Simply/optimize downConverter

src/Protocols/PacketStream/Converters.hs

@@ -128,109 +128,65 @@ upConverterC ::
   Circuit (PacketStream dom 1 ()) (PacketStream dom dataWidth ())
 upConverterC = forceResetSanity |> fromSignals upConverter
 
-data DownConverterState (dataWidth :: Nat) = DownConverterState
-  { _dcBuf :: Vec dataWidth (BitVector 8)
-  -- ^ Buffer
-  , _dcSize :: Index (dataWidth + 1)
-  -- ^ Number of valid bytes in _dcBuf
-  , _dcLastVec :: Bool
-  -- ^ True if last byte of _dcBuf was marked as last byte by incoming stream
-  , _dcAborted :: Bool
-  -- ^ If True, outgoing bytes should be marked as aborted until _dcBuf is replaced
-  }
-  deriving (Generic, NFDataX)
-
--- | Computes new state from incoming data
-fromPacketStreamM2S ::
-  forall (dataWidth :: Nat).
-  (KnownNat dataWidth) =>
-  PacketStreamM2S dataWidth () ->
-  DownConverterState dataWidth
-fromPacketStreamM2S (PacketStreamM2S vs lastIdx _ aborted) =
+data DownConverterState (dataWidth :: Nat) =
   DownConverterState
-    { _dcBuf = vs
-    , _dcSize = maybe (natToNum @dataWidth) (succ . resize) lastIdx -- lastIdx points to the last valid byte, so the buffer size is one more
-    , _dcLastVec = isJust lastIdx
-    , _dcAborted = aborted
+    { _dcBuf :: Vec dataWidth (BitVector 8)
+      -- ^ Buffer
+    , _dcSize :: Index (dataWidth + 1)
+      -- ^ Number of valid bytes in _dcBuf
     }
-
--- | Computes output of down converter
-toMaybePacketStreamM2S ::
-  forall (dataWidth :: Nat).
-  (1 <= dataWidth) =>
-  (KnownNat dataWidth) =>
-  DownConverterState dataWidth ->
-  Maybe (PacketStreamM2S 1 ())
-toMaybePacketStreamM2S DownConverterState{..} = toMaybe (_dcSize > 0) out
- where
-  out =
-    PacketStreamM2S
-      { _data = leToPlusKN @1 @dataWidth head _dcBuf :> Nil
-      , _last = toMaybe (_dcSize == 1 && _dcLastVec) 0
-      , _meta = ()
-      , _abort = _dcAborted
-      }
-
-downConverter ::
-  forall (dataWidth :: Nat) (dom :: Domain).
-  (HiddenClockResetEnable dom) =>
-  (1 <= dataWidth) =>
-  (KnownNat dataWidth) =>
-  -- | Input packet stream from the source and backpressure from the sink
-  ( Signal dom (Maybe (PacketStreamM2S dataWidth ()))
-  , Signal dom PacketStreamS2M
-  ) ->
-  -- | Output backpressure to the source
-  --   Output packet stream to the sink
-  ( Signal dom PacketStreamS2M
-  , Signal dom (Maybe (PacketStreamM2S 1 ()))
-  )
-downConverter = mealyB go s0
- where
-  s0 =
-    DownConverterState
+    deriving (Generic, NFDataX)
+
+downConverterT
+  :: forall (dataWidth :: Nat).
+     1 <= dataWidth
+  => KnownNat dataWidth
+  => DownConverterState dataWidth
+  -> (Maybe (PacketStreamM2S dataWidth ()), PacketStreamS2M)
+  -> (DownConverterState dataWidth, (PacketStreamS2M, Maybe (PacketStreamM2S 1 ())))
+downConverterT st (Nothing, _) = (st, (PacketStreamS2M True, Nothing))
+downConverterT st@DownConverterState{..} (Just inPkt, bwdIn) = (nextSt, (PacketStreamS2M outReady, Just outPkt))
+  where
+    -- If _dcSize == 0, then we have received a new transfer and should use
+    -- its corresponding _data. Else, we should use our stored buffer.
+    (nextSize, buf) = case (_dcSize == 0, _last inPkt) of
