写一个基于VHDL的出租车计价器

以下是一个简单的基于VHDL的出租车计价器的代码实现：

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity taxi_meter is
    Port ( clk : in STD_LOGIC;
           reset : in STD_LOGIC;
           start_trip : in STD_LOGIC;
           stop_trip : in STD_LOGIC;
           distance : in STD_LOGIC_VECTOR (7 downto 0);
           fare : out STD_LOGIC_VECTOR (7 downto 0));
end taxi_meter;

architecture Behavioral of taxi_meter is

    type state_type is (IDLE, TRIP_STARTED, TRIP_STOPPED);
    signal state : state_type := IDLE;
    signal total_distance : integer range 0 to 255 := 0;
    signal total_fare : integer range 0 to 255 := 0;
    constant fare_rate : integer := 10;

begin

    process (clk, reset)
    begin
        if (reset = '1') then
            state <= IDLE;
            total_distance <= 0;
            total_fare <= 0;
            fare <= "00000000";
        elsif (rising_edge(clk)) then
            case state is
                when IDLE =>
                    if (start_trip = '1') then
                        state <= TRIP_STARTED;
                        total_distance <= 0;
                        total_fare <= 0;
                        fare <= "00000000";
                    end if;
                when TRIP_STARTED =>
                    if (stop_trip = '1') then
                        state <= TRIP_STOPPED;
                        total_fare <= total_distance * fare_rate;
                        fare <= std_logic_vector(to_unsigned(total_fare, 8));
                    else
                        total_distance <= total_distance + to_integer(unsigned(distance));
                    end if;
                when TRIP_STOPPED =>
                    if (start_trip = '1') then
                        state <= TRIP_STARTED;
                        total_distance <= 0;
                        total_fare <= 0;
                        fare <= "00000000";
                    end if;
            end case;
        end if;
    end process;

end Behavioral;

该计价器包含一个状态机，它可以在空闲、行程开始和行程结束之间转换。在行程开始状态下，计价器将累加距离并计算总费用。在行程结束状态下，计价器将输出最终费用并等待下一个行程的开始。

请注意，此代码仅用于演示目的，可能需要进行更多测试和验证才能用于实际应用。