1)) else Bits(1))
  val beat_done = buf_v.andR
  val (beat_cnt, all_beats_done) = Counter(io.release.fire(), outerDataBeats)
  val req = Reg(new WritebackReq)

  io.release.valid := false
  when (active) {
    r1_data_req_fired := false
    r2_data_req_fired := r1_data_req_fired
    when (io.data_req.fire() && io.meta_read.fire()) {
      r1_data_req_fired := true
      data_req_cnt := data_req_cnt + 1
    }
    when (r2_data_req_fired) {
      io.release.valid := beat_done
      when(beat_done) {
        when(!io.release.ready) {
          r1_data_req_fired := false
          r2_data_req_fired := false
          data_req_cnt := data_req_cnt - Mux[UInt](Bool(refillCycles > 1) && r1_data_req_fired, 2, 1)
        } .otherwise { if(refillCyclesPerBeat > 1) buf_v := 0 }
      }
      when(!r1_data_req_fired) {
        // We're done if this is the final data request and the Release can be sent
        active := data_req_cnt < UInt(refillCycles) || !io.release.ready
      }
    }
  }
  when (io.req.fire()) {
    active := true
    data_req_cnt := 0
    if(refillCyclesPerBeat > 1) buf_v := 0
    req := io.req.bits
  }

  io.req.ready := !active

  val req_idx = req.addr_block(idxBits-1, 0)
  val fire = active && data_req_cnt < UInt(refillCycles)

  // We reissue the meta read as it sets up the mux ctrl for s2_data_muxed
  io.meta_read.valid := fire
  io.meta_read.bits.idx := req_idx
  io.meta_read.bits.tag := req.addr_block >> idxBits

  io.data_req.valid := fire
  io.data_req.bits.way_en := req.way_en
  io.data_req.bits.addr := (if(refillCycles > 1) 
                              Cat(req_idx, data_req_cnt(log2Up(refillCycles)-1,0))
                            else req_idx) << rowOffBits

  io.release.bits := req
  io.release.bits.addr_beat := beat_cnt
  io.release.bits.data := (if(refillCyclesPerBeat > 1) {
    // If the cache rows are narrower than a TLDataBeat, 
    //   then buffer enough data_resps to make a whole beat
    val data_buf = Reg(Bits())
    when(active && r2_data_req_fired && !beat_done) {
      data_buf := Cat(io.data_resp, data_buf((refillCyclesPerBeat)*encRowBits-1, encRowBits))
      buf_v := (if(refillCyclesPerBeat > 2)
                  Cat(UInt(1), buf_v(refillCyclesPerBeat-2,1))
                else UInt(1))
    }
    Cat(io.data_resp, data_buf)
  } else { io.data_resp })
}

class ProbeUnit(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val req = Decoupled(new ProbeInternal).flip
    val rep = Decoupled(new Release)
    val meta_read = Decoupled(new L1MetaReadReq)
    val meta_write = Decoupled(new L1MetaWriteReq)
    val wb_req = Decoupled(new WritebackReq)
    val way_en = Bits(INPUT, nWays)
    val mshr_rdy = Bool(INPUT)
    val block_state = new ClientMetadata().asInput
  }

  val (s_invalid :: s_meta_read :: s_meta_resp :: s_mshr_req ::
       s_mshr_resp :: s_release :: s_writeback_req :: s_writeback_resp :: 
       s_meta_write :: Nil) = Enum(UInt(), 9)
  val state = Reg(init=s_invalid)
  val old_coh = Reg(new ClientMetadata)
  val way_en = Reg(Bits())
  val req = Reg(new ProbeInternal)
  val tag_matches = way_en.orR

  val miss_coh = ClientMetadata.onReset
  val reply_coh = Mux(tag_matches, old_coh, miss_coh)
  val reply = reply_coh.makeRelease(req)
  io.req.ready := state === s_invalid
  io.rep.valid := state === s_release
  io.rep.bits := reply

  assert(!io.rep.valid || !io.rep.bits.hasData(),
    "ProbeUnit should not send releases with data")

  io.meta_read.valid := state === s_meta_read
  io.meta_read.bits.idx := req.addr_block
  io.meta_read.bits.tag := req.addr_block >> idxBits

  io.meta_write.valid := state === s_meta_write
  io.meta_write.bits.way_en := way_en
  io.meta_write.bits.idx := req.addr_block
  io.meta_write.bits.data.tag := req.addr_block >> idxBits
  io.meta_write.bits.data.coh := old_coh.onProbe(req)

  io.wb_req.valid := state === s_writeback_req
  io.wb_req.bits := reply
  io.wb_req.bits.way_en := way_en

