riscv/rocket-chip
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Mitigate D$ hit -> branch -> NPC critical path

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This commit is contained in:
Andrew Waterman 2013-11-24 14:19:46 -08:00
parent 53f726008b
commit 65b8340cea
3 changed files with 6 additions and 8 deletions
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8
rocket/src/main/scala/ctrl.scala
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@ -459,7 +459,7 @@ class Control(implicit conf: RocketConfiguration) extends Module
.otherwise {
ex_reg_br_type := id_br_type;
ex_reg_jalr := id_jalr
ex_reg_btb_hit := io.imem.resp.bits.taken
ex_reg_btb_hit := io.imem.resp.bits.taken && !id_jalr
ex_reg_div_mul_val := id_mul_val || id_div_val
ex_reg_mem_val := id_mem_val.toBool;
ex_reg_valid := Bool(true)
@ -484,9 +484,7 @@ class Control(implicit conf: RocketConfiguration) extends Module
val replay_ex_other = wb_dcache_miss && ex_reg_load_use || mem_reg_replay_next
val replay_ex = replay_ex_structural || replay_ex_other
ctrl_killx := take_pc_wb || replay_ex
val take_pc_ex = Mux(ex_reg_jalr,
!(ex_reg_btb_hit && io.dpath.jalr_eq) && !replay_ex_other,
ex_reg_btb_hit != io.dpath.ex_br_taken)
val take_pc_ex = ex_reg_jalr && !io.dpath.jalr_eq || io.dpath.ex_br_taken
// detect 2-cycle load-use delay for LB/LH/SC
val ex_slow_bypass = ex_reg_mem_cmd === M_XSC || AVec(MT_B, MT_BU, MT_H, MT_HU).contains(ex_reg_mem_type)
@ -714,7 +712,7 @@ class Control(implicit conf: RocketConfiguration) extends Module
io.dpath.pcr := wb_reg_pcr.toUInt
io.dpath.eret := wb_reg_eret
io.dpath.ex_mem_type := ex_reg_mem_type
io.dpath.ex_br_type := ex_reg_br_type
io.dpath.ex_br_type := ex_reg_br_type ^ ex_reg_btb_hit
io.dpath.ex_rs2_val := ex_reg_mem_val && isWrite(ex_reg_mem_cmd) || ex_reg_rocc_val
io.dpath.ex_rocc_val := ex_reg_rocc_val
io.dpath.mem_rocc_val := mem_reg_rocc_val

2
rocket/src/main/scala/dpath.scala
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@ -185,7 +185,7 @@ class Datapath(implicit conf: RocketConfiguration) extends Module
e(0)))
}
val ex_br_base = Mux(io.ctrl.ex_jalr, ex_rs1, ex_reg_pc)
val ex_br_offset = Mux(io.ctrl.ex_predicted_taken && !io.ctrl.ex_jalr, SInt(4), ex_imm(19,0).toSInt)
val ex_br_offset = Mux(io.ctrl.ex_predicted_taken, SInt(4), ex_imm(19,0).toSInt)
val ex_br64 = ex_br_base + ex_br_offset
val ex_br_msb = Mux(io.ctrl.ex_jalr, vaSign(ex_rs1, ex_br64), vaSign(ex_reg_pc, ex_br64))
val ex_br_addr = Cat(ex_br_msb, ex_br64(VADDR_BITS-1,0))

4
rocket/src/main/scala/icache.scala
View File

@ -160,11 +160,11 @@ class ICache(implicit c: ICacheConfig, tl: TileLinkConfiguration) extends Module
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)
val s0_pgoff = Mux(s1_valid && stall, s1_pgoff, io.req.bits.idx)
s1_valid := io.req.valid && rdy || s1_valid && stall && !io.req.bits.kill
when (io.req.valid && rdy) {
s1_pgoff := s0_pgoff
s1_pgoff := io.req.bits.idx
}
s2_valid := s1_valid && rdy && !io.req.bits.kill || io.resp.valid && stall