【FPGA零基础学习之旅#17】搭建串口收发与储存双口RAM系统

🎉欢迎来到FPGA专栏~搭建串口收发与储存双口RAM系统

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一、效果演示

🥝输入数据：

🥝输出数据：

🥝串口助手分析：

按下第一次按键，FPGA开始连续发送数据，按下第二次按键，FPGA停止发送数据。

二、基础知识

2.1 实现目标

使用按键消抖、串口发送与接收模块，以及双端口RAM模块实现串口发送数据到FPGA中，FPGA接收到数据后将数据存储在双口RAM中，当按下按键时FPGA将RAM中存储的数据再通过串口发送出去，再次按下按键后，FPGA停止发送数据。

2.2 所需基础模块

相关模块学习文章：
🥝【FPGA零基础学习之旅#10】按键消抖模块设计与验证（一段式状态机实现）；
🥝【FPGA零基础学习之旅#13】串口发送模块设计与验证；
🥝【FPGA零基础学习之旅#14】串口发送字符串；
🥝【FPGA零基础学习之旅#15】串口接收模块设计与验证（工业环境）；
🥝【FPGA零基础学习之旅#16】嵌入式块RAM-双口ram的使用。

三、系统分析

参考小梅哥FPGA设计的系统框图：

通过串口发送数据到FPGA中，FPGA接收到数据后将数据存储在双口RAM的一段连续空间中。当需要时，按下按键S0，则FPGA将RAM中存储的数据通过串口发送出去；再次按下S0，则停止数据发送。

进行功能划分：串口接收模块、按键消抖模块、RAM模块、串口发送模块以及控制模块。

在此给出所需使用的模块代码：

按键消抖模块：

//
//模块：按键消抖模块
//key_state：输出消抖之后按键的状态
//key_flag：按键消抖结束时产生一个时钟周期的高电平脉冲
//
module KeyFilter(
	input 		Clk,
	input 		Rst_n,
	input 		key_in,
	output reg 	key_flag,
	output reg 	key_state
);

	//按键的四个状态
	localparam
		IDLE 		= 4'b0001,
		FILTER1 	= 4'b0010,
		DOWN 		= 4'b0100,
		FILTER2 	= 4'b1000;

	//状态寄存器
	reg [3:0] curr_st;
	
	//边沿检测输出上升沿或下降沿
	wire pedge;
	wire nedge;
	
	//计数寄存器
	reg [19:0]cnt;
	
	//使能计数寄存器
	reg en_cnt;
	
	//计数满标志信号
	reg cnt_full;//计数满寄存器
	
//------<边沿检测电路的实现>------
	//边沿检测电路寄存器
	reg key_tmp0;
	reg key_tmp1;
	
	//边沿检测
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			key_tmp0 <= 1'b0;
			key_tmp1 <= 1'b0;
		end
		else begin
			key_tmp0 <= key_in;
			key_tmp1 <= key_tmp0;
		end	
	end
		
	assign nedge = (!key_tmp0) & (key_tmp1);
	assign pedge = (key_tmp0)  & (!key_tmp1);

//------<状态机主程序>------	
	//状态机主程序
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			curr_st <= IDLE;
			en_cnt <= 1'b0;
			key_flag <= 1'b0;
			key_state <= 1'b1;
		end
		else begin
			case(curr_st)
				IDLE:begin
					key_flag <= 1'b0;
					if(nedge)begin
						curr_st <= FILTER1;
						en_cnt <= 1'b1;
					end
					else
						curr_st <= IDLE;
				end
				
				FILTER1:begin
					if(cnt_full)begin
						key_flag <= 1'b1;
						key_state <= 1'b0;
						curr_st <= DOWN;
						en_cnt <= 1'b0;
					end	
					else if(pedge)begin
						curr_st <= IDLE;
						en_cnt <= 1'b0;
					end
					else
						curr_st <= FILTER1;
				end
				
				DOWN:begin
					key_flag <= 1'b0;
					if(pedge)begin
						curr_st <= FILTER2;
						en_cnt <= 1'b1;
					end
					else
						curr_st <= DOWN;
				end
				