  // state === s_invalid
  when (io.req.fire()) {
    state := s_meta_read
    req := io.req.bits
  }

  // state === s_meta_read
  when (io.meta_read.fire()) {
    state := s_meta_resp
  }

  // we need to wait one cycle for the metadata to be read from the array
  when (state === s_meta_resp) {
    state := s_mshr_req
  }

  when (state === s_mshr_req) {
    state := s_mshr_resp
    old_coh := io.block_state
    way_en := io.way_en
    // if the read didn't go through, we need to retry
    when (!io.mshr_rdy) { state := s_meta_read }
  }

  when (state === s_mshr_resp) {
    val needs_writeback = tag_matches && old_coh.requiresVoluntaryWriteback() 
    state := Mux(needs_writeback, s_writeback_req, s_release)
  }

  when (state === s_release && io.rep.ready) {
    state := Mux(tag_matches, s_meta_write, s_invalid)
  }

  // state === s_writeback_req
  when (io.wb_req.fire()) {
    state := s_writeback_resp
  }

  // wait for the writeback request to finish before updating the metadata
  when (state === s_writeback_resp && io.wb_req.ready) {
    state := s_meta_write
  }

  when (io.meta_write.fire()) {
    state := s_invalid
  }
}

class DataArray(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val read = Decoupled(new L1DataReadReq).flip
    val write = Decoupled(new L1DataWriteReq).flip
    val resp = Vec(nWays, Bits(OUTPUT, encRowBits))
  }

  val waddr = io.write.bits.addr >> rowOffBits
  val raddr = io.read.bits.addr >> rowOffBits

  if (doNarrowRead) {
    for (w <- 0 until nWays by rowWords) {
      val wway_en = io.write.bits.way_en(w+rowWords-1,w)
      val rway_en = io.read.bits.way_en(w+rowWords-1,w)
      val resp = Wire(Vec(rowWords, Bits(width = encRowBits)))
      val r_raddr = RegEnable(io.read.bits.addr, io.read.valid)
      for (p <- 0 until resp.size) {
        val array = SeqMem(nSets*refillCycles, Vec(rowWords, Bits(width=encDataBits)))
        when (wway_en.orR && io.write.valid && io.write.bits.wmask(p)) {
          val data = Vec.fill(rowWords)(io.write.bits.data(encDataBits*(p+1)-1,encDataBits*p))
          array.write(waddr, data, wway_en.toBools)
        }
        resp(p) := array.read(raddr, rway_en.orR && io.read.valid).toBits
      }
      for (dw <- 0 until rowWords) {
        val r = Vec(resp.map(_(encDataBits*(dw+1)-1,encDataBits*dw)))
        val resp_mux =
          if (r.size == 1) r
          else Vec(r(r_raddr(rowOffBits-1,wordOffBits)), r.tail:_*)
        io.resp(w+dw) := resp_mux.toBits
      }
    }
  } else {
    for (w <- 0 until nWays) {
      val array = SeqMem(nSets*refillCycles, Vec(rowWords, Bits(width=encDataBits)))
      when (io.write.bits.way_en(w) && io.write.valid) {
        val data = Vec.tabulate(rowWords)(i => io.write.bits.data(encDataBits*(i+1)-1,encDataBits*i))
        array.write(waddr, data, io.write.bits.wmask.toBools)
      }
      io.resp(w) := array.read(raddr, io.read.bits.way_en(w) && io.read.valid).toBits
    }
  }

