diff --git a/dc11.py b/dc11.py
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+# MIT License
+#
+# Copyright (c) 2023 Neil Webber
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+# Emulate a DC-11 multi-device serial adapter.
+
+
+# The "emulation", such as it is right now, is entirely dummy.
+# This is needed just so Unix doesn't crash trying to establish a getty
+# on /dev/tty0 .. /dev/tty3 (though, alternatively, the entries in /etc/ttys
+# could just have been disabled; this is more robust though).
+#
+# Essentially it is emulating serial cables that are never plugged in. :)
+#
+
+class DC11:
+    DC11_DEFAULT = 0o14000           # offset within I/O page
+    DC11_NDEVS = 4                   # four devices, each is 4 16-bit registers
+
+    def __init__(self, ub, baseaddr=DC11_DEFAULT):
+        self.ub = ub
+        self.addr = ub.mmio.register(
+            None, self.DC11_DEFAULT, self.DC11_NDEVS * 4)