Use non static length constant as option in case statement

Hi,

I am writing a case statement for register definitions. The options for case statement are register addresses which I want to be of variable length. I have written a package and rtl as follows:

Package content:

constant reg_address_bits : integer := 9;

constant addr_1 : std_logic_vector(reg_address_bits-1 downto 0) := x"00";

constant addr_2 : std_logic_vector(reg_address_bits-1 downto 0) := x"04";

RTL content:

signal S_reg_addr : std_logic_vector(reg_address_bits-1 downto 0);

case S_reg_addr is

when addr_1 =>

when addr_2 =>

.

.

.

Assume all the syntax that I have missed to be correct.

In this implementation I am getting ncvhdl_p: CSODAS error. I am thinking that it is not considering the constant declaration in package as static constant and thus it gives this error. Kindly tell me the correct implementation.