riscv/rocket-chip
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Make BTB more complexity-effective

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BTB entries reference a small number of unique pages, so we separate the
storage of pages from indices.  This makes much larger BTBs feasible.  It's
easy to exacerbate cycle time this way, so one-hot encoding is used as needed.
This commit is contained in:
Andrew Waterman
2014-03-25 05:22:04 -07:00
parent 804b09c8c5
commit e3b12e0b85
4 changed files with 142 additions and 79 deletions
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31
rocket/src/main/scala/util.scala
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@ -11,12 +11,15 @@ object Util {
implicit def intToUInt(x: Int): UInt = UInt(x)
implicit def booleanToBool(x: Boolean): Bits = Bool(x)
implicit def intSeqToUIntSeq(x: Iterable[Int]): Iterable[UInt] = x.map(UInt(_))
implicit def seqToVec[T <: Data](x: Iterable[T]): Vec[T] = Vec(x)
implicit def wcToUInt(c: WideCounter): UInt = c.value
implicit def booleanToInt(x: Boolean): Int = if (x) 1 else 0
implicit def intToBooleanToInt(x: Int): BooleanToInt = new BooleanToInt(x)
}
import Util._
object AVec
{
def apply[T <: Data](elts: Seq[T]): Vec[T] = Vec(elts)
@ -141,18 +144,20 @@ case class WideCounter(width: Int, inc: UInt = UInt(1))
object Random
{
def apply(mod: Int, inc: Bool = Bool(true)): UInt = {
if (isPow2(mod)) {
require(mod <= 65536)
LFSR16(inc)(log2Up(mod)-1,0).toUInt
} else {
val max = 1 << log2Up(mod*8)
val rand_pow2 = apply(max, inc)
var res = UInt(mod-1)
for (i <- mod-1 to 1 by -1)
res = Mux(rand_pow2 < UInt(i*max/mod), UInt(i-1), res)
res
}
def apply(mod: Int, random: UInt): UInt = {
if (isPow2(mod)) random(log2Up(mod)-1,0)
else PriorityEncoder(partition(apply(1 << log2Up(mod*8), random), mod))
}
def apply(mod: Int): UInt = apply(mod, randomizer)
def oneHot(mod: Int, random: UInt): UInt = {
if (isPow2(mod)) UIntToOH(random(log2Up(mod)-1,0))
else PriorityEncoderOH(partition(apply(1 << log2Up(mod*8), random), mod)).toBits
}
def oneHot(mod: Int): UInt = oneHot(mod, randomizer)
private def randomizer = LFSR16()
private def round(x: Double): Int =
if (x.toInt.toDouble == x) x.toInt else (x.toInt + 1) & -2
private def partition(value: UInt, slices: Int) =
Vec.tabulate(slices)(i => value < round((i << value.getWidth).toDouble / slices))
}