litex/gen: add io with SDRInput/SDROutput (if not overrided, register is supposed to be infered).

litex/gen/io.py

@@ -0,0 +1,39 @@
+# This file is Copyright (c) 2020 Florent Kermarrec <florent@enjoy-digital.fr>
+# License: BSD
+
+from migen import *
+from migen.fhdl.specials import Special
+
+
+class InferedSDRIO(Module):
+    def __init__(self, i, o, clk, clk_domain):
+        if clk_domain is None:
+            raise NotImplementedError("Attempted to use an InferedSDRIO but no clk_domain specified.")
+        sync = getattr(self.sync, clk_domain)
+        sync += o.eq(i)
+
+
+class SDRIO(Special):
+    def __init__(self, i, o, clk=ClockSignal()):
+        assert len(i) == len(o)
+        Special.__init__(self)
+        print(o)
+        self.i            = wrap(i)
+        self.o            = wrap(o)
+        self.clk          = wrap(clk)
+        self.clk_domain   = None if not hasattr(clk, "cd") else clk.cd
+
+    def iter_expressions(self):
+        yield self, "i",   SPECIAL_INPUT
+        yield self, "o",   SPECIAL_OUTPUT
+        yield self, "clk", SPECIAL_INPUT
+
+    @staticmethod
+    def lower(dr):
+        return InferedSDRIO(dr.i, dr.o, dr.clk, dr.clk_domain)
+
+
+class SDRInput(SDRIO): pass
+
+
+class SDROutput(SDRIO): pass