accumulator

[Dương Dương]

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.numeric_std.ALL;

ENTITY accumulator IS

PORT (
clk : IN STD_LOGIC;
rst_n : IN STD_LOGIC;
set : IN STD_LOGIC;
data_in : IN SIGNED(7 DOWNTO 0);
enable : IN STD_LOGIC;
accumulator_out : OUT SIGNED(11 DOWNTO 0));

END ENTITY accumulator;

ARCHITECTURE beh OF accumulator IS
SIGNAL accumulator_reg : SIGNED(11 DOWNTO 0);
BEGIN -- ARCHITECTURE beh
accumulator_proc : PROCESS (clk, rst_n, set, enable) IS
BEGIN -- PROCESS accumulator_proc
if rst_n = '0' then
accumulator_reg <= (OTHERS => '0');
elsif rst_n = '1' and set = '1' then
accumulator_reg <= "0000" & data_in;
elsif rst_n = '1' and set = '0' and enable = '1' then
accumulator_reg <= accumulator_reg + data_in;
end if;
END PROCESS accumulator_proc;

accumulator_out <= accumulator_reg;
END ARCHITECTURE beh;

My rst_n signal is synchronous or asynchronous.
Help me design this signal in the remaining way. Thanks