  io.read.ready := Bool(true)
  io.write.ready := Bool(true)
}

class HellaCache(implicit p: Parameters) extends L1HellaCacheModule()(p) {
  val io = new Bundle {
    val cpu = (new HellaCacheIO).flip
    val ptw = new TLBPTWIO()
    val mem = new ClientTileLinkIO
  }
 
  require(isPow2(nWays)) // TODO: relax this

  val wb = Module(new WritebackUnit)
  val prober = Module(new ProbeUnit)
  val mshrs = Module(new MSHRFile)

  io.cpu.req.ready := Bool(true)
  val s1_valid = Reg(next=io.cpu.req.fire(), init=Bool(false))
  val s1_req = Reg(io.cpu.req.bits)
  val s1_valid_masked = s1_valid && !io.cpu.s1_kill
  val s1_replay = Reg(init=Bool(false))
  val s1_clk_en = Reg(Bool())

  val s2_valid = Reg(next=s1_valid_masked, init=Bool(false))
  val s2_req = Reg(io.cpu.req.bits)
  val s2_replay = Reg(next=s1_replay, init=Bool(false)) && s2_req.cmd =/= M_FLUSH_ALL
  val s2_recycle = Wire(Bool())
  val s2_valid_masked = Wire(Bool())

  val s3_valid = Reg(init=Bool(false))
  val s3_req = Reg(io.cpu.req.bits)
  val s3_way = Reg(Bits())

  val s1_recycled = RegEnable(s2_recycle, Bool(false), s1_clk_en)
  val s1_read  = isRead(s1_req.cmd)
  val s1_write = isWrite(s1_req.cmd)
  val s1_readwrite = s1_read || s1_write || isPrefetch(s1_req.cmd)

  val dtlb = Module(new TLB)
  io.ptw <> dtlb.io.ptw
  dtlb.io.req.valid := s1_valid_masked && s1_readwrite
  dtlb.io.req.bits.passthrough := s1_req.phys
  dtlb.io.req.bits.vpn := s1_req.addr >> pgIdxBits
  dtlb.io.req.bits.instruction := Bool(false)
  dtlb.io.req.bits.store := s1_write
  when (!dtlb.io.req.ready && !io.cpu.req.bits.phys) { io.cpu.req.ready := Bool(false) }
  
  when (io.cpu.req.valid) {
    s1_req := io.cpu.req.bits
  }
  when (wb.io.meta_read.valid) {
    s1_req.addr := Cat(wb.io.meta_read.bits.tag, wb.io.meta_read.bits.idx) << blockOffBits
    s1_req.phys := Bool(true)
  }
  when (prober.io.meta_read.valid) {
    s1_req.addr := Cat(prober.io.meta_read.bits.tag, prober.io.meta_read.bits.idx) << blockOffBits
    s1_req.phys := Bool(true)
  }
  when (mshrs.io.replay.valid) {
    s1_req := mshrs.io.replay.bits
  }
  when (s2_recycle) {
    s1_req := s2_req
  }
  val s1_addr = Cat(dtlb.io.resp.ppn, s1_req.addr(pgIdxBits-1,0))

  when (s1_clk_en) {
    s2_req.typ := s1_req.typ
    s2_req.phys := s1_req.phys
    s2_req.addr := s1_addr
    when (s1_write) {
      s2_req.data := Mux(s1_replay, mshrs.io.replay.bits.data, io.cpu.s1_data)
    }
    when (s1_recycled) { s2_req.data := s1_req.data }
    s2_req.tag := s1_req.tag
    s2_req.cmd := s1_req.cmd
  }

  val misaligned = new StoreGen(s1_req.typ, s1_req.addr, UInt(0), wordBytes).misaligned
  io.cpu.xcpt.ma.ld := s1_read && misaligned
  io.cpu.xcpt.ma.st := s1_write && misaligned
  io.cpu.xcpt.pf.ld := s1_read && dtlb.io.resp.xcpt_ld
  io.cpu.xcpt.pf.st := s1_write && dtlb.io.resp.xcpt_st

  assert (!(Reg(next=
    (io.cpu.xcpt.ma.ld || io.cpu.xcpt.ma.st || io.cpu.xcpt.pf.ld || io.cpu.xcpt.pf.st)) &&
    s2_valid_masked),
      "DCache exception occurred - cache response not killed.")

