题解 | #脉冲同步器（快到慢）#

`timescale 100ps/100ps

module pulse_detect(
	input 				clka	, 
	input 				clkb	,   
	input 				rst_n		,
	input				sig_a		,

	output  		 	sig_b
);

reg sig_a_trans;//来一个sig_a脉冲翻转一下
always@(posedge clka or negedge rst_n)
  if(!rst_n)
     sig_a_trans <= 0;
  else if(sig_a)
     sig_a_trans <= ~sig_a_trans;
  else 
     sig_a_trans <= sig_a_trans;

//在clkb时钟域里打三拍
reg sig_a_trans0,sig_a_trans1,sig_a_trans2;
always@(posedge clkb or negedge rst_n)
  if(!rst_n) begin
	sig_a_trans0 <= 0;
	sig_a_trans1 <= 0;
	sig_a_trans2 <= 0;
  end
  else begin
	sig_a_trans0 <= sig_a_trans;//第一拍用于降低亚稳态
	sig_a_trans1 <= sig_a_trans0;//二三拍用于边沿检测
	sig_a_trans2 <= sig_a_trans1;
  end

assign sig_b = sig_a_trans1 ^ sig_a_trans2;//这里用异或，是因为每次sig_a脉冲到来sig_a_trans翻转，所以sig_a_trans：0->1 和 1->0都代表检测到sig_a脉冲；

     
endmodule