11.x XST - "ERROR:HDLCompiler:545 - "<file>.vhd" Line xx: Initial value for constant declaration is not constant"
Description
Keywords: XST, Spartan-6, Virtex-6, 11.2 , Parser, HDLCompiler:940
The following error occurs in XST when I target Virtex-6 or Spartan-6 devices, but I do not have any issues when I target older devices. Why?
ERROR:HDLCompiler:545 - "<file>.vhd" Line xx: Initial value for constant declaration is not constant
Example code:
library ieee;
use ieee.std_logic_1164.all;
entity ex_0009 is
port(clk,a : in std_logic;
res : out std_logic
);
end ex_0009;
architecture bhv of ex_0009 is
constant my_const: std_logic:='0';
signal tmp: std_logic;
begin
tmp <= my_const;
process (clk)
constant local_const: std_logic := tmp; -- Note: Error points here
begin
if clk'event and clk='1' then
res <= a or local_const;
end if;
end process;
end;
Solution
The example above is not a VHDL LRM compliant code. To solve this issue, initialize local_const constant directly with my_const constant.library ieee;
use ieee.std_logic_1164.all;
entity ex_0009 is
port(clk,a : in std_logic;
res : out std_logic
);
end ex_0009;
architecture bhv of ex_0009 is
constant my_const: std_logic:='0';
signal tmp: std_logic;
begin
tmp <= my_const;
process (clk)
constant local_const: std_logic := my_const; -- Note: Error points here
begin
if clk'event and clk='1' then
res <= a or local_const;
end if;
end process;
end;
In 11.2 XST introduced a new VHDL/Verilog parser for Virtex-6 and Spartan-6 families. For more information on this change please refer (Xilinx Answer 32927)