  // tags
  def onReset = L1Metadata(UInt(0), ClientMetadata.onReset)
  val meta = Module(new MetadataArray(onReset _))
  val metaReadArb = Module(new Arbiter(new MetaReadReq, 5))
  val metaWriteArb = Module(new Arbiter(new L1MetaWriteReq, 2))
  meta.io.read <> metaReadArb.io.out
  meta.io.write <> metaWriteArb.io.out

  // data
  val data = Module(new DataArray)
  val readArb = Module(new Arbiter(new L1DataReadReq, 4))
  val writeArb = Module(new Arbiter(new L1DataWriteReq, 2))
  data.io.write.valid := writeArb.io.out.valid
  writeArb.io.out.ready := data.io.write.ready
  data.io.write.bits := writeArb.io.out.bits
  val wdata_encoded = (0 until rowWords).map(i => code.encode(writeArb.io.out.bits.data(coreDataBits*(i+1)-1,coreDataBits*i)))
  data.io.write.bits.data := wdata_encoded.toBits

  // tag read for new requests
  metaReadArb.io.in(4).valid := io.cpu.req.valid
  metaReadArb.io.in(4).bits.idx := io.cpu.req.bits.addr >> blockOffBits
  when (!metaReadArb.io.in(4).ready) { io.cpu.req.ready := Bool(false) }

  // data read for new requests
  readArb.io.in(3).valid := io.cpu.req.valid
  readArb.io.in(3).bits.addr := io.cpu.req.bits.addr
  readArb.io.in(3).bits.way_en := ~UInt(0, nWays)
  when (!readArb.io.in(3).ready) { io.cpu.req.ready := Bool(false) }

  // recycled requests
  metaReadArb.io.in(0).valid := s2_recycle
  metaReadArb.io.in(0).bits.idx := s2_req.addr >> blockOffBits
  readArb.io.in(0).valid := s2_recycle
  readArb.io.in(0).bits.addr := s2_req.addr
  readArb.io.in(0).bits.way_en := ~UInt(0, nWays)

  // tag check and way muxing
  def wayMap[T <: Data](f: Int => T) = Vec((0 until nWays).map(f))
  val s1_tag_eq_way = wayMap((w: Int) => meta.io.resp(w).tag === (s1_addr >> untagBits)).toBits
  val s1_tag_match_way = wayMap((w: Int) => s1_tag_eq_way(w) && meta.io.resp(w).coh.isValid()).toBits
  s1_clk_en := metaReadArb.io.out.valid //TODO: should be metaReadArb.io.out.fire(), but triggers Verilog backend bug
  val s1_writeback = s1_clk_en && !s1_valid && !s1_replay
  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_state = Mux1H(s2_tag_match_way, wayMap((w: Int) => RegEnable(meta.io.resp(w).coh, s1_clk_en)))
  val s2_hit = s2_tag_match && 
                s2_hit_state.isHit(s2_req.cmd) && 
                s2_hit_state === s2_hit_state.onHit(s2_req.cmd)

  // load-reserved/store-conditional
  val lrsc_count = Reg(init=UInt(0))
  val lrsc_valid = lrsc_count.orR
  val lrsc_addr = Reg(UInt())
  val (s2_lr, s2_sc) = (s2_req.cmd === M_XLR, s2_req.cmd === M_XSC)
  val s2_lrsc_addr_match = lrsc_valid && lrsc_addr === (s2_req.addr >> blockOffBits)
  val s2_sc_fail = s2_sc && !s2_lrsc_addr_match
  when (lrsc_valid) { lrsc_count := lrsc_count - 1 }
  when (s2_valid_masked && s2_hit || s2_replay) {
    when (s2_lr) {
      when (!lrsc_valid) { lrsc_count := lrscCycles-1 }
      lrsc_addr := s2_req.addr >> blockOffBits
    }
    when (s2_sc) {
      lrsc_count := 0
    }
  }
  when (io.cpu.invalidate_lr) { lrsc_count := 0 }

