File Input
Require file and line variables:
InputProcess: process (clk)
file input : text is “input.txt”;
variable op1_in, op2_in :
std_logic_vector(3 downto 0);
if clk'event and clk='1' then
if not endfile(input) then
readline(input, line_in);
ieee.std_logic_textio.all;