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

// See LICENSE.Berkeley for license details.
// See LICENSE.SiFive for license details.

package freechips.rocketchip.rocket

import Chisel._
import Chisel.ImplicitConversions._
import chisel3.core.withReset
import freechips.rocketchip.config._
import freechips.rocketchip.coreplex._
import freechips.rocketchip.diplomacy.{LazyModule, LazyModuleImp}
import freechips.rocketchip.tilelink._
import freechips.rocketchip.tile._
import freechips.rocketchip.util._

class FrontendReq(implicit p: Parameters) extends CoreBundle()(p) {
  val pc = UInt(width = vaddrBitsExtended)
  val speculative = Bool()
}

class FrontendExceptions extends Bundle {
  val pf = new Bundle {
    val inst = Bool()
  }
  val ae = new Bundle {
    val inst = Bool()
  }
}

class FrontendResp(implicit p: Parameters) extends CoreBundle()(p) {
  val btb = Valid(new BTBResp)
  val pc = UInt(width = vaddrBitsExtended)  // ID stage PC
  val data = UInt(width = fetchWidth * coreInstBits)
  val mask = Bits(width = fetchWidth)
  val xcpt = new FrontendExceptions
  val replay = Bool()
}

class FrontendPerfEvents extends Bundle {
  val acquire = Bool()
  val tlbMiss = Bool()
}

class FrontendIO(implicit p: Parameters) extends CoreBundle()(p) {
  val req = Valid(new FrontendReq)
  val sfence = Valid(new SFenceReq)
  val resp = Decoupled(new FrontendResp).flip
  val btb_update = Valid(new BTBUpdate)
  val bht_update = Valid(new BHTUpdate)
  val ras_update = Valid(new RASUpdate)
  val flush_icache = Bool(OUTPUT)
  val npc = UInt(INPUT, width = vaddrBitsExtended)
  val perf = new FrontendPerfEvents().asInput
}

class Frontend(val icacheParams: ICacheParams, hartid: Int)(implicit p: Parameters) extends LazyModule {
  lazy val module = new FrontendModule(this)
  val icache = LazyModule(new ICache(icacheParams, hartid))
  val masterNode = TLOutputNode()
  val slaveNode = TLInputNode()

  masterNode := icache.masterNode
  // Avoid breaking tile dedup due to address constants in the monitor
  icache.slaveNode.map { _ connectButDontMonitor slaveNode }
}

class FrontendBundle(outer: Frontend) extends CoreBundle()(outer.p) {
  val cpu = new FrontendIO().flip
  val ptw = new TLBPTWIO()
  val tl_out = outer.masterNode.bundleOut
  val tl_in = outer.slaveNode.bundleIn
  val resetVector = UInt(INPUT, vaddrBitsExtended)
  val hartid = UInt(INPUT, hartIdLen)
}

class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
    with HasCoreParameters
    with HasL1ICacheParameters {
  val io = new FrontendBundle(outer)
  implicit val edge = outer.masterNode.edgesOut.head
  val icache = outer.icache.module
  require(fetchWidth*coreInstBytes == outer.icacheParams.fetchBytes)

  val fetchBytes = coreInstBytes * fetchWidth
  val tlb = Module(new TLB(log2Ceil(fetchBytes), nTLBEntries))
  val fq = withReset(reset || io.cpu.req.valid) { Module(new ShiftQueue(new FrontendResp, 5, flow = true)) }

  val s0_valid = io.cpu.req.valid || !fq.io.mask(fq.io.mask.getWidth-3)
  val s1_valid = RegNext(s0_valid)
  val s1_pc = Reg(UInt(width=vaddrBitsExtended))
  val s1_speculative = Reg(Bool())
  val s2_valid = RegInit(false.B)
  val s2_pc = RegInit(alignPC(io.resetVector))
  val s2_btb_resp_valid = if (usingBTB) Reg(Bool()) else false.B
  val s2_btb_resp_bits = Reg(new BTBResp)
  val s2_tlb_resp = Reg(tlb.io.resp)
  val s2_xcpt = s2_tlb_resp.ae.inst || s2_tlb_resp.pf.inst
  val s2_speculative = Reg(init=Bool(false))
  val s2_partial_insn_valid = RegInit(false.B)
  val s2_partial_insn = Reg(UInt(width = coreInstBits))
  val wrong_path = Reg(Bool())