				FILTER2:begin
					if(cnt_full)begin
						key_flag <= 1'b1;
						key_state <= 1'b1;
						curr_st <= IDLE;
						en_cnt <= 1'b0;
					end	
					else if(nedge)begin
						curr_st <= DOWN;
						en_cnt <= 1'b0;
					end
					else
						curr_st <= FILTER2;
				end
				
				default:begin
					curr_st <= IDLE;
					en_cnt <= 1'b0;
					key_flag <= 1'b0;
					key_state <= 1'b1;
				end
			endcase
		end
	end
	
//------<20ms计数器>------		
	//20ms计数器
	//Clk 50_000_000Hz
	//一个时钟周期为20ns
	//需要计数20_000_000 / 20 = 1_000_000次
	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			cnt <= 20'd0;
		else if(en_cnt)
			cnt <= cnt + 1'b1;
		else
			cnt <= 20'd0;
	end
	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			cnt_full <= 1'b0;
		else if(cnt == 999_999)
			cnt_full <= 1'b1;
		else
			cnt_full <= 1'b0;
	end
	
endmodule

串口接收模块：

//
//模块名称：串口接收模块（工业环境）
//
module uart_byte_rx(
	input 					Clk,//50M
	input 					Rst_n,
	input 			[2:0]	baud_set,
	input 					data_rx,
	output 	reg 	[7:0]	data_byte,
	output 	reg			Rx_Done
);

	reg s0_Rx,s1_Rx;//同步寄存器
	
	reg tmp0_Rx,tmp1_Rx;//数据寄存器
	
	reg [15:0]bps_DR;//分频计数器计数最大值
	reg [15:0]div_cnt;//分频计数器
	reg bps_clk;//波特率时钟
	reg [7:0]bps_cnt;
	
	reg uart_state;
	
	reg [2:0] r_data_byte [7:0];
	
	reg [2:0]START_BIT;
	reg [2:0]STOP_BIT;
	
	wire nedge;
	
//--------<同步寄存器处理>--------		
//用于消除亚稳态
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			s0_Rx <= 1'b0;
			s1_Rx <= 1'b0;
		end
		else begin
			s0_Rx <= data_rx;
			s1_Rx <= s0_Rx;
		end
	end
	
//--------<数据寄存器处理>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			tmp0_Rx <= 1'b0;
			tmp1_Rx <= 1'b0;
		end
		else begin
			tmp0_Rx <= s1_Rx;
			tmp1_Rx <= tmp0_Rx;
		end
	end
	
//--------<下降沿检测>--------	
	assign nedge = !tmp0_Rx & tmp1_Rx;
	
//--------<div_cnt模块>--------	
//得到不同计数周期的计数器
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			div_cnt <= 16'd0;
		else if(uart_state)begin
			if(div_cnt == bps_DR)
				div_cnt <= 16'd0;
			else
				div_cnt <= div_cnt + 1'b1;
		end
		else
			div_cnt <= 16'd0;
	end
//--------<bps_clk信号的产生>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_clk <= 1'b0;
		else if(div_cnt == 16'd1)
			bps_clk <= 1'b1;
		else
			bps_clk <= 1'b0;
	end
	
//--------<bps_clk计数模块>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_cnt <= 8'd0;
		else if(bps_cnt == 8'd159 || (bps_cnt == 8'd12 && (START_BIT > 2)))
			bps_cnt <= 8'd0;
		else if(bps_clk)
			bps_cnt <= bps_cnt + 1'b1;
		else
			bps_cnt <= bps_cnt;
	end
	
//--------<Rx_Done模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			Rx_Done <= 1'b0;
		else if(bps_cnt == 8'd159)
			Rx_Done <= 1'b1;
		else
			Rx_Done <= 1'b0;
	end	
	
//--------<波特率查找表>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_DR <= 16'd324;
		else begin
			case(baud_set)
				0:bps_DR <= 16'd324;
				1:bps_DR <= 16'd162;
				2:bps_DR <= 16'd80;
				3:bps_DR <= 16'd53;
				4:bps_DR <= 16'd26;
				default:bps_DR <= 16'd324;
			endcase
		end	
	end

