--***************************************************************************

ENTITY counter IS
  PORT ( ck, i, reset: IN BIT; 
         o: OUT BIT;
         -- These flags are for debugging purposes only
         s0_flag, s1_flag, s2_flag, s3_flag, s4_flag : OUT BIT 
  );
END counter;

--***************************************************************************

ARCHITECTURE automate OF counter IS

TYPE STATE_TYPE IS ( S0, S1, S2, S3, S4 );

-- pragma CLOCK ck
-- pragma CUR_STATE CURRENT_STATE
-- pragma NEX_STATE NEXT_STATE

SIGNAL CURRENT_STATE, NEXT_STATE: STATE_TYPE;

BEGIN
  PROCESS ( CURRENT_STATE, i, reset )
  BEGIN
    IF ( reset = '1' ) THEN
      NEXT_STATE <= S0;
      o <= '0';
    ELSE
    CASE CURRENT_STATE IS

      WHEN S0 => s0_flag <= '1';
        s1_flag <= '0';
        s2_flag <= '0';
        s3_flag <= '0';
        s4_flag <= '0';
        IF ( i = '1' ) THEN
          NEXT_STATE <= S1;
        ELSE
          NEXT_STATE <= S0;
        END IF;
        o <= '0';

      WHEN S1 => s1_flag <= '1';
        s0_flag <= '0';
        s2_flag <= '0';
        s3_flag <= '0';
        s4_flag <= '0';
        IF ( i = '1' ) THEN
          NEXT_STATE <= S2;
        ELSE
          NEXT_STATE <= S0;
        END IF;
        o <= '0';

      WHEN S2 => s2_flag <= '1';
        s0_flag <= '0';
        s1_flag <= '0';
        s3_flag <= '0';
        s4_flag <= '0';
        IF ( i = '1' ) THEN
          NEXT_STATE <= S3;
        ELSE
          NEXT_STATE <= S0;
        END IF;
        o <= '0';

      WHEN S3 => s3_flag <= '1';
        s0_flag <= '0';
        s1_flag <= '0';
        s2_flag <= '0';
        s4_flag <= '0';
        IF ( i = '1' ) THEN
          NEXT_STATE <= S4;
        ELSE
          NEXT_STATE <= S0;
        END IF;
        o <= '0';

      WHEN S4 => s4_flag <= '1';
        s0_flag <= '0';
        s1_flag <= '0';
        s2_flag <= '0';
        s3_flag <= '0';
        IF ( i = '1' ) THEN
          NEXT_STATE <= S4;
        ELSE
          NEXT_STATE <= S0;
        END IF;
        o <= '1';

      WHEN OTHERS =>
        ASSERT ( '1' )
        REPORT "Illegal State";

    END CASE;
  END IF;
  END PROCESS;

  PROCESS ( ck )
  BEGIN
    IF ( ck = '1' AND NOT ck'STABLE ) THEN
      CURRENT_STATE <= NEXT_STATE;
    END IF;
  END PROCESS;

END automate;