  val s1_base_pc = ~(~s1_pc | (fetchBytes - 1))
  val ntpc = s1_base_pc + fetchBytes.U
  val predicted_npc = Wire(init = ntpc)
  val predicted_taken = Wire(init = Bool(false))

  val s2_replay = Wire(Bool())
  s2_replay := (s2_valid && !fq.io.enq.fire()) || RegNext(s2_replay && !s0_valid, true.B)
  val npc = Mux(s2_replay, s2_pc, predicted_npc)

  s1_pc := io.cpu.npc
  // consider RVC fetches across blocks to be non-speculative if the first
  // part was non-speculative
  val s0_speculative =
    if (usingCompressed) s1_speculative || s2_valid && !s2_speculative || predicted_taken
    else Bool(true)
  s1_speculative := Mux(io.cpu.req.valid, io.cpu.req.bits.speculative, Mux(s2_replay, s2_speculative, s0_speculative))

  val s2_redirect = Wire(init = io.cpu.req.valid)
  s2_valid := false
  when (!s2_replay && !s2_redirect) {
    s2_valid := true
    s2_pc := s1_pc
    s2_speculative := s1_speculative
    s2_tlb_resp := tlb.io.resp
  }

  io.ptw <> tlb.io.ptw
  tlb.io.req.valid := !s2_replay
  tlb.io.req.bits.vaddr := s1_pc
  tlb.io.req.bits.passthrough := Bool(false)
  tlb.io.req.bits.instruction := Bool(true)
  tlb.io.req.bits.sfence := io.cpu.sfence
  tlb.io.req.bits.size := log2Ceil(coreInstBytes*fetchWidth)

  icache.io.hartid := io.hartid
  icache.io.req.valid := s0_valid
  icache.io.req.bits.addr := io.cpu.npc
  icache.io.invalidate := io.cpu.flush_icache
  icache.io.s1_paddr := tlb.io.resp.paddr
  icache.io.s2_vaddr := s2_pc
  icache.io.s1_kill := s2_redirect || tlb.io.resp.miss || s2_replay
  icache.io.s2_kill := s2_speculative && !s2_tlb_resp.cacheable || s2_xcpt
  icache.io.s2_prefetch := s2_tlb_resp.prefetchable

  fq.io.enq.valid := RegNext(s1_valid) && s2_valid && (icache.io.resp.valid || !s2_tlb_resp.miss && icache.io.s2_kill)
  fq.io.enq.bits.pc := s2_pc
  io.cpu.npc := alignPC(Mux(io.cpu.req.valid, io.cpu.req.bits.pc, npc))

  fq.io.enq.bits.data := icache.io.resp.bits.data
  fq.io.enq.bits.mask := UInt((1 << fetchWidth)-1) << s2_pc.extract(log2Ceil(fetchWidth)+log2Ceil(coreInstBytes)-1, log2Ceil(coreInstBytes))
  fq.io.enq.bits.replay := icache.io.resp.bits.replay || icache.io.s2_kill && !icache.io.resp.valid && !s2_xcpt
  fq.io.enq.bits.btb.valid := s2_btb_resp_valid
  fq.io.enq.bits.btb.bits := s2_btb_resp_bits
  fq.io.enq.bits.xcpt := s2_tlb_resp
  when (icache.io.resp.valid && icache.io.resp.bits.ae) { fq.io.enq.bits.xcpt.ae.inst := true }

