ise 7.1 Input clk is never used.

Jul 13, 2005 6 Replies

i'm just starting out with fpgas and i'm having what's probably a basic newbie problem. i have the following simple entity:



library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL;



entity test1 is Port ( clk : in std_logic); end test1;



architecture Behavioral of test1 is begin process (clk) is variable i : integer := 0; begin if clk = '1' and clk'event then i := i + 1; end if; end process; end Behavioral;



and i have ISE webpack set to xc2vp2-6ff672 and in the ucf file i have:



NET "clk" LOC = "g14" ;



which i believe is the correct clock pin. when i synthesize that code, i get the following warning:



Synthesizing Unit . Related source file is "C:/temp/test1/test1.vhd". WARNING:Xst:647 - Input is never used. Unit synthesized.



what am i doing wrong?



thanks!



"jeff murphy" schrieb im Newsbeitrag news: snipped-for-privacy@g47g2000cwa.googlegroups.com...

1 designs with outputs are optimized to nothing, its empty !

2 do not use variable but signals if you can

antti

#include

Well, you've declared i as a variable, and I doesn't get used anywhere, so my guess is that XST optimized it away. XST figures that you weren't doing anything useful with your counter.

-a

No output defined so everything is "optimized" away.

Please use

ieee.numeric_std.all;

instead of

ieee.std_logic_arith.all; ieee.std_logic_unsigned.all;

Rgds Andr=E9

thanks, that was, ofcourse, exactly the problem. is there a faq on why i should use std.all instead of arith.all unsigned.all? ISE inserts the use statements for me... so i was just trusting that it put in the appropriate statements.

See here

formatting link

I wish Xilinx would get themselves up-to-date on this front. Numeric_std has been around a hell of a long time!

Cheers, Martin

martin.j.thompson@trw.com TRW Conekt, Solihull, UK http://www.trw.com/conekt

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required