2014-03-25 13:22:04 +01:00
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package rocket
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import Chisel._
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import Util._
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import Node._
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import uncore.constants.AddressConstants._
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2014-04-08 00:58:49 +02:00
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case class BTBConfig(entries: Int, nras: Int = 0) {
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2014-03-25 13:22:04 +01:00
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val matchBits = PGIDX_BITS
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2014-04-08 00:58:49 +02:00
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val pages0 = 1 max log2Up(entries) // is this sensible?
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2014-03-25 13:22:04 +01:00
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val pages = (pages0+1)/2*2 // control logic assumes 2 divides pages
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2014-04-02 00:01:27 +02:00
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val opaqueBits = log2Up(entries)
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2014-04-08 00:58:49 +02:00
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val nbht = 1 << log2Up(entries * 2)
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}
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class RAS(implicit conf: BTBConfig) {
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def push(addr: UInt): Unit = {
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when (count < conf.nras) { count := count + 1 }
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val nextPos = Mux(Bool(isPow2(conf.nras)) || pos > 0, pos+1, UInt(0))
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stack(nextPos) := addr
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pos := nextPos
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}
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def peek: UInt = stack(pos)
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def pop: Unit = when (!isEmpty) {
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count := count - 1
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pos := Mux(Bool(isPow2(conf.nras)) || pos > 0, pos-1, UInt(conf.nras-1))
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}
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def clear: Unit = count := UInt(0)
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def isEmpty: Bool = count === UInt(0)
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private val count = Reg(init=UInt(0,log2Up(conf.nras+1)))
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private val pos = Reg(init=UInt(0,log2Up(conf.nras)))
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private val stack = Vec.fill(conf.nras){Reg(UInt())}
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}
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class BHTResp(implicit conf: BTBConfig) extends Bundle {
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val index = UInt(width = log2Up(conf.nbht).max(1))
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val value = UInt(width = 2)
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}
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class BHT(implicit conf: BTBConfig) {
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def get(addr: UInt): BHTResp = {
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val res = new BHTResp
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res.index := addr(log2Up(conf.nbht)+1,2) ^ history
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res.value := table(res.index)
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res
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}
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def update(d: BHTResp, taken: Bool): Unit = {
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table(d.index) := Cat(taken, (d.value(1) & d.value(0)) | ((d.value(1) | d.value(0)) & taken))
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history := Cat(taken, history(log2Up(conf.nbht)-1,1))
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}
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private val table = Mem(UInt(width = 2), conf.nbht)
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val history = Reg(UInt(width = log2Up(conf.nbht)))
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2014-04-02 00:01:27 +02:00
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}
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class BTBUpdate(implicit conf: BTBConfig) extends Bundle {
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val prediction = Valid(new BTBResp)
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val pc = UInt(width = VADDR_BITS)
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val target = UInt(width = VADDR_BITS)
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val returnAddr = UInt(width = VADDR_BITS)
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val taken = Bool()
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2014-04-08 00:58:49 +02:00
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val isJump = Bool()
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2014-04-02 00:01:27 +02:00
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val isCall = Bool()
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val isReturn = Bool()
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val incorrectTarget = Bool()
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override def clone = new BTBUpdate().asInstanceOf[this.type]
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}
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class BTBResp(implicit conf: BTBConfig) extends Bundle {
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val taken = Bool()
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val target = UInt(width = VADDR_BITS)
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2014-04-08 00:58:49 +02:00
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val entry = UInt(width = conf.opaqueBits)
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val bht = new BHTResp
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2014-04-02 00:01:27 +02:00
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override def clone = new BTBResp().asInstanceOf[this.type]
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}
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2014-03-25 13:22:04 +01:00
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// fully-associative branch target buffer
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2014-04-02 00:01:27 +02:00
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class BTB(implicit conf: BTBConfig) extends Module {
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2014-03-25 13:22:04 +01:00
