VHDL Parametric case - vhdl

Question

I've some problem with my synthesis tool. I'm writing a module and I'm tryng to make it parametric and scalable. In my design I've a FSM and some counters. The counters have a parametric width ( they are function of the width of the datapath ). The problem is that I'm using that counter to drive a case statements. The synthesizer gives me back this error :
2049990 ERROR - (VHDL-1544) array type case expression must be of a locally static subtype
I've also tried to use subtype, but it doesnt work. The declaration is :
constant LENGTH_COUNTER_WORD : integer := integer(ceil(log2(real(WIDTH_DATA/WIDTH_WORD))));
subtype type_counter_word is std_logic_vector( LENGTH_COUNTER_WORD - 1 downto 0);
signal counter_word : std_logic_vector( LENGTH_COUNTER_WORD - 1 downto 0);
The case :
case type_counter_word'(counter_word) is
when (others => '1') =>
do_stuff();
when others =>
do_other_stuff();
end case;
I cannot switch to VHDL-2008. I've read I can use variable, but I'd like to find a different solution, if it exists. I cannot imagine there isn't any way to give parameters to synthesizer before the synthesis.

Answer 1

This is fixed in VHDL-2008. You can only work around it in earlier standards by using cascaded if statements (with the attendant priority logic). Variables don't make a difference when determining if choices are locally static.

Answer 2

I'm not sure how complicated your do_stuff() and do_other_stuff() operations are, but if you are just doing simple signal assignments, you could look into the and_reduce() function in the ieee.std_logic_misc library.
As an example:
output <= '1' when and_reduce(type_counter_word'(counter_word)) = '1' else '0';
Otherwise, as Kevin's answer suggests, a process block using if statements might be your best option.

Answer 3

About the time of Kevin's good enough answer, I had written this to demonstrate:
library ieee;
use ieee.std_logic_1164.all;
use ieee.math_real.all;
entity counterword is
generic (
WIDTH_DATA: positive := 16;
WIDTH_WORD: positive := 8
);
end entity;
architecture foo of counterword is
constant LENGTH_COUNTER_WORD : integer :=
integer(ceil(log2(real(WIDTH_DATA/WIDTH_WORD))));
subtype type_counter_word is
std_logic_vector( LENGTH_COUNTER_WORD - 1 downto 0);
signal counter_word : std_logic_vector( LENGTH_COUNTER_WORD - 1 downto 0);
procedure do_stuff is
begin
end;
procedure do_other_stuff is
begin
end;
begin
UNLABELLED:
process (counter_word)
begin
-- case type_counter_word'(counter_word) is
-- when (others => '1') =>
-- do_stuff;
-- when others =>
-- do_other_stuff;
-- end case;
if counter_word = type_counter_word'(others => '1') then
do_stuff;
else
do_other_stuff;
end if;
end process;
end architecture;
Note because type_counter_word is a subtype you can provide the subtype constraints in a qualified expression for the aggregate:
if counter_word = type_counter_word'(others => '1') then
From IEEE Std 1076-2008:
9.3.5 Qualified expressions
A qualified expression is a basic operation (see 5.1) that is used to explicitly state the type, and possibly the subtype, of an operand that is an expression or an aggregate.
This example analyzes, elaborates and simulates while doing nothing in particular. It'll call the sequential procedure statement do_other_stuff, which does nothing.
(For do_stuff and do_other stuff, empty interface lists aren't allowed).