64 lines
2.0 KiB
Scala
64 lines
2.0 KiB
Scala
// See LICENSE.SiFive for license details.
|
|
|
|
package freechips.rocketchip.util
|
|
|
|
import Chisel._
|
|
|
|
/** Implements the same interface as chisel3.util.Queue, but uses a shift
|
|
* register internally. It is less energy efficient whenever the queue
|
|
* has more than one entry populated, but is faster on the dequeue side.
|
|
* It is efficient for usually-empty flow-through queues. */
|
|
class ShiftQueue[T <: Data](gen: T,
|
|
val entries: Int,
|
|
pipe: Boolean = false,
|
|
flow: Boolean = false)
|
|
extends Module {
|
|
val io = IO(new QueueIO(gen, entries) {
|
|
val mask = UInt(OUTPUT, entries)
|
|
})
|
|
|
|
private val valid = RegInit(Vec.fill(entries) { Bool(false) })
|
|
private val elts = Reg(Vec(entries, gen))
|
|
|
|
for (i <- 0 until entries) {
|
|
def paddedValid(i: Int) = if (i == -1) true.B else if (i == entries) false.B else valid(i)
|
|
|
|
val wdata = if (i == entries-1) io.enq.bits else Mux(valid(i+1), elts(i+1), io.enq.bits)
|
|
val wen =
|
|
Mux(io.deq.ready,
|
|
paddedValid(i+1) || io.enq.fire() && (Bool(i == 0 && !flow) || valid(i)),
|
|
io.enq.fire() && paddedValid(i-1) && !valid(i))
|
|
when (wen) { elts(i) := wdata }
|
|
|
|
valid(i) :=
|
|
Mux(io.deq.ready,
|
|
paddedValid(i+1) || io.enq.fire() && (Bool(i == 0 && !flow) || valid(i)),
|
|
io.enq.fire() && paddedValid(i-1) || valid(i))
|
|
}
|
|
|
|
io.enq.ready := !valid(entries-1)
|
|
io.deq.valid := valid(0)
|
|
io.deq.bits := elts.head
|
|
|
|
if (flow) {
|
|
when (io.enq.valid) { io.deq.valid := true.B }
|
|
when (!valid(0)) { io.deq.bits := io.enq.bits }
|
|
}
|
|
|
|
if (pipe) {
|
|
when (io.deq.ready) { io.enq.ready := true.B }
|
|
}
|
|
|
|
io.mask := valid.asUInt
|
|
io.count := PopCount(io.mask)
|
|
}
|
|
|
|
object ShiftQueue
|
|
{
|
|
def apply[T <: Data](enq: DecoupledIO[T], entries: Int = 2, pipe: Boolean = false, flow: Boolean = false): DecoupledIO[T] = {
|
|
val q = Module(new ShiftQueue(enq.bits.cloneType, entries, pipe, flow))
|
|
q.io.enq <> enq
|
|
q.io.deq
|
|
}
|
|
}
|