vhdl 编写仿真文件以及测试文件代码 模仿十字路口的交通灯控制效果，实验过程采用实验平台上的红黄绿三种色彩的 LED 灯代表红灯、黄灯与绿灯，在东西和南北方向各有一组红黄绿灯，通过 VHDL 编程 控制不同方向不同色彩的 LED 按照交通指挥的规律亮灭，另外设计一个紧急状态按钮， 当紧急状态出现时，两个方向都禁止通行，指示红灯。紧急状态解除时，LED 重新正常 工作。 设计时如果设东西方向和南北方向的车流量大致相同，因此东西方向和南北方向的 红黄绿灯的时长也相同。学有余力的同学，也可假设某一个方向车流量较大，需要更长 的绿灯时间，在 VHDL 代码中体现这一功能。

以下是 vhdl 编写仿真文件以及测试文件代码，模仿十字路口的交通灯控制效果：

entity traffic_light is
Port ( NS_light : out std_logic_vector(2 downto 0);
EW_light : out std_logic_vector(2 downto 0);
emergency_button : in std_logic;
clk : in std_logic);
end traffic_light;

architecture Behavioral of traffic_light is
signal NS_state : std_logic_vector(1 downto 0);
signal EW_state : std_logic_vector(1 downto 0);
signal NS_timer : integer range 0 to 100000000;
signal EW_timer : integer range 0 to 100000000;
signal emergency_state : std_logic;
begin

NS_light <= "000" when (emergency_state = '1') else NS_state;
EW_light <= "000" when (emergency_state = '1') else EW_state;

process(clk)
begin
if rising_edge(clk) then
if (emergency_button = '1') then
emergency_state <= '1';
end if;

if (emergency_state = '1') then
NS_state <= "001";
EW_state <= "001";
else
case NS_state is
when "00" => --NS green, EW red
NS_light <= "001";
EW_light <= "100";
if (NS_timer >= 100000000) then
NS_state <= "01";
NS_timer <= 0;
else
NS_timer <= NS_timer + 1;
end if;
when "01" => --NS yellow, EW red
NS_light <= "010";
EW_light <= "100";
if (NS_timer >= 10000000) then
NS_state <= "10";
NS_timer <= 0;
else
NS_timer <= NS_timer + 1;
end if;
when "10" => --NS red, EW green
NS_light <= "100";
EW_light <= "001";
if (EW_timer >= 100000000) then
NS_state <= "00";
EW_state <= "00";
EW_timer <= 0;
else
EW_timer <= EW_timer + 1;
end if;
end case;

case EW_state is
when "00" => --EW green, NS red
NS_light <= "100";
EW_light <= "001";
if (EW_timer >= 100000000) then
EW_state <= "01";
EW_timer <= 0;
else
EW_timer <= EW_timer + 1;
end if;
when "01" => --EW yellow, NS red
NS_light <= "100";
EW_light <= "010";
if (EW_timer >= 10000000) then
EW_state <= "10";
EW_timer <= 0;
else
EW_timer <= EW_timer + 1;
end if;
when "10" => --EW red, NS green
NS_light <= "001";
EW_light <= "100";
if (NS_timer >= 100000000) then
NS_state <= "00";
EW_state <= "00";
NS_timer <= 0;
else
NS_timer <= NS_timer + 1;
end if;
end case;
end if;
end if;
end process;
end Behavioral

需要注意的是，此代码只是一个简化的示例，实际情况中可能需要更加复杂的控制逻辑和时间计算。