top down 的写法之流水呼吸灯综合

流水灯的编写：
module liushui1(
input wire clk ,
input wire rst_n ,
output reg[3:0] led

);
reg[26:0] cnt_s;
reg flag ;
parameter CNT_MAX=100000000-1;

//cnt_s
always@(posedge clk or negedge rst_n)
if(rst_n==0)
cnt_s <= 0;
else if(cnt_s==CNT_MAX)
cnt_s <= 0;
else
cnt_s <= cnt_s +1;

//flag
always@(posedge clk or negedge rst_n)
if(rst_n==0)
flag <= 0;
else if(led==4’b1000)
flag <= 1;
else if(led==4’b0001)
flag <= 0;

//led
always@(posedge clk or negedge rst_n)
if(rst_n==0)
led <= 4’b0001;
else if(flag==0&&cnt_s==CNT_MAX)
led <= {led[2:0],led[3]};
else if(flag==1&&cnt_s==CNT_MAX)
led <= {led[0],led[3:1]};

endmodule

呼吸灯：
module huxi1(
input w