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

package rocket

import Chisel._
import uncore._
import Util._

case class ICacheConfig(sets: Int, assoc: Int,
                        ntlb: Int = 8, nbtb: Int = 8,
                        code: Code = new IdentityCode)
{
  val w = 1
  val ibytes = 4

  val dm = assoc == 1
  val lines = sets * assoc
  val databits = MEM_DATA_BITS
  val idxbits = log2Up(sets)
  val offbits = OFFSET_BITS
  val untagbits = idxbits + offbits
  val tagbits = PADDR_BITS - untagbits

  require(isPow2(sets) && isPow2(assoc))
  require(isPow2(w) && isPow2(ibytes))
  require(PGIDX_BITS >= untagbits)
}

class FrontendReq extends Bundle {
  val pc = UInt(width = VADDR_BITS+1)
  val mispredict = Bool()
  val taken = Bool()
  val currentpc = UInt(width = VADDR_BITS+1)
}

class FrontendResp(implicit conf: ICacheConfig) extends Bundle {
  val pc = UInt(width = VADDR_BITS+1)  // ID stage PC
  val data = Bits(width = conf.ibytes*8)
  val taken = Bool()
  val xcpt_ma = Bool()
  val xcpt_if = Bool()

  override def clone = new FrontendResp().asInstanceOf[this.type]
}

class CPUFrontendIO(implicit conf: ICacheConfig) extends Bundle {
  val req = Valid(new FrontendReq)
  val resp = Decoupled(new FrontendResp).flip
  val ptw = new TLBPTWIO().flip
  val invalidate = Bool(OUTPUT)
}

class Frontend(implicit c: ICacheConfig, tl: TileLinkConfiguration) extends Module
{
  val io = new Bundle {
    val cpu = new CPUFrontendIO()(c).flip
    val mem = new UncachedTileLinkIO
  }
  
  val btb = Module(new rocketDpathBTB(c.nbtb))
  val icache = Module(new ICache)
  val tlb = Module(new TLB(c.ntlb))

  val s1_pc = Reg(UInt())
  val s1_same_block = Reg(Bool())
  val s2_valid = Reg(init=Bool(true))
  val s2_pc = Reg(init=UInt(START_ADDR))
  val s2_btb_hit = Reg(init=Bool(false))
  val s2_xcpt_if = Reg(init=Bool(false))

  val btbTarget = Cat(btb.io.target(VADDR_BITS-1), btb.io.target)
  val pcp4_0 = s1_pc + UInt(c.ibytes)
  val pcp4 = Cat(s1_pc(VADDR_BITS-1) & pcp4_0(VADDR_BITS-1), pcp4_0(VADDR_BITS-1,0))
  val icmiss = s2_valid && !icache.io.resp.valid
  val predicted_npc = Mux(btb.io.hit, btbTarget, pcp4)
  val npc = Mux(icmiss, s2_pc, predicted_npc).toUInt
  val s0_same_block = !icmiss && !io.cpu.req.valid && (predicted_npc >> log2Up(c.databits/8)) === (s1_pc >> log2Up(c.databits/8))

  val stall = io.cpu.resp.valid && !io.cpu.resp.ready
  when (!stall) {
    s1_same_block := s0_same_block && !tlb.io.resp.miss
    s1_pc := npc
    s2_valid := !icmiss
    when (!icmiss) {
      s2_pc := s1_pc
      s2_btb_hit := btb.io.hit
      s2_xcpt_if := tlb.io.resp.xcpt_if
    }
  }
  when (io.cpu.req.valid) {
    s1_same_block := Bool(false)
    s1_pc := io.cpu.req.bits.pc
    s2_valid := Bool(false)
  }

  btb.io.current_pc := s1_pc
  btb.io.wen := io.cpu.req.bits.mispredict
  btb.io.clr := !io.cpu.req.bits.taken
  btb.io.correct_pc := io.cpu.req.bits.currentpc
  btb.io.correct_target := io.cpu.req.bits.pc
  btb.io.invalidate := io.cpu.invalidate || io.cpu.ptw.invalidate

  tlb.io.ptw <> io.cpu.ptw
  tlb.io.req.valid := !stall && !icmiss
  tlb.io.req.bits.vpn := s1_pc >> UInt(PGIDX_BITS)
  tlb.io.req.bits.asid := UInt(0)
  tlb.io.req.bits.passthrough := Bool(false)
  tlb.io.req.bits.instruction := Bool(true)

