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Xilinx ISE : type real

 
 
charsi
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      05-19-2005
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

 
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Mohammed A khader
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      05-20-2005
Hi,

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

-- Mohammed A Khader.

 
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Alain
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      05-21-2005
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" <(E-Mail Removed)> a écrit dans le message de
news: 40074f5037b6cee8f57fca3db2ee05b5@loc...rogramming.com...
> 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
>



 
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David Bishop
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      05-22-2005
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-20...tions_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.
 
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