gen: override FSM to add filter file generation

litex/gen/genlib/fsm.py

@@ -0,0 +1,19 @@
+from migen import *
+
+class nFSM(FSM):
+    def __init__(self, reset_state=None, name=None, with_filter=True):
+        super().__init__(reset_state)
+        self.name = name
+        self.with_filter = with_filter
+
+    def _finalize_sync(self, ls):
+        if self.with_filter and self.name:
+            self.generate_fsm_filter()
+        super()._finalize_sync(ls)
+
+    def generate_fsm_filter(self):
+        with open(f"filter_{self.name}.txt", "w") as f:
+            for i, state in enumerate(self.actions):
+                f.write("{} {}\n".format(i, state))
+
+        self.state.name_override = self.name