使用verilog写一个程序，驱动us100超声波模块检测距离，并返回结果保存到一个变量中。

下面是一个简单的Verilog代码示例，用于驱动US-100超声波模块检测距离，并将结果保存到一个变量中：

module us100_distance(
    input clk,
    input reset,
    output reg trig,
    input echo,
    output reg [11:0] distance,
    output reg valid
    );

    reg [11:0] temp_distance;
    reg [1:0] state;

    parameter IDLE = 2'd0;
    parameter SEND_PULSE = 2'd1;
    parameter WAIT_ECHO = 2'd2;

    always @(posedge clk) begin
        if (reset) begin
            state <= IDLE;
            trig <= 0;
            temp_distance <= 0;
            distance <= 0;
            valid <= 0;
        end
        else begin
            case (state)
                IDLE: begin
                    trig <= 0;
                    if (echo) begin
                        state <= WAIT_ECHO;
                    end
                    else begin
                        state <= SEND_PULSE;
                    end
                end
                SEND_PULSE: begin
                    trig <= 1;
                    state <= WAIT_ECHO;
                end
                WAIT_ECHO: begin
                    trig <= 0;
                    if (echo) begin
                        temp_distance <= (pulse_width * 10) / 58;
                        distance <= temp_distance;
                        valid <= 1;
                        state <= IDLE;
                    end
                    else if (timeout >= 80) begin
                        valid <= 0;
                        state <= IDLE;
                    end
                    else begin
                        timeout <= timeout + 1;
                    end
                end
            endcase
        end
    end

    parameter PULSE_DURATION = 12;

    reg [7:0] count;
    reg [7:0] timeout;
    reg [11:0] pulse_width;

    always @(posedge clk) begin
        if (reset) begin
            count <= 0;
            timeout <= 0;
            pulse_width <= 0;
        end
        else begin
            case (state)
                SEND_PULSE: begin
                    count <= count + 1;
                    if (count >= PULSE_DURATION) begin
                        count <= 0;
                        pulse_width <= count;
                    end
                end
                WAIT_ECHO: begin
                    if (echo) begin
                        pulse_width <= pulse_width + 1;
                        timeout <= 0;
                    end
                    else begin
                        pulse_width <= 0;
                    end
                    if (pulse_width >= 600) begin
                        pulse_width <= 0;
                        state <= IDLE;
                    end
                    else if (timeout >= 80) begin
                        pulse_width <= 0;
                        state <= IDLE;
                    end
                    else begin
                        timeout <= timeout + 1;
                    end
                end
            endcase
        end
    end
endmodule

该代码包含一个状态机和一个计时器。状态机用于控制超声波信号的发送和接收过程，计时器用于生成超声波信号的脉宽和计算回波信号的脉宽。在状态机中，模块会根据需要生成一个Trig信号来发送超声波信号，并等待Echo信号的响应。如果Echo信号在规定的时间内没有响应，模块将返回IDLE状态。如果Echo信号响应了信号，模块将根据返回的信号宽度计算距离，并将结果保存到变量中。在这个过程中，模块会根据需要生成一些延迟和计时信号，以控制超声波信号的发送和接收。