Synthesis of galois adder

Discussion in 'VHDL' started by Patrick, Feb 11, 2005.

  1. Patrick

    Patrick Guest

    hello everybody,

    When I synthesise this component under Quartus 4.1 :

    library IEEE;
    use IEEE.STD_LOGIC_1164.ALL;

    entity add_galois is
    port(
    a : in std_logic_vector(7 downto 0);
    b : in std_logic_vector(7 downto 0);
    c : out std_logic_vector(7 downto 0)
    );
    end add_galois;

    architecture plus of add_galois is
    begin
    OUEX:for i in 0 to 7 generate c(i)<=a(i) xor b(i); end
    generate;
    end plus;

    Quartus implemente this with 8 logic element, OK.

    When I use this add_galois in an other design, Quartus takes 87 logic
    element per add_galois !!!!

    And when I visualise the add_galois in RTL Viewer, there's only 8 XOR
    per add_galois !!!

    What's happen ?
    Patrick, Feb 11, 2005
    #1
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  2. Patrick wrote:
    > hello everybody,
    >
    > When I synthesise this component under Quartus 4.1 :
    >
    > library IEEE;
    > use IEEE.STD_LOGIC_1164.ALL;
    >
    > entity add_galois is
    > port(
    > a : in std_logic_vector(7 downto 0);
    > b : in std_logic_vector(7 downto 0);
    > c : out std_logic_vector(7 downto 0)
    > );
    > end add_galois;
    >
    > architecture plus of add_galois is
    > begin
    > OUEX:for i in 0 to 7 generate
    > c(i)<=a(i) xor b(i);
    > end generate;
    > end plus;
    >
    > Quartus implemente this with 8 logic element, OK.
    >
    > When I use this add_galois in an other design, Quartus takes 87 logic
    > element per add_galois !!!!
    >
    > And when I visualise the add_galois in RTL Viewer, there's only 8 XOR
    > per add_galois !!!
    >
    > What's happen ?


    I have no idea, never worked with Quartus. Seems to be a quirck in
    Quartus which has nothing to do with VHDL. The only thing I can say is
    that you don't need to use a generate loop here. Just write:

    OUEX: c <= a xor b;

    And as far I am concerned, I would not bother to create an entity for
    such a simple construction.

    Paul.
    Paul Uiterlinden, Feb 11, 2005
    #2
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