vhdl: object subtype is not locally static

Question

using GHDL to compile some VHDL getting a weird error. simulation compiler for VHDL fails on line: "case i_cli_adr is" with error message: "vhdl: object subtype is not locally static". How to fix it?

library ieee;
use ieee.std_logic_1164.all;

entity sim_regs is
    generic(
        LW                        : integer := 16
    );
    port(
        i_sys_clk                 : in    std_logic;
        i_sys_rst_n               : in    std_logic;

        i_cli_vld                 : in    std_logic;
        i_cli_wnr                 : in    std_logic;
        i_cli_adr                 : in    std_logic_vector(LW-1 downto 0);
        i_cli_dat                 : in    std_logic_vector(LW-1 downto 0);
    );
end entity;

architecture sim of sim_regs is
    signal     testreg0                  : std_logic_vector(LW-1 downto 0);
    signal     testreg1                  : std_logic_vector(LW-1 downto 0);
    signal     awrite                    : std_logic;
begin

awrite <= i_cli_vld and i_cli_wnr;

process(i_sys_clk)
begin
    if (i_sys_clk = '1' and i_sys_clk'event) then
        if (i_sys_rst_n = '0') then
            testreg0   <= (others => '0');
            testreg1   <= (others => '0');
        end if;

    else 
       o_cli_rvld <= '0';      

        if (awrite = '1') then
            case i_cli_adr is
            when 0 => testreg0 <= i_cli_dat;
            when 1 => testreg1 <= i_cli_dat;
            end case;   
        end if;
    end if;

end process;

end architecture;

Its not locally static because the size of the vector is determined by a generic. Case object must have a size known at compile time (not elaboration). You also cannot use integer literals on a std_logic_vector and you must cover ALL possible cases. — Tricky

pico pico · Accepted Answer · 2019-04-30T16:11:57

The fix was to hard code the size of address internally

architecture sim of sim_regs is

    signal     aaddr                     : std_logic_vector(15 downto 0);

begin

    aaddr  <= i_cli_adr and X"FFFF";

    --- now can use aaddr in place of i_cli_adr in "case"

Complete Example:

library ieee;
use ieee.std_logic_1164.all;
use IEEE.numeric_std.all;

entity sim_regs is
    generic(
        LW                        : integer := 16
    );
    port(
        i_sys_clk                 : in    std_logic;
        i_sys_rst_n               : in    std_logic;

        i_cli_vld                 : in    std_logic;
        i_cli_wnr                 : in    std_logic;
        i_cli_adr                 : in    std_logic_vector(LW-1 downto 0);
        i_cli_dat                 : in    std_logic_vector(LW-1 downto 0);
        o_cli_rdat                : out   std_logic_vector(LW-1 downto 0);
        o_cli_rvld                : out   std_logic;
        i_cli_rbsy                : in    std_logic        
    );
end entity;

architecture sim of sim_regs is
    signal     testreg0                  : std_logic_vector(LW-1 downto 0);
    signal     testreg1                  : std_logic_vector(LW-1 downto 0);
    signal     testreg2                  : std_logic_vector(LW-1 downto 0);
    signal     testreg3                  : std_logic_vector(LW-1 downto 0);
    signal     aaddr                     : std_logic_vector(15 downto 0);
    signal     awrite                    : std_logic;
    signal     aread                     : std_logic;
begin

awrite <= i_cli_vld and i_cli_wnr;
aread  <= i_cli_vld and  not i_cli_wnr and not i_cli_rbsy;
aaddr  <= i_cli_adr and X"FFFF";

process(i_sys_clk)
begin
    if (i_sys_clk = '1' and i_sys_clk'event) then
        if (i_sys_rst_n = '0') then
            o_cli_rvld <= '0';
            o_cli_rdat <= (others => '0');
            testreg0   <= (others => '0');
            testreg1   <= (others => '0');
            testreg2   <= (others => '0');
            testreg3   <= (others => '0');
        end if;

    else 
       o_cli_rvld <= '0';      

        if (awrite = '1') then
            case aaddr is
            when X"0000" => testreg0 <= i_cli_dat;
            when X"0001" => testreg1 <= i_cli_dat;
            when X"0002" => testreg2 <= i_cli_dat;
            when X"0003" => testreg3 <= i_cli_dat;
            when others  => null;
            end case;

        elsif (aread = '1') then
            o_cli_rvld <= '1';  

            case aaddr is
            when X"0000" => o_cli_rdat <= testreg0;
            when X"0001" => o_cli_rdat <= testreg1;
            when X"0002" => o_cli_rdat <= testreg2;
            when X"0003" => o_cli_rdat <= testreg3;
            when others  => o_cli_rdat <= (others => '0');
            end case;      
        end if;
    end if;

end process;

end architecture;

vhdl: object subtype is not locally static

1 Answers