riscv/rocket-chip
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Add option to execute JAL from decode stage

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This is particularly helpful for designs that don't have a BTB, but
it becomes the critical path for designs with RVC.  Caveat emptor.
This commit is contained in:
Andrew Waterman
2016-09-13 02:32:00 -07:00
parent 2979badf75
commit 61cbe6164d
2 changed files with 15 additions and 8 deletions
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1
src/main/scala/coreplex/Configs.scala
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@@ -123,6 +123,7 @@ class BaseCoreplexConfig extends Config (
case NPerfEvents => 0
case FastLoadWord => true
case FastLoadByte => false
case FastJAL => false
case XLen => 64
case FPUKey => Some(FPUConfig())
case MulDivKey => Some(MulDivConfig(mulUnroll = 8, mulEarlyOut = (site(XLen) > 32), divEarlyOut = true))

22
src/main/scala/rocket/rocket.scala
View File

@@ -22,6 +22,7 @@ case object UseAtomics extends Field[Boolean]
case object UseCompressed extends Field[Boolean]
case object FastLoadWord extends Field[Boolean]
case object FastLoadByte extends Field[Boolean]
case object FastJAL extends Field[Boolean]
case object CoreInstBits extends Field[Int]
case object NCustomMRWCSRs extends Field[Int]
case object MtvecWritable extends Field[Boolean]
@@ -47,6 +48,7 @@ trait HasCoreParameters extends HasAddrMapParameters {
val usingRoCC = !p(BuildRoCC).isEmpty
val fastLoadWord = p(FastLoadWord)
val fastLoadByte = p(FastLoadByte)
val fastJAL = p(FastJAL)
val nBreakpoints = p(NBreakpoints)
val nPerfCounters = p(NPerfCounters)
val nPerfEvents = p(NPerfEvents)
@@ -205,8 +207,9 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p) {
val wb_reg_rs2 = Reg(Bits())
val take_pc_wb = Wire(Bool())
val take_pc_id = Wire(Bool())
val take_pc_mem_wb = take_pc_wb || take_pc_mem
val take_pc = take_pc_mem_wb
val take_pc = take_pc_mem_wb || take_pc_id
// decode stage
val ibuf = Module(new IBuf)
@@ -228,6 +231,8 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p) {
val rf = new RegFile(31, xLen)
val id_rs = id_raddr.map(rf.read _)
val ctrl_killd = Wire(Bool())
val id_npc = (ibuf.io.pc.asSInt + ImmGen(IMM_UJ, id_inst(0))).asUInt
take_pc_id := Bool(fastJAL) && !ctrl_killd && id_ctrl.jal
val csr = Module(new CSRFile)
val id_csr_en = id_ctrl.csr =/= CSR.N
@@ -385,14 +390,14 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p) {
val mem_br_taken = mem_reg_wdata(0)
val mem_br_target = mem_reg_pc.asSInt +
Mux(mem_ctrl.branch && mem_br_taken, ImmGen(IMM_SB, mem_reg_inst),
Mux(mem_ctrl.jal, ImmGen(IMM_UJ, mem_reg_inst),
Mux(Bool(!fastJAL) && mem_ctrl.jal, ImmGen(IMM_UJ, mem_reg_inst),
Mux(mem_reg_rvc, SInt(2), SInt(4))))
val mem_npc = (Mux(mem_ctrl.jalr, encodeVirtualAddress(mem_reg_wdata, mem_reg_wdata).asSInt, mem_br_target) & SInt(-2)).asUInt
val mem_wrong_npc = Mux(ex_pc_valid, mem_npc =/= ex_reg_pc, Mux(ibuf.io.inst(0).valid, mem_npc =/= ibuf.io.pc, Bool(true)))
val mem_npc_misaligned = !csr.io.status.isa('c'-'a') && mem_npc(1)
val mem_int_wdata = Mux(!mem_reg_xcpt && (mem_ctrl.jalr ^ mem_npc_misaligned), mem_br_target, mem_reg_wdata.asSInt).asUInt
val mem_cfi = mem_ctrl.branch || mem_ctrl.jalr || mem_ctrl.jal
val mem_cfi_taken = (mem_ctrl.branch && mem_br_taken) || mem_ctrl.jalr || mem_ctrl.jal
val mem_cfi_taken = (mem_ctrl.branch && mem_br_taken) || mem_ctrl.jalr || (Bool(!fastJAL) && mem_ctrl.jal)
val mem_misprediction =
if (p(BtbKey).nEntries == 0) mem_cfi_taken
else mem_wrong_npc
@@ -576,20 +581,21 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p) {
id_ctrl.rocc && rocc_blocked || // reduce activity while RoCC is busy
id_do_fence ||
csr.io.csr_stall
ctrl_killd := !ibuf.io.inst(0).valid || ibuf.io.inst(0).bits.replay || take_pc || ctrl_stalld || csr.io.interrupt
ctrl_killd := !ibuf.io.inst(0).valid || ibuf.io.inst(0).bits.replay || take_pc_mem_wb || ctrl_stalld || csr.io.interrupt
io.imem.req.valid := take_pc
io.imem.req.bits.speculative := !take_pc_wb
io.imem.req.bits.pc :=
Mux(wb_xcpt || csr.io.eret, csr.io.evec, // exception or [m|s]ret
Mux(replay_wb, wb_reg_pc, // replay
mem_npc)) // mispredicted branch
Mux(wb_xcpt || csr.io.eret, csr.io.evec, // exception or [m|s]ret
Mux(replay_wb, wb_reg_pc, // replay
Mux(take_pc_mem || Bool(!fastJAL), mem_npc, // branch misprediction
id_npc))) // JAL
io.imem.flush_icache := wb_reg_valid && wb_ctrl.fence_i && !io.dmem.s2_nack
io.imem.flush_tlb := csr.io.fatc
ibuf.io.inst(0).ready := !ctrl_stalld || csr.io.interrupt
io.imem.btb_update.valid := (mem_reg_replay && mem_reg_btb_hit) || (mem_reg_valid && !take_pc_wb && (mem_cfi_taken || !mem_cfi) && mem_wrong_npc)
io.imem.btb_update.valid := (mem_reg_replay && mem_reg_btb_hit) || (mem_reg_valid && !take_pc_wb && (((mem_cfi_taken || !mem_cfi) && mem_wrong_npc) || (Bool(fastJAL) && mem_ctrl.jal && !mem_reg_btb_hit)))
io.imem.btb_update.bits.isValid := !mem_reg_replay && mem_cfi
io.imem.btb_update.bits.isJump := mem_ctrl.jal || mem_ctrl.jalr
io.imem.btb_update.bits.isReturn := mem_ctrl.jalr && mem_reg_inst(19,15) === BitPat("b00??1")