/
Frontend.scala
367 lines (323 loc) · 14.9 KB
/
Frontend.scala
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// See LICENSE.Berkeley for license details.
// See LICENSE.SiFive for license details.
package freechips.rocketchip.rocket
import Chisel._
import Chisel.ImplicitConversions._
import chisel3.{withClock,withReset}
import chisel3.internal.sourceinfo.SourceInfo
import chisel3.experimental.chiselName
import freechips.rocketchip.config._
import freechips.rocketchip.subsystem._
import freechips.rocketchip.diplomacy._
import freechips.rocketchip.tilelink._
import freechips.rocketchip.tile._
import freechips.rocketchip.util._
import freechips.rocketchip.util.property._
import freechips.rocketchip.diplomaticobjectmodel.logicaltree.ICacheLogicalTreeNode
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 = 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 might_request = Bool(OUTPUT)
val clock_enabled = Bool(INPUT)
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 = icache.masterNode
val slaveNode = icache.slaveNode
}
class FrontendBundle(val outer: Frontend) extends CoreBundle()(outer.p)
with HasExternallyDrivenTileConstants {
val cpu = new FrontendIO().flip
val ptw = new TLBPTWIO()
val errors = new ICacheErrors
}
@chiselName
class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
with HasRocketCoreParameters
with HasL1ICacheParameters {
val io = IO(new FrontendBundle(outer))
implicit val edge = outer.masterNode.edges.out(0)
val icache = outer.icache.module
require(fetchWidth*coreInstBytes == outer.icacheParams.fetchBytes)
val fq = withReset(reset || io.cpu.req.valid) { Module(new ShiftQueue(new FrontendResp, 5, flow = true)) }
val clock_en_reg = Reg(Bool())
val clock_en = clock_en_reg || io.cpu.might_request
io.cpu.clock_enabled := clock_en
assert(!(io.cpu.req.valid || io.cpu.sfence.valid || io.cpu.flush_icache || io.cpu.bht_update.valid || io.cpu.btb_update.valid) || io.cpu.might_request)
val gated_clock =
if (!rocketParams.clockGate) clock
else ClockGate(clock, clock_en, "icache_clock_gate")
icache.clock := gated_clock
icache.io.clock_enabled := clock_en
withClock (gated_clock) { // entering gated-clock domain
val tlb = Module(new TLB(true, log2Ceil(fetchBytes), TLBConfig(nTLBEntries)))
val s1_valid = Reg(Bool())
val s2_valid = RegInit(false.B)
val s0_fq_has_space =
!fq.io.mask(fq.io.mask.getWidth-3) ||
(!fq.io.mask(fq.io.mask.getWidth-2) && (!s1_valid || !s2_valid)) ||
(!fq.io.mask(fq.io.mask.getWidth-1) && (!s1_valid && !s2_valid))
val s0_valid = io.cpu.req.valid || s0_fq_has_space
s1_valid := s0_valid
val s1_pc = Reg(UInt(width=vaddrBitsExtended))
val s1_speculative = Reg(Bool())
val s2_pc = RegInit(t = UInt(width = vaddrBitsExtended), alignPC(io.reset_vector))
val s2_btb_resp_valid = if (usingBTB) Reg(Bool()) else false.B
val s2_btb_resp_bits = Reg(new BTBResp)
val s2_btb_taken = s2_btb_resp_valid && s2_btb_resp_bits.taken
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_valid := !s2_redirect
s2_pc := s1_pc
s2_speculative := s1_speculative
s2_tlb_resp := tlb.io.resp
}
io.ptw <> tlb.io.ptw
tlb.io.req.valid := s1_valid && !s2_replay
tlb.io.req.bits.vaddr := s1_pc
tlb.io.req.bits.passthrough := Bool(false)
tlb.io.req.bits.size := log2Ceil(coreInstBytes*fetchWidth)
tlb.io.sfence := io.cpu.sfence
tlb.io.kill := !s2_valid
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
val s2_can_speculatively_refill = s2_tlb_resp.cacheable && !io.ptw.customCSRs.asInstanceOf[RocketCustomCSRs].disableSpeculativeICacheRefill
icache.io.s2_kill := s2_speculative && !s2_can_speculatively_refill || s2_xcpt
icache.io.s2_prefetch := s2_tlb_resp.prefetchable && !io.ptw.customCSRs.asInstanceOf[RocketCustomCSRs].disableICachePrefetch
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 := s2_btb_resp_bits
fq.io.enq.bits.btb.taken := s2_btb_taken
fq.io.enq.bits.xcpt := s2_tlb_resp
assert(!(s2_speculative && io.ptw.customCSRs.asInstanceOf[RocketCustomCSRs].disableSpeculativeICacheRefill && !icache.io.s2_kill))
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.flush := false
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)
}
val force_taken = io.ptw.customCSRs.bpmStatic
when (io.ptw.customCSRs.flushBTB) { btb.io.flush := true }
when (force_taken) { btb.io.bht_update.valid := false }
val s2_base_pc = ~(~s2_pc | (fetchBytes-1))
val taken_idx = Wire(UInt())
val after_idx = Wire(UInt())
val useRAS = Wire(init=false.B)
val updateBTB = Wire(init=false.B)
def scanInsns(idx: Int, prevValid: Bool, prevBits: UInt, prevTaken: Bool): Bool = {
def insnIsRVC(bits: UInt) = bits(1,0) =/= 3
val prevRVI = prevValid && !insnIsRVC(prevBits)
val valid = fq.io.enq.bits.mask(idx) && !prevRVI
val bits = fq.io.enq.bits.data(coreInstBits*(idx+1)-1, coreInstBits*idx)
val rvc = insnIsRVC(bits)
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, xLen).bImm.asSInt, new RVCDecoder(bits, xLen).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 predict_taken = s2_btb_resp_bits.bht.taken || force_taken
val taken =
prevRVI && (rviJump || rviJALR || rviBranch && predict_taken) ||
valid && (rvcJump || rvcJALR || rvcJR || rvcBranch && predict_taken)
val predictReturn = btb.io.ras_head.valid && (prevRVI && rviReturn || valid && rvcReturn)
val predictJump = prevRVI && rviJump || valid && rvcJump
val predictBranch = predict_taken && (prevRVI && rviBranch || valid && rvcBranch)
when (s2_valid && s2_btb_resp_valid && s2_btb_resp_bits.bridx === idx && valid && !rvc) {
// The BTB has predicted that the middle of an RVI instruction is
// a branch! Flush the BTB and the pipeline.
