1
2-- Copyright (C) 2002 Morgan Kaufmann Publishers, Inc
3
4-- This file is part of VESTs (Vhdl tESTs).
5
6-- VESTs is free software; you can redistribute it and/or modify it
7-- under the terms of the GNU General Public License as published by the
8-- Free Software Foundation; either version 2 of the License, or (at
9-- your option) any later version.
10
11-- VESTs is distributed in the hope that it will be useful, but WITHOUT
12-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13-- FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14-- for more details.
15
16-- You should have received a copy of the GNU General Public License
17-- along with VESTs; if not, write to the Free Software Foundation,
18-- Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
19
20library ieee;  use ieee.math_real.all;
21
22entity pendulum is
23end entity pendulum;
24
25----------------------------------------------------------------
26
27architecture constrained of pendulum is
28
29  constant mass : real := 10.0;
30  constant arm_length : real := 5.0;
31  constant pin_angle : real := 0.25 * math_pi;
32  constant pin_distance : real := 2.5;
33  constant damping : real := 1.0;
34  constant gravity : real := 9.81;
35  constant short_length : real := arm_length - pin_distance;
36  quantity phi : real := -0.5*math_pi;
37  quantity current_length : real := arm_length;
38
39begin
40
41  if phi'above(pin_angle) use
42    current_length == short_length;
43  else
44    current_length == arm_length;
45  end use;
46
47  break phi'dot => phi'dot * arm_length/short_length
48    when phi'above(pin_angle);
49
50  break phi'dot => phi'dot * short_length/arm_length
51    when not phi'above(pin_angle);
52
53  mass * current_length * phi'dot'dot
54    == - mass * gravity * sin(phi) - damping * current_length * phi'dot;
55
56end architecture constrained;
57