have multiple outstanding requests in CacheFillTest

groundtest/src/main/scala/cachetest.scala

@@ -11,30 +11,33 @@ class CacheFillTest(implicit p: Parameters) extends GroundTest()(p)
   val s_start :: s_prefetch :: s_retrieve :: s_finished :: Nil = Enum(Bits(), 4)
   val state = Reg(init = s_start)
 
-  val inflight = Reg(init = Bool(false))
   val active = state === s_prefetch || state === s_retrieve
 
+  val xact_pending = Reg(init = UInt(0, tlMaxClientXacts))
+  val xact_id = PriorityEncoder(~xact_pending)
+
   disablePorts(mem = false)
 
-  val (xact_id, xact_flip) = Counter(io.mem.acquire.fire(), tlMaxClientXacts)
   val (req_block, round_done) = Counter(io.mem.acquire.fire(), nblocks)
 
-  io.mem.acquire.valid := active && !inflight
+  io.mem.acquire.valid := active && !xact_pending.andR
   io.mem.acquire.bits := Mux(state === s_prefetch,
     GetPrefetch(xact_id, UInt(memStartBlock) + req_block),
     GetBlock(xact_id, UInt(memStartBlock) + req_block))
-  io.mem.grant.ready := inflight
+  io.mem.grant.ready := xact_pending.orR
 
-  when (io.mem.acquire.fire()) {
-    inflight := Bool(true)
+  def add_pending(acq: DecoupledIO[Acquire]): UInt =
+    Mux(acq.fire(), UIntToOH(acq.bits.client_xact_id), UInt(0))
+
+  def remove_pending(gnt: DecoupledIO[Grant]): UInt = {
+    val last_grant = !gnt.bits.hasMultibeatData() ||
+                      gnt.bits.addr_beat === UInt(tlDataBeats - 1)
+    ~Mux(gnt.fire() && last_grant, UIntToOH(gnt.bits.client_xact_id), UInt(0))
   }
 
-  val last_grant = !io.mem.grant.bits.hasMultibeatData() ||
-                    io.mem.grant.bits.addr_beat === UInt(tlDataBeats - 1)
-
-  when (io.mem.grant.fire() && last_grant) {
-    inflight := Bool(false)
-  }
+  xact_pending := (xact_pending |
+    add_pending(io.mem.acquire)) &
+    remove_pending(io.mem.grant)
 
   when (state === s_start) { state := s_prefetch }
   when (state === s_prefetch && round_done) { state := s_retrieve }