  val s2_data = Wire(Vec(nWays, Bits(width=encRowBits)))
  for (w <- 0 until nWays) {
    val regs = Reg(Vec(rowWords, Bits(width = encDataBits)))
    val en1 = s1_clk_en && s1_tag_eq_way(w)
    for (i <- 0 until regs.size) {
      val en = en1 && ((Bool(i == 0) || !Bool(doNarrowRead)) || s1_writeback)
      when (en) { regs(i) := data.io.resp(w) >> encDataBits*i }
    }
    s2_data(w) := regs.toBits
  }
  val s2_data_muxed = Mux1H(s2_tag_match_way, s2_data)
  val s2_data_decoded = (0 until rowWords).map(i => code.decode(s2_data_muxed(encDataBits*(i+1)-1,encDataBits*i)))
  val s2_data_corrected = s2_data_decoded.map(_.corrected).toBits
  val s2_data_uncorrected = s2_data_decoded.map(_.uncorrected).toBits
  val s2_word_idx = if(doNarrowRead) UInt(0) else s2_req.addr(log2Up(rowWords*coreDataBytes)-1,log2Up(wordBytes))
  val s2_data_correctable = s2_data_decoded.map(_.correctable).toBits()(s2_word_idx)

  // store/amo hits
  s3_valid := (s2_valid_masked && s2_hit || s2_replay) && !s2_sc_fail && isWrite(s2_req.cmd)
  val amoalu = Module(new AMOALU)
  when ((s2_valid || s2_replay) && (isWrite(s2_req.cmd) || s2_data_correctable)) {
    s3_req := s2_req
    s3_req.data := Mux(s2_data_correctable, s2_data_corrected, amoalu.io.out)
    s3_way := s2_tag_match_way
  }

  writeArb.io.in(0).bits.addr := s3_req.addr
  writeArb.io.in(0).bits.wmask := UIntToOH(s3_req.addr.extract(rowOffBits-1,offsetlsb))
  writeArb.io.in(0).bits.data := Fill(rowWords, s3_req.data)
  writeArb.io.in(0).valid := s3_valid
  writeArb.io.in(0).bits.way_en :=  s3_way

  // replacement policy
  val replacer = p(Replacer)()
  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)

  // miss handling
  mshrs.io.req.valid := s2_valid_masked && !s2_hit && (isPrefetch(s2_req.cmd) || isRead(s2_req.cmd) || isWrite(s2_req.cmd))
  mshrs.io.req.bits := s2_req
  mshrs.io.req.bits.tag_match := s2_tag_match
  mshrs.io.req.bits.old_meta := Mux(s2_tag_match, L1Metadata(s2_repl_meta.tag, s2_hit_state), s2_repl_meta)
  mshrs.io.req.bits.way_en := Mux(s2_tag_match, s2_tag_match_way, s2_replaced_way_en)
  mshrs.io.req.bits.data := s2_req.data
  when (mshrs.io.req.fire()) { replacer.miss }
  io.mem.acquire <> mshrs.io.mem_req

  // replays
  readArb.io.in(1).valid := mshrs.io.replay.valid
  readArb.io.in(1).bits := mshrs.io.replay.bits
  readArb.io.in(1).bits.way_en := ~UInt(0, nWays)
  mshrs.io.replay.ready := readArb.io.in(1).ready
  s1_replay := mshrs.io.replay.valid && readArb.io.in(1).ready
  metaReadArb.io.in(1) <> mshrs.io.meta_read
  metaWriteArb.io.in(0) <> mshrs.io.meta_write

  // probes and releases
  val releaseArb = Module(new LockingArbiter(
                                new Release, 2, outerDataBeats,
                                Some((r: Release) => r.hasMultibeatData())))
  io.mem.release <> releaseArb.io.out

  prober.io.req.valid := io.mem.probe.valid && !lrsc_valid
  io.mem.probe.ready := prober.io.req.ready && !lrsc_valid
  prober.io.req.bits := io.mem.probe.bits
  releaseArb.io.in(1) <> prober.io.rep
  prober.io.way_en := s2_tag_match_way
  prober.io.block_state := s2_hit_state
  metaReadArb.io.in(2) <> prober.io.meta_read
  metaWriteArb.io.in(1) <> prober.io.meta_write
  prober.io.mshr_rdy := mshrs.io.probe_rdy

