back.rtlil: explain logic for CD reset insertion.

diff --git a/nmigen/back/rtlil.py b/nmigen/back/rtlil.py
index 9ef5a23f55c23a1abed76a25cbd02aeedac05908..490e3e7fcde97c953243cb49a3741f7e3b66a21a 100644 (file)
--- a/nmigen/back/rtlil.py
+++ b/nmigen/back/rtlil.py
@@ -510,6 +510,8 @@ def convert_fragment(builder, fragment, name, top, clock_domains):
 
 
 def convert(fragment, ports=[], clock_domains={}):
+    # Clock domain reset always takes priority over all other logic. To ensure this, insert
+    # decision trees for clock domain reset as the very last step before synthesis.
     fragment = xfrm.ResetInserter({
         cd.name: cd.reset for cd in clock_domains.values() if cd.reset is not None
     })(fragment)