//--------<采样数据接收模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			START_BIT <= 3'd0;
			r_data_byte[0] <= 3'd0; 
			r_data_byte[1] <= 3'd0;
			r_data_byte[2] <= 3'd0; 
			r_data_byte[3] <= 3'd0;
			r_data_byte[4] <= 3'd0; 
			r_data_byte[5] <= 3'd0;
			r_data_byte[6] <= 3'd0; 
			r_data_byte[7] <= 3'd0;
			STOP_BIT <= 3'd0;
		end
		else if(bps_clk)begin
			case(bps_cnt)
				0:begin
					START_BIT <= 3'd0;
					r_data_byte[0] <= 3'd0;
					r_data_byte[1] <= 3'd0;
					r_data_byte[2] <= 3'd0;
					r_data_byte[3] <= 3'd0;
					r_data_byte[4] <= 3'd0;
					r_data_byte[5] <= 3'd0;
					r_data_byte[6] <= 3'd0;
					r_data_byte[7] <= 3'd0;
					STOP_BIT <= 3'd0; 
				end
				6,7,8,9,10,11:START_BIT <= START_BIT + s1_Rx;
				22,23,24,25,26,27:r_data_byte[0] <= r_data_byte[0] + s1_Rx;
				38,39,40,41,42,43:r_data_byte[1] <= r_data_byte[1] + s1_Rx;
				54,55,56,57,58,59:r_data_byte[2] <= r_data_byte[2] + s1_Rx;
				70,71,72,73,74,75:r_data_byte[3] <= r_data_byte[3] + s1_Rx;
				86,87,88,89,90,91:r_data_byte[4] <= r_data_byte[4] + s1_Rx;
				102,103,104,105,106,107:r_data_byte[5] <= r_data_byte[5] + s1_Rx;
				118,119,120,121,122,123:r_data_byte[6] <= r_data_byte[6] + s1_Rx;
				134,135,136,137,138,139:r_data_byte[7] <= r_data_byte[7] + s1_Rx;
				150,151,152,153,154,155:STOP_BIT <= STOP_BIT + s1_Rx;
				default:begin
					START_BIT <= START_BIT;
					r_data_byte[0] <= r_data_byte[0];
					r_data_byte[1] <= r_data_byte[1];
					r_data_byte[2] <= r_data_byte[2];
					r_data_byte[3] <= r_data_byte[3];
					r_data_byte[4] <= r_data_byte[4];
					r_data_byte[5] <= r_data_byte[5];
					r_data_byte[6] <= r_data_byte[6];
					r_data_byte[7] <= r_data_byte[7];
					STOP_BIT <= STOP_BIT;
				end
			endcase
		end
	end

//--------<数据状态判定模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			data_byte <= 8'd0;
		else if(bps_cnt == 8'd159)begin
			data_byte[0] <= r_data_byte[0][2];
			data_byte[1] <= r_data_byte[1][2];
			data_byte[2] <= r_data_byte[2][2];
			data_byte[3] <= r_data_byte[3][2];
			data_byte[4] <= r_data_byte[4][2];
			data_byte[5] <= r_data_byte[5][2];
			data_byte[6] <= r_data_byte[6][2];
			data_byte[7] <= r_data_byte[7][2];
		end
		else
			;
	end

//--------<uart_state模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			uart_state <= 1'b0;
		else if(nedge)
			uart_state <= 1'b1;
		else if(Rx_Done || (bps_cnt == 8'd12 && (START_BIT > 2)))
			uart_state <= 1'b0;
		else
			uart_state <= uart_state;
	end

endmodule

串口发送模块：

//
//模块名称：串口发送模块
//
module uart_byte_tx(
	input 		Clk,
	input 		Rst_n,
	input [7:0]	data_byte,
	input 		send_en,
	input [2:0]	baud_set,
	
	output reg uart_tx,
	output reg Tx_Done,
	output reg uart_state
);

	reg bps_clk;//波特率时钟
	
	reg [15:0]div_cnt;//分频计数器
		
	reg [15:0]bps_DR;//分频计数最大值
	
	reg [3:0]bps_cnt;//波特率计数时钟
		
	//定义数据的起始位和停止位
	localparam START_BIT = 1'b0;
	localparam STOP_BIT  = 1'b1;
	
	reg [7:0]r_data_byte;//数据寄存器
	
//--------<uart状态模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			uart_state <= 1'b0;
		else if(send_en)
			uart_state <= 1'b1;
		else if(bps_cnt == 4'd11)//bps_cnt计数达到11次，即发送结束
			uart_state <= 1'b0;
		else
			uart_state <= uart_state;
	end

