Add read-under-write checks for memory emission

* Stop ignoring read-under-write (RUW) parameter
* Add conservative check: blackbox only when RUW is "undefined"
* VerilogMemDelays now throws InternalError for read-first memories
* Previously, read-first mems were incorrectly implemented as write-first

2 files changed, 6 insertions, 3 deletions

diff --git a/src/main/scala/firrtl/passes/memlib/ToMemIR.scala b/src/main/scala/firrtl/passes/memlib/ToMemIR.scala
index a9f4b330..554a3572 100644
--- a/src/main/scala/firrtl/passes/memlib/ToMemIR.scala
+++ b/src/main/scala/firrtl/passes/memlib/ToMemIR.scala
@@ -11,14 +11,15 @@ import firrtl.ir._
   *   - read latency and write latency of one
   *   - only one readwrite port or write port
   *   - zero or one read port
+  *   - undefined read-under-write behavior
   */
 object ToMemIR extends Pass {
   /** Only annotate memories that are candidates for memory macro replacements
-    * i.e. rw, w + r (read, write 1 cycle delay)
+    * i.e. rw, w + r (read, write 1 cycle delay) and read-under-write "undefined."
     */
+  import ReadUnderWrite._
   def updateStmts(s: Statement): Statement = s match {
-    case m: DefMemory if m.readLatency == 1 && m.writeLatency == 1 &&
-        (m.writers.length + m.readwriters.length) == 1 && m.readers.length <= 1 =>
+    case m @ DefMemory(_,_,_,_,1,1,r,w,rw,Undefined) if (w.length + rw.length) == 1 && r.length <= 1 =>
       DefAnnotatedMemory(m)
     case sx => sx map updateStmts
   }
diff --git a/src/main/scala/firrtl/passes/memlib/VerilogMemDelays.scala b/src/main/scala/firrtl/passes/memlib/VerilogMemDelays.scala
index 335e1121..89d4e6f0 100644
--- a/src/main/scala/firrtl/passes/memlib/VerilogMemDelays.scala
+++ b/src/main/scala/firrtl/passes/memlib/VerilogMemDelays.scala
@@ -33,6 +33,8 @@ object VerilogMemDelays extends Pass {
       repl: Netlist,
       stmts: mutable.ArrayBuffer[Statement])
       (s: Statement): Statement = s.map(memDelayStmt(netlist, namespace, repl, stmts)) match {
+    case sx: DefMemory if (sx.readUnderWrite == ir.ReadUnderWrite.Old) =>
+      throwInternalError("VerilogMemDelays does not support read-first (readunderwrite == 'old') memories")
     case sx: DefMemory =>
       val ports = (sx.readers ++ sx.writers).toSet
       def newPortName(rw: String, p: String) = (for {