// See LICENSE for license details.

package uncore.agents

import Chisel._
import uncore.coherence._
import uncore.tilelink._
import uncore.constants._
import uncore.devices._
import cde.{Parameters, Field, Config}

/** The ManagerToClientStateless Bridge does not maintain any state for the messages
  *  which pass through it. It simply passes the messages back and forth without any
  *  tracking or translation. 
  *  
  * This can reduce area and timing in very constrained situations:
  *   - The Manager and Client implement the same coherence protocol
  *   - There are no probe or finish messages.
  *   - The outer transaction ID is large enough to handle all possible inner
  *     transaction IDs, such that no remapping state must be maintained.
  *
  */

class ManagerToClientStatelessBridge(implicit p: Parameters) extends HierarchicalCoherenceAgent()(p) {

  val icid = io.inner.acquire.bits.client_id.getWidth
  val ixid = io.inner.acquire.bits.client_xact_id.getWidth
  val oxid = io.outer.acquire.bits.client_xact_id.getWidth

  // Stateless Bridge is only usable in certain constrained situations.
  // Sanity check its usage here.
  // Additional requirements are that the inner and outer Coherence policies
  // are the same (e.g. MEI != MESI), and that NTiles == 1,
  // but this is not checked here.
  require (p(NTiles) == 1)

  require(icid + ixid <= oxid)
  require(icid == io.inner.release.bits.client_id.getWidth)
  require(ixid == io.inner.release.bits.client_xact_id.getWidth)
  require(oxid == io.outer.release.bits.client_xact_id.getWidth)

  io.outer.acquire.valid := io.inner.acquire.valid
  io.inner.acquire.ready := io.outer.acquire.ready
  io.outer.acquire.bits := io.inner.acquire.bits
  io.outer.acquire.bits.client_xact_id := Cat(io.inner.acquire.bits.client_id, io.inner.acquire.bits.client_xact_id)

  io.outer.release.valid := io.inner.release.valid
  io.inner.release.ready := io.outer.release.ready
  io.outer.release.bits := io.inner.release.bits
  io.outer.release.bits.client_xact_id := Cat(io.inner.release.bits.client_id, io.inner.release.bits.client_xact_id)

  io.inner.grant.valid := io.outer.grant.valid
  io.outer.grant.ready := io.inner.grant.ready
  io.inner.grant.bits := io.outer.grant.bits
  io.inner.grant.bits.client_xact_id := io.outer.grant.bits.client_xact_id(ixid-1, 0)
  io.inner.grant.bits.client_id := io.outer.grant.bits.client_xact_id(icid+ixid-1, ixid)

  io.inner.probe.valid := Bool(false)
  io.inner.finish.ready := Bool(true)
}