03【Verilog实战】UART通信协议，半双工通信方式（附源码）

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虚拟机：VMware -14.0.0.24051
环 境：ubuntu 18.04.1
脚 本：makefile（点击直达）
应用工具：vcs 和 verdi

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一、Overview

（1）Theory

  UART(Universal Asynchronous Receiver/Transmitter)，通用异步收发器，是一种异步全双工串行通信协议，可实现单工通信、半双工通信和全双工通信。

单工通信方式：主机只能发送数据，从机只能接收数据，数据流向始终由发送端流向接收端；
半双工通信方式：同一时刻，只能由主机向从机或从机向主机发送数据；
全双工通信方式：同一时刻，主机和从机都可以互发数据。

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  UART由Tx和Rx两根数据线组成，因为没有参考时钟信号，所以通信的双方必须约定串口波特率、数据位宽、奇偶校验位、停止位等配置参数，从而按照相同的速率进行通信。

UART协议相关概念：

1. 波特率(baud rate)
   单位bps(bit per second)，每秒传输的二进制位数
2. 起始位(start bit)
   开始发起传输的标志
3. 停止位(stop bit)
   结束传输的标志
4. 校验位(check bit)
   为了保证传输可靠性增加的校验信息。奇校验: 数据+校验位中总的1的个数为奇数；偶校验反之。

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（2）Baud Rate

• 每bit时间宽度及每bit时钟周期数
  bit_width = 1/(baud rate)；
  bit_clk_num = bit_width/T，注意单位要统一

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（3）Check Bit

• data中”1”个数计算
  奇校验：^data[7:0]==1’b1，1的个数为奇数；
  偶校验：^data[7:0]==1’b0，1的个数为偶数

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（4）Demand

1. 接收上一级模块并行数据（cmd_i），将数据按照UART协议发送出去

模块工作类型	信号名	方向	位宽	描述
master	tx	output	1	发送信号
master	rx	input	1	接收信号
slave	tx	input	1	接收数据
slave	rx	output	1	发送数据

2. 采用奇校验
3. 1bit停止位
4. 波特率115200，波特率可配置
5. 工作时钟50MHz
6. 当接收到rx数据时，将并行数据反馈给上一级模块（半双工通信）
7. 规定数据包一帧数据是8bit，两次数据传输之间要求有delay，且delay可配置 。
   

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二、Interface Description

Signal Name	Width	Direction	Description
clk	1	input	System clk signal, 50Mhz
rst_n	1	input	System reset signal，negedge
cmd_i	16	input	[15]：读写指示；1：写，0：读 [14:8]:地址位 [7:0]:数据位
cmd_rdy	1	output	握手信号ready
cmd_vld	1	input	握手信号valid
tx	1	output	uart发送数据端
rx	1	input	uart接收数据端
read_vld	1	output	读数据valid
read_data	8	output	读到的数据

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三、Block Diagram

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四、Timeing

（1）write timing

（2）read timing

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五、Design and Functional Verification

（1）RTL

/*-- modified by xlinxdu, 2022/04/30
  -- cmd_i 16bit,rw_flag:1bit,data addr:7bit,data:8bit
  -- clock freq:50MHz
  -- band rate :115200bps
  -- check bit :odd
  -- stop bit  :1bit
  -- clock num of uart :freq/band_rate = 50M/115200 = 434clk
*/

module uart#(
  parameter CMD_ADDR_WIDTH = 7,
  parameter CMD_DATA_WIDTH = 8,
  parameter RW_FLAG        = 1,
  parameter CMD_WIDTH      = CMD_ADDR_WIDTH +CMD_DATA_WIDTH+RW_FLAG,
  parameter DELAY_CLK      = 1

