组合逻辑与时序逻辑分开写有什么好处吗？求解
例如
always @(posedge clk or negedge rst)
   if(!rst) cnt <= 4'd0;
   else if(cnt == 4'd9) cnt <= 4'd0;
  else cnt <= cnt + 1'b1;

always @(posedge clk or negedge rst)
   if(!rst) cnt <= 4'd0;
   else cnt <=cnt_n;

always @(*)
   if(cnt == 4'd9) cnt_n = 4'd0;
   else cnt_n = cnt + 1'b1;