  // refills
  val narrow_grant = FlowThroughSerializer(io.mem.grant, refillCyclesPerBeat)
  mshrs.io.mem_grant.valid := narrow_grant.fire()
  mshrs.io.mem_grant.bits := narrow_grant.bits
  narrow_grant.ready := writeArb.io.in(1).ready || !narrow_grant.bits.hasData()
  /* The last clause here is necessary in order to prevent the responses for
   * the IOMSHRs from being written into the data array. It works because the
   * IOMSHR ids start right the ones for the regular MSHRs. */
  writeArb.io.in(1).valid := narrow_grant.valid && narrow_grant.bits.hasData() &&
                             narrow_grant.bits.client_xact_id < UInt(nMSHRs)
  writeArb.io.in(1).bits.addr := mshrs.io.refill.addr
  writeArb.io.in(1).bits.way_en := mshrs.io.refill.way_en
  writeArb.io.in(1).bits.wmask := ~UInt(0, rowWords)
  writeArb.io.in(1).bits.data := narrow_grant.bits.data(encRowBits-1,0)
  data.io.read <> readArb.io.out
  readArb.io.out.ready := !narrow_grant.valid || narrow_grant.ready // insert bubble if refill gets blocked
  io.mem.finish <> mshrs.io.mem_finish

  // writebacks
  val wbArb = Module(new Arbiter(new WritebackReq, 2))
  wbArb.io.in(0) <> prober.io.wb_req
  wbArb.io.in(1) <> mshrs.io.wb_req
  wb.io.req <> wbArb.io.out
  metaReadArb.io.in(3) <> wb.io.meta_read
  readArb.io.in(2) <> wb.io.data_req
  wb.io.data_resp := s2_data_corrected
  releaseArb.io.in(0) <> wb.io.release

  // store->load bypassing
  val s4_valid = Reg(next=s3_valid, init=Bool(false))
  val s4_req = RegEnable(s3_req, s3_valid && metaReadArb.io.out.valid)
  val bypasses = List(
    ((s2_valid_masked || s2_replay) && !s2_sc_fail, s2_req, amoalu.io.out),
    (s3_valid, s3_req, s3_req.data),
    (s4_valid, s4_req, s4_req.data)
  ).map(r => (r._1 && (s1_addr >> wordOffBits === r._2.addr >> wordOffBits) && isWrite(r._2.cmd), r._3))
  val s2_store_bypass_data = Reg(Bits(width = coreDataBits))
  val s2_store_bypass = Reg(Bool())
  when (s1_clk_en) {
    s2_store_bypass := false
    when (bypasses.map(_._1).reduce(_||_)) {
      s2_store_bypass_data := PriorityMux(bypasses)
      s2_store_bypass := true
    }
  }

  // load data subword mux/sign extension
  val s2_data_word_prebypass = s2_data_uncorrected >> Cat(s2_word_idx, Bits(0,log2Up(coreDataBits)))
  val s2_data_word = Mux(s2_store_bypass, s2_store_bypass_data, s2_data_word_prebypass)
  val loadgen = new LoadGen(s2_req.typ, s2_req.addr, s2_data_word, s2_sc, wordBytes)
  
  amoalu.io.addr := s2_req.addr
  amoalu.io.cmd := s2_req.cmd
  amoalu.io.typ := s2_req.typ
  amoalu.io.lhs := s2_data_word
  amoalu.io.rhs := s2_req.data