  icache.io.mem <> io.mem
  icache.io.req.valid := !stall && !s0_same_block
  icache.io.req.bits.idx := Mux(io.cpu.req.valid, io.cpu.req.bits.pc, npc)
  icache.io.invalidate := io.cpu.invalidate
  icache.io.req.bits.ppn := tlb.io.resp.ppn
  icache.io.req.bits.kill := io.cpu.req.valid || tlb.io.resp.miss || icmiss
  icache.io.resp.ready := !stall && !s1_same_block

  io.cpu.resp.valid := s2_valid && (s2_xcpt_if || icache.io.resp.valid)
  io.cpu.resp.bits.pc := s2_pc
  io.cpu.resp.bits.data := icache.io.resp.bits.datablock >> (s2_pc(log2Up(c.databits/8)-1,log2Up(c.ibytes)) << log2Up(c.ibytes*8))
  io.cpu.resp.bits.taken := s2_btb_hit
  io.cpu.resp.bits.xcpt_ma := s2_pc(log2Up(c.ibytes)-1,0) != UInt(0)
  io.cpu.resp.bits.xcpt_if := s2_xcpt_if
}

class ICacheReq extends Bundle {
  val idx = UInt(width = PGIDX_BITS)
  val ppn = UInt(width = PPN_BITS) // delayed one cycle
  val kill = Bool() // delayed one cycle
}

class ICacheResp(implicit c: ICacheConfig) extends Bundle {
  val data = Bits(width = c.ibytes*8)
  val datablock = Bits(width = c.databits)
  override def clone = new ICacheResp().asInstanceOf[this.type]
}

class ICache(implicit c: ICacheConfig, tl: TileLinkConfiguration) extends Module
{
  implicit val lnConf = tl.ln
  val io = new Bundle {
    val req = Valid(new ICacheReq).flip
    val resp = Decoupled(new ICacheResp)
    val invalidate = Bool(INPUT)
    val mem = new UncachedTileLinkIO
  }

  val s_ready :: s_request :: s_refill_wait :: s_refill :: Nil = Enum(4) { UInt() }
  val state = Reg(init=s_ready)
  val invalidated = Reg(Bool())
  val stall = !io.resp.ready
  val rdy = Bool()

  val s2_valid = Reg(init=Bool(false))
  val s2_addr = Reg(UInt(width = PADDR_BITS))
  val s2_any_tag_hit = Bool()

  val s1_valid = Reg(init=Bool(false))
  val s1_pgoff = Reg(UInt(width = PGIDX_BITS))
  val s1_addr = Cat(io.req.bits.ppn, s1_pgoff).toUInt
  val s1_tag = s1_addr(c.tagbits+c.untagbits-1,c.untagbits)

  val s0_valid = io.req.valid || s1_valid && stall
  val s0_pgoff = Mux(io.req.valid, io.req.bits.idx, s1_pgoff)

  s1_valid := io.req.valid && rdy || s1_valid && stall && !io.req.bits.kill
  when (io.req.valid && rdy) {
    s1_pgoff := s0_pgoff
  }

  s2_valid := s1_valid && rdy && !io.req.bits.kill || io.resp.valid && stall
  when (s1_valid && rdy && !stall) {
    s2_addr := s1_addr
  }

  val s2_tag = s2_addr(c.tagbits+c.untagbits-1,c.untagbits)
  val s2_idx = s2_addr(c.untagbits-1,c.offbits)
  val s2_offset = s2_addr(c.offbits-1,0)
  val s2_hit = s2_valid && s2_any_tag_hit
  val s2_miss = s2_valid && !s2_any_tag_hit
  rdy := state === s_ready && !s2_miss

  //assert(!co.isVoluntary(io.mem.grant.bits.payload) || !io.mem.grant.valid, "UncachedRequestors shouldn't get voluntary grants.")
  val (rf_cnt, refill_done) = Counter(io.mem.grant.valid, REFILL_CYCLES)
  val repl_way = if (c.dm) UInt(0) else LFSR16(s2_miss)(log2Up(c.assoc)-1,0)

  val enc_tagbits = c.code.width(c.tagbits)
  val tag_array = Mem(Bits(width = enc_tagbits*c.assoc), c.sets, seqRead = true)
  val tag_raddr = Reg(UInt())
  when (refill_done) {
    val wmask = FillInterleaved(enc_tagbits, if (c.dm) Bits(1) else UIntToOH(repl_way))
    val tag = c.code.encode(s2_tag).toUInt
    tag_array.write(s2_idx, Fill(c.assoc, tag), wmask)
  }
//  /*.else*/when (s0_valid) { // uncomment ".else" to infer 6T SRAM
  .elsewhen (s0_valid) {
    tag_raddr := s0_pgoff(c.untagbits-1,c.offbits)
  }