//--------<使能分频计数模块>-------	
//	assign en_cnt = uart_state;
	
//--------<寄存待发送的数据，使数据保持稳定>--------
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			r_data_byte <= 8'd0;
		else if(send_en)
			r_data_byte <= data_byte;
		else
			r_data_byte <= r_data_byte;
	end
	
//--------<波特率查找表>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_DR <= 16'd5207;
		else begin
			case(baud_set)
				0:bps_DR <= 16'd5207;
				1:bps_DR <= 16'd2603;
				2:bps_DR <= 16'd1301;
				3:bps_DR <= 16'd867;
				4:bps_DR <= 16'd433;
				default:bps_DR <= 16'd5207;
			endcase
		end	
	end
	
//--------<Div_Cnt模块>--------	
//得到不同计数周期的计数器
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			div_cnt <= 16'd0;
		else if(uart_state)begin	//	assign en_cnt = uart_state;
			if(div_cnt == bps_DR)
				div_cnt <= 16'd0;
			else
				div_cnt <= div_cnt + 1'b1;
		end
		else
			div_cnt <= 16'd0;
	end
//--------<bps_clk信号的产生>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_clk <= 1'b0;
		else if(div_cnt == 16'd1)
			bps_clk <= 1'b1;
		else
			bps_clk <= 1'b0;
	end
	
//--------<bps_cnt计数模块>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			bps_cnt <= 4'd0;
		else if(bps_cnt == 4'd11)//clr信号
			bps_cnt <= 4'd0;
		else if(bps_clk)
			bps_cnt <= bps_cnt + 1'b1;
		else
			bps_cnt <= bps_cnt;
	end

//--------<Tx_Done模块>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			Tx_Done <= 1'b0;
		else if(bps_cnt == 4'd11)
			Tx_Done <= 1'b1;
		else
			Tx_Done <= 1'b0;
	end
	
//--------<数据位输出模块-10选1多路器>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			uart_tx <= 1'b1;
		else begin
			case(bps_cnt)
				0:uart_tx <= 1'b1;
				1:uart_tx <= START_BIT;
				2:uart_tx <= r_data_byte[0];
				3:uart_tx <= r_data_byte[1];
				4:uart_tx <= r_data_byte[2];
				5:uart_tx <= r_data_byte[3];
				6:uart_tx <= r_data_byte[4];
				7:uart_tx <= r_data_byte[5];
				8:uart_tx <= r_data_byte[6];
				9:uart_tx <= r_data_byte[7];
				10:uart_tx <= STOP_BIT;
				default:uart_tx <= 1'b1;
			endcase
		end
	end
	
endmodule

四、代码编写

上述已给出按键消抖模块和串口收发模块，在本文中主要编写控制模块和顶层模块。

4.1 控制模块

为了实现FPGA将接收到的数据存储到双口RAM的一段连续空间中，就需要设计一个可以实现写地址数据自加的控制逻辑，且其控制信号为串口接收模块输出的Rx_Done信号。每来一个Rx_Done就表明接收成功一字节数，地址数进行加一：

assign wren = Rx_Done;

always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)
		wraddress <= 8'd0;
	else if(Rx_Done)
		wraddress <= wraddress + 1'b1;
	else
		wraddress <= wraddress;
end

当按下按键S0，FPGA将RAM中存储的数据通过串口发送出去。需要实现按键按下即启动连续读操作，再次按下可暂停读操作：

reg do_send;

always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)
		do_send <= 1'd0;
	else if(Key_flag && !Key_state)
		do_send <= ~do_send;
end

always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n) 
		rdaddress <= 8'd0;
	else if(do_send && Tx_Done)
		rdaddress <= rdaddress + 8'd1;
	else
		rdaddress <= rdaddress;
end

在仿真双端口RAM时发现其输出会延迟两个系统时钟周期。这是为了保证数据变化稳定之后才进行数据输出，所以在此将驱动Send_en的信号接两级寄存器进行延迟两拍。当按键按下后启动一次发送，然后判断上一字节是否发送结束，是则进行下一字节发送否则不进行下一次发送：

reg r0_send_done,r1_send_done;

always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)begin
		r0_send_done <= 1'b0;
		r1_send_done <= 1'b0;
	end
	else begin
		r0_send_done <= (do_send && Tx_Done);
		r1_send_done <= r0_send_done; 
	end
end

always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)
		Send_en <= 1'b0;
	else if(Key_flag && !Key_state)
		Send_en <= 1'b1;
	else if(r1_send_done)
		Send_en <= 1'b1;
	else
		Send_en <= 1'b0;
end

