-------------------------------------------------------------------------------
--  EE 126 Project # 2, Serial Binary Multimplier
--  VHDL implementation by: Frank Bruno
--  Part of a project for Professor Chang
-------------------------------------------------------------------------------
LIBRARY work;
USE work.am2900_pkg.all;
USE work.bv_arithmetic.ALL;

ENTITY mult IS
  PORT(multiplier      : IN     bit_vector(3 DOWNTO 0);
       multiplicand    : IN     bit_vector(3 DOWNTO 0);
       clock           : IN     bit;
       init            : IN     bit;
       ac              : BUFFER bit_vector(3 DOWNTO 0);
       qout            : BUFFER bit_vector(3 DOWNTO 0);
       sc              : BUFFER integer range 0 to 4;
       qr              : BUFFER bit_vector(4 DOWNTO 0);
       br              : BUFFER bit_vector(3 DOWNTO 0);
       done            : OUT    bit);
END mult;

ARCHITECTURE behave_mult OF mult IS
  
BEGIN  --  behave

  multiply:
  PROCESS
    VARIABLE state : integer range 0 to 3;
    VARIABLE status : bit_vector(3 DOWNTO 0);
    VARIABLE result : bit_vector(3 DOWNTO 0);
    VARIABLE as : bit;
    VARIABLE temp : bit_vector(3 DOWNTO 0);
    
    BEGIN
      WAIT UNTIL clock'EVENT and clock='1';
      IF (init = '0') THEN
        ac <= "0000";
        br <= multiplicand;
        qr(4 DOWNTO 1) <= multiplier;
        ac <= "0000";
        sc <= 4;
        qr(0) <= '0';
        done <= '0';
        state := 0;
      ELSE
        CASE state IS
          WHEN 0 =>
            CASE qr(1 DOWNTO 0) IS
              WHEN "01" =>
                add_sub('0', ac, br, '0', result, status);
                ac <= result;
                --ac <= ac + br;
              WHEN "10" =>
                add_sub('1', ac, br, '0', result, status);
                ac <= result;
                --ac <= ac - br;
              WHEN OTHERS =>
            END CASE;                    --  qr(1 DOWNTO 0)
            state := 1;
          WHEN 1 =>
            qr(0) <= qr(1);
            qr(1) <= qr(2);
            qr(2) <= qr(3);
            qr(3) <= qr(4);
            qr(4) <= ac(0);
            ac(0) <= ac(1);
            ac(1) <= ac(2);
            ac(2) <= ac(3);
            sc <= sc - 1;
            state := 2;
          WHEN 2 =>
            IF (sc = 0) THEN
              state := 3;
            ELSE
              state := 0;
            END IF;
          WHEN 3 =>
            done <= '1';
            qout <= qr(4 DOWNTO 1);
            state := 0;
          WHEN others =>
            
        END CASE;                        --  state
      END IF;

      
  END PROCESS;
END behave_mult;

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