Change frequency calculation to use periodToHz

Currently, the frequency calculation dependens on the unit of the
period of a `KnownDomain` (picoseconds). If this unit is to be changed
internally in the future (to femtoseconds), this calculation would
produce the wrong frequency. By using `periodToHz`, the unit of the
period no longer matters and can be changed internally.

clash-lib/src/Clash/Primitives/Xilinx/ClockGen.hs

@@ -15,6 +15,7 @@ import Clash.Backend (Backend)
 import Clash.Netlist.BlackBox.Util (exprToString)
 import Clash.Netlist.Types
 import Clash.Netlist.Util (stripVoid)
+import Clash.Signal (periodToHz)
 
 import Control.Monad.State (State)
 import qualified Data.String.Interpolate as I
@@ -47,9 +48,9 @@ clockWizardTclTemplate bbCtx
   =
   let
     clkInFreq :: Double
-    clkInFreq  = (1.0 / (fromInteger clkInPeriod  * 1e-12)) / 1e6
+    clkInFreq = periodToHz clkInPeriod / 1e6
     clkOutFreq :: Double
-    clkOutFreq = (1.0 / (fromInteger clkOutPeriod * 1e-12)) / 1e6
+    clkOutFreq = periodToHz clkOutPeriod / 1e6
 
     bbText = [I.__i|
       namespace eval $tclIface {
@@ -105,9 +106,9 @@ clockWizardDifferentialTclTemplate bbCtx
   =
   let
     clkInFreq :: Double
-    clkInFreq  = (1.0 / (fromInteger clkInPeriod  * 1e-12)) / 1e6
+    clkInFreq = periodToHz clkInPeriod / 1e6
     clkOutFreq :: Double
-    clkOutFreq = (1.0 / (fromInteger clkOutPeriod * 1e-12)) / 1e6
+    clkOutFreq = periodToHz clkOutPeriod / 1e6
 
     bbText = [I.__i|
       namespace eval $tclIface {