  )(
  input                       clk_i        ,
  input                       rst_n_i      ,
//-- tx
  input       [CMD_WIDTH-1:0] cmd_data_i   ,
  input                       cmd_vld_i    ,
  output reg                  cmd_rdy_o    ,
  output reg                  tx_o         ,
//-- rx
  input                       rx_i         ,
  output reg                  rd_vld_o     ,
  output reg  [CMD_DATA_WIDTH-1:0] rd_data_o
  );
  reg                    uart_en      ;
  reg    [          8:0] tx_bit_cnt   ;
  reg    [          3:0] tx_bit_num   ;
  reg    [CMD_WIDTH-1:0] cmd_data_buf ;
  wire   [          7:0] cmd_data_high;
  wire   [          7:0] cmd_data_low ;
  wire                   rw_flag      ;
  reg                    wr_data_flag ;
  reg                    tx_uart_done ;

  reg                    dly_cnt_en   ;
  reg    [          6:0] dly_cnt      ;
  reg                    rd_uart_en   ;
  reg    [          8:0] rx_bit_cnt   ;
  reg    [          3:0] rx_bit_num   ;
  reg    [CMD_DATA_WIDTH-1:0] rx_data_buf  ;
  reg    [          2:0] rx_dly       ;
  wire                   negedge_rx   ;
  wire                   rx_sync      ;
  wire                   rx_done      ;
  reg                    rx_uart_done ;
  
  wire                   rd_vld ;//assign --wire-->reg_o
  wire   [CMD_DATA_WIDTH-1:0] rd_data;
//-- cmd_rdy_o
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    cmd_rdy_o <= 1'b1;
  end
  else if (tx_uart_done) begin
    cmd_rdy_o <= 1'b1;
  end
  else if(cmd_vld_i) begin
    cmd_rdy_o <= 'b0;
  end
end

//-- uart_en
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    uart_en <= 1'b0;
  end
  else if(rw_flag && tx_bit_num == 4'd10 && tx_bit_cnt == 9'd433 || dly_cnt_en) begin
    uart_en <= 1'b0;
  end
  else if(tx_uart_done) begin
    uart_en <= 1'b0;
  end
  else if(cmd_vld_i)begin
    uart_en <= 1'b1;
  end
end

//-- tx_bit_cnt
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    tx_bit_cnt <= 9'd0;
  end
  else if(uart_en) begin
    if(tx_bit_cnt == 9'd433) begin
      tx_bit_cnt <= 9'd0;
    end
    else begin
      tx_bit_cnt <= tx_bit_cnt + 1'd1;
    end
  end
  else if(dly_cnt_en) begin
    tx_bit_cnt <= 9'd0; 
  end
end

//-- tx_bit_num
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    tx_bit_num <= 4'd0;
  end
  else if(uart_en) begin 
    //--uart_en keep high,tx_bit_num=11~12-->delay 2bit
    if(tx_bit_num == 4'd10 && tx_bit_cnt == 9'd433) begin
      tx_bit_num <= 4'd0;
    end
    else if(tx_bit_cnt == 9'd433)begin
      tx_bit_num <= tx_bit_num +1'd1;
    end  
  end
  else if(dly_cnt_en)begin
      tx_bit_num <= 4'd0;
  end
end

//-- cmd_data_buf
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    cmd_data_buf <= {CMD_WIDTH{1'B0}};
  end
  else if(cmd_vld_i && cmd_rdy_o)begin
    cmd_data_buf <= cmd_data_i;
  end
end

//-- 
assign {cmd_data_high,cmd_data_low} = cmd_data_buf;
assign rw_flag = cmd_data_buf[CMD_WIDTH-1];

//-- wr_data_flag
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    wr_data_flag <= 1'b0;
  end
  else if (tx_uart_done)begin
    wr_data_flag <= 1'b0;
  end
  else if(rw_flag && tx_bit_num == 4'd10 && tx_bit_cnt == 9'd433) begin
    wr_data_flag <= 1'b1;
  end
end

