riscv/rocket-chip
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Bypass scoreboard updates

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This reduces div/mul/D$ miss latency by 1 cycle.
This commit is contained in:
Andrew Waterman
2013-08-24 14:39:23 -07:00
parent d4a0db4575
commit 52e31f3298
3 changed files with 28 additions and 23 deletions
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30
rocket/src/main/scala/ctrl.scala
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@ -37,6 +37,8 @@ class CtrlDpathIO extends Bundle()
val ex_mem_type = Bits(OUTPUT, 3)
val ex_rs2_val = Bool(OUTPUT)
val mem_rs2_val = Bool(OUTPUT)
val mem_ll_bypass_rs1 = Bool(OUTPUT)
val mem_ll_bypass_rs2 = Bool(OUTPUT)
// exception handling
val exception = Bool(OUTPUT);
val cause = UInt(OUTPUT, 6);
@ -605,11 +607,17 @@ class Control(implicit conf: RocketConfiguration) extends Module
class Scoreboard(n: Int)
{
val r = Reg(init=Bits(0, n))
var _next = r
private var _next = r
private var cur = r
var ens = Bool(false)
def apply(addr: UInt) = r(addr)
def set(en: Bool, addr: UInt): Unit = update(en, _next | mask(en, addr))
def clear(en: Bool, addr: UInt): Unit = update(en, _next & ~mask(en, addr))
def clear(en: Bool, addr: UInt): Unit = {
val m = ~mask(en, addr)
update(en, _next & m)
//cur = cur & m
}
def read(addr: UInt) = r(addr)
def readBypassed(addr: UInt) = cur(addr)
private def mask(en: Bool, addr: UInt) = Mux(en, UInt(1) << addr, UInt(0))
private def update(en: Bool, update: UInt) = {
_next = update
@ -628,10 +636,10 @@ class Control(implicit conf: RocketConfiguration) extends Module
fp_sboard.clear(io.dpath.fp_sboard_clr, io.dpath.fp_sboard_clra)
fp_sboard.clear(io.fpu.sboard_clr, io.fpu.sboard_clra)
io.fpu.dec.ren1 && fp_sboard(id_raddr1) ||
io.fpu.dec.ren2 && fp_sboard(id_raddr2) ||
io.fpu.dec.ren3 && fp_sboard(id_raddr3) ||
io.fpu.dec.wen && fp_sboard(id_waddr)
io.fpu.dec.ren1 && fp_sboard.readBypassed(id_raddr1) ||
io.fpu.dec.ren2 && fp_sboard.readBypassed(id_raddr2) ||
io.fpu.dec.ren3 && fp_sboard.readBypassed(id_raddr3) ||
io.fpu.dec.wen && fp_sboard.readBypassed(id_waddr)
} else Bool(false)
// write cause to PCR on an exception
@ -699,10 +707,12 @@ class Control(implicit conf: RocketConfiguration) extends Module
val id_wb_hazard = data_hazard_wb && (wb_dcache_miss || wb_reg_div_mul_val) ||
fp_data_hazard_wb && (wb_dcache_miss || wb_reg_fp_val)
io.dpath.mem_ll_bypass_rs1 := io.dpath.mem_ll_wb && io.dpath.mem_ll_waddr === id_raddr1
io.dpath.mem_ll_bypass_rs2 := io.dpath.mem_ll_wb && io.dpath.mem_ll_waddr === id_raddr2
val id_sboard_hazard =
(id_raddr1 != UInt(0) && id_renx1 && sboard(id_raddr1) ||
id_raddr2 != UInt(0) && id_renx2 && sboard(id_raddr2) ||
id_waddr != UInt(0) && id_wen && sboard(id_waddr))
(id_raddr1 != UInt(0) && id_renx1 && sboard.read(id_raddr1) && !io.dpath.mem_ll_bypass_rs1 ||
id_raddr2 != UInt(0) && id_renx2 && sboard.read(id_raddr2) && !io.dpath.mem_ll_bypass_rs2 ||
id_waddr != UInt(0) && id_wen && sboard.read(id_waddr))
val ctrl_stalld =
id_ex_hazard || id_mem_hazard || id_wb_hazard || id_sboard_hazard ||