1. 基于状态机的按键消抖
1.1 什么是按键？
从按键结构图10-1可知，按键按下时，接点（端子）与导线接通，松开时，由于弹簧的反作用力，接点（端子）与导线断开。
从原理图10-2可知，按键按下时为低电平，未按下为高电平
1.2 为什么要消抖？
1.3 基于按键消抖的状态转移图
2. 写设计代码，仿真代码并仿真（未使用随机函数的测试）
- 设计代码
cpp
module key_filter(
clk,
rstn,
key,
// key_p_flag,
// key_r_flag,
key_flag,
key_state
);
input clk;
input rstn;
input key;
// output reg key_p_flag;
// output reg key_r_flag;
output reg key_flag;
output reg key_state;
//边沿检测
reg [1:0] r_key;
always@(posedge clk)
r_key <= {r_key[0], key};
// reg [1:0] r_key;
// always@(posedge clk)begin
// r_key[0] <= key;
// r_key[1] <= r_key[0];
// end
wire nedge_key;
wire pedge_key;
assign nedge_key = (r_key == 2'b10);
assign pedge_key = (r_key == 2'b01);
reg [1:0]state;
reg [19:0] cnt;
always@(posedge clk or negedge rstn)
if(!rstn)begin
state <= 0;
cnt <= 0;
// key_p_flag <= 0;
// key_r_flag <= 0;
key_flag <= 0;
key_state <= 1;
end
else
case(state)
0:
begin
// key_r_flag <= 0;
key_flag <= 0;
if(nedge_key == 1) begin
state <= 1;
end
else
state <= 0;
end
1:
begin
if((pedge_key == 1) && (cnt < 1000000 - 1))begin
state <= 0;
cnt <= 0;
end
else if((pedge_key == 0) && (cnt >= 1000000 - 1))begin
state <= 2;
// key_p_flag <= 1'd1;
key_flag <= 1'd1;
key_state <= 0;
cnt <= 0;
end
else
cnt <= cnt + 1'd1;
end
2:
begin
// key_p_flag <= 0;
key_flag <= 0;
if(pedge_key == 1)
state <= 3;
else
state <= 2;
end
3:
begin
if((nedge_key == 1) && (cnt < 1000000 - 1))begin
state <= 2;
cnt <= 0;
end
else if((nedge_key == 0) && (cnt >= 1000000 - 1))begin
state <= 0;
// key_r_flag <= 1;
key_flag <= 1'd1;
key_state <= 1;
cnt <= 0;
end
else
cnt <= cnt + 1'd1;
end
endcase
endmodule- 仿真代码
cpp
`timescale 1ns / 1ps
module key_filter_tb();
reg clk;
reg rstn;
reg key;
// wire key_p_flag;
// wire key_r_flag;
wire key_flag;
wire key_state;
key_filter key_filter_inst(
.clk(clk),
.rstn(rstn),
.key(key),
// .key_p_flag(key_p_flag),
// .key_r_flag(key_r_flag),
.key_flag(key_flag),
.key_state(key_state)
);
initial clk = 1;
always #10 clk = ~clk;
initial begin
rstn = 0;
key = 1;
#201;
rstn = 1;
#200;
key = 1;
#50000000;
key = 0;
#30000;
key = 1;
#30000;
key = 0;
#30000;
key = 1;
#30000;
key = 0;
#50000000;
key = 1;
#30000;
key = 0;
#30000;
key = 1;
#30000;
key = 0;
#30000;
key = 1;
#50000000;
$stop;
end
endmodule- 仿真波形
3. 基于verilog系统函数random的随机测试下的按键抖动（tb编写语法）
通过系统函数random产生一个随机的延迟值，来模拟真实情况下的延迟。
3.1 系统函数random的两个例子：
- 产生一个[-(b+1): (b-1)]的随机数：$random% b；
2.产生一个[0: b-1]的随机数：{$random}% b；；
修改后的仿真代码：
cpp
`timescale 1ns / 1ps
module key_filter_tb();
reg clk;
reg rstn;
reg key;
// wire key_p_flag;
// wire key_r_flag;
wire key_flag;
wire key_state;
key_filter key_filter_inst(
.clk(clk),
.rstn(rstn),
.key(key),
// .key_p_flag(key_p_flag),
// .key_r_flag(key_r_flag),
.key_flag(key_flag),
.key_state(key_state)
);
initial clk = 1;
always #10 clk = ~clk;
reg [19:0] rand;
initial begin
rstn = 0;
key = 1;
#201;
rstn = 1;
#200;
press_key(1);
$stop;
end
task press_key;
input [2:0] seed;
begin
key = 1;
#20000000;
repeat(5) begin
rand = {$random(seed)} % 9999999; //产生0到9999999ns的延迟
#rand key = ~key;
end
key = 0;
#40000000;
repeat(5) begin
rand = {$random(seed)} % 9999999; //产生0到9999999ns的延迟
#rand key = ~key;
end
key = 1;
#40000000;
end
endtask
endmodule4. 调试（产生多余38ns的原因）