//-- TX
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    tx_o <= 1'd1;
  end
  else if(uart_en) begin
    //-- send start bit
    if(tx_bit_num == 4'd0)begin
      tx_o <= 1'b0;
    end
    //-- send data bit
    else if(tx_bit_num >= 4'd1 && tx_bit_num <= 4'd8)begin
      //--1:send cmd_data_high and cm_data_low
      if(rw_flag)begin
        if(wr_data_flag)begin//1:low
          tx_o <= cmd_data_low[tx_bit_num-1];
        end
        else begin
          tx_o <= cmd_data_high[tx_bit_num-1];
        end
      end
      //--0:only send cmd_data_high
      else begin
        tx_o <= cmd_data_high[tx_bit_num-1];
      end
    end
    //-- send check bit
    else if(tx_bit_num == 4'd9) begin
      if(rw_flag)begin//-- 1:write
        tx_o <= wr_data_flag ? ~(^cmd_data_low) : ~(^cmd_data_high);
      end
      else begin
        tx_o <= ~(^cmd_data_high);
      end
    end
    //-- send stop bit
    else if(tx_bit_num == 4'd10) begin
      tx_o <= 1'b1;
    end
  end
  else begin
    if(dly_cnt_en) begin
      tx_o <= 1'b1;
    end
  end
end

//-- tx_uart_done
assign tx_uart_done = (~rw_flag || wr_data_flag) && tx_bit_num == 4'd10 && tx_bit_cnt == 9'd433;

//assign tx_uart_done = (~rw_flag && tx_bit_num == 4'd10&& tx_bit_cnt == 9'd433)||
//                   ( rw_flag && tx_bit_num == 4'd10&& tx_bit_cnt == 9'd433 && wr_data_flag);


//-- dly_cnt_en
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    dly_cnt_en <= 1'b0;
  end
  else if(rw_flag && tx_bit_num == 4'd10 && tx_bit_cnt == 9'd433)begin
    dly_cnt_en <= 1'b1;
  end
  else if(dly_cnt == 7'd99)begin
    dly_cnt_en <= 1'b0;
  end
end

//-- dly_cnt
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    dly_cnt <= 7'd0;
  end
  else if(dly_cnt_en)begin
    dly_cnt <= dly_cnt +1'b1;
  end
  else begin
    dly_cnt <= 7'd0;
  end
end


//-- RX
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rx_dly <= 3'b000;
  end
  else begin
    rx_dly <= {rx_dly[1:0],rx_i};
  end
end
assign negedge_rx = {rx_dly[2:1] == 2'b10};
assign rx_sync = rx_dly[2];

//-- rx_uart_done
assign rx_done = ~rw_flag && rx_bit_num == 4'd10&& rx_bit_cnt == 9'd433;
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rx_uart_done <= 1'b0;
  end
  else begin
    rx_uart_done <= rx_done;
  end
end
//-- rd_uart_en
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rd_uart_en <= 1'b0;
  end
  else if(negedge_rx)begin
    rd_uart_en <= 1'b1;
  end
  else if(rx_done)begin
    rd_uart_en <= 1'b0;
  end
end
//-- rx_bit_cnt
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rx_bit_cnt <= 9'd0;
  end
  else if(rd_uart_en) begin
    if(rx_bit_cnt == 9'd433) begin
      rx_bit_cnt <= 1'd0;
    end
    else begin
      rx_bit_cnt <= rx_bit_cnt + 1'd1;
    end
  end
end

//-- rx_bit_num
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rx_bit_num <= 4'd0;
  end
  else if(rd_uart_en) begin 
    //--rd_uart_en keep high,tx_bit_num=11~12-->delay 2bit
    if(rx_bit_num == 4'd10 && rx_bit_cnt == 9'd433) begin
      rx_bit_num <= 4'd0;
    end
    else if(rx_bit_cnt == 9'd433)begin
      rx_bit_num <= rx_bit_num +1'd1;
    end  
  end
  else begin
      rx_bit_num <= 4'd0;
  end
end
//-- rx_data_buf

always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rx_data_buf <= 8'd0;
  end
  else if(rx_bit_cnt == 9'd216 && rx_bit_num >= 4'd1 && rx_bit_num <= 4'd8)begin
    rx_data_buf <= {rx_sync,rx_data_buf[7:1]};
  end
end

