Subversion Repositories common_components

-------------------------------------------------------------------------------

--

-- Copyright (C) 2009

-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>

-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands

--

-- 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, either version 3 of the License, or

-- (at your option) any later version.

--

-- 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.

--

-- You should have received a copy of the GNU General Public License

-- along with this program.  If not, see <http://www.gnu.org/licenses/>.

--

-------------------------------------------------------------------------------

-- Purpose : Switch output high or low

-- Description:

-- . The output goes high when switch_high='1' and low when switch_low='1'.

-- . If g_or_high is true then the output follows the switch_high immediately,

--   else it goes high in the next clk cycle.

-- . If g_and_low is true then the output follows the switch_low immediately,

--   else it goes low in the next clk cycle.

--   The g_priority_lo defines which input has priority when switch_high and

--   switch_low are active simultaneously.

LIBRARY ieee;

USE ieee.std_logic_1164.ALL;

ENTITY common_switch IS

  GENERIC (

    g_rst_level    : STD_LOGIC := '0';  -- Defines the output level at reset.

    g_priority_lo  : BOOLEAN := TRUE;   -- When TRUE then input switch_low has priority, else switch_high. Don't care when switch_high and switch_low are pulses that do not occur simultaneously.

    g_or_high      : BOOLEAN := FALSE;  -- When TRUE and priority hi then the registered switch_level is OR-ed with the input switch_high to get out_level, else out_level is the registered switch_level

    g_and_low      : BOOLEAN := FALSE   -- When TRUE and priority lo then the registered switch_level is AND-ed with the input switch_low to get out_level, else out_level is the registered switch_level

  );

  PORT (

    rst         : IN  STD_LOGIC;

    clk         : IN  STD_LOGIC;

    clken       : IN  STD_LOGIC := '1';

    switch_high : IN  STD_LOGIC;    -- A pulse on switch_high makes the out_level go high

    switch_low  : IN  STD_LOGIC;    -- A pulse on switch_low makes the out_level go low

    out_level   : OUT STD_LOGIC

  );

END;

ARCHITECTURE rtl OF common_switch IS

  SIGNAL switch_level         : STD_LOGIC := g_rst_level;

  SIGNAL nxt_switch_level     : STD_LOGIC;

BEGIN

  gen_wire : IF g_or_high=FALSE AND g_and_low=FALSE GENERATE

    out_level <= switch_level;

  END GENERATE;

  gen_or : IF g_or_high=TRUE AND g_and_low=FALSE GENERATE

    out_level <= switch_level OR switch_high;

  END GENERATE;

  gen_and : IF g_or_high=FALSE AND g_and_low=TRUE GENERATE

    out_level <= switch_level AND (NOT switch_low);

  END GENERATE;

  gen_or_and : IF g_or_high=TRUE AND g_and_low=TRUE GENERATE

    out_level <= (switch_level OR switch_high) AND (NOT switch_low);

  END GENERATE;

  p_reg : PROCESS(rst, clk)

  BEGIN

    IF rst='1' THEN

      switch_level <= g_rst_level;

    ELSIF rising_edge(clk) THEN

      IF clken='1' THEN

        switch_level <= nxt_switch_level;

      END IF;

    END IF;

  END PROCESS;

  p_switch_level : PROCESS(switch_level, switch_low, switch_high)

  BEGIN

    nxt_switch_level <= switch_level;

    IF g_priority_lo=TRUE THEN

      IF switch_low='1' THEN

        nxt_switch_level <= '0';

      ELSIF switch_high='1' THEN

        nxt_switch_level <= '1';

      END IF;

    ELSE

      IF switch_high='1' THEN

        nxt_switch_level <= '1';

      ELSIF switch_low='1' THEN

        nxt_switch_level <= '0';

      END IF;

    END IF;

  END PROCESS;

END rtl;