Preliminary cleaning before repairing TagEngine

* clean up state machine in Top
 * `requestTag` method now emits Maybe type
 * put more thought into comments around asynchronous bus

bs/TagEngine.bs

@@ -9,7 +9,7 @@ import Util
 #define UIntLog2N(n) (UInt (TLog n))
 
 interface (TagEngine :: # -> *) numTags =
-    requestTag :: ActionValue UIntLog2N(numTags)
+    requestTag :: ActionValue (Maybe UIntLog2N(numTags))
     retireTag  :: UIntLog2N(numTags) -> ActionValue BasicResult
 
 -- The tag engine returns a tag that is unique for the duration of
@@ -19,6 +19,7 @@ interface (TagEngine :: # -> *) numTags =
 mkTagEngine :: Module (TagEngine numTags)
 mkTagEngine =
     do
+
         let reifiedNumTags = fromInteger |> valueOf numTags
 
         freeStackVec :: Vector numTags (Reg UIntLog2N(numTags))
@@ -30,8 +31,20 @@ mkTagEngine =
         stackPtr :: (Reg (Maybe(UIntLog2N(numTags))))
         stackPtr <- mkReg |> Just |> reifiedNumTags - 1
 
+        methodRequestTagCalled :: PulseWire
+        methodRequestTagCalled <- mkPulseWire
+
+
+        methodRetireTagCalled :: PulseWire
+        methodRetireTagCalled <- mkPulseWire
+
+        tagResponse :: RWire UIntLog2N(numTags)
+        tagResponse <- mkRWireSBR
+
         debugOnce <- mkReg True
 
+        tt :: Reg Bool <- mkReg False
+
         addRules $
             rules
                 "display": when (debugOnce == True) ==>
@@ -40,20 +53,30 @@ mkTagEngine =
                         $display "inUseVec : " (fshow |> readVReg inUseVec)
                         $display "stackPtr : " (fshow stackPtr)
                         debugOnce := False
+            <+>
+            rules
+                when (methodRequestTagCalled && methodRetireTagCalled) ==>
+                    do
+                        $display "ho ho ho"
+                        -- let 
+                        --     nextStackPtr = 
+                        --         case of (methodRequestTagCalled, methodRetireTagCalled) of
+                        --             (True, True) -> 
 
         counter <- mkReg(0 :: UIntLog2N(numTags))
         return $
           interface TagEngine
 
-            requestTag :: ActionValue UIntLog2N(numTags)
+            requestTag :: ActionValue (Maybe UIntLog2N(numTags))
             requestTag =
                 do
+                    methodRequestTagCalled.send
                     stackPtr :=
                         if sampledStackPtr == 0
                             then Nothing
                             else Just |> sampledStackPtr - 1
                     (select inUseVec sampledStackPtr) := True
-                    return |> readReg (select freeStackVec sampledStackPtr)
+                    return |> Just |> readReg (select freeStackVec sampledStackPtr)
                 when
                     Just sampledStackPtr <- stackPtr
 
@@ -64,6 +87,7 @@ mkTagEngine =
             retireTag :: UIntLog2N(numTags) -> ActionValue BasicResult
             retireTag tag =
                 do
+                    methodRetireTagCalled.send
                     let
                         tagValid = tag < reifiedNumTags
                         tagInUse = readReg (select inUseVec tag)