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--            _   _            __   ____                                      --

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--           | |_| |  _   _  / /   | |_                                       --

--           |  _  | | | | | | |   |  _|                                      --

--           | | | | | |_| | \ \_  | |__                                      --

--           |_| |_| \_____|  \__| |____| microLab                            --

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--           Room HG 4.33                                                     --

--           2501 Biel/Bienne                                                 --

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--           http://www.microlab.ch                                           --

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--   GECKO4com

--  

--   2010/2011 Dr. Theo Kluter

--  

--   This VHDL code is free code: 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 VHDL code 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 these sources.  If not, see <http://www.gnu.org/licenses/>.

--

-- The unisim library is used for simulation of the xilinx specific components

-- For generic usage please use:

-- LIBRARY work;

-- USE work.xilinx_generic.all;

-- And use the xilinx generic package found in the xilinx generic module

LIBRARY unisim;

USE unisim.all;

ARCHITECTURE xilinx OF fifo_2kb IS

   COMPONENT RAMB16_S9_S9

      GENERIC ( WRITE_MODE_A : string := "READ_FIRST";

                WRITE_MODE_B : string := "READ_FIRST" );

      PORT (  DOA   : OUT std_logic_vector( 7 DOWNTO 0);

              ADDRA : IN  std_logic_vector(10 DOWNTO 0);

              DIA   : IN  std_logic_vector( 7 DOWNTO 0);

              ENA   : IN  std_ulogic;

              WEA   : IN  std_ulogic;

              DOPA  : OUT std_logic_vector( 0 DOWNTO 0);

              CLKA  : IN  std_ulogic;

              DIPA  : IN  std_logic_vector( 0 DOWNTO 0);

              SSRA  : IN  std_ulogic;

              DOPB  : OUT std_logic_vector( 0 DOWNTO 0);

              CLKB  : IN  std_ulogic;

              DIPB  : IN  std_logic_vector( 0 DOWNTO 0);

              SSRB  : IN  std_ulogic;

              DOB   : OUT std_logic_vector( 7 DOWNTO 0);

              ADDRB : IN  std_logic_vector(10 DOWNTO 0);

              DIB   : IN  std_logic_vector( 7 DOWNTO 0);

              ENB   : IN  std_ulogic;

              WEB   : IN  std_ulogic );

   END COMPONENT;

   CONSTANT c_threshold        : std_logic_vector(11 DOWNTO 0 ) := X"7FD";

   SIGNAL s_write_address_reg  : std_logic_vector(10 DOWNTO 0 );

   SIGNAL s_write_address_next : std_logic_vector(10 DOWNTO 0 );

   SIGNAL s_read_address_reg   : std_logic_vector(10 DOWNTO 0 );

   SIGNAL s_read_address_next  : std_logic_vector(10 DOWNTO 0 );

   SIGNAL s_nr_of_bytes_reg    : std_logic_vector(11 DOWNTO 0 );

   SIGNAL s_nr_of_bytes_next   : std_logic_vector(11 DOWNTO 0 );

   SIGNAL s_full               : std_logic;

   SIGNAL s_empty              : std_logic;

   SIGNAL s_execute_push       : std_logic;

   SIGNAL s_execute_pop        : std_logic;

   SIGNAL s_n_clock            : std_logic;

BEGIN

-- Assign outputs

   fifo_full   <= s_full;

   fifo_empty  <= s_empty;

-- Assign control signals

   s_read_address_next  <= unsigned(s_read_address_reg) + 1;

   s_write_address_next <= unsigned(s_write_address_reg) + 1;

   s_nr_of_bytes_next   <= unsigned(s_nr_of_bytes_reg) - 1

                             WHEN s_execute_pop = '1' AND

                                  s_execute_push = '0' ELSE

                           unsigned(s_nr_of_bytes_reg) + 1

                             WHEN s_execute_pop = '0' AND

                                  s_execute_push = '1' ELSE

                           s_nr_of_bytes_reg;

   s_execute_push       <= push AND NOT(s_nr_of_bytes_reg(11));

   s_execute_pop        <= pop  AND NOT(s_empty);

   s_n_clock            <= NOT(clock);

   s_full               <= '1' WHEN unsigned(s_nr_of_bytes_reg) >

                                    unsigned(c_threshold) ELSE '0';

   s_empty              <= '1' WHEN s_nr_of_bytes_reg = "000000000000" ELSE '0';

-- define processes

   make_read_address_reg : PROCESS( clock , reset , s_execute_pop ,

                                    s_read_address_next )

   BEGIN

      IF (clock'event AND (clock = '1')) THEN

         IF (reset = '1') THEN s_read_address_reg <= (OTHERS => '0');

         ELSIF (s_execute_pop = '1') THEN

            s_read_address_reg <= s_read_address_next;

         END IF;

      END IF;

   END PROCESS make_read_address_reg;

   make_write_address_reg : PROCESS( clock , reset , s_execute_push ,

                                     s_write_address_next )

   BEGIN

      IF (clock'event AND (clock = '1')) THEN

         IF (reset = '1') THEN s_write_address_reg <= (OTHERS => '0');

         ELSIF (s_execute_push = '1') THEN

            s_write_address_reg <= s_write_address_next;

         END IF;

      END IF;

   END PROCESS make_write_address_reg;

   make_nr_of_bytes_reg : PROCESS( clock , reset , s_nr_of_bytes_next )

   BEGIN

      IF (clock'event AND (clock = '1')) THEN

         IF (reset = '1') THEN s_nr_of_bytes_reg <= (OTHERS => '0');

                          ELSE s_nr_of_bytes_reg <= s_nr_of_bytes_next;

         END IF;

      END IF;

   END PROCESS make_nr_of_bytes_reg;

-- map components

   ram1 : RAMB16_S9_S9

          GENERIC MAP ( WRITE_MODE_A => "READ_FIRST",

                        WRITE_MODE_B => "READ_FIRST" )

          PORT MAP (  DOA     => OPEN,

                      ADDRA   => s_write_address_reg,

                      DIA     => push_data,

                      ENA     => s_execute_push,

                      WEA     => s_execute_push,

                      DOPA    => OPEN,

                      CLKA    => clock,

                      DIPA(0) => push_size,

                      SSRA    => '0',

                      DOPB(0) => pop_size,

                      CLKB    => s_n_clock,

                      DIPB    => "0",

                      SSRB    => '0',

                      DOB     => pop_data,

                      ADDRB   => s_read_address_reg,

                      DIB     => X"00",

                      ENB     => '1',

                      WEB     => '0' );

END xilinx;