-------------------------------------------------------------------------------
-- Copyright (c) 2001 Mentor Graphics Corporation
--
-- This model is a component of the Mentor Graphics VHDL-AMS educational open 
-- source model library, and is covered by this license agreement. This model,
-- including any updates, modifications, revisions, copies, and documentation 
-- are copyrighted works of Mentor Graphics. USE OF THIS MODEL INDICATES YOUR 
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-- IN THIS LICENSE AGREEMENT.  Mentor Graphics grants you a non-exclusive 
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-- compilations distributed in accordance with Section (d) of this license 
-- agreement; (b) the comment text embedded in this model is included verbatim
-- in each copy of this model made or distributed by you, whether or not such 
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-- notice that this model has been modified and the date of modification; and 
-- (d) any compilations sold by you that include this model must include a 
-- conspicuous notice that this model is available from Mentor Graphics in its
-- original form at no charge.
--
-- THIS MODEL IS LICENSED TO YOU "AS IS" AND WITH NO WARRANTIES, EXPRESS OR 
-- IMPLIED.  MENTOR GRAPHICS SPECIFICALLY DISCLAIMS ALL IMPLIED WARRANTIES OF 
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-- HAVE NO RESPONSIBILITY FOR ANY DAMAGES WHATSOEVER.
-------------------------------------------------------------------------------
-- File       : MeasFreq.vhd
-- Author     : Mentor Graphics
-- Created    : 2001/06/16
-- Last update: 2002-04-30
-------------------------------------------------------------------------------
-- Description: Measure Frequency of an electrical input signal (voltage)
--              Output signal unitless quantity
-------------------------------------------------------------------------------
-- Revisions  :
-- Date        Version     Author              Description
-- 2001/06/16  1.0         Mentor Graphics     Created
-- 2001/07/05  1.1         Mentor Graphics     Added f_init parameter for
--                                             initializing output
-- 2001/11/27  1.2         Mentor Graphics     Changed output to Quantity Port
-- 2002/04/29  2.0         Mentor Graphics     Simplified model based on
--                                             suggestions from Peter Ashenden
--                                             Changed output to real signal.
--                                             Removed initialization.
--                                             Simplified process.
-------------------------------------------------------------------------------
library ieee;  
use ieee.electrical_systems.all;

entity MeasFreq is
  generic ( thres : real := 0.0 );    -- threshold crossing
  port ( terminal input : electrical;
         signal f_out : out real := 0.0);
end entity MeasFreq;
-------------------------------------------------------------------------------
-- ThresDetect Architecture
-- Uses threshold detection to measure frequency
-------------------------------------------------------------------------------
architecture ThresDetect of MeasFreq is
  quantity vin across input;
--  signal freq : real := 0.0;           
begin
--  f_out <= freq; 
  detect : process (vin'above(thres)) is
    variable t_old : real := real'low;
  begin
    if vin'above(thres) then
      f_out <= 1.0 / (now - t_old);
      t_old := now;
    end if;
  end process detect;
end ThresDetect;
-------------------------------------------------------------------------------
-- Copyright (c) 2001 Mentor Graphics Corporation
-------------------------------------------------------------------------------