1
0
rocket-chip/src/main/scala/rocket/Multiplier.scala
2017-03-09 11:29:51 -08:00

169 lines
6.0 KiB
Scala

// See LICENSE.Berkeley for license details.
// See LICENSE.SiFive for license details.
package rocket
import Chisel._
import ALU._
import util._
import Chisel.ImplicitConversions._
class MultiplierReq(dataBits: Int, tagBits: Int) extends Bundle {
val fn = Bits(width = SZ_ALU_FN)
val dw = Bits(width = SZ_DW)
val in1 = Bits(width = dataBits)
val in2 = Bits(width = dataBits)
val tag = UInt(width = tagBits)
override def cloneType = new MultiplierReq(dataBits, tagBits).asInstanceOf[this.type]
}
class MultiplierResp(dataBits: Int, tagBits: Int) extends Bundle {
val data = Bits(width = dataBits)
val tag = UInt(width = tagBits)
override def cloneType = new MultiplierResp(dataBits, tagBits).asInstanceOf[this.type]
}
class MultiplierIO(dataBits: Int, tagBits: Int) extends Bundle {
val req = Decoupled(new MultiplierReq(dataBits, tagBits)).flip
val kill = Bool(INPUT)
val resp = Decoupled(new MultiplierResp(dataBits, tagBits))
}
case class MulDivParams(
mulUnroll: Int = 1,
divUnroll: Int = 1,
mulEarlyOut: Boolean = false,
divEarlyOut: Boolean = false
)
class MulDiv(cfg: MulDivParams, width: Int, nXpr: Int = 32) extends Module {
val io = new MultiplierIO(width, log2Up(nXpr))
val w = io.req.bits.in1.getWidth
val mulw = (w + cfg.mulUnroll - 1) / cfg.mulUnroll * cfg.mulUnroll
val s_ready :: s_neg_inputs :: s_busy :: s_move_rem :: s_neg_output :: s_done :: Nil = Enum(UInt(), 6)
val state = Reg(init=s_ready)
val req = Reg(io.req.bits)
val count = Reg(UInt(width = log2Ceil((w/cfg.divUnroll + 1) max (w/cfg.mulUnroll))))
val neg_out = Reg(Bool())
val isMul = Reg(Bool())
val isHi = Reg(Bool())
val divisor = Reg(Bits(width = w+1)) // div only needs w bits
val remainder = Reg(Bits(width = 2*mulw+2)) // div only needs 2*w+1 bits
val cmdMul :: cmdHi :: lhsSigned :: rhsSigned :: Nil =
DecodeLogic(io.req.bits.fn, List(X, X, X, X), List(
FN_DIV -> List(N, N, Y, Y),
FN_REM -> List(N, Y, Y, Y),
FN_DIVU -> List(N, N, N, N),
FN_REMU -> List(N, Y, N, N),
FN_MUL -> List(Y, N, X, X),
FN_MULH -> List(Y, Y, Y, Y),
FN_MULHU -> List(Y, Y, N, N),
FN_MULHSU -> List(Y, Y, Y, N))).map(_ toBool)
require(w == 32 || w == 64)
def halfWidth(req: MultiplierReq) = Bool(w > 32) && req.dw === DW_32
def sext(x: Bits, halfW: Bool, signed: Bool) = {
val sign = signed && Mux(halfW, x(w/2-1), x(w-1))
val hi = Mux(halfW, Fill(w/2, sign), x(w-1,w/2))
(Cat(hi, x(w/2-1,0)), sign)
}
val (lhs_in, lhs_sign) = sext(io.req.bits.in1, halfWidth(io.req.bits), lhsSigned)
val (rhs_in, rhs_sign) = sext(io.req.bits.in2, halfWidth(io.req.bits), rhsSigned)
val subtractor = remainder(2*w,w) - divisor
val negated_remainder = -remainder(w-1,0)
when (state === s_neg_inputs) {
when (remainder(w-1) || isMul) {
remainder := negated_remainder
}
when (divisor(w-1) || isMul) {
divisor := subtractor
}
state := s_busy
}
when (state === s_neg_output) {
remainder := negated_remainder
state := s_done
}
when (state === s_move_rem) {
remainder := remainder(2*w, w+1)
state := Mux(neg_out, s_neg_output, s_done)
}
when (state === s_busy && isMul) {
val mulReg = Cat(remainder(2*mulw+1,w+1),remainder(w-1,0))
val mplier = mulReg(mulw-1,0)
val accum = mulReg(2*mulw,mulw).asSInt
val mpcand = divisor.asSInt
val prod = mplier(cfg.mulUnroll-1, 0) * mpcand + accum
val nextMulReg = Cat(prod, mplier(mulw-1, cfg.mulUnroll))
val eOutMask = (SInt(BigInt(-1) << mulw) >> (count * cfg.mulUnroll)(log2Up(mulw)-1,0))(mulw-1,0)
val eOut = Bool(cfg.mulEarlyOut) && count =/= mulw/cfg.mulUnroll-1 && count =/= 0 &&
!isHi && (mplier & ~eOutMask) === UInt(0)
val eOutRes = (mulReg >> (mulw - count * cfg.mulUnroll)(log2Up(mulw)-1,0))
val nextMulReg1 = Cat(nextMulReg(2*mulw,mulw), Mux(eOut, eOutRes, nextMulReg)(mulw-1,0))
remainder := Cat(nextMulReg1 >> w, Bool(false), nextMulReg1(w-1,0))
count := count + 1
when (eOut || count === mulw/cfg.mulUnroll-1) {
state := Mux(isHi, s_move_rem, s_done)
}
}
when (state === s_busy && !isMul) {
val unrolls = ((0 until cfg.divUnroll) scanLeft remainder) { case (rem, i) =>
// the special case for iteration 0 is to save HW, not for correctness
val difference = if (i == 0) subtractor else rem(2*w,w) - divisor(w-1,0)
val less = difference(w)
Cat(Mux(less, rem(2*w-1,w), difference(w-1,0)), rem(w-1,0), !less)
} tail
remainder := unrolls.last
when (count === w/cfg.divUnroll) {
state := Mux(isHi, s_move_rem, Mux(neg_out, s_neg_output, s_done))
if (w % cfg.divUnroll < cfg.divUnroll - 1)
remainder := unrolls(w % cfg.divUnroll)
}
count := count + 1
val divby0 = count === 0 && !subtractor(w)
if (cfg.divEarlyOut) {
val divisorMSB = Log2(divisor(w-1,0), w)
val dividendMSB = Log2(remainder(w-1,0), w)
val eOutPos = UInt(w-1) + divisorMSB - dividendMSB
val eOutZero = divisorMSB > dividendMSB
val eOut = count === 0 && !divby0 && (eOutPos >= cfg.divUnroll || eOutZero)
when (eOut) {
val inc = Mux(eOutZero, UInt(w-1), eOutPos) >> log2Floor(cfg.divUnroll)
val shift = inc << log2Floor(cfg.divUnroll)
remainder := remainder(w-1,0) << shift
count := inc
}
}
when (divby0 && !isHi) { neg_out := false }
}
when (io.resp.fire() || io.kill) {
state := s_ready
}
when (io.req.fire()) {
state := Mux(lhs_sign || rhs_sign && !cmdMul, s_neg_inputs, s_busy)
isMul := cmdMul
isHi := cmdHi
count := 0
neg_out := !cmdMul && Mux(cmdHi, lhs_sign, lhs_sign =/= rhs_sign)
divisor := Cat(rhs_sign, rhs_in)
remainder := lhs_in
req := io.req.bits
}
io.resp.bits <> req
io.resp.bits.data := Mux(halfWidth(req), Cat(Fill(w/2, remainder(w/2-1)), remainder(w/2-1,0)), remainder(w-1,0))
io.resp.valid := state === s_done
io.req.ready := state === s_ready
}