FPGA单比特信号跨时钟域处理

输入：singal_in，来自10MHz慢速时钟域的单比特信号
输出：singal_out，输出100MHz快速时钟域的单比特信号

10MHz = 100ns
100MHz = 10ns

/* 从慢速时钟域同步到快速时钟域 */

module top(
    //inputs
    input clk,          //快速时钟，时钟100MHz
    input rst_n,
    input signal_in,    //来自慢速时钟域，时钟10MHz

    //outputs
    output signal_out   //同步到快速时钟域之后的信号
);

reg signal_in_reg1;
reg signal_in_reg2;
reg signal_in_reg3;

assign signal_out = signal_in_reg3;

always @ (posedge clk)
begin
    if(!rst_n)
    begin
        signal_in_reg1 <= 0;
        signal_in_reg2 <= 0;
        signal_in_reg3 <= 0;
    end
    else 
    begin
        signal_in_reg1 <= signal_in;
        signal_in_reg2 <= signal_in_reg1;
        signal_in_reg3 <= signal_in_reg2;
    end
end

endmodule

`timescale 1ns/1ps

module top_tb;

reg clk_100m;      //Period=10ns;
reg rst_n;
reg signal_in;

wire signal_out;

initial 
begin
    clk_100m = 1;
    rst_n = 0;
    signal_in = 0;
    #50
    rst_n = 1;
    #100
    signal_in = 1;
    #100
    signal_in = 0;
    #100
    $stop;
end

always #(10/2) clk_100m <= !clk_100m;

top top_ut(
    //inputs
    .clk(clk_100m),
    .rst_n(rst_n),
    .signal_in(signal_in),

    //outputs
    .signal_out(signal_out)
);

endmodule

输入：singal_a，来自100MHz快速时钟域的单比特信号
输出：singal_b，输出10MHz慢速时钟域的单比特信号

10MHz = 100ns
100MHz = 10ns

/* 快速时钟域同步到慢速时钟域,针对脉冲宽度只有1个clk的信号 */

module fast_to_low(
    //inputs
    input clk_a,    //快速时钟100MHz
    input rst_n_a,    //复位信号
    input signal_a, //快速时钟信号，单比特，1个clk宽度脉冲

    input clk_b,    //慢速时钟20MHz
    input rst_n_b,

    //outputs
    output signal_b  //同步之后的慢速时钟域的信号
);

reg tmp;
reg tmp_reg1;
reg tmp_reg2;
reg tmp_reg3;

assign signal_b = tmp_reg2 ^ tmp_reg3;  //电平信号转换为边沿

/* 在快速时钟域下，把单clk脉冲信号，转换为边沿信号，在高电平时翻转，要求两个脉冲间隔时间不能太短 */
always @ (posedge clk_a)
begin
    if(!rst_n_a)
        tmp <= 0;
    else if(signal_a)
        tmp <= ~tmp; 
end

/* 在慢速时钟域下对 */
always @ (posedge clk_b)
begin
    if(!rst_n_b)
    begin
        tmp_reg1 <= 0;
        tmp_reg2 <= 0;
        tmp_reg3 <= 0;
    end
    else 
    begin
        tmp_reg1 <= tmp;
        tmp_reg2 <= tmp_reg1;
        tmp_reg3 <= tmp_reg2;
    end
end

endmodule;

`timescale 1ns/1ps

module top_tb;

reg clk_a;      //100MHz = 10ns;
reg clk_b;      //10MHz = 100ns;

reg rst_n_a;
reg rst_n_b;

reg signal_a;   //快速时钟域信号

wire signal_b;  //慢速时钟域信号

initial 
begin
    clk_a = 1;
    clk_b = 1;
    rst_n_a = 0;
    rst_n_b = 0;
    signal_a = 0;
    #300
    rst_n_a = 1;
    rst_n_b = 1;
    #500
    signal_a = 1;
    #10
    signal_a = 0;
    #500        //两次脉冲时间间隔应该大于2*100ns=200ns，否则不能还原
    signal_a = 1;
    #10
    signal_a = 0;
    #1000

    $stop;
end

always #(10/2) clk_a <= !clk_a;     //100MHz = 10ns
always #(100/2) clk_b <= !clk_b;    //10MHz = 100ns

fast_to_low fast_to_low_ut(
    //inputs
    .clk_a(clk_a),
    .rst_n_a(rst_n_a),
    .signal_a(signal_a),

    .clk_b(clk_b),
    .rst_n_b(rst_n_b),

    //outputs
    .signal_b(signal_b)
);

endmodule