LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.std_logic_unsigned.ALL;

ENTITY CSCD IS

  PORT (
    SWCBA : IN STD_LOGIC_VECTOR(2 DOWNTO 0);
    IR : IN STD_LOGIC_VECTOR(7 DOWNTO 4);
    C, Z : IN STD_LOGIC;
    W : IN STD_LOGIC_VECTOR(3 DOWNTO 1);
    T3, QD : IN STD_LOGIC;
    CLR : IN STD_LOGIC;
    DRW, MEMW : OUT STD_LOGIC;
    PCINC, ARINC : OUT STD_LOGIC;
    LPC, LAR, LIR : OUT STD_LOGIC;
    PCADD : OUT STD_LOGIC;
    SELCTL : OUT STD_LOGIC;
    STOP : OUT STD_LOGIC;
    LDZ, LDC : OUT STD_LOGIC;
    CIN : OUT STD_LOGIC;
    S : OUT STD_LOGIC_VECTOR(3 DOWNTO 0);
    M : OUT STD_LOGIC;
    ABUS, SBUS, MBUS : OUT STD_LOGIC;
    SHORT, LONG : OUT STD_LOGIC;
    SEL : OUT STD_LOGIC_VECTOR(3 DOWNTO 0)
  );

END CSCD;

ARCHITECTURE struct OF CSCD IS
  SIGNAL ST0, SST0 : STD_LOGIC;
BEGIN
  PROCESS (W, T3, SWCBA, IR, CLR)
  BEGIN
    S <= "0000";
    SEL <= "0000";
    DRW <= '0';
    MEMW <= '0';
    PCINC <= '0';
    PCADD <= '0';
    LPC <= '0';
    LAR <= '0';
    LIR <= '0';
    LDZ <= '0';
    LDC <= '0';
    ARINC <= '0';
    STOP <= '0';
    SELCTL <= '0';
    CIN <= '0';
    M <= '0';
    MEMW <= '0';
    ABUS <= '0';
    SBUS <= '0';
    MBUS <= '0';
    SHORT <= '0';
    LONG <= '0';

    IF CLR = '0' THEN
      ST0 <= '0';
      SST0 <= '0';
    ELSIF falling_edge(T3) THEN
      IF SST0 = '1' THEN
        ST0 <= '1';
      END IF;
    END IF;

    CASE SWCBA IS
      WHEN "001" =>
        SBUS <= W(1);
        STOP <= W(1);
        SHORT <= W(1);
        SELCTL <= W(1);
        LAR <= W(1) AND NOT ST0;
        SST0 <= W(1) AND NOT ST0;
        MEMW <= W(1) AND ST0;
        ARINC <= W(1) AND ST0;
      WHEN "010" =>
        STOP <= W(1);
        SHORT <= W(1);
        SELCTL <= W(1);
        SST0 <= W(1) AND NOT ST0;
        SBUS <= W(1) AND NOT ST0;
        LAR <= W(1) AND NOT ST0;
        MBUS <= W(1) AND ST0;
        ARINC <= W(1) AND ST0;
      WHEN "011" =>
        SBUS <= W(1) OR W(2);
        SEL(3) <= ST0;
        SEL(2) <= W(2);
        SEL(1) <= (NOT ST0 AND W(1)) OR (ST0 AND W(2));
        SEL(0) <= W(1);
        SST0 <= W(1) AND NOT ST0;
        SELCTL <= W(1) OR W(2);
        DRW <= W(1) OR W(2);
        STOP <= W(1) OR W(2);
      WHEN "100" =>
        SEL(3) <= W(2);
        SEL(2) <= '0';
        SEL(1) <= W(2);
        SEL(0) <= W(1) OR W(2);
        SELCTL <= W(1) OR W(2);
        STOP <= W(1) OR W(2);
      WHEN "000" =>
        IF ST0 = '0' THEN
          SBUS <= W(1);
          LPC <= W(1);
          STOP <= W(1);
          SELCTL <= W(1);
          SHORT <= W(1);
          SST0 <= W(1);
        ELSE
          LIR <= W(1);
          PCINC <= W(1);
          CASE IR IS
            WHEN "0001" => --ADD
              S(3) <= W(2);
              S(0) <= W(2);
              CIN <= W(2);
              ABUS <= W(2);
              DRW <= W(2);
              LDZ <= W(2);
              LDC <= W(2);
            WHEN "0010" => --SUB
              S(2) <= W(2);
              S(1) <= W(2);
              ABUS <= W(2);
              DRW <= W(2);
              LDZ <= W(2);
              LDC <= W(2);
            WHEN "0011" => --AND
              M <= W(2);
              S(3) <= W(2);
              S(1) <= W(2);
              S(0) <= W(2);
              ABUS <= W(2);
              DRW <= W(2);
              LDZ <= W(2);
            WHEN "0100" => --INC
              ABUS <= W(2);
              DRW <= W(2);
              LDZ <= W(2);
              LDC <= W(2);
            WHEN "0101" => --LD
              M <= W(2);
              S(3) <= W(2);
              S(1) <= W(2);
              ABUS <= W(2);
              LAR <= W(2);
              LONG <= W(2);
              DRW <= W(3);
              MBUS <= W(3);
            WHEN "0110" => --ST
              M <= W(2) OR W(3);
              S(3) <= W(2) OR W(3);
              S(2) <= W(2);
              S(1) <= W(2) OR W(3);
              S(0) <= W(2);
              ABUS <= W(2) OR W(3);
              LAR <= W(2);
              LONG <= W(2);
              MEMW <= W(3);
            WHEN "0111" => --JC
              IF C = '1' THEN
                PCADD <= W(2);
              END IF;
            WHEN "1000" => --JZ
              IF Z = '1' THEN
                PCADD <= W(2);
              END IF;
            WHEN "1001" => --JMP
              M <= W(2);
              S(3) <= W(2);
              S(2) <= W(2);
              S(1) <= W(2);
              S(0) <= W(2);
              ABUS <= W(2);
              LPC <= W(2);
            WHEN "1010" => --OUT
            WHEN "1011" => --IRET
            WHEN "1100" => --DI
            WHEN "1101" => --EI
            WHEN "1110" => --STP
              STOP <= W(2);
            WHEN OTHERS => NULL;
          END CASE;
        END IF;
      WHEN OTHERS => NULL;
    END CASE;
  END PROCESS;
END struct;