diff --git a/common/hw-port_io.ads b/common/hw-port_io.ads
new file mode 100644
index 0000000..a5d0e9e
--- /dev/null
+++ b/common/hw-port_io.ads
@@ -0,0 +1,61 @@
+--
+-- 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.Port_IO
+with
+   Abstract_State => (State with External => (Async_Readers, Async_Writers))
+is
+
+   type Port_Type is mod 2**16;
+
+   procedure InB (Value : out Word8; Port : Port_Type)
+   with
+      Global   => (In_Out => State),
+      Depends  => ((Value, State) => (Port, State)),
+      Inline_Always;
+
+   procedure InW (Value : out Word16; Port : Port_Type)
+   with
+      Global   => (In_Out => State),
+      Depends  => ((Value, State) => (Port, State)),
+      Pre      => Port mod 2 = 0,
+      Inline_Always;
+
+   procedure InL (Value : out Word32; Port : Port_Type)
+   with
+      Global   => (In_Out => State),
+      Depends  => ((Value, State) => (Port, State)),
+      Pre      => Port mod 4 = 0,
+      Inline_Always;
+
+   procedure OutB (Port : Port_Type; Value : Word8)
+   with
+      Global   => (In_Out => State),
+      Depends  => (State =>+ (Port, Value)),
+      Inline_Always;
+
+   procedure OutW (Port : Port_Type; Value : Word16)
+   with
+      Global   => (In_Out => State),
+      Depends  => (State =>+ (Port, Value)),
+      Pre      => Port mod 2 = 0,
+      Inline_Always;
+
+   procedure OutL (Port : Port_Type; Value : Word32)
+   with
+      Global   => (In_Out => State),
+      Depends  => (State =>+ (Port, Value)),
+      Pre      => Port mod 4 = 0,
+      Inline_Always;
+
+end HW.Port_IO;