前文分析請看：https://www.cnblogs.com/shadow-fish/p/13451214.html

快時鐘域同步到慢時鐘域--單bit同步程式碼：

module test (
    input clka,
    input clkb,
    input rst,
    input d_in,
    output reg d_out
);
    reg req_a;
    reg req_a_1;
    reg req_a_2;
    reg req_a_3;
    reg ack_b;
    reg ack_b_1;
    reg ack_b_2;

    
 
always @(posedge clkb or negedge rst) begin//將req_a同步到慢時鐘域，告訴慢時鐘域，資料已經準備好
        if(!rst) begin
            req_a_1 <= 'b0;
            req_a_2 <= 'b0;
            req_a_3 <= 'b0;
        end
        else begin
            req_a_1 <= req_a;
            req_a_2 <= req_a_1;
            req_a_3 
 
<= req_a_2;
        end
    end
    always @(posedge clkb or negedge rst) begin
        if(!rst) begin
            d_out <= 'b0;
        end
        else if (req_a_2 == 1'b1) begin
            d_out <= req_a_2 & (~req_a_3);
        end
        else begin
            d_out <= d_out;
        
 
end
    end
    always @(posedge clkb or negedge rst) begin//傳送ack，告訴慢時鐘域，資料已經讀取結束
        if(!rst) begin
            ack_b <= 'b0;
        end
        else if(req_a_2 == 1'b1) begin
            ack_b <= 'b1;
        end
        else begin
            ack_b <= 'b0;
        end
    end
    always @(posedge clka or negedge rst) begin//將慢時鐘域發出的ack訊號同步到快時鐘域，表示讀取結束
        if(!rst) begin
            ack_b_1 <= 'b0;
            ack_b_2 <= 'b0;
        end
        else begin
            ack_b_1 <= ack_b;
            ack_b_2 <= ack_b_1;
        end
    end
    always @(posedge clka or negedge rst) begin//快時鐘將資料放到總線上，然後傳送req訊號繼續提醒
        if(!rst) begin
            req_a <= 'b0;
        end
        else if(d_in == 1'b1)begin
            req_a <= 1'b1;
        end
        else begin
            req_a <= 'b0;
        end
    end
    always @(posedge clka or negedge rst) begin
        if(!rst) begin
            req_a <= 'b0;
        end
        else if (ack_b_2 == 1'b1) begin
            req_a <= 'b0;
        end
        else begin
            req_a <= req_a;
        end
    end
endmodule

測試用例：

`timescale 1ns/10ps
module test_tb;
    
    reg clka;
    reg clkb;
    reg rst;
    reg d_in;
    wire d_out;

    test u1(
    .clka(clka),
    .clkb(clkb),
    .rst(rst),
    .d_in(d_in),
    .d_out(d_out)
);

    initial begin
        clka = 'b1;
        clkb = 'b1;
        rst = 'b0;
        #8 rst = 'b1;
    end
    always #5 clka = ~clka;
    always #12 clkb = ~clkb;
    initial begin
    d_in = 'b0;
        #20;
        d_in = 'd1;
        #10 d_in = 'd0;
    end
endmodule

questasim模擬波形：

快時鐘域同步到慢時鐘域--多bit同步程式碼：多bit的程式碼透露著一絲古怪，如發現問題請留言，以便改進。

module test (
 input clka,
 input clkb,
 input rst,
 input [7:0]d_in,
 output reg [7:0]d_out
);
 reg req_a;
 reg req_a_1;
 reg req_a_2;
 reg ack_b;
 reg ack_b_1;
 reg ack_b_2;
 reg [7:0]d_in_line;

 always @(posedge clkb or negedge rst) begin//將req_a同步到慢時鐘域，告訴慢時鐘域，資料已經準備好
 if(!rst) begin
 req_a_1 <= 'b0;
 req_a_2 <= 'b0;
 end
 else begin
 req_a_1 <= req_a;
 req_a_2 <= req_a_1;
 end
 end
 always @(posedge clkb or negedge rst) begin//檢測到req_a，將讀取需要傳輸的資料
 if(!rst) begin
 d_out <= 'b0;
 end
 else if (req_a_2 == 1'b1) begin
 d_out <= d_in_line;
 end
 else begin
 d_out <= d_out;
 end
 end
 always @(posedge clkb or negedge rst) begin//傳送ack，告訴慢時鐘域，資料已經讀取結束
 if(!rst) begin
 ack_b <= 'b0;
 end
 else if(req_a_2 == 1'b1) begin
 ack_b <= 'b1;
 end
 else begin
 ack_b <= 'b0;
 end
 end
 always @(posedge clka or negedge rst) begin//將慢時鐘域發出的ack訊號同步到快時鐘域，表示讀取結束
 if(!rst) begin
 ack_b_1 <= 'b0;
 ack_b_2 <= 'b0;
 end
 else begin
 ack_b_1 <= ack_b;
 ack_b_2 <= ack_b_1;
 end
 end
 always @(posedge clka or negedge rst) begin//快時鐘將資料放到總線上，然後傳送req訊號繼續提醒
 if(!rst) begin
 req_a <= 'b0;
 end
 else if(d_in_line != 'b0)begin
 req_a <= 1'b1;
 end
 else begin
 req_a <= 'b0;
 end
 end
 always @(posedge clka or negedge rst) begin
 if(!rst) begin
 d_in_line <= 'b0;
 end
 else begin
 d_in_line <= d_in;
 end
 end
 always @(posedge clka or negedge rst) begin
 if(!rst) begin
 req_a <= 'b0;
 end
 else if (ack_b_2 == 1'b1) begin
 req_a <= 'b0;
 end
 else begin
 req_a <= req_a;
 end
 end
endmodule

測試用例：

`timescale 1ns/10ps
module test_tb;
    
    reg clka;
    reg clkb;
    reg rst;
    reg [7:0]d_in;
    wire [7:0]d_out;

    test u1(
    .clka(clka),
    .clkb(clkb),
    .rst(rst),
    .d_in(d_in),
    .d_out(d_out)
);

    initial begin
        clka = 'b1;
        clkb = 'b1;
        rst = 'b0;
        #6 rst = 'b1;
    end
    always #5 clka = ~clka;
    always #22 clkb = ~clkb;
    initial begin
    d_in = 'b0;
        #80;
        d_in = 'd1;
        #160 d_in = 'd2;
        #160 d_in = 'd3;
        #160 d_in = 'd4;
        #160 d_in = 'd5;
        #160 d_in = 'd6;
        #160;
    end
endmodule