verilog 异步复位代码

module reset_sync
  (input clk,
   input reset_in,
   output  reset_out);

   (* ASYNC_REG = "TRUE" *) reg reset_int = 1'b1;
   (* ASYNC_REG = "TRUE" *) reg reset_out_tmp = 1'b1;

   always @(posedge clk or posedge reset_in)
     if(reset_in)
       {reset_out_tmp,reset_int} <= 2'b11;
     else
       {reset_out_tmp,reset_int} <= {reset_int,1'b0};

   assign reset_out = reset_out_tmp;


endmodule // reset_sync