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rocket-chip/src/main/scala/util/Arbiters.scala

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Scala
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// See LICENSE.Berkeley for license details.
package freechips.rocketchip.util
import Chisel._
import freechips.rocketchip.config.Parameters
/** A generalized locking RR arbiter that addresses the limitations of the
* version in the Chisel standard library */
abstract class HellaLockingArbiter[T <: Data](typ: T, arbN: Int, rr: Boolean = false)
extends Module {
val io = new Bundle {
val in = Vec(arbN, Decoupled(typ.cloneType)).flip
val out = Decoupled(typ.cloneType)
}
def rotateLeft[T <: Data](norm: Vec[T], rot: UInt): Vec[T] = {
val n = norm.size
Vec.tabulate(n) { i =>
Mux(rot < UInt(n - i), norm(UInt(i) + rot), norm(rot - UInt(n - i)))
}
}
val lockIdx = Reg(init = UInt(0, log2Up(arbN)))
val locked = Reg(init = Bool(false))
val choice = if (rr) {
PriorityMux(
rotateLeft(Vec(io.in.map(_.valid)), lockIdx + UInt(1)),
rotateLeft(Vec((0 until arbN).map(UInt(_))), lockIdx + UInt(1)))
} else {
PriorityEncoder(io.in.map(_.valid))
}
val chosen = Mux(locked, lockIdx, choice)
for (i <- 0 until arbN) {
io.in(i).ready := io.out.ready && chosen === UInt(i)
}
io.out.valid := io.in(chosen).valid
io.out.bits := io.in(chosen).bits
}
/** This locking arbiter determines when it is safe to unlock
* by peeking at the data */
class HellaPeekingArbiter[T <: Data](
typ: T, arbN: Int,
canUnlock: T => Bool,
needsLock: Option[T => Bool] = None,
rr: Boolean = false)
extends HellaLockingArbiter(typ, arbN, rr) {
def realNeedsLock(data: T): Bool =
needsLock.map(_(data)).getOrElse(Bool(true))
when (io.out.fire()) {
when (!locked && realNeedsLock(io.out.bits)) {
lockIdx := choice
locked := Bool(true)
}
// the unlock statement takes precedent
when (canUnlock(io.out.bits)) {
locked := Bool(false)
}
}
}
/** This arbiter determines when it is safe to unlock by counting transactions */
class HellaCountingArbiter[T <: Data](
typ: T, arbN: Int, count: Int,
val needsLock: Option[T => Bool] = None,
rr: Boolean = false)
extends HellaLockingArbiter(typ, arbN, rr) {
def realNeedsLock(data: T): Bool =
needsLock.map(_(data)).getOrElse(Bool(true))
// if count is 1, you should use a non-locking arbiter
require(count > 1, "CountingArbiter cannot have count <= 1")
val lock_ctr = Counter(count)
when (io.out.fire()) {
when (!locked && realNeedsLock(io.out.bits)) {
lockIdx := choice
locked := Bool(true)
lock_ctr.inc()
}
when (locked) {
when (lock_ctr.inc()) { locked := Bool(false) }
}
}
}
/** This arbiter preserves the order of responses */
class InOrderArbiter[T <: Data, U <: Data](reqTyp: T, respTyp: U, n: Int)
(implicit p: Parameters) extends Module {
val io = new Bundle {
val in_req = Vec(n, Decoupled(reqTyp)).flip
val in_resp = Vec(n, Decoupled(respTyp))
val out_req = Decoupled(reqTyp)
val out_resp = Decoupled(respTyp).flip
}
if (n > 1) {
val route_q = Module(new Queue(UInt(width = log2Up(n)), 2))
val req_arb = Module(new RRArbiter(reqTyp, n))
req_arb.io.in <> io.in_req
val req_helper = DecoupledHelper(
req_arb.io.out.valid,
route_q.io.enq.ready,
io.out_req.ready)
io.out_req.bits := req_arb.io.out.bits
io.out_req.valid := req_helper.fire(io.out_req.ready)
route_q.io.enq.bits := req_arb.io.chosen
route_q.io.enq.valid := req_helper.fire(route_q.io.enq.ready)
req_arb.io.out.ready := req_helper.fire(req_arb.io.out.valid)
val resp_sel = route_q.io.deq.bits
val resp_ready = io.in_resp(resp_sel).ready
val resp_helper = DecoupledHelper(
resp_ready,
route_q.io.deq.valid,
io.out_resp.valid)
val resp_valid = resp_helper.fire(resp_ready)
for (i <- 0 until n) {
io.in_resp(i).bits := io.out_resp.bits
io.in_resp(i).valid := resp_valid && resp_sel === UInt(i)
}
route_q.io.deq.ready := resp_helper.fire(route_q.io.deq.valid)
io.out_resp.ready := resp_helper.fire(io.out_resp.valid)
} else {
io.out_req <> io.in_req.head
io.in_resp.head <> io.out_resp
}
}