Xilinx ISE : type real

Discussion in 'VHDL' started by charsi, May 19, 2005.

  1. charsi

    charsi Guest

    i'm using Xilinx ISE 6.3i...i'm required to calculate logarithm in my
    design...Xilinx wont support type real.

    Is there any cure for this..i intend to use Xilinx only.

    plz help...thanks
     
    charsi, May 19, 2005
    #1
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  2. Hi,

    Real Numbers are not synthesizable . Consider using fix point format
    ..

    -- Mohammed A Khader.
     
    Mohammed A khader, May 20, 2005
    #2
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  3. charsi

    Alain Guest

    Hi,

    Which kind log do you want to implement ? Log2, for instance easy to
    implement for integer.

    function Log2(input : integer) return integer is
    variable n : integer;
    variable logn : integer;
    begin
    n := 1;
    for i in 0 to 31 loop
    logn := i;
    exit when (n >= input);
    n := n * 2;
    end loop;
    return logn;
    end;


    "charsi" <> a écrit dans le message de
    news: ...
    > i'm using Xilinx ISE 6.3i...i'm required to calculate logarithm in my
    > design...Xilinx wont support type real.
    >
    > Is there any cure for this..i intend to use Xilinx only.
    >
    > plz help...thanks
    >
     
    Alain, May 21, 2005
    #3
  4. charsi

    David Bishop Guest

    charsi wrote:

    > i'm using Xilinx ISE 6.3i...i'm required to calculate logarithm in my
    > design...Xilinx wont support type real.
    >
    > Is there any cure for this..i intend to use Xilinx only.


    First, according to 1076.6 the type "real" is not synthesisizable.

    I think that the function you really want is in the new "numeric_std"
    package.

    Download this file:
    http://www.eda.org/vhdl-200x/vhdl-200x-ft/packages/additions_11.tar.Z

    Compile the file "numeric_std_additions.vhd" (this are just the new
    functions, not the whole thing)

    Use this function:

    signal XXX : UNSIGNED (16 downto 0);
    signal log_base_2 : integer;

    log_base_2 := find_msb (XXX, '1');

    This package will synthesize with XST, the fixed point and floating
    point packages will not until Xilinx 8.0 because they use a negative index.
     
    David Bishop, May 22, 2005
    #4
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