+      (True, Nothing) -> (natToNum @(dataWidth - 1), _data inPkt)
+      (True, Just i)  -> (resize i, _data inPkt)
+      (False, _)      -> (pred _dcSize, _dcBuf)
+
+    outPkt =
+      PacketStreamM2S
+        { _data = singleton (leToPlus @1 @dataWidth head buf)
+        , _last = outLast
+        , _meta = ()
+        , _abort = _abort inPkt
+        }
+
+    (outReady, outLast)
+      | nextSize == 0 = (_ready bwdIn, 0 <$ _last inPkt)
+      | otherwise     = (False, Nothing)
+
+    -- Keep the buffer in the state and rotate it once the byte is acknowledged to avoid
+    -- dynamic indexing.
+    nextSt
+      | _ready bwdIn = DownConverterState (rotateLeftS buf d1) nextSize
+      | otherwise    = st
+
+-- | Converts packet streams of arbitrary data widths to packet streams of single bytes.
+-- If @_abort@ is asserted on an input transfer, it will be asserted on all
+-- corresponding output transfers as well.
+--
+-- Has one clock cycle of latency, but optimal throughput, i.e. a packet of n bytes is
+-- sent out in n clock cycles, even if `_last` is set.
+downConverterC
+  :: forall (dataWidth :: Nat) (dom :: Domain).
+  HiddenClockResetEnable dom
+  => 1 <= dataWidth
+  => KnownNat dataWidth
+  => Circuit (PacketStream dom dataWidth ()) (PacketStream dom 1 ())
+downConverterC = forceResetSanity |> fromSignals (mealyB downConverterT s0)
+  where
+    s0 = DownConverterState
       { _dcBuf = errorX "downConverter: undefined initial value"
       , _dcSize = 0
-      , _dcLastVec = False
-      , _dcAborted = False
       }
-  go ::
-    DownConverterState dataWidth ->
-    (Maybe (PacketStreamM2S dataWidth ()), PacketStreamS2M) ->
-    (DownConverterState dataWidth, (PacketStreamS2M, Maybe (PacketStreamM2S 1 ())))
-  go st@(DownConverterState{..}) (fwdIn, PacketStreamS2M inReady) = (st', (bwdOut, fwdOut))
-   where
-    (_dcSize', _dcBuf') =
-      if _dcSize > 0 && inReady
-        then (_dcSize - 1, _dcBuf <<+ 0)
-        else (_dcSize, _dcBuf)
-
-    -- If the next buffer contains no valid bytes,
-    -- and the final byte was acknowledged, we can
-    -- acknowledge the newly received data.
-    -- The || is lazy, and we need this: if the output
-    -- of the downconverter is Nothing, we are not allowed to
-    -- evaluate inReady.
-    outReady = _dcSize == 0 || (_dcSize == 1 && inReady)
-    st' = case fwdIn of
-      Just inp | outReady -> fromPacketStreamM2S inp
-      _ ->
-        st
-          { _dcBuf = _dcBuf'
-          , _dcSize = _dcSize'
-          }
-
-    bwdOut = PacketStreamS2M outReady
-    fwdOut = toMaybePacketStreamM2S st
-
-{- | Converts packet streams of arbitrary data widths to packet streams of single bytes.
-Has one clock cycle of latency, but optimal throughput, i.e. a packet of n bytes is
-sent out in n clock cycles, even if `_last` is set.
--}
-downConverterC ::
-  forall (dataWidth :: Nat) (dom :: Domain).
-  (HiddenClockResetEnable dom) =>
-  (1 <= dataWidth) =>
-  (KnownNat dataWidth) =>
-  Circuit (PacketStream dom dataWidth ()) (PacketStream dom 1 ())
-downConverterC = forceResetSanity |> fromSignals downConverter