1. 一個小細節

[email protected](posedge I_clk)
   begin
      if(I_rst_p)
         cnt <= 2'd0;
      else if(cnt == 2'd2)
         cnt <= 2'd0;
      else
         cnt <= cnt + 1;          
   end

[email protected](posedge I_clk)
   begin
      if(I_rst_p)
         O_a <= 1
 
'b0;
      else if((cnt == 2'd1) & valid)
         O_a <= 1'b1;
      else
         O_a <= 1'b0;      
   end

[email protected](posedge I_clk)
  begin
     if(I_rst_p)
        O_b <= 1'b0;
     else
        O_b <= ((cnt == 2'd1) & valid);
  end
assign  valid = (cnt == 2'd1);

模擬如下：