//-- check bit
assign check_flag = rx_bit_num == 4'd9 &&rx_bit_cnt ==9'd216 && rx_sync == ~^rx_data_buf;

assign rd_vld = check_flag;
assign rd_data = rd_vld?rx_data_buf:rd_data;

always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rd_vld_o <= 1'b1;
  end
  else if(rd_vld)begin 
    rd_vld_o <= 1'b1;
  end
  else if(negedge_rx && rx_bit_num == 4'd0)begin
    rd_vld_o <= 1'b0;
  end
end
always @ (posedge clk_i or negedge rst_n_i) begin
  if (!rst_n_i) begin
    rd_data_o <= 8'd0;
  end
  else if(rx_done)begin 
    rd_data_o <= rd_data;
  end
end
endmodule

（2）Test Bench

module uart_tb;
  reg          clk_i      ; 
  reg          rst_n_i    ;

  reg          cmd_vld_i  ;  
  reg  [15:0]  cmd_data_i ; 
  wire         cmd_rdy_o  ;
  wire         tx_o       ;
  
  reg          rx_i       ;
  wire         rd_vld_o   ;
  wire [ 7:0]  rd_data_o  ;

initial begin
  clk_i = 1;
end

always begin
  #10 clk_i = ~clk_i;
end
initial begin
  rst_n_i    = 1;
  cmd_vld_i  = 0;
  cmd_data_i= 16'b1000_0010_0011_0010;//16'h8232
  rx_i = 1; 
  #5 rst_n_i = 0;
  #5 rst_n_i = 1;
  #10 cmd_vld_i=1;
  #180000 cmd_data_i = 16'b0110_1011_0001_1000;//16'h6b14
  #90000 cmd_vld_i =0;
end
initial begin
  #360020 
  rx_i = 0;//start bit
  
  #8660 rx_i = 0;
  #8660 rx_i = 1;
  #8660 rx_i = 0;
  #8660 rx_i = 0;
  #8660 rx_i = 1;
  #8660 rx_i = 1;
  #8660 rx_i = 0;
  #8660 rx_i = 0;
  
  #8660 rx_i = 0;//check bit
  #8660 rx_i = 1;//stop bit
  #8660 rx_i = 1;//delay bit
  #8660;
end


uart u_uart
(
  .clk_i     (clk_i     ),
  .rst_n_i   (rst_n_i   ),
  .cmd_vld_i (cmd_vld_i ),
  .cmd_data_i(cmd_data_i),
  .cmd_rdy_o (cmd_rdy_o ),
  .tx_o      (tx_o      ),
  .rx_i      (rx_i      ),
  .rd_vld_o  (rd_vld_o  ),
  .rd_data_o (rd_data_o )
);

initial begin
	#700000 $finish;
  $fsdbDumpfile("uart.fsdb");
  $fsdbDumpvars             ;
  $fsdbDumpMDA              ;
end

endmodule

六、Result

（1）write

• 发送16’h8232(1000_0010_0011_0010)和16’h6B18（0110_1011_0001_1000）
  1、 M1-M3发送0100_0001；
  2、 M3-M4发送校验位1；
  3、 M4-M5为停止位，M5-M6为延时
  4、 M7-M9发送0100_1100；
  5、 M9-M10发送校验位0；
  6、 M13-M15发送1101_0110；只发送地址位。

（2）read

• 接收数据8’h32(0011_0010)
  1、 M18下降沿来临，开始接收数据。
  2、 M19-M20接收到数据0100_1100；
  3、 M20-M21接收校验位0。
  4、 C1：在接收完stop位后，如果校验位和传过来的校验位一致，将数据输出到rd_data_o。此处数据为8’h32。校验成功。

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作者：xlinxdu
版权：本文是作者原创，版权归作者所有。
转载：未经作者允许，禁止转载，转载必须保留此段声明，必须在文章中给出原文连接。