【手撕代码】握手机制

文章目录

- 为什么要握手
- - 握手信号无非3种可能
- 怎样实现握手
- - 案例一：数据反压
- 参考链接

为什么要握手

跨时钟域处理：
握手信号法其实也用到了脉冲展宽的方法，只是展宽信号的变化条件不同。因为如果不对脉冲进行展宽，慢速时钟域的时钟很有可能无法采集到快速时钟域的信号，所以要在脉冲展宽的基础上加反馈信号，即握手机制。

握手信号无非3种可能

valid先变高：上游master提供的valid信号随数据一起拉高，但下游slave过一段时间才能准备好ready信号
ready先变高：
valid、ready一起变高：

怎样实现握手

案例一：数据反压

代码

`timescale 1ns/1nsmodule handshake(input   clk,input   rst_n,input           valid_i,input   [7:0]   data_i,output          ready_o,output  [7:0]   data_o,input           ready_i,output          valid_o
);reg [7:0]   data_o_r;
reg valid_o_r;assign ready_o = ready_i;always@(posedge clk or negedge rst_n)beginif(!rst_n)begindata_o_r <= 8'b0;end else if(valid_i && ready_i)begindata_o_r <= data_i * 2;end
endalways@(posedge clk or negedge rst_n)beginif(!rst_n)beginvalid_o_r <= 1'b0;end else if(ready_i)beginvalid_o_r <= valid_i;end
endassign data_o = data_o_r;
assign valid_o = valid_o_r;endmodule

testbench

`timescale 1ns/10psmodule handshake_tb();reg clk;
reg rst_n;reg         valid_i;
reg [7:0]   data_i;
wire        ready_o;wire    data_o;
reg     ready_i;
wire    valid_o;always #10 clk = ~clk;initial beginclk = 0;rst_n = 0;data_i = 8'd0;valid_i = 1'd0;ready_i = 1'd1;#15rst_n = 1'b1;#15rst_n   <= 1'b1;data_i  <= 8'b0000_1000;valid_i <= 1'd0;    //upstream data invalidready_i <= 1'd1;    //downstream ready#20data_i <= 8'b0111_1000;valid_i <= 1'd1;     //upstream data valid#20data_i  <= 8'b0100_0100;    //upstream data change#20valid_i <= 1'd0;     //upstream data invalid#20data_i  <= 8'b0010_0100;valid_i <= 1'd1;    //upstream data validready_i <= 1'd0;    //downstream not ready#20ready_i <= 1'b1;    //downstream ready#20valid_i <= 1'b0;    //upstream data invalid#500$stop();
endhandshake u_handshake(.clk            (clk    ),.rst_n          (rst_n  ),.valid_i        (valid_i),.data_i         (data_i ),.ready_o        (ready_o),.data_o         (data_o ),.ready_i        (ready_i),.valid_o        (valid_o)    );endmodule