1.key0 按下第一次，LEDO 点亮。key0按下第二次，LEDO、LED1 点亮。key0 按下第三次，LEDO、LED1、LED2 点亮。key0 按下第四次，LEDO、LED1、LED2、LED3点亮。key0按下第五次，灯全灭。verilog代码

在Verilog中，你可以使用状态机或循环结构来实现这个功能。这里是一个简单的例子，假设我们有一个4位的状态变量`led_state`，对应于LED灯的数量。当按键`key0`按下时，我们会更新`led_state`并控制相应的LED亮起。当`led_state`满四位后，再按下`key0`会清零所有LED：

module led_controller (
    input wire key0,
    output reg [3:0] led_array // Array of LEDs with led0 being the least significant bit
);

reg [3:0] led_state = 0; // Initial state, all LED off

always @(posedge key0) begin // Trigger on rising edge of key0
    if (led_state < 4) begin // Increment state if less than max
        led_state <= led_state + 1;
    end else if (led_state == 4 && key0) begin // If at max and key pressed again, reset to 0
        led_state <= 0;
    end
    case(led_state)
        0: led_array = 8'b0000; // led0 only
        1: led_array = 8'b0001; // led0, led1
        2: led_array = 8'b0010; // led0, led1, led2
        3: led_array = 8'b0011; // led0, led1, led2, led3
    endcase
end

endmodule