Fix convertReset polarity change (#2548)

The `convertReset` function did not account for the possibility that the
two domains might not have the same reset polarity.

changelog/2023-07-17T18_31_48+02_00_convert_reset

@@ -0,0 +1 @@
+FIXED: When `convertReset` was used with two domains that had a different reset polarity, the polarity of the signal was not changed.

clash-prelude/src/Clash/Explicit/Reset.hs

@@ -1,5 +1,5 @@
 {-|
-Copyright  :  (C) 2020-2021, QBayLogic B.V.
+Copyright  :  (C) 2020-2023, QBayLogic B.V.,
                   2022     , Google LLC
 License    :  BSD2 (see the file LICENSE)
 Maintainer :  QBayLogic B.V. <devops@qbaylogic.com>
@@ -278,10 +278,16 @@ convertReset
   -> Clock domB
   -> Reset domA
   -> Reset domB
-convertReset clkA clkB rstA0 = rstA2
+convertReset clkA clkB rstA0 = rstB1
  where
-  rstA1 = unsafeToReset (unsafeSynchronizer clkA clkB (unsafeFromReset rstA0))
+  rstA1 = unsafeFromReset rstA0
   rstA2 =
+    case (resetPolarity @domA, resetPolarity @domB) of
+      (SActiveLow, SActiveLow)   -> rstA1
+      (SActiveHigh, SActiveHigh) -> rstA1
+      _                          -> not <$> rstA1
+  rstB0 = unsafeToReset $ unsafeSynchronizer clkA clkB rstA2
+  rstB1 =
     case (sameDomain @domA @domB) of
       Just Refl -> rstA0
-      Nothing   -> resetSynchronizer clkB rstA1
+      Nothing   -> resetSynchronizer clkB rstB0

clash-prelude/tests/Clash/Tests/Reset.hs

@@ -13,12 +13,12 @@ import Test.Tasty.HUnit
 import Test.Tasty.TH
 import Clash.Explicit.Prelude
 
+import qualified Prelude as P
+
 -- Testing with explicit declaration of the Low type alias
 type Low = ("Low" :: Domain)
 createDomain vSystem{vName="Low", vResetPolarity=ActiveLow}
 
-createDomain vSystem{vName="NoInit", vInitBehavior=Unknown}
-
 sampleResetN :: KnownDomain dom => Int -> Reset dom -> [Bool]
 sampleResetN n = sampleN n . unsafeToActiveHigh
 
@@ -41,6 +41,16 @@ case_onePeriodGlitch_LowPolarity =
       [True,True,True,True,False,False,False,False,False,True,True,False]
   @=? sampleResetN 12 (resetGlitchFilter d2 (clockGen @Low) onePeriodGlitchReset)
 
+-- Check that the meaning of @Reset@ is maintained when converting from
+-- active-low to active-high.
+case_convertReset_polarity_change :: Assertion
+case_convertReset_polarity_change =
+      -- In domains with synchronous resets and defined initial values,
+      -- @resetSynchronizer@ will start with an asserted reset.
+      True : True : P.replicate 8 False
+  @=? sampleResetN 10 (convertReset (clockGen @Low) (clockGen @System)
+                                    (resetFromList $ P.repeat False))
+
 tests :: TestTree
 tests = testGroup "Reset"
   [ $(testGroupGenerator)