soc.base: add socproperty(weak=True) for optional properties.

diff --git a/lambdasoc/soc/base.py b/lambdasoc/soc/base.py
index 79cb6c2a03ab3bdd65cb05df0cdfebc2998d5a69..ceb3663c021c6a5e2365f6470f0983282cbecbc8 100644 (file)
--- a/lambdasoc/soc/base.py
+++ b/lambdasoc/soc/base.py
@@ -14,14 +14,14 @@ from ..periph import Peripheral
 __all__ = ["socproperty", "SoC", "ConfigBuilder"]
 
 
-def socproperty(cls, src_loc_at=0):
+def socproperty(cls, *, weak=False, src_loc_at=0):
     name   = tracer.get_var_name(depth=2 + src_loc_at)
     __name = "__{}".format(name)
 
     def getter(self):
         assert isinstance(self, SoC)
         attr = getattr(self, __name, None)
-        if attr is None:
+        if attr is None and not weak:
             raise NotImplementedError("SoC {!r} does not have a {}"
                                       .format(self, name))
         return attr