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val io = new Bundle {
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2014-04-02 00:01:27 +02:00
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val req = UInt(INPUT, VADDR_BITS)
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val resp = Valid(new BTBResp)
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val update = Valid(new BTBUpdate).flip
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val invalidate = Bool(INPUT)
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2014-03-25 13:22:04 +01:00
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}
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val idxValid = Vec.fill(conf.entries){Reg(init=Bool(false))}
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val idxs = Vec.fill(conf.entries){Reg(UInt(width=conf.matchBits))}
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val idxPages = Vec.fill(conf.entries){Reg(UInt(width=log2Up(conf.pages)))}
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val tgts = Vec.fill(conf.entries){Reg(UInt(width=conf.matchBits))}
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val tgtPages = Vec.fill(conf.entries){Reg(UInt(width=log2Up(conf.pages)))}
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val pages = Vec.fill(conf.pages){Reg(UInt(width=VADDR_BITS-conf.matchBits))}
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val pageValid = Vec.fill(conf.pages){Reg(init=Bool(false))}
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2014-04-02 00:01:27 +02:00
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val idxPagesOH = idxPages.map(UIntToOH(_)(conf.pages-1,0))
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val tgtPagesOH = tgtPages.map(UIntToOH(_)(conf.pages-1,0))
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val useRAS = Vec.fill(conf.entries){Reg(Bool())}
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2014-04-08 00:58:49 +02:00
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val isJump = Vec.fill(conf.entries){Reg(Bool())}
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2014-03-25 13:22:04 +01:00
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private def page(addr: UInt) = addr >> conf.matchBits
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private def pageMatch(addr: UInt) = {
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val p = page(addr)
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Vec(pages.map(_ === p)).toBits & pageValid.toBits
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}
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private def tagMatch(addr: UInt, pgMatch: UInt): UInt = {
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val idx = addr(conf.matchBits-1,0)
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val idxMatch = idxs.map(_ === idx).toBits
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val idxPageMatch = idxPagesOH.map(_ & pgMatch).map(_.orR).toBits
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idxValid.toBits & idxMatch & idxPageMatch
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}
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2014-04-02 00:01:27 +02:00
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val update = Pipe(io.update)
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val update_target = io.req
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val pageHit = pageMatch(io.req)
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val hits = tagMatch(io.req, pageHit)
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val updatePageHit = pageMatch(update.bits.pc)
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val updateHits = tagMatch(update.bits.pc, updatePageHit)
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2014-03-25 13:22:04 +01:00
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2014-04-02 00:01:27 +02:00
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private var lfsr = LFSR16(update.valid)
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2014-03-25 13:22:04 +01:00
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def rand(width: Int) = {
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lfsr = lfsr(lfsr.getWidth-1,1)
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Random.oneHot(width, lfsr)
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}
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2014-04-08 00:58:49 +02:00
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val updateHit = update.bits.prediction.valid
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val updateValid = update.bits.incorrectTarget || updateHit && Bool(conf.nbht > 0)
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val updateTarget = updateValid && update.bits.incorrectTarget
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2014-03-25 13:22:04 +01:00
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2014-04-02 00:01:27 +02:00
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val useUpdatePageHit = updatePageHit.orR
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2014-04-08 00:58:49 +02:00
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val doIdxPageRepl = updateTarget && !useUpdatePageHit
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val idxPageRepl = UInt()
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val idxPageUpdateOH = Mux(useUpdatePageHit, updatePageHit, idxPageRepl)
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val idxPageUpdate = OHToUInt(idxPageUpdateOH)
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2014-03-25 13:22:04 +01:00
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val idxPageReplEn = Mux(doIdxPageRepl, idxPageRepl, UInt(0))
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2014-04-02 00:01:27 +02:00
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val samePage = page(update.bits.pc) === page(update_target)
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val usePageHit = (pageHit & ~idxPageReplEn).orR
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2014-04-08 00:58:49 +02:00
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val doTgtPageRepl = updateTarget && !samePage && !usePageHit
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val tgtPageRepl = Mux(samePage, idxPageUpdateOH, idxPageUpdateOH(conf.pages-2,0) << 1 | idxPageUpdateOH(conf.pages-1))
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val tgtPageUpdate = OHToUInt(Mux(usePageHit, pageHit, tgtPageRepl))
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2014-03-25 13:22:04 +01:00
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val tgtPageReplEn = Mux(doTgtPageRepl, tgtPageRepl, UInt(0))
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val pageReplEn = idxPageReplEn | tgtPageReplEn
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2014-04-08 00:58:49 +02:00
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idxPageRepl := UIntToOH(Counter(update.valid && (doIdxPageRepl || doTgtPageRepl), conf.pages)._1)
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when (update.valid && !(updateValid && !updateTarget)) {
