Hi guys I am writing code for shifting rows section in an AES algorithm stuck getting errors.

I am trying to create a matrix from a vector using for loops then mapping a matrix to move them to there required positions. but i keep getting the error Error (10028): Can't resolve multiple constant drivers for net "matrix1[15][4]" at sf.vhd(48)

This keeps occurring for all aspects of the array i have included a full script of the code. Thanks in advance. Ciaran.

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.NUMERIC_STD.ALL;

entity sf is

Generic ( DATA_LENGTH : integer := 128 );

Port ( data_out : out STD_LOGIC_VECTOR (DATA_LENGTH-1 downto 0);

finish : out STD_LOGIC;

data_in : in STD_LOGIC_VECTOR (DATA_LENGTH-1 downto 0);

start : in STD_LOGIC;

clock : in STD_LOGIC;

reset : in STD_LOGIC);

end sf;

architecture RTL of sf is

-----------------------------

----------- TYPES -----------

-----------------------------

TYPE matrix_index IS array (15 downto 0) OF std_logic_vector(7 downto 0);

-----------------------------

---------- SIGNALS ----------

-----------------------------

SIGNAL matrix1, matrix2 : matrix_index;

begin

-- Initialize and Reset process

reset_n_init_process : process(reset)

begin

if(rising_edge(reset)) then

for i in 15 downto 0 loop

matrix1(15-i) <= (others => '0');

matrix2(15-i) <= (others => '0');

end loop;

end if;

end process reset_n_init_process;

-- map the 128 bit input to matrix1 so we can shift it.

vector_to_matrix1: PROCESS(start)

BEGIN

if(rising_edge(start) and clock = '1') then

FOR i IN 15 downto 0 LOOP

matrix1(15-i) <= data_in(8*i+7 downto 8*i);

END LOOP;

end if;

END PROCESS vector_to_matrix1;

-- matrix2 is actually matrix1 shifted as shown in the above example.

-- combinatorial logic

-- first column

matrix2(0) <= matrix1(0);

matrix2(1) <= matrix1(5);

matrix2(2) <= matrix1(10);

matrix2(3) <= matrix1(15);

-- second column

matrix2(4) <= matrix1(4);

matrix2(5) <= matrix1(9);

matrix2(6) <= matrix1(14);

matrix2(7) <= matrix1(3);

-- third column

matrix2(8) <= matrix1(8);

matrix2(9) <= matrix1(13);

matrix2(10) <= matrix1(2);

matrix2(11) <= matrix1(7);

-- forth column

matrix2(12) <= matrix1(12);

matrix2(13) <= matrix1(1);

matrix2(14) <= matrix1(6);

matrix2(15) <= matrix1(11);

--map matrix2 back to 128 bit vector

matrix2_to_vector: PROCESS(matrix2)

BEGIN

if(clock = '1') then

FOR i IN 15 downto 0 LOOP

data_out(8*i+7 DOWNTO 8*i) <= matrix2(15-i);

END LOOP;

finish <= '1';

end if;

END PROCESS matrix2_to_vector;

end RTL;