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1 d93979b7 Arnaud Dieumegard
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-- Copyright (C) 1996 Morgan Kaufmann Publishers, Inc
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-- This file is part of VESTs (Vhdl tESTs).
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-- VESTs is free software; you can redistribute it and/or modify it
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-- under the terms of the GNU General Public License as published by the
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-- Free Software Foundation; either version 2 of the License, or (at
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-- your option) any later version. 
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-- VESTs is distributed in the hope that it will be useful, but WITHOUT
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-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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-- FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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-- for more details. 
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-- You should have received a copy of the GNU General Public License
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-- along with VESTs; if not, write to the Free Software Foundation,
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-- Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
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-- ---------------------------------------------------------------------
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--
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-- $Id: ch_05_fg_05_19.vhd,v 1.2 2001-10-26 16:29:34 paw Exp $
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-- $Revision: 1.2 $
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--
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-- ---------------------------------------------------------------------
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entity fg_05_19 is
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end entity fg_05_19;
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architecture test of fg_05_19 is
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  constant scheduling_delay : delay_length := 5 ns;
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  subtype request_type is natural range 0 to 20;
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  type server_status_type is (ready, busy);
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  signal first_priority_request,
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    first_normal_request,
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    reset_request : request_type := 0;
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  signal functional_request, equivalent_request : request_type;
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  signal priority_waiting : boolean := false;
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  signal server_status : server_status_type := busy;
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begin
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  functional_scheduler : block is
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                                 port ( request : out request_type );
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                               port map ( request => functional_request );
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  begin
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    -- code from book
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    scheduler :
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      request <= first_priority_request after scheduling_delay
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                 when priority_waiting and server_status = ready else
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                 first_normal_request after scheduling_delay
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                 when not priority_waiting and server_status = ready else
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                 unaffected
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                 when server_status = busy else
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                 reset_request after scheduling_delay;
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    -- end code from book
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  end block functional_scheduler;
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  --------------------------------------------------
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  equivalent_scheduler : block is
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                                 port ( request : out request_type );
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                               port map ( request => equivalent_request );
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  begin
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    -- code from book
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    scheduler : process is
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    begin
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      if priority_waiting and server_status = ready then
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        request <= first_priority_request after scheduling_delay;
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      elsif not priority_waiting and server_status = ready then
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        request <= first_normal_request after scheduling_delay;
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      elsif server_status = busy then
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        null;
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      else
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        request <= reset_request after scheduling_delay;
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      end if;
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      wait on first_priority_request, priority_waiting, server_status,
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        first_normal_request, reset_request;
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    end process scheduler;
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    -- end code from book
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  end block equivalent_scheduler;
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  --------------------------------------------------
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  stimulus : process is
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  begin
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    first_priority_request <= 10;	wait for 20 ns;
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    first_normal_request <= 5;		wait for 20 ns;
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    server_status <= ready;		wait for 20 ns;
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    server_status <= busy;		wait for 20 ns;
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    priority_waiting <= true;		wait for 20 ns;
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    server_status <= ready;		wait for 20 ns;
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    first_normal_request <= 7;		wait for 20 ns;
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    first_priority_request <= 12;	wait for 20 ns;
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    wait;
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  end process stimulus;
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  verifier :
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    assert functional_request = equivalent_request
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      report "Functional and equivalent models give different results";
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end architecture test;