Build a tone generator which takes a 24.000 MHz clock signal, and produces a 440 Hz (A4) square wave (i.e., low for half the period and then high for half the period).
Since the hardware has no concept of time, you'll need to keep track of clock cycles to do the timing.
entity tone440 is
clk : in std_logic;
reset : in std_logic;
tone : out std_logic
architecture synth of tone440 is
tone <= '0'; -- A very flat tone