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val nextRepl = Counter(!updateHit && updateValid, conf.entries)._1
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val waddr = Mux(updateHit, update.bits.prediction.bits.entry, nextRepl)
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2014-03-25 13:22:04 +01:00
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for (i <- 0 until conf.entries) {
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2014-04-08 00:58:49 +02:00
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when (waddr === i) {
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idxValid(i) := updateValid
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when (updateTarget) {
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if (i == 0) assert(io.req === update.bits.target, "BTB request != I$ target")
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2014-04-02 00:01:27 +02:00
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idxs(i) := update.bits.pc
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2014-04-08 00:58:49 +02:00
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idxPages(i) := idxPageUpdate
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2014-04-02 00:01:27 +02:00
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tgts(i) := update_target
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2014-04-08 00:58:49 +02:00
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tgtPages(i) := tgtPageUpdate
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useRAS(i) := update.bits.isReturn
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isJump(i) := update.bits.isJump
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2014-03-25 13:22:04 +01:00
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}
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}.elsewhen ((pageReplEn & (idxPagesOH(i) | tgtPagesOH(i))).orR) {
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idxValid(i) := false
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}
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}
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require(conf.pages % 2 == 0)
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2014-04-08 00:58:49 +02:00
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val idxWritesEven = (idxPageUpdateOH & Fill(conf.pages/2, UInt(1,2))).orR
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2014-03-25 13:22:04 +01:00
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def writeBank(i: Int, mod: Int, en: Bool, data: UInt) = {
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for (i <- i until conf.pages by mod) {
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when (en && pageReplEn(i)) {
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pages(i) := data
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pageValid(i) := true
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}
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}
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}
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writeBank(0, 2, Mux(idxWritesEven, doIdxPageRepl, doTgtPageRepl),
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2014-04-02 00:01:27 +02:00
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Mux(idxWritesEven, page(update.bits.pc), page(update_target)))
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2014-03-25 13:22:04 +01:00
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writeBank(1, 2, Mux(idxWritesEven, doTgtPageRepl, doIdxPageRepl),
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2014-04-02 00:01:27 +02:00
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Mux(idxWritesEven, page(update_target), page(update.bits.pc)))
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2014-03-25 13:22:04 +01:00
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}
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when (io.invalidate) {
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idxValid.foreach(_ := false)
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pageValid.foreach(_ := false)
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}
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2014-04-02 00:01:27 +02:00
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io.resp.valid := hits.toBits.orR
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io.resp.bits.taken := io.resp.valid
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io.resp.bits.target := Cat(Mux1H(Mux1H(hits, tgtPagesOH), pages), Mux1H(hits, tgts))
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2014-04-08 00:58:49 +02:00
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io.resp.bits.entry := OHToUInt(hits)
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if (conf.nbht > 0) {
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val bht = new BHT
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val res = bht.get(io.req)
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when (update.valid && updateHit && !update.bits.isJump) { bht.update(update.bits.prediction.bits.bht, update.bits.taken) }
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when (!res.value(0) && !Mux1H(hits, isJump)) { io.resp.bits.taken := false }
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io.resp.bits.bht := res
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}
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2014-04-02 00:01:27 +02:00
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if (conf.nras > 0) {
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val ras = new RAS
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when (!ras.isEmpty && Mux1H(hits, useRAS)) {
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2014-04-08 00:58:49 +02:00
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io.resp.bits.target := ras.peek
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2014-04-02 00:01:27 +02:00
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}
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2014-04-08 00:58:49 +02:00
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when (io.update.valid) {
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when (io.update.bits.isCall) {
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ras.push(io.update.bits.returnAddr)
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}.elsewhen (io.update.bits.isReturn && io.update.bits.prediction.valid) {
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ras.pop
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}
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2014-04-02 00:01:27 +02:00
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}
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when (io.invalidate) { ras.clear }
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}
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2014-03-25 13:22:04 +01:00
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}
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