設計一個8路彩燈控制器，要求實現如下花樣：
（1）從左到右逐個亮，從右到左逐個滅；
（2）從兩邊往中間逐個亮，從中間往兩邊逐個滅；
（3）重複上面1、2。
文本文件：
module caideng(clk,light,res);
input clk,res;
output[3:0] light;
reg[3:0] state;
reg[3:0] light;
parameter
FIRST=4'd0,
A=4'd1, B=4'd2,
C=4'd3, D=4'd4,
E=4'd5, F=4'd6,
G=4'd7, H=4'd8,
I=4'd9, J=4'd10,
K=4'd11, L=4'd12;
always @(posedge clk)
begin
if(!res)
begin
state=FIRST;
end
else
casex(state)
FIRST:state<=A;
A:begin
light=4'b1000;
state<=B;
end
B:begin
light=4'b1100;
state<=C;
end
C:begin
light=4'b1110;
state<=D;
end
D:begin
light=4'b1111;
state<=E;
end
E:begin
light=4'b1110;
state<=F;
end
F:begin
light=4'b1100;
state<=G;
end
G:begin
light=4'b1000;
state<=H;
end
H:begin
light=4'b0000;
state<=I;
end
I:begin
light=4'b1001;
state<=J;
end
J:begin
light=4'b1111;
state<=K;
end
K:begin
light=4'b1001;
state<=L;
end
L:begin
light=4'b0000;
state<=A;
end
default:state=FIRST;
endcase
end
endmodule