I am trying to make a simple MACC to work, but it does unexpected things.
The multiplication is not working. 00001 * 00001 outputs 00000
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity macc is
Port ( clk : in STD_LOGIC;
rst : in STD_LOGIC;
en : in STD_LOGIC;
A : in STD_LOGIC_VECTOR (4 downto 0);
B : in STD_LOGIC_VECTOR (4 downto 0);
P : out STD_LOGIC_VECTOR (8 downto 0));
end macc;
architecture Behavioral of macc is
signal product : STD_LOGIC_VECTOR (8 downto 0);
signal acc_in : STD_LOGIC_VECTOR (8 downto 0);
signal acc_out : STD_LOGIC_VECTOR (8 downto 0);
begin
product <= A*B;
acc_in <= acc_out + product;
acc: process is
begin
wait until rising_edge(clk);
if (rst = '1') then
acc_out <= (others => '0');
elsif (en = '1') then
acc_out <= acc_in;
end if;
end process acc;
P <= acc_out;
end Behavioral;
Best Answer
If you multiply 2 5-bit numbers (
A
andB
are bothstd_logic_vector(4 downto 0)
) don't you need 10 bits (not 9) to store it in (soP
should bestd_logic_vector(9 downto 0)
? (31*31 = 961: needs 10 bits)But also - don't use
std_logic_arith
/_unsigned
. Useieee.numeric_std
and then use theunsigned
data type.