diff --git a/common/hw-gfx-i2c.ads b/common/hw-gfx-i2c.ads
new file mode 100644
index 0000000..db5e5cc
--- /dev/null
+++ b/common/hw-gfx-i2c.ads
@@ -0,0 +1,21 @@
+--
+-- Copyright (C) 2015 secunet Security Networks AG
+--
+-- This program is free software; you can redistribute it and/or modify
+-- it under the terms of the GNU General Public License as published by
+-- the Free Software Foundation; version 2 of the License.
+--
+-- This program is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU General Public License for more details.
+--
+
+package HW.GFX.I2C is
+
+   type Transfer_Address is mod 2 ** 7;
+   subtype Transfer_Length is Natural range 0 .. 128;
+   subtype Transfer_Index is Natural range 0 .. Transfer_Length'Last - 1;
+   subtype Transfer_Data is Buffer (Transfer_Index);
+
+end HW.GFX.I2C;