vendor.xilinx_spartan_3_6: fix typo.

This was introduced in commit 2f8669ca.

Fixes #549.

diff --git a/nmigen/vendor/xilinx_spartan_3_6.py b/nmigen/vendor/xilinx_spartan_3_6.py
index 527d089cf6b36d4054e4e6fc77bc8ea2ae91ea33..21cbda03acb07578f4ab1d2bbeffae09b0452a17 100644 (file)
--- a/nmigen/vendor/xilinx_spartan_3_6.py
+++ b/nmigen/vendor/xilinx_spartan_3_6.py
@@ -437,7 +437,7 @@ class XilinxSpartan3Or6Platform(TemplatedPlatform):
         return m
 
     def get_async_ff_sync(self, async_ff_sync):
-        if self._max_input_delay is not None:
+        if async_ff_sync._max_input_delay is not None:
             raise NotImplementedError("Platform '{}' does not support constraining input delay "
                                       "for AsyncFFSynchronizer"
                                       .format(type(self).__name__))