  // nack it like it's hot
  val s1_nack = dtlb.io.req.valid && dtlb.io.resp.miss ||
                s1_req.addr(idxMSB,idxLSB) === prober.io.meta_write.bits.idx && !prober.io.req.ready
  val s2_nack_hit = RegEnable(s1_nack, s1_valid || s1_replay)
  when (s2_nack_hit) { mshrs.io.req.valid := Bool(false) }
  val s2_nack_victim = s2_hit && mshrs.io.secondary_miss
  val s2_nack_miss = !s2_hit && !mshrs.io.req.ready
  val s2_nack = s2_nack_hit || s2_nack_victim || s2_nack_miss
  s2_valid_masked := s2_valid && !s2_nack

  val s2_recycle_ecc = (s2_valid || s2_replay) && s2_hit && s2_data_correctable
  val s2_recycle_next = Reg(init=Bool(false))
  when (s1_valid || s1_replay) { s2_recycle_next := s2_recycle_ecc }
  s2_recycle := s2_recycle_ecc || s2_recycle_next

  // after a nack, block until nack condition resolves to save energy
  val block_miss = Reg(init=Bool(false))
  block_miss := (s2_valid || block_miss) && s2_nack_miss
  when (block_miss) {
    io.cpu.req.ready := Bool(false)
  }

  val cache_resp = Wire(Valid(new HellaCacheResp))
  cache_resp.valid := (s2_replay || s2_valid_masked && s2_hit) && !s2_data_correctable
  cache_resp.bits := s2_req
  cache_resp.bits.has_data := isRead(s2_req.cmd)
  cache_resp.bits.data := loadgen.data | s2_sc_fail
  cache_resp.bits.store_data := s2_req.data
  cache_resp.bits.replay := s2_replay

  val uncache_resp = Wire(Valid(new HellaCacheResp))
  uncache_resp.bits := mshrs.io.resp.bits
  uncache_resp.valid := mshrs.io.resp.valid
  mshrs.io.resp.ready := Reg(next= !(s1_valid || s1_replay))

  io.cpu.s2_nack := s2_valid && s2_nack
  io.cpu.resp := Mux(mshrs.io.resp.ready, uncache_resp, cache_resp)
  io.cpu.resp.bits.data_word_bypass := loadgen.wordData
  io.cpu.ordered := mshrs.io.fence_rdy && !s1_valid && !s2_valid
  io.cpu.replay_next := (s1_replay && s1_read) || mshrs.io.replay_next
}

/**
 * This module buffers requests made by the SimpleHellaCacheIF in case they
 * are nacked. Nacked requests must be replayed in order, and no other requests
 * must be allowed to go through until the replayed requests are successfully
 * completed.
 */
class SimpleHellaCacheIFReplayQueue(depth: Int)
    (implicit val p: Parameters) extends Module
    with HasL1HellaCacheParameters {
  val io = new Bundle {
    val req = Decoupled(new HellaCacheReq).flip
    val nack = Valid(Bits(width = coreDCacheReqTagBits)).flip
    val resp = Valid(new HellaCacheResp).flip
    val replay = Decoupled(new HellaCacheReq)
  }

  // Registers to store the sent request
  // When a request is sent the first time,
  // it is stored in one of the reqs registers
  // and the corresponding inflight bit is set.
  // The reqs register will be deallocated once the request is
  // successfully completed.
  val inflight = Reg(init = UInt(0, depth))
  val reqs = Reg(Vec(depth, new HellaCacheReq))

  // The nack queue stores the index of nacked requests (in the reqs vector)
  // in the order that they were nacked. A request is enqueued onto nackq
  // when it is newly nacked (i.e. not a nack for a previous replay).
  // The head of the nack queue will be replayed until it is
  // successfully completed, at which time the request is dequeued.
  // No new requests will be made or other replays attempted until the head
  // of the nackq is successfully completed.
  val nackq = Module(new Queue(UInt(width = log2Up(depth)), depth))
  val replaying = Reg(init = Bool(false))

  val next_inflight_onehot = PriorityEncoderOH(~inflight)
  val next_inflight = OHToUInt(next_inflight_onehot)

  val next_replay = nackq.io.deq.bits
  val next_replay_onehot = UIntToOH(next_replay)
  val next_replay_req = reqs(next_replay)

