diff --git a/common/hw-time.ads b/common/hw-time.ads
new file mode 100644
index 0000000..743279b
--- /dev/null
+++ b/common/hw-time.ads
@@ -0,0 +1,75 @@
+--
+-- Copyright (C) 2015-2016 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.Time
+   with Abstract_State => (State with External => Async_Writers)
+is
+
+   type T is private;
+
+   function Now return T
+   with
+      Volatile_Function,
+      Global => (Input => State);
+
+   function US_From_Now (US : Natural) return T
+   with
+      Volatile_Function,
+      Global => (Input => State);
+
+   function MS_From_Now (MS : Natural) return T
+   with
+      Volatile_Function,
+      Global => (Input => State);
+
+   function Now_US return Int64
+   with
+      Volatile_Function,
+      Global => (Input => State);
+
+   ----------------------------------------------------------------------------
+
+   pragma Warnings
+     (GNATprove, Off, "subprogram ""*Delay*"" has no effect",
+      Reason => "No effect on dataflow but time always passes.");
+
+   -- Delay execution until Deadline has been reached.
+   procedure Delay_Until (Deadline : T)
+   with
+      Global => (Input => State);
+
+   procedure U_Delay (US : Natural)
+   with
+      Global => (Input => State);
+
+   procedure M_Delay (MS : Natural)
+   with
+      Global => (Input => State);
+
+   pragma Warnings
+     (GNATprove, On, "subprogram ""*Delay*"" has no effect");
+
+   ----------------------------------------------------------------------------
+
+   function Timed_Out (Deadline : T) return Boolean
+   with
+      Volatile_Function,
+      Global => (Input => State);
+
+private
+
+   type T is new Word64;
+
+end HW.Time;
+
+--  vim: set ts=8 sts=3 sw=3 et: