LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY Speakera IS
    PORT (   clk  : IN STD_LOGIC;
             Tone : IN STD_LOGIC_VECTOR (10 DOWNTO 0);
             SpkS : OUT STD_LOGIC  );
END;
ARCHITECTURE one OF Speakera IS
    SIGNAL PreCLK, FullSpkS : STD_LOGIC;
BEGIN
 DivideCLK : PROCESS(clk)
        VARIABLE Count4 : STD_LOGIC_VECTOR (3 DOWNTO 0) ;
    BEGIN
        PreCLK <= '0';  --  將CLK進行16分頻，PreCLK為CLK的16分頻
        IF Count4>11 THEN PreCLK <= '1';  Count4 := "0000";
        ELSIF clk'EVENT AND clk = '1' THEN  Count4 := Count4 + 1;     
        END IF;
    END PROCESS;
    GenSpkS : PROCESS(PreCLK, Tone)-- 11位可預置計數器
        VARIABLE Count11 : STD_LOGIC_VECTOR (10 DOWNTO 0);
BEGIN
      IF PreCLK'EVENT AND PreCLK = '1' THEN
       IF Count11 = 16#7FF# THEN Count11 := Tone ; FullSpkS <= '1';  
            ELSE Count11 := Count11 + 1; FullSpkS <= '0'; END IF;
        END IF;
   END PROCESS;
 DelaySpkS : PROCESS(FullSpkS)--將輸出再2分頻，展寬脈沖，使揚聲器有足夠功率發音
        VARIABLE Count2 : STD_LOGIC;
BEGIN
    IF FullSpkS'EVENT AND FullSpkS = '1' THEN  Count2 := NOT Count2;
            IF Count2 = '1' THEN  SpkS <= '1';
            ELSE SpkS <= '0';  END IF;
        END IF;
    END PROCESS;
END;