为了保证RAM地址操作的有效性，在写地址和读地址代码部分加上范围限制：

//--------<dpram写地址加1>--------	
always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)
		wraddress <= 8'd0;
	else if(Rx_Done)
		wraddress <= wraddress + 1'b1;
	else if(wraddress > 8'd255) //当写地址大于配置ip核时的值时，返回到0地址；
		wraddress <= 8'd0;
	else
		wraddress <= wraddress;
end

//--------<dpram读地址加1>--------		
always@(posedge Clk or negedge Rst_n)begin
	if(!Rst_n)
		rdaddress <= 8'd0;
	else if(do_send && Tx_Done)
		rdaddress <= rdaddress + 8'd1;
	else if(rdaddress > 8'd255)	//当读地址大于255时，返回到0地址；
		rdaddress <= 8'd0;
	else
		rdaddress <= rdaddress;
end

完整的控制模块代码：system_ctrl.v

module system_ctrl(
	input 				Clk,
	input 				Rst_n,
	input 				Key_flag,
	input 				Key_state,
	input 				Rx_Done,
	input 				Tx_Done,
	output 				wren,
	output reg			Send_en,
	output reg [7:0]	rdaddress,
	output reg [7:0]	wraddress
);

	assign wren = Rx_Done;
	
	reg do_send;
	
	reg r0_send_done;
	reg r1_send_done;

//--------<dpram写地址加1>--------	
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			wraddress <= 8'd0;
		else if(Rx_Done)
			wraddress <= wraddress + 1'b1;
		else if(wraddress > 8'd255) //当写地址大于配置ip核时的值时，返回到0地址；
			wraddress <= 8'd0;
		else
			wraddress <= wraddress;
	end

//--------<翻转标志信号>--------
//按下一次按键开始连续发送数据，再按一次按键停止发送;
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			do_send <= 1'b0;
		else if(Key_flag && !Key_state)
			do_send <= ~do_send;
	end

//--------<dpram读地址加1>--------		
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			rdaddress <= 8'd0;
		else if(do_send && Tx_Done)
			rdaddress <= rdaddress + 8'd1;
		else if(rdaddress > 8'd255)	//当读地址大于255时，返回到0地址；
			rdaddress <= 8'd0;
		else
			rdaddress <= rdaddress;
	end

//--------<RAM的两拍延迟>--------	
//双端口RAM的输出延迟两个系统时钟周期;
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)begin
			r0_send_done <= 1'b0;
			r1_send_done <= 1'b1;
		end
		else begin
			r0_send_done <= (do_send && Tx_Done);
			r1_send_done <= r0_send_done;
		end
	end

//--------<按键控制与连续读操作>--------	
//Send_en由按键信号和r1_send_done信号同时控制;
//r1_send_done信号使得串口连续读取dpram的数据;
	always@(posedge Clk or negedge Rst_n)begin
		if(!Rst_n)
			Send_en <= 1'b0;
		else if(Key_flag && !Key_state)
			Send_en <= 1'b1;
		else if(r1_send_done)
			Send_en <= 1'b1;
		else
			Send_en <= 1'b0;
	end

endmodule

控制模块的RTL视图：

4.2 顶层模块

将串口接收模块、按键消抖模块、RAM模块、串口发送模块以及控制模块例化到顶层模块中。

uart_system_top.v：

module uart_system_top(
	input 	Clk,
	input 	Rst_n,
	input		key_in,
	input 	uart_rx,
	output 	uart_tx
);
	
	wire [7:0]rx_data;
	wire [7:0]tx_data;
	wire Key_flag;
	wire Key_state;
	wire Rx_Done;
	wire Tx_Done;
	wire wren;
	wire Send_en;
	wire [7:0]rdaddress;
	wire [7:0]wraddress;
	
	uart_byte_rx uart_byte_rx(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.baud_set(3'd0),
		.data_rx(uart_rx),
		.data_byte(rx_data),
		.Rx_Done(Rx_Done)
	);
	
	dpram dpram(
		.clock(Clk),
		.data(rx_data),
		.rdaddress(rdaddress),
		.wraddress(wraddress),
		.wren(wren),
		.q(tx_data)
	);
		
