Assert that roundrobinCollect Parallel is left-biased

Fixes #169

Author: martijnbastiaan

clash-protocols/src/Protocols/Df.hs

@@ -740,7 +740,7 @@ data CollectMode
   | -- | Collect in a /round-robin/ fashion. If a source does not produce
     -- data, skip it and check the next source on the next cycle.
     Skip
-  | -- | Check all sources in parallel. Biased towards the /last/ source.
+  | -- | Check all sources in parallel. Biased towards the /first/ source.
     -- If the number of sources is high, this is more expensive than other
     -- modes.
     Parallel

clash-protocols/src/Protocols/PacketStream/Routing.hs

@@ -54,7 +54,7 @@ packetArbiterC mode =
       (Df.NoSkip, _) -> satSucc SatWrap i
       (Df.Skip, _) -> satSucc SatWrap i
       (Df.Parallel, _) ->
-        -- Index of last sink with data
+        -- Index of first sink with data
         fromMaybe maxBound
           $ fold @(sources - 1) (<|>) (zipWith (<$) indicesI fwds)
 

clash-protocols/tests/Tests/Protocols/Df.hs

@@ -14,7 +14,9 @@ import Prelude
 
 -- clash-prelude
 
-import Clash.Prelude (type (<=))
+import Clash.Explicit.Prelude qualified as E
+import Clash.Explicit.Reset (noReset)
+import Clash.Prelude (Vec (Nil, (:>)), type (<=))
 import Clash.Prelude qualified as C
 
 -- containers
@@ -37,6 +39,7 @@ import Hedgehog.Range qualified as Range
 
 -- tasty
 import Test.Tasty
+import Test.Tasty.HUnit (Assertion, testCase, (@?=))
 import Test.Tasty.Hedgehog (HedgehogTestLimit (HedgehogTestLimit))
 import Test.Tasty.Hedgehog.Extra (testProperty)
 import Test.Tasty.TH (testGroupGenerator)
@@ -47,6 +50,8 @@ import Protocols.Df qualified as Df
 import Protocols.Hedgehog
 
 -- tests
+
+import Data.Bifunctor (Bifunctor (first))
 import Util
 
 newtype PlusInt = PlusInt Int
@@ -319,6 +324,36 @@ prop_roundrobinCollectParallel =
   prop :: [Int] -> [Int] -> PropertyT IO ()
   prop expected actual = HashSet.fromList expected === HashSet.fromList actual
 
+{- | Asserts that roundrobinCollect with Parallel mode behaves in a left-biased
+fashion.
+-}
+case_roundrobinCollectParallel :: Assertion
+case_roundrobinCollectParallel = do
+  expected @?= actual
+ where
+  actual =
+    E.sampleN 5
+      . C.bundle
+      . first C.bundle
+      $ dut (input0 :> input1 :> input2 :> Nil, pure $ Ack True)
+
+  expected =
+    [ (Ack True :> Ack False :> Ack False :> Nil, Just (1 :: Int))
+    , (Ack True :> Ack False :> Ack False :> Nil, Just 2)
+    , (Ack False :> Ack True :> Ack False :> Nil, Just 10)
+    , (Ack False :> Ack True :> Ack False :> Nil, Just 40)
+    , (Ack False :> Ack False :> Ack True :> Nil, Just 100)
+    ]
+
+  input0 = C.fromList @_ @C.System [Just 1, Just 2, Nothing, Nothing, Nothing]
+  input1 = C.fromList @_ @C.System [Just 10, Just 10, Just 10, Just 40, Nothing]
+  input2 = C.fromList @_ @C.System [Just 100, Just 100, Just 100, Just 100, Just 100]
+
+  dut =
+    toSignals $
+      C.withClockResetEnable @C.System C.clockGen noReset C.enableGen $
+        Df.roundrobinCollect @3 Df.Parallel
+
 prop_unbundleVec :: Property
 prop_unbundleVec =
   idWithModelSingleDomain