Compiling Error : "Value of index is not static"

Hi,
I'm implementing a simple ripple carry adder using instances of a simple adder (called CLA...that works..).The ripple carry adder is generic , N is the bit widht.
Unfortunately when I loop to generate the simple adders ("CLA" components..) ,
I receive 2 errors : value "I" is not static (at the component "as": entity) , and value of index is not static(at aLess1: entity) .

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


entity RCA is
	 
	 generic(N:integer:=4);

    Port ( A : in  STD_LOGIC_VECTOR(N-1 downto 0);--nel caso da 3 a 0 (cioè 4)
           B : in  STD_LOGIC_VECTOR(N-1 downto 0);
           S : out  STD_LOGIC_VECTOR(N-1 downto 0);
           Carry_in : in  STD_LOGIC;--un solo bit di uscita globale
           Carry_out : out  STD_LOGIC);--un solo bit di uscita globale
end RCA;

architecture behavioral of RCA is
  
  signal c : std_logic_vector(N-1 to 0); -- internal carry signal

COMPONENT  CLA --
 	
		GENERIC (N: INTEGER := 32);  

	PORT (	a     : IN	UNSIGNED ((N-1) DOWNTO 0);
				b		: IN	UNSIGNED ((N-1) DOWNTO 0);				
				c_in	: IN	STD_LOGIC;
				s		: OUT   UNSIGNED ((N-1) DOWNTO 0);
				c_out	: OUT	STD_LOGIC;
				overflow   : OUT STD_LOGIC
	      
			);
	END COMPONENT;
	
	
	
	

begin

  a0: entity CLA generic map(1) port map(A(0)=>a(0),B(0)=>b(0),C_in=>Carry_in,C_out=>c(0),S(0)=>S(0));
  
  
  middle: for I in 1 to N-2 generate
				
			as: entity CLA generic map(1) port map(A(I)=>a(I),B(I)=>b(I),C_in=> c(I-1),C_out=>c(I), S(I)=>s(I));
         
			end generate middle;
			
			
  
  aLess1: entity CLA generic map(1) port map(A(N-1)=>a(N-1),B(N-1)=>b(N-1),C_in=> c(N-2) ,C_out=>Carry_out,S(N-1)=>s(N-1));



end Behavioral;

Could you help me please?
Thanks a lot in advance..

andrew_ross

[jeppe]

How come your having two different values of the Generic N?

Are your planning to implement this in a FPGA?

jeppe

[andrew_ross]

Just because COMPONENT CLA is a module itself implemented with generics..xilinx compiler apparently don't get any errors for that..

I have to implementit to fpga spartan III

andrew_ross