drink-cnt.vhd

design compile synthesis user guide

entity DRINK_COUNT_VHDL is
  port(NICKEL_IN, DIME_IN, QUARTER_IN, RESET: BOOLEAN;
       CLK: BIT;
       NICKEL_OUT, DIME_OUT, DISPENSE: out BOOLEAN);
end;

architecture BEHAVIOR of DRINK_COUNT_VHDL is
  signal CURRENT_NICKEL_COUNT,
         NEXT_NICKEL_COUNT: INTEGER range 0 to 7;
  signal CURRENT_RETURN_CHANGE, NEXT_RETURN_CHANGE : BOOLEAN;
begin

  process
    variable TEMP_NICKEL_COUNT: INTEGER range 0 to 12;
  begin
    -- Default assignments
    NICKEL_OUT <= FALSE;
    DIME_OUT <= FALSE;
    DISPENSE <= FALSE;
    -- CURRENT_NICKEL_COUNT <= 0;
    NEXT_NICKEL_COUNT <= 0;
    NEXT_RETURN_CHANGE <= FALSE;

    -- Synchronous reset
    if (not RESET) then
      TEMP_NICKEL_COUNT := CURRENT_NICKEL_COUNT;

      -- Check whether money has come in
      if (NICKEL_IN) then
        -- NOTE:  This design will be flattened, so
        --   these multiple adders will be optimized
        TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT + 1;
      elsif(DIME_IN) then
        TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT + 2;
      elsif(QUARTER_IN) then
        TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT + 5;
      end if;

      -- Enough deposited so far?
      if(TEMP_NICKEL_COUNT >= 7) then
        TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT - 7;
        DISPENSE <= TRUE;
      end if;

      -- Return change
      if(TEMP_NICKEL_COUNT >= 1 or
         CURRENT_RETURN_CHANGE) then
        if(TEMP_NICKEL_COUNT >= 2) then
          DIME_OUT <= TRUE;
          TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT - 2;
          NEXT_RETURN_CHANGE <= TRUE;
        end if;
        if(TEMP_NICKEL_COUNT = 1) then
          NICKEL_OUT <= TRUE;
          TEMP_NICKEL_COUNT := TEMP_NICKEL_COUNT - 1;
        end if;
      end if;

      NEXT_NICKEL_COUNT <= TEMP_NICKEL_COUNT;
    end if;
  end process;

  -- Remember the return-change flag and
  -- the nickel count for the next cycle
  process
  begin
    wait until CLK'event and CLK = '1';
    CURRENT_RETURN_CHANGE <= NEXT_RETURN_CHANGE;
    CURRENT_NICKEL_COUNT <= NEXT_NICKEL_COUNT;
  end process;

end BEHAVIOR;