bs/TagEngine.bs

@@ -7,27 +7,55 @@ import Util
 
 #define UIntLog2N(n) (UInt (TLog n))
 
+data Tag numTags
+    = Next UIntLog2N(numTags)
+    | Freed
+    | Tail
+    deriving (Bits, Eq, FShow)
+
+data TagPtr numTags
+    = SomeTagPtr UIntLog2N(numTags)
+    | None
+    deriving (Bits, Eq, FShow)
+
 interface (TagEngine :: # -> *) numTags =
     requestTag :: ActionValue UIntLog2N(numTags)
     retireTag  :: UIntLog2N(numTags) -> Action
 
--- The tag engine returns a tag that is unique for the duration of
--- the lifetime of the tag. Useful when you need to tag transactions
--- on a bus for example.
--- This implementation is stack based.
+instance FShow (Reg (Tag numTags)) where
+    fshow value = fshow (readReg value)
+
+initTagNext :: Integer -> Module(Reg (Tag numTags))
+initTagNext i = do
+    t :: Reg (Tag numTags)
+    t <- mkReg (Next (fromInteger i))
+    return t
+
+initTagTail :: Module(Reg (Tag numTags))
+initTagTail = do
+    t :: Reg (Tag numTags)
+    t <- mkReg Tail
+    return t
+
+initTagVec :: Module(Vector numTags (Reg (Tag numTags)))
+initTagVec =
+    let
+        lastIdx :: Integer = (fromInteger |> valueOf numTags) - 1
+        initByIdx currIdx =
+            if (currIdx < lastIdx)
+                then initTagNext (currIdx + 1)
+                else initTagTail
+    in
+        mapM initByIdx genVector
+
 mkTagEngine :: Module (TagEngine numTags)
 mkTagEngine =
     do
-        let reifiedNumTags = fromInteger |> valueOf numTags
+        tagVec :: Vector numTags (Reg (Tag numTags))
+        tagVec <- initTagVec
 
-        freeStackVec :: Vector numTags (Reg UIntLog2N(numTags))
-        freeStackVec <- mapM (\i -> mkReg |> fromInteger i) genVector
-
-        inUseVec :: Vector numTags (Reg Bool)
-        inUseVec <- replicateM |> mkReg False
-
-        stackPtr :: (Reg (Maybe(UIntLog2N(numTags))))
-        stackPtr <- mkReg |> Just |> reifiedNumTags - 1
+        head :: Reg(TagPtr(numTags)) <- mkReg(SomeTagPtr(0))
+        tail :: Reg(TagPtr(numTags)) <- mkReg(SomeTagPtr(lastIdx))
 
         debugOnce <- mkReg True
 
@@ -35,37 +63,35 @@ mkTagEngine =
             rules
                 "display": when (debugOnce == True) ==>
                     do
-                        $display "freeStackVec : " (fshow |> readVReg freeStackVec)
-                        $display "inUseVec : " (fshow |> readVReg inUseVec)
-                        $display "stackPtr : " (fshow stackPtr)
+                        $display (fshow tagVec)
                         debugOnce := False
 
         counter <- mkReg(0 :: UIntLog2N(numTags))
         return $
           interface TagEngine
-
             requestTag :: ActionValue UIntLog2N(numTags)
             requestTag =
                 do
-                    stackPtr := 
-                        if sampledStackPtr == 0
-                            then Nothing
-                            else Just |> sampledStackPtr - 1
-                    (select inUseVec sampledStackPtr) := True
-                    return |> readReg (select freeStackVec sampledStackPtr)
+                    let currHeadPtr :: UIntLog2N(numTags) =
+                            case head of
+                                SomeTagPtr ptr -> ptr
+                                -- we technically will never hit this arm
+                                -- due to when guard `SomeTagPtr ptr <- head`
+                                None -> 0
+                    let currHead :: (Reg (Tag numTags)) = (select tagVec currHeadPtr)
+                    let nextHeadPtr :: UIntLog2N(numTags) =
+                            case currHead of
+                                Next ptr -> ptr
+                                -- TODO : handle tail correctly
+                                Tail -> 0
+                    currHead := Freed
+                    head := SomeTagPtr(nextHeadPtr)
+                    return nextHeadPtr
                 when
-                    Just sampledStackPtr <- stackPtr
-
+                    SomeTagPtr ptr <- head
             retireTag :: UIntLog2N(numTags) -> Action
-            retireTag tag = 
-                do
-                    let nextStackPtrUint = 
-                            case stackPtr of
-                                Nothing -> 0
-                                Just n -> n + 1
-                    (select inUseVec tag) := False
-                    (select freeStackVec nextStackPtrUint) := tag
-                    stackPtr := Just nextStackPtrUint
-                -- when
-                --     tag < (reifiedNumTags - 1),
-                --     readReg (select inUseVec tag)
+            retireTag tag = do
+                -- placeholder
+                counter := 0
+    where
+        lastIdx :: UIntLog2N(numTags) = (fromInteger |> valueOf numTags) - 1

bs/Util.bs

@@ -1,7 +1,5 @@
 package Util((|>), simulate_for) where
 
-infixr 0 |>
-
 (|>) :: (a -> b) -> a -> b
 f |> x = f x;