fhdl: support inverted clock ports in instances

migen/fhdl/structure.py

@@ -274,9 +274,10 @@ class Instance:
 			self.value = value
 	
 	class _CR:
-		def __init__(self, name_inst, domain="sys"):
+		def __init__(self, name_inst, domain="sys", invert=False):
 			self.name_inst = name_inst
 			self.domain = domain
+			self.invert = invert
 	class ClockPort(_CR):
 		pass
 	class ResetPort(_CR):

migen/fhdl/verilog.py

@@ -210,6 +210,8 @@ def _printinstances(f, ns, clock_domains):
 			elif isinstance(p, Instance.ClockPort):
 				name_inst = p.name_inst
 				name_design = ns.get_name(clock_domains[p.domain].clk)
+				if p.invert:
+					name_design = "~" + name_design
 			elif isinstance(p, Instance.ResetPort):
 				name_inst = p.name_inst
 				name_design = ns.get_name(clock_domains[p.domain].rst)