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[/] [mblite/] [trunk/] [hw/] [std/] [sram_4en.vhd] - Blame information for rev 7

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----------------------------------------------------------------------------------------------
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--
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--      Input file         : sram_4en.vhd
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--      Design name        : sram_4en
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--      Author             : Tamar Kranenburg
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--      Company            : Delft University of Technology
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--                         : Faculty EEMCS, Department ME&CE
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--                         : Systems and Circuits group
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--
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--      Description          : Single Port Synchronous Random Access Memory with 4 write enable
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--                             ports.
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--      Architecture 'arch'  : Default implementation
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--      Architecture 'arch2' : Alternative implementation
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--
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----------------------------------------------------------------------------------------------
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LIBRARY ieee;
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USE ieee.std_logic_1164.ALL;
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USE ieee.std_logic_unsigned.ALL;
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LIBRARY mblite;
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USE mblite.std_Pkg.ALL;
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ENTITY sram_4en IS GENERIC
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(
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    WIDTH : positive := 32;
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    SIZE  : positive := 16
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);
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PORT
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(
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    dat_o : OUT std_logic_vector(WIDTH - 1 DOWNTO 0);
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    dat_i : IN std_logic_vector(WIDTH - 1 DOWNTO 0);
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    adr_i : IN std_logic_vector(SIZE - 1 DOWNTO 0);
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    wre_i : IN std_logic_vector(WIDTH/8 - 1 DOWNTO 0);
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    ena_i : IN std_logic;
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    clk_i : IN std_logic
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);
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END sram_4en;
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-- Although this memory is very easy to use in conjunction with Modelsims mem load, it is not
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-- supported by many devices (although it comes straight from the library. Many devices give
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-- cryptic synthesization errors on this implementation, so it is not the default.
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ARCHITECTURE arch2 OF sram_4en IS
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    TYPE ram_type IS array(2 ** SIZE - 1 DOWNTO 0) OF std_logic_vector(WIDTH - 1 DOWNTO 0);
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    TYPE sel_type IS array(WIDTH/8 - 1 DOWNTO 0) OF std_logic_vector(7 DOWNTO 0);
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    SIGNAL ram: ram_type;
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    SIGNAL di: sel_type;
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BEGIN
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    PROCESS(wre_i, dat_i, adr_i)
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    BEGIN
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        FOR i IN 0 TO WIDTH/8 - 1 LOOP
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            IF wre_i(i) = '1' THEN
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                di(i) <= dat_i((i+1)*8 - 1 DOWNTO i*8);
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            ELSE
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                di(i) <= ram(my_conv_integer(adr_i))((i+1)*8 - 1 DOWNTO i*8);
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            END IF;
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        END LOOP;
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    END PROCESS;
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    PROCESS(clk_i)
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    BEGIN
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        IF rising_edge(clk_i) THEN
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            IF ena_i = '1' THEN
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                ram(my_conv_integer(adr_i)) <= di(3) & di(2) & di(1) & di(0);
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                dat_o <= di(3) & di(2) & di(1) & di(0);
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            END IF;
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        END IF;
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    END PROCESS;
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END arch2;
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-- Less convenient but very general memory block with four separate write
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-- enable signals. (4x8 bit)
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ARCHITECTURE arch OF sram_4en IS
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BEGIN
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   mem: FOR i IN 0 TO WIDTH/8 - 1 GENERATE
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       mem : sram GENERIC MAP
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       (
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           WIDTH   => 8,
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           SIZE    => SIZE
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       )
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       PORT MAP
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       (
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           dat_o   => dat_o((i+1)*8 - 1 DOWNTO i*8),
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           dat_i   => dat_i((i+1)*8 - 1 DOWNTO i*8),
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           adr_i   => adr_i,
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           wre_i   => wre_i(i),
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           ena_i   => ena_i,
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           clk_i   => clk_i
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       );
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   END GENERATE;
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END arch;

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