From 24f577c156f1fa0bb3f5c76319cb4827b279a8e4 Mon Sep 17 00:00:00 2001
From: "Wesley W. Terpstra" <wesley@sifive.com>
Date: Fri, 21 Apr 2017 17:12:35 -0700
Subject: [PATCH] axi4: Deinterleaver ensures R channel ID does not change till
 last

---
 .../scala/uncore/axi4/Deinterleaver.scala     | 102 ++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 src/main/scala/uncore/axi4/Deinterleaver.scala

diff --git a/src/main/scala/uncore/axi4/Deinterleaver.scala b/src/main/scala/uncore/axi4/Deinterleaver.scala
new file mode 100644
index 00000000..bc926c69
--- /dev/null
+++ b/src/main/scala/uncore/axi4/Deinterleaver.scala
@@ -0,0 +1,102 @@
+// See LICENSE.SiFive for license details.
+
+package uncore.axi4
+
+import Chisel._
+import chisel3.internal.sourceinfo.SourceInfo
+import chisel3.util.IrrevocableIO
+import config._
+import diplomacy._
+import scala.math.{min,max}
+import uncore.tilelink2.{leftOR, rightOR, UIntToOH1, OH1ToOH}
+
+class AXI4Deinterleaver(maxReadBytes: Int)(implicit p: Parameters) extends LazyModule
+{
+  require (maxReadBytes >= 1 && isPow2(maxReadBytes))
+
+  val node = AXI4AdapterNode(
+    masterFn = { mp => mp },
+    slaveFn  = { sp => sp.copy(slaves = sp.slaves.map(s => s.copy(
+      supportsRead = s.supportsRead.intersect(TransferSizes(1, maxReadBytes)),
+      interleavedId = Some(0))))
+  })
+
+  lazy val module = new LazyModuleImp(this) {
+    val io = new Bundle {
+      val in  = node.bundleIn
+      val out = node.bundleOut
+    }
+
+    ((io.in zip io.out) zip (node.edgesIn zip node.edgesOut)) foreach { case ((in, out), (edgeIn, edgeOut)) =>
+      val queues = edgeOut.master.endId
+      val beatBytes = edgeOut.slave.beatBytes
+      val beats = (maxReadBytes+beatBytes-1) / beatBytes
+
+      // This adapter leaves the control + write paths completely untouched
+      out.ar <> in.ar
+      out.aw <> in.aw
+      out.w <> in.w
+      in.b <> out.b
+
+      if (queues == 1) {
+        // Gracefully do nothing
+        in.r <> out.r
+      } else {
+        // Buffer R response
+        val count = RegInit(Vec.fill(queues) { UInt(0, width=log2Ceil(beats+1)) })
+        val qs = Seq.fill(queues) { Module(new Queue(out.r.bits, beats)) }
+
+        // Which ID is being enqueued and dequeued?
+        val locked = RegInit(Bool(false))
+        val deq_id = Reg(UInt(width=log2Ceil(queues)))
+        val enq_id = out.r.bits.id
+        val deq_OH = UIntToOH(deq_id, queues)
+        val enq_OH = UIntToOH(enq_id, queues)
+
+        // Track the number of completely received bursts per FIFO id
+        val next_count = Wire(count)
+        ((count zip next_count) zip (enq_OH.toBools zip deq_OH.toBools)) foreach { case ((p, n), (i, d)) =>
+          val inc = i && out.r.fire() && out.r.bits.last
+          val dec = d && in.r.fire() && in.r.bits.last
+          n := p + inc.asUInt - dec.asUInt
+          // Bounds checking
+          assert (!dec || p =/= UInt(0))
+          assert (!inc || p =/= UInt(beats))
+        }
+        count := next_count
+
+        // Select which Q will we start sending next cycle
+        val pending = Cat(next_count.map(_ =/= UInt(0)).reverse)
+        val winner  = pending & ~(leftOR(pending) << 1)
+        when (!locked || (in.r.fire() && in.r.bits.last)) {
+          locked := pending.orR
+          deq_id := OHToUInt(winner)
+        }
+
+        // Transmit the selected burst to inner
+        in.r.valid := locked
+        in.r.bits  := Vec(qs.map(_.io.deq.bits))(deq_id)
+        (deq_OH.toBools zip qs) foreach { case (s, q) =>
+          q.io.deq.ready := s && in.r.fire()
+        }
+
+        // Feed response into matching Q
+        out.r.ready := Vec(qs.map(_.io.enq.ready))(enq_id)
+        (enq_OH.toBools zip qs) foreach { case (s, q) =>
+          q.io.enq.valid := s && out.r.valid
+          q.io.enq.bits := out.r.bits
+        }
+      }
+    }
+  }
+}
+
+object AXI4Deinterleaver
+{
+  // applied to the AXI4 source node; y.node := AXI4Deinterleaver()(x.node)
+  def apply(maxReadBytes: Int)(x: AXI4OutwardNode)(implicit p: Parameters, sourceInfo: SourceInfo): AXI4OutwardNode = {
+    val deinterleaver = LazyModule(new AXI4Deinterleaver(maxReadBytes))
+    deinterleaver.node := x
+    deinterleaver.node
+  }
+}