Reading a Text File

This undefined 'U' states occur when signals do not have a defined state right from the beginning of the simulation.

    read_file : PROCESS IS
        FILE file_in     : text;          -- file ID
        VARIABLE line_rd : line;          -- text line
        VARIABLE data_in : integer;       -- integer data input
        VARIABLE i       : integer := 0;  -- line counter
    BEGIN
        file_open(file_in, filename, read_mode);
        pixel_value <= (OTHERS => '0');
        WAIT UNTIL rising_edge(start);
        WHILE (NOT endfile(file_in)) LOOP
            readline(file_in, line_rd);
            read(line_rd, data_in);
            read_frame_array(i) <= std_logic_vector(to_unsigned(data_in, 8));
            pixel_value         <= std_logic_vector(to_unsigned(data_in, 8));
            i := i + 1;
            WAIT UNTIL rising_edge(start);
        END LOOP;
        file_close(file_in);
        WAIT;
    END PROCESS read_file;