  if (usingBTB) {
    val btb = Module(new BTB)
    btb.io.req.valid := false
    btb.io.req.bits.addr := s1_pc
    btb.io.btb_update := io.cpu.btb_update
    btb.io.bht_update := io.cpu.bht_update
    btb.io.ras_update.valid := false
    btb.io.bht_advance.valid := false
    when (!s2_replay) {
      btb.io.req.valid := !s2_redirect
      s2_btb_resp_valid := btb.io.resp.valid
      s2_btb_resp_bits := btb.io.resp.bits
    }
    when (btb.io.resp.valid && btb.io.resp.bits.taken) {
      predicted_npc := btb.io.resp.bits.target.sextTo(vaddrBitsExtended)
      predicted_taken := Bool(true)
    }

    if (!coreParams.jumpInFrontend) {
      // push RAS speculatively
      btb.io.ras_update.valid := btb.io.req.valid && btb.io.resp.valid && btb.io.resp.bits.cfiType.isOneOf(CFIType.call, CFIType.ret)
      val returnAddrLSBs = btb.io.resp.bits.bridx +& 1
      btb.io.ras_update.bits.returnAddr :=
        Mux(returnAddrLSBs(log2Ceil(fetchWidth)), ntpc, s1_base_pc | ((returnAddrLSBs << log2Ceil(coreInstBytes)) & (fetchBytes - 1)))
      btb.io.ras_update.bits.cfiType := btb.io.resp.bits.cfiType
      btb.io.ras_update.bits.prediction.valid := true
    } else {
      val s2_btb_hit = s2_btb_resp_valid && s2_btb_resp_bits.taken
      val s2_base_pc = ~(~s2_pc | (fetchBytes-1))
      val taken_idx = Wire(UInt())
      val after_idx = Wire(UInt())
      val useRAS = Wire(init=false.B)

      def scanInsns(idx: Int, prevValid: Bool, prevBits: UInt, prevTaken: Bool): Bool = {
        val prevRVI = prevValid && prevBits(1,0) === 3
        val valid = fq.io.enq.bits.mask(idx) && !prevRVI
        val bits = fq.io.enq.bits.data(coreInstBits*(idx+1)-1, coreInstBits*idx)
        val rvc = bits(1,0) =/= 3
        val rviBits = Cat(bits, prevBits)
        val rviBranch = rviBits(6,0) === Instructions.BEQ.value.asUInt()(6,0)
        val rviJump = rviBits(6,0) === Instructions.JAL.value.asUInt()(6,0)
        val rviJALR = rviBits(6,0) === Instructions.JALR.value.asUInt()(6,0)
        val rviReturn = rviJALR && !rviBits(7) && BitPat("b00?01") === rviBits(19,15)
        val rviCall = (rviJALR || rviJump) && rviBits(7)
        val rvcBranch = bits === Instructions.C_BEQZ || bits === Instructions.C_BNEZ
        val rvcJAL = Bool(xLen == 32) && bits === Instructions.C_JAL
        val rvcJump = bits === Instructions.C_J || rvcJAL
        val rvcImm = Mux(bits(14), new RVCDecoder(bits).bImm.asSInt, new RVCDecoder(bits).jImm.asSInt)
        val rvcJR = bits === Instructions.C_MV && bits(6,2) === 0
        val rvcReturn = rvcJR && BitPat("b00?01") === bits(11,7)
        val rvcJALR = bits === Instructions.C_ADD && bits(6,2) === 0
        val rvcCall = rvcJAL || rvcJALR
        val rviImm = Mux(rviBits(3), ImmGen(IMM_UJ, rviBits), ImmGen(IMM_SB, rviBits))
        val taken =
          prevRVI && (rviJump || rviJALR || rviBranch && s2_btb_resp_bits.bht.taken) ||
          valid && (rvcJump || rvcJALR || rvcJR || rvcBranch && s2_btb_resp_bits.bht.taken)
        val predictReturn = btb.io.ras_head.valid && (prevRVI && rviReturn || valid && rvcReturn)
        val predictBranch =
          prevRVI && (rviJump || rviBranch && s2_btb_resp_bits.bht.taken) ||
          valid && (rvcJump || rvcBranch && s2_btb_resp_bits.bht.taken)

