using a ram megafunction

While Quartus may infer a RAM from this code, it's not using best practices.

First, you should be using ieee.numeric_std.all instead of std_logic_arith, and std_logic_unsigned.

Second, your memory access process should have a sensitivity list and look something like this:

    access_memory : process( clock )
    begin
        if( rising_edge(clock) ) then
            dout <= ram( to_integer( addr ) ) ;
        end if ;
    end process ; -- access_memory

There are also some templates available inside of Quartus which may also be helpful.