阿里巴巴2021年数字IC-笔试题

问题1. 检测序列1001001，输入单bit，检测成功的次数用cnt表示，使用verilog描述？

Module	AAA
#(
parameter	width = 4 ;
)
(
Input	clk,
Input	rst_n,
Input	data_in,
Output	reg	[width-1:0]	cnt
);
//可以使用真实状态表示,也可以用gray或者binary表示。
Parameter	idle = 7’b0000000;
Parameter	s1 = 7’b0000001;
Parameter	s2 = 7’b0000010;
Parameter	s3 = 7’b0000100;
Parameter	s4 = 7’b0001001;
Parameter	s5 = 7’b0010010;
Parameter	s6 = 7’b0100100;
Parameter	s7 = 7’b1001001;
Reg		[6:0]	state_current ;
always@(posedge clk or negedge rst_n)
begin
	if(rst_n==0)
begin
		state_current <= idle ;
cnt <= 0;
end
else
begin
	case(state_current)
		idle:
if(data_in==0)		state_current<=idle;
else				state_current<=s1;
s1:
if(data_in==0)		state_current<=s2;
else				state_current<=s1;
s2:
if(data_in==0)		state_current<=s3;
else				state_current<=s1;
s3:
if(data_in==0)		state_current<=idle;
else				state_current<=s4;
s4:
if(data_in==0)		state_current<=s5;
else				state_current<=s1;
s5:
if(data_in==0)		state_current<=s6;
else				state_current<=s1;
s6:
if(data_in==0)		state_current<=idle;
else				state_current<=s7;
s7:
if(data_in==0)		state_current<=idle;
else				state_current<=s1;

default:
begin
state_current <= idle ;
cnt <= 0;

end

end
end

always@(posedge clk or negedge rst_n)
begin
if(rst_n==0)
begin
cnt<=0;
end
else
if(state_current == s7)
cnt <= cnt+1 ;


end
endmodule

问题2：设计32bit计数器

问题3： 跨时钟域处理的几种方法，并用简单的代码进行描述

回答：

对于单bit信号使用两级寄存器

对于多bit信号，使用异步端口ram，异步fifo，格雷码转换。

问题4：

饮料价格是2.5元，每次投币一枚，分为0.5元和1元两种硬币。当投入2.5元时候，则售卖一瓶饮料，若投3元，则售卖一瓶饮料并找零0.5元,画出状态图，使用verilog描述？

 

Module AAA(
Input	clk，
Input	rst_n,
Input	wujiao_in,
Input	yiyuan_in,
Output	sell,
Output	zhaoling

);
Reg		[3:0]	currrent_state;
Parameter	s0 = 3’b000; //0yuan
Parameter	s1 = 3’b001; //0.5yuan
Parameter	s2 = 3’b010; //1.0yuan
Parameter	s3 = 3’b011; //1.5yuan
Parameter	s4 = 3’b100; //2.0yuan
Parameter	s5 = 3’b101; //2.5yuan
Parameter	s6 = 3’b110; //3.0yuan
always@(posedge clk or negedge rst_n)
begin
if(rst_n==0)
begin
sell <= 0;
zhaoling <= 0 ;
currrent_state <= s0;
end
end
else
begin
case(currrent_state)
s0://0yuan
begin
sell <= 0;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s1;
else 	    if(yiyuan_in)	currrent_state<=s2;
end

s1://0.5yuan
begin
sell <= 0;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s2;
else 	    if(yiyuan_in)	currrent_state<=s3;
end

s2://1.0yuan
begin
sell <= 0;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s3;
else 	    if(yiyuan_in)	currrent_state<=s4;
end
s3://1.5yuan
begin
sell <= 0;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s4;
else 	    if(yiyuan_in)	currrent_state<=s5;
end
s4://2.0yuan
begin
sell <= 0;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s5;
else 	    if(yiyuan_in)	currrent_state<=s6;
end
s5://2.5yuan
begin
sell <= 1;
zhaoling <= 0 ;
			    	if(wujiao_in)	currrent_state<=s1;
else 	    if(yiyuan_in)	currrent_state<=s2;
end
s6://3.0yuan
begin
sell <= 1;
zhaoling <= 1 ;
			    	if(wujiao_in)	currrent_state<=s1;
else 	    if(yiyuan_in)	currrent_state<=s2;
end

default: 
begin
currrent_state <= s0;
sell <= 0;
zhaoling <= 0 ;
end
endcase
end

Endmodule