        when (!prevTaken) {
          taken_idx := idx
          after_idx := idx + 1
          btb.io.ras_update.valid := fq.io.enq.fire() && !wrong_path && (prevRVI && (rviCall || rviReturn) || valid && (rvcCall || rvcReturn))
          btb.io.ras_update.bits.prediction.valid := true
          btb.io.ras_update.bits.cfiType := Mux(Mux(prevRVI, rviReturn, rvcReturn), CFIType.ret, CFIType.call)

          when (!s2_btb_hit) {
            when (fq.io.enq.fire() && taken && !predictBranch && !predictReturn) {
              wrong_path := true
            }
            when (s2_valid && predictReturn) {
              useRAS := true
            }
            when (s2_valid && predictBranch) {
              val pc = s2_base_pc | (idx*coreInstBytes)
              val npc =
                if (idx == 0) pc.asSInt + Mux(prevRVI, rviImm -& 2.S, rvcImm)
                else Mux(prevRVI, pc - coreInstBytes, pc).asSInt + Mux(prevRVI, rviImm, rvcImm)
              predicted_npc := npc.asUInt
            }

            when (prevRVI && rviBranch || valid && rvcBranch) {
              btb.io.bht_advance.valid := fq.io.enq.fire() && !wrong_path && !s2_btb_resp_valid
              btb.io.bht_advance.bits := s2_btb_resp_bits
            }
          }
        }

        if (idx == fetchWidth-1) {
          when (fq.io.enq.fire()) {
            s2_partial_insn_valid := false
            when (valid && !prevTaken && !rvc) {
              s2_partial_insn_valid := true
              s2_partial_insn := bits | 0x3
            }
          }
          prevTaken || taken
        } else {
          scanInsns(idx + 1, valid, bits, prevTaken || taken)
        }
      }

      btb.io.ras_update.bits.returnAddr := s2_base_pc + (after_idx << log2Ceil(coreInstBytes))

      val taken = scanInsns(0, s2_partial_insn_valid, s2_partial_insn, false.B)
      when (useRAS) {
        predicted_npc := btb.io.ras_head.bits
      }
      when (fq.io.enq.fire() && s2_btb_hit) {
        s2_partial_insn_valid := false
      }
      when (!s2_btb_hit) {
        fq.io.enq.bits.btb.bits.bridx := taken_idx
        when (taken) {
          fq.io.enq.bits.btb.valid := true
          fq.io.enq.bits.btb.bits.taken := true
          fq.io.enq.bits.btb.bits.entry := UInt(tileParams.btb.get.nEntries)
          when (fq.io.enq.fire()) { s2_redirect := true }
        }
      }
    }
    when (s2_redirect) { s2_partial_insn_valid := false }
    when (io.cpu.req.valid) { wrong_path := false }
  }

  io.cpu.resp <> fq.io.deq

  // performance events
  io.cpu.perf := icache.io.perf
  io.cpu.perf.tlbMiss := io.ptw.req.fire()

  def alignPC(pc: UInt) = ~(~pc | (coreInstBytes - 1))
}

/** Mix-ins for constructing tiles that have an ICache-based pipeline frontend */
trait HasICacheFrontend extends CanHavePTW with HasTileLinkMasterPort {
  val module: HasICacheFrontendModule
  val frontend = LazyModule(new Frontend(tileParams.icache.get, hartid: Int))
  val hartid: Int
  tileBus.node := frontend.masterNode
  nPTWPorts += 1
}

trait HasICacheFrontendBundle extends HasTileLinkMasterPortBundle {
  val outer: HasICacheFrontend
}

trait HasICacheFrontendModule extends CanHavePTWModule with HasTileLinkMasterPortModule {
  val outer: HasICacheFrontend
  ptwPorts += outer.frontend.module.io.ptw
}