diff --git a/common/hw-port_io.adb b/common/hw-port_io.adb
new file mode 100644
index 0000000..e8adfc2
--- /dev/null
+++ b/common/hw-port_io.adb
@@ -0,0 +1,71 @@
+--
+-- 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.
+--
+
+with System;
+with System.Machine_Code;
+
+package body HW.Port_IO
+with
+   Refined_State  => (State => null),
+   SPARK_Mode     => Off
+is
+
+   generic
+      type Word is private;
+   procedure Port_In (Value : out Word; Port : Port_Type);
+
+   procedure Port_In (Value : out Word; Port : Port_Type) is
+   begin
+      System.Machine_Code.Asm
+        ("in %1, %0",
+         Inputs   => (Port_Type'Asm_Input ("Nd", Port)),
+         Outputs  => (Word'Asm_Output ("=a", Value)),
+         Volatile => True);
+   end Port_In;
+
+   procedure InB_Body is new Port_In (Word => Word8);
+   procedure InB (Value : out Word8; Port : Port_Type) renames InB_Body;
+
+   procedure InW_Body is new Port_In (Word => Word16);
+   procedure InW (Value : out Word16; Port : Port_Type) renames InW_Body;
+
+   procedure InL_Body is new Port_In (Word => Word32);
+   procedure InL (Value : out Word32; Port : Port_Type) renames InL_Body;
+
+   ----------------------------------------------------------------------------
+
+   generic
+      type Word is private;
+   procedure Port_Out (Port : Port_Type; Value : Word);
+
+   procedure Port_Out (Port : Port_Type; Value : Word) is
+   begin
+      System.Machine_Code.Asm
+        ("out %1, %0",
+         Inputs   => (Port_Type'Asm_Input ("Nd", Port),
+                      Word'Asm_Input ("a", Value)),
+         Volatile => True);
+   end Port_Out;
+
+   procedure OutB_Body is new Port_Out (Word => Word8);
+   procedure OutB (Port : Port_Type; Value : Word8) renames OutB_Body;
+
+   procedure OutW_Body is new Port_Out (Word => Word16);
+   procedure OutW (Port : Port_Type; Value : Word16) renames OutW_Body;
+
+   procedure OutL_Body is new Port_Out (Word => Word32);
+   procedure OutL (Port : Port_Type; Value : Word32) renames OutL_Body;
+
+end HW.Port_IO;
+
+--  vim: set ts=8 sts=3 sw=3 et: