问题在哪？always @ (posedge clk or negedge rst_n) begin if(!rst_n) begin bps_start_r <= 1'bz;//波特率时钟启动信号 tx_en <= 1'b0; tx_data <= 1'b0; count <= 1'b0; end else if(start) begin //接收数据完毕，准备把接收到的数据发回去 bps_start_r <= 1'b1;//波特率时钟状态为1 case(count) 1'b00:begin tx_data <= data[2'd0]; count <= 1'b01; end 1'b01:begin tx_data <= data[2'd1]; count <= 1'b10; end 1'b10:begin//不做这个？ tx_data <= data[2'd2]; count <= 1'b00; end default:count <= 1'b00; endcase tx_en <= 1'b1; //进入发送数据状态中 end else if(num==8'd11) begin //数据发送完成，复位 bps_start_r <= 1'b0; tx_en <= 1'b0; end end assign bps_start = bps_start_r; //--------------------------------------------------------- reg rs232_tx_r; always @ (posedge clk or negedge rst_n) begin if(!rst_n) begin num <= 8'd0; rs232_tx_r <= 1'b1; end else if(tx_en)//发送数据使能信号 begin if(clk_bps) begin num <= num+1'b1; case (num) 8'd0: rs232_tx_r <= 1'b0; //发送起始位 8'd1: rs232_tx_r <= tx_data[0] ; //发送第0bit 8'd2: rs232_tx_r <= tx_data[1] ; //发送第1bit 8'd3: rs232_tx_r <= tx_data[2] ; //发送第2bit 8'd4: rs232_tx_r <= tx_data[3] ; //发送第3bit 8'd5: rs232_tx_r <= tx_data[4] ; //发送第4bit 8'd6: rs232_tx_r <= tx_data[5] ; //发送第5bit 8'd7: rs232_tx_r <= tx_data[6] ; //发送第6bit 8'd8: rs232_tx_r <= tx_data[7] ; //发送第7bit 8'd9: rs232_tx_r <= 1'b1; //发送结束位 default: rs232_tx_r <= 1'b1; endcase end else if(num==8'd11) num <= 8'd0; //复位 end end assign rs232_tx = rs232_tx_r;

这段代码中存在一个潜在的问题，就是在 always 块中对多个寄存器进行了赋值。例如，在第一个 always 块中，同时对 bps_start_r、tx_en、tx_data 和 count 进行了赋值；在第二个 always 块中，同时对 num 和 rs232_tx_r 进行了赋值。

这样的赋值方式可能会导致多个时钟周期内的冲突，从而导致意料之外的结果。为了避免这个问题，建议将每个 always 块中的赋值分开，确保每个寄存器在同一时钟周期内只被赋值一次，例如：

always @ (posedge clk or negedge rst_n) begin
  if (!rst_n) begin
    bps_start_r <= 1'bz;
    tx_en <= 1'b0;
    tx_data <= 1'b0;
    count <= 1'b0;
  end else begin
    if (start) begin
      case (count)
        2'd0: tx_data <= data[0];
        2'd1: tx_data <= data[1];
        2'd2: tx_data <= data[2];
        default: tx_data <= 1'b0;
      endcase
      count <= count + 1'b1;
      if (count == 3'd3) begin
        count <= 1'b0;
        tx_en <= 1'b1;
      end
      bps_start_r <= 1'b1;
    end else if (num == 8'd11) begin
      bps_start_r <= 1'b0;
      tx_en <= 1'b0;
    end
  end
end

always @ (posedge clk or negedge rst_n) begin
  if (!rst_n) begin
    num <= 8'd0;
    rs232_tx_r <= 1'b1;
  end else begin
    if (tx_en && clk_bps) begin
      case (num)
        8'd0: rs232_tx_r <= 1'b0;
        8'd1: rs232_tx_r <= tx_data[0];
        8'd2: rs232_tx_r <= tx_data[1];
        8'd3: rs232_tx_r <= tx_data[2];
        8'd4: rs232_tx_r <= tx_data[3];
        8'd5: rs232_tx_r <= tx_data[4];
        8'd6: rs232_tx_r <= tx_data[5];
        8'd7: rs232_tx_r <= tx_data[6];
        8'd8: rs232_tx_r <= tx_data[7];
        8'd9: rs232_tx_r <= 1'b1;
        default: rs232_tx_r <= 1'b1;
      endcase
      num <= num + 1'b1;
      if (num == 8'd11) begin
        num <= 8'd0;
      end
    end
  end
end

在这个修改后的代码中，每个 always 块中的赋值被分开，避免了多个寄存器在同一时钟周期内被同时赋值的情况。这样可以增强代码的可读性和可维护性，同时也能避免一些不必要的问题。