  val vb_array = Reg(init=Bits(0, c.lines))
  when (refill_done && !invalidated) {
    vb_array := vb_array.bitSet(Cat(repl_way, s2_idx), Bool(true))
  }
  when (io.invalidate) {
    vb_array := Bits(0)
    invalidated := Bool(true)
  }
  val s2_disparity = Vec.fill(c.assoc){Bool()}
  for (i <- 0 until c.assoc)
    when (s2_valid && s2_disparity(i)) { vb_array := vb_array.bitSet(Cat(UInt(i), s2_idx), Bool(false)) }

  val s1_tag_match = Vec.fill(c.assoc){Bool()}
  val s2_tag_hit = Vec.fill(c.assoc){Bool()}
  val s2_dout = Vec.fill(c.assoc){Reg(Bits())}

  for (i <- 0 until c.assoc) {
    val s1_vb = vb_array(Cat(UInt(i), s1_pgoff(c.untagbits-1,c.offbits))).toBool
    val s2_vb = Reg(Bool())
    val s2_tag_disparity = Reg(Bool())
    val s2_tag_match = Reg(Bool())
    val tag_out = tag_array(tag_raddr)(enc_tagbits*(i+1)-1, enc_tagbits*i)
    when (s1_valid && rdy && !stall) {
      s2_vb := s1_vb
      s2_tag_disparity := c.code.decode(tag_out).error
      s2_tag_match := s1_tag_match(i)
    }
    s1_tag_match(i) := tag_out(c.tagbits-1,0) === s1_tag
    s2_tag_hit(i) := s2_vb && s2_tag_match
    s2_disparity(i) := s2_vb && (s2_tag_disparity || c.code.decode(s2_dout(i)).error)
  }
  s2_any_tag_hit := s2_tag_hit.reduceLeft(_||_) && !s2_disparity.reduceLeft(_||_)

  for (i <- 0 until c.assoc) {
    val data_array = Mem(Bits(width = c.code.width(c.databits)), c.sets*REFILL_CYCLES, seqRead = true)
    val s1_raddr = Reg(UInt())
    when (io.mem.grant.valid && repl_way === UInt(i)) {
      val d = io.mem.grant.bits.payload.data
      data_array(Cat(s2_idx,rf_cnt)) := c.code.encode(d)
    }
//    /*.else*/when (s0_valid) { // uncomment ".else" to infer 6T SRAM
    .elsewhen (s0_valid) {
      s1_raddr := s0_pgoff(c.untagbits-1,c.offbits-rf_cnt.getWidth)
    }
    // if s1_tag_match is critical, replace with partial tag check
    when (s1_valid && rdy && !stall && (Bool(c.dm) || s1_tag_match(i))) { s2_dout(i) := data_array(s1_raddr) }
  }
  val s2_dout_word = s2_dout.map(x => (x >> (s2_offset(log2Up(c.databits/8)-1,log2Up(c.ibytes)) << log2Up(c.ibytes*8)))(c.ibytes*8-1,0))
  io.resp.bits.data := Mux1H(s2_tag_hit, s2_dout_word)
  io.resp.bits.datablock := Mux1H(s2_tag_hit, s2_dout)

  val finish_q = Module(new Queue(new GrantAck, 1))
  finish_q.io.enq.valid := refill_done && tl.co.requiresAck(io.mem.grant.bits.payload)
  finish_q.io.enq.bits.master_xact_id := io.mem.grant.bits.payload.master_xact_id

  // output signals
  io.resp.valid := s2_hit
  io.mem.acquire.meta.valid := (state === s_request) && finish_q.io.enq.ready
  io.mem.acquire.meta.bits.payload := Acquire(tl.co.getUncachedReadAcquireType, s2_addr >> UInt(c.offbits), UInt(0))
  io.mem.acquire.data.valid := Bool(false)
  io.mem.grant_ack <> FIFOedLogicalNetworkIOWrapper(finish_q.io.deq)
  io.mem.grant.ready := Bool(true)

  // control state machine
  switch (state) {
    is (s_ready) {
      when (s2_miss) { state := s_request }
      invalidated := Bool(false)
    }
    is (s_request) {
      when (io.mem.acquire.meta.ready && finish_q.io.enq.ready) { state := s_refill_wait }
    }
    is (s_refill_wait) {
      when (io.mem.grant.valid) { state := s_refill }
    }
    is (s_refill) {
      when (refill_done) { state := s_ready }
    }
  }
}