	KeyFilter KeyFilter(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.key_in(key_in),
		.key_flag(Key_flag),
		.key_state(Key_state)
	);

	uart_byte_tx uart_byte_tx(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.data_byte(tx_data),
		.send_en(Send_en),
		.baud_set(3'd0),
		.uart_tx(uart_tx),
		.Tx_Done(Tx_Done),
		.uart_state()
	);

	system_ctrl system_ctrl(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.Key_flag(Key_flag),
		.Key_state(Key_state),
		.Rx_Done(Rx_Done),
		.Tx_Done(Tx_Done),
		.wren(wren),
		.Send_en(Send_en),
		.rdaddress(rdaddress),
		.wraddress(wraddress)
	);

endmodule

顶层模块的RTL视图：

五、仿真测试激励文件

5.1 key_model

key_model仿真模型用于有按键控制信号的项目进行仿真测试，模拟实际情况中的按键抖动。 在仿真时将该模型也添加到工程中使用。

key_model.v：

`timescale 1ns/1ns

module key_model(press,key);
	
	input press;
	output reg key;
	
	reg [15:0]myrand;
	
	initial begin
		key = 1'b1;		
	end
	
	always@(posedge press)
		press_key;
		
	task press_key;
		begin
			repeat(50)begin
				myrand = {$random}%65536;//0~65535;
				#myrand key = ~key;			
			end
			key = 0;
			#25000000;
			
			repeat(50)begin
				myrand = {$random}%65536;//0~65535;
				#myrand key = ~key;			
			end
			key = 1;
			#25000000;		
		end	
	endtask

endmodule

5.2 testbench编写

完整的仿真测试激励文件：

uart_system_top_tb.v：

`timescale 1ns/1ns
`define clock_period 20

module uart_system_top_tb;
	
	reg Clk;
	reg Rst_n;
	wire Key_in;
	wire uart_rx;
	wire uart_tx;
	
	reg [7:0]data_byte_t;
	reg send_en;
	wire [2:0]baud_set;
	wire Tx_Done;
	reg press;
	
	assign baud_set = 3'd0;
	
	uart_system_top uart_system_top(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.key_in(Key_in),
		.uart_rx(uart_tx),
		.uart_tx(uart_rx)
	);
	
	uart_byte_tx uart_byte_tx(
		.Clk(Clk),
		.Rst_n(Rst_n),
		.data_byte(data_byte_t),
		.send_en(send_en),
		.baud_set(baud_set),
		.uart_tx(uart_tx),
		.Tx_Done(Tx_Done),
		.uart_state()
	);
	
	key_model key_model(
		.press(press),
		.key(Key_in)
	);
	
	initial Clk = 1;
	always#(`clock_period / 2) Clk = ~Clk;

	initial begin
		Rst_n = 1'b0;
		press = 0;
		data_byte_t = 8'd0;
		send_en = 1'd0;
		#(`clock_period*20 + 1 );
		Rst_n = 1'b1;
		#(`clock_period*50);
		
		data_byte_t = 8'haa;
		send_en = 1'd1;
		#`clock_period;
		send_en = 1'd0;		
		@(posedge Tx_Done)
		
		#(`clock_period*5000);
		
		data_byte_t = 8'h55;
		send_en = 1'd1;
		#`clock_period;
		send_en = 1'd0;
		@(posedge Tx_Done)
		
		#(`clock_period*5000);
		
		data_byte_t = 8'h33;
		send_en = 1'd1;
		#`clock_period;
		send_en = 1'd0;		
		@(posedge Tx_Done)
		
		#(`clock_period*5000);
		
		data_byte_t = 8'haf;
		send_en = 1'd1;
		#`clock_period;
		send_en = 1'd0;
		@(posedge Tx_Done)
		
		#(`clock_period*5000);
		
		press = 1;
		#(`clock_period*3)
		press = 0;
		
		#(`clock_period*2000000)
		
		$stop;
	end

endmodule

5.3 仿真结果

六、板级验证

🥝输入数据储存到双口RAM中：

🥝输出RAM中的数据：

🧸结尾文章来源地址https://www.toymoban.com/news/detail-713679.html

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