关于信号的延迟---verilog

关于信号的延迟---verilog

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: 
// Engineer: chensimin
// 
// Create Date: 2018/02/08 11:39:20
// Design Name: 
// Module Name: signal_detect
// Project Name: 
// Target Devices: 
// Tool Versions: 
// Description: 
// 
// Dependencies: 
// 
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
// 
//////////////////////////////////////////////////////////////////////////////////


module signal_detect(

    input wire clk,
    input wire rst,
    input wire signal_en
    //input wire signal
    //output wire signal_existence
    );



    reg signal;
    always @(posedge clk or posedge rst)
    begin
        if(rst)
            signal <= 1'b0;
        else if(signal_en)
            signal <= 1'b1;
        else
            signal <= 1'b0;
    end



    reg signal_delay;
    wire signal_rise;
    always @(posedge clk or posedge rst)
    begin
        if(rst)
            signal_delay <= 1'b0;
        else
            signal_delay <= signal;
    end

    assign signal_rise = !signal_delay && signal;


endmodule




/*

add_force {/signal_detect/clk} -radix hex {1 0ns} {0 50000ps} -repeat_every 100000ps
add_force {/signal_detect/rst} -radix hex {1 0ns} {0 150ns}
add_force {/signal_detect/signal_en} -radix hex {0 0ns} {1 300ns} {0 400ns}


*/

仿真波形：

容易犯下这样一种错误：

module signal_detect(

    input wire clk,
    input wire rst,
    input wire signal
    //input wire signal
    //output wire signal_existence
    );


    reg signal_delay;
    wire signal_rise;
    always @(posedge clk or posedge rst)
    begin
        if(rst)
            signal_delay <= 1'b0;
        else
            signal_delay <= signal;
    end

    assign signal_rise = !signal_delay && signal;


endmodule




/*

add_force {/signal_detect/clk} -radix hex {1 0ns} {0 50000ps} -repeat_every 100000ps
add_force {/signal_detect/rst} -radix hex {1 0ns} {0 150ns}
add_force {/signal_detect/signal} -radix hex {0 0ns} {1 300ns} {0 400ns}


*/

仿真波形：

像这种写法，根本就起不到边沿检测的作用，只是对外部信号进行一次采集。