btb.io.flush := true
fq.io.enq.bits.replay := true
wrong_path := true
ccover(wrong_path, "BTB_NON_CFI_ON_WRONG_PATH", "BTB predicted a non-branch was taken while on the wrong path")
}
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.cfiType := Mux(Mux(prevRVI, rviReturn, rvcReturn), CFIType.ret,
Mux(Mux(prevRVI, rviCall, rvcCall), CFIType.call,
Mux(Mux(prevRVI, rviBranch, rvcBranch) && !force_taken, CFIType.branch,
CFIType.jump)))
when (!s2_btb_taken) {
when (fq.io.enq.fire() && taken && !predictBranch && !predictJump && !predictReturn) {
wrong_path := true
}
when (s2_valid && predictReturn) {
useRAS := true
}
when (s2_valid && (predictBranch || predictJump)) {
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
btb.io.bht_advance.bits := s2_btb_resp_bits
}
when (!s2_btb_resp_valid && (predictBranch && s2_btb_resp_bits.bht.strongly_taken || predictJump || predictReturn)) {
updateBTB := true
}
}
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)
}
}
when (!io.cpu.btb_update.valid) {
val fetch_bubble_likely = !fq.io.mask(1)
btb.io.btb_update.valid := fq.io.enq.fire() && !wrong_path && fetch_bubble_likely && updateBTB
btb.io.btb_update.bits.prediction.entry := UInt(tileParams.btb.get.nEntries)
btb.io.btb_update.bits.isValid := true
btb.io.btb_update.bits.cfiType := btb.io.ras_update.bits.cfiType
btb.io.btb_update.bits.br_pc := s2_base_pc | (taken_idx << log2Ceil(coreInstBytes))
btb.io.btb_update.bits.pc := s2_base_pc
}
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_taken || taken)) {
s2_partial_insn_valid := false
}
when (!s2_btb_taken) {
when (taken) {
fq.io.enq.bits.btb.bridx := taken_idx
fq.io.enq.bits.btb.taken := true
fq.io.enq.bits.btb.entry := UInt(tileParams.btb.get.nEntries)
when (fq.io.enq.fire()) { s2_redirect := true }
}
}
assert(!s2_partial_insn_valid || fq.io.enq.bits.mask(0))
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()
io.errors := icache.io.errors
// gate the clock
clock_en_reg := !rocketParams.clockGate ||
io.cpu.might_request || // chicken bit
icache.io.keep_clock_enabled || // I$ miss or ITIM access
s1_valid || s2_valid || // some fetch in flight
!tlb.io.req.ready || // handling TLB miss
!fq.io.mask(fq.io.mask.getWidth-1) // queue not full
} // leaving gated-clock domain
def alignPC(pc: UInt) = ~(~pc | (coreInstBytes - 1))
def ccover(cond: Bool, label: String, desc: String)(implicit sourceInfo: SourceInfo) =
cover(cond, s"FRONTEND_$label", "Rocket;;" + desc)
}
/** Mix-ins for constructing tiles that have an ICache-based pipeline frontend */
trait HasICacheFrontend extends CanHavePTW { this: BaseTile =>
val module: HasICacheFrontendModule
val frontend = LazyModule(new Frontend(tileParams.icache.get, hartId))
tlMasterXbar.node := frontend.masterNode
connectTLSlave(frontend.slaveNode, tileParams.core.fetchBytes)
nPTWPorts += 1
// This should be a None in the case of not having an ITIM address, when we
// don't actually use the device that is instantiated in the frontend.
private val deviceOpt = if (tileParams.icache.get.itimAddr.isDefined) Some(frontend.icache.device) else None
val iCacheLogicalTreeNode = new ICacheLogicalTreeNode(frontend.icache, deviceOpt, tileParams.icache.get)
}
trait HasICacheFrontendModule extends CanHavePTWModule {
val outer: HasICacheFrontend
ptwPorts += outer.frontend.module.io.ptw
}