  // Keep sending the head of the nack queue until it succeeds
  io.replay.valid := nackq.io.deq.valid && !replaying
  io.replay.bits := next_replay_req
  // Don't allow new requests if there is are replays waiting
  // or something being nacked.
  io.req.ready := !inflight.andR && !nackq.io.deq.valid && !io.nack.valid

  // Match on the tags to determine the index of nacks or responses
  val nack_onehot = Cat(reqs.map(_.tag === io.nack.bits).reverse) & inflight
  val resp_onehot = Cat(reqs.map(_.tag === io.resp.bits.tag).reverse) & inflight

  val replay_complete = io.resp.valid && replaying && io.resp.bits.tag === next_replay_req.tag
  val nack_head = io.nack.valid && nackq.io.deq.valid && io.nack.bits === next_replay_req.tag

  // Enqueue to the nack queue if there is a nack that is not in response to
  // the previous replay
  nackq.io.enq.valid := io.nack.valid && !nack_head
  nackq.io.enq.bits := OHToUInt(nack_onehot)
  assert(!nackq.io.enq.valid || nackq.io.enq.ready,
    "SimpleHellaCacheIF: ReplayQueue nack queue overflow")

  // Dequeue from the nack queue if the last replay was successfully completed
  nackq.io.deq.ready := replay_complete
  assert(!nackq.io.deq.ready || nackq.io.deq.valid,
    "SimpleHellaCacheIF: ReplayQueue nack queue underflow")

  // Set inflight bit when a request is made
  // Clear it when it is successfully completed
  inflight := (inflight | Mux(io.req.fire(), next_inflight_onehot, UInt(0))) &
                          ~Mux(io.resp.valid, resp_onehot, UInt(0))

  when (io.req.fire()) {
    reqs(next_inflight) := io.req.bits
  }

  // Only one replay outstanding at a time
  when (io.replay.fire()) { replaying := Bool(true) }
  when (nack_head || replay_complete) { replaying := Bool(false) }
}

// exposes a sane decoupled request interface
class SimpleHellaCacheIF(implicit p: Parameters) extends Module
{
  val io = new Bundle {
    val requestor = new HellaCacheIO().flip
    val cache = new HellaCacheIO
  }

  val replayq = Module(new SimpleHellaCacheIFReplayQueue(2))
  val req_arb = Module(new Arbiter(new HellaCacheReq, 2))

  val req_helper = DecoupledHelper(
    req_arb.io.in(1).ready,
    replayq.io.req.ready,
    io.requestor.req.valid)

  req_arb.io.in(0) <> replayq.io.replay
  req_arb.io.in(1).valid := req_helper.fire(req_arb.io.in(1).ready)
  req_arb.io.in(1).bits := io.requestor.req.bits
  io.requestor.req.ready := req_helper.fire(io.requestor.req.valid)
  replayq.io.req.valid := req_helper.fire(replayq.io.req.ready)
  replayq.io.req.bits := io.requestor.req.bits

  val s0_req_fire = io.cache.req.fire()
  val s1_req_fire = Reg(next = s0_req_fire)
  val s2_req_fire = Reg(next = s1_req_fire)
  val s1_req_tag = Reg(next = io.cache.req.bits.tag)
  val s2_req_tag = Reg(next = s1_req_tag)
  val s2_kill = Reg(next = io.cache.s1_kill)

  io.cache.invalidate_lr := io.requestor.invalidate_lr
  io.cache.req <> req_arb.io.out
  io.cache.req.bits.phys := Bool(true)
  io.cache.s1_kill := io.cache.s2_nack
  io.cache.s1_data := RegEnable(req_arb.io.out.bits.data, s0_req_fire)

  replayq.io.nack.valid := (io.cache.s2_nack || s2_kill) && s2_req_fire
  replayq.io.nack.bits := s2_req_tag
  replayq.io.resp := io.cache.resp
  io.requestor.resp := io.cache.resp

  assert(!Reg(next = io.cache.req.fire()) ||
         !(io.cache.xcpt.ma.ld || io.cache.xcpt.ma.st ||
           io.cache.xcpt.pf.ld || io.cache.xcpt.pf.st),
         "SimpleHellaCacheIF exception")
}