hdlc源码 verilog

以下是一个简单的 HDLC 协议的 Verilog 实现：

module hdlc (
  input clk,
  input reset,
  input rx,
  input tx,
  output reg tx_reg,
  output reg rx_reg
);

parameter IDLE = 2'b00;
parameter FLAG = 2'b01;
parameter DATA = 2'b10;
parameter ESC  = 2'b11;

parameter ESCAPE = 8'h7D;
parameter FLAG_BYTE = 8'h7E;

reg [1:0] state = IDLE;
reg [7:0] data;
reg [3:0] count;
reg [7:0] rx_buffer;
reg [7:0] tx_buffer;
reg [1:0] rx_state = IDLE;
reg [1:0] tx_state = IDLE;

always @(posedge clk) begin
  if (reset) begin
    state <= IDLE;
    data <= 8'h00;
    count <= 4'b0000;
    rx_state <= IDLE;
    tx_state <= IDLE;
    tx_reg <= 1'b1;
  end
  else begin
    case (state)
      IDLE: begin
        if (rx == 1'b0) begin
          state <= FLAG;
          rx_state <= FLAG;
          count <= 4'b0001;
          rx_buffer <= 8'h00;
        end
        if (tx_state == FLAG) begin
          tx_buffer <= FLAG_BYTE;
          tx_state <= DATA;
          tx_reg <= 1'b0;
        end
      end
      FLAG: begin
        if (rx == 1'b0) begin
          count <= count + 1;
          rx_buffer[count-1] <= rx;
          if (count == 4'b0111) begin
            state <= DATA;
            rx_state <= DATA;
            count <= 4'b0000;
          end
        end
        else begin
          state <= IDLE;
          rx_state <= IDLE;
          count <= 4'b0000;
        end
      end
      DATA: begin
        if (rx == 1'b0) begin
          count <= count + 1;
          rx_buffer[count-1] <= rx;
          if (count == 4'b1000) begin
            state <= FLAG;
            rx_state <= FLAG;
            count <= 4'b0000;
            rx_reg <= 1'b1;
          end
        end
        else if (rx == 1'b1) begin
          count <= count + 1;
          rx_buffer[count-1] <= rx;
          if (count == 4'b1000) begin
            state <= ESC;
            rx_state <= ESC;
            count <= 4'b0000;
          end
        end
      end
      ESC: begin
        if (rx == 1'b0) begin
          count <= count + 1;
          rx_buffer[count-1] <= rx;
          state <= DATA;
          rx_state <= DATA;
          count <= 4'b0000;
        end
        else if (rx == 1'b1) begin
          count <= count + 1;
          rx_buffer[count-1] <= rx;
          if (count == 4'b1000) begin
            state <= FLAG;
            rx_state <= FLAG;
            count <= 4'b0000;
            rx_reg <= 1'b1;
          end
        end
      end
      default: begin
        state <= IDLE;
        rx_state <= IDLE;
        count <= 4'b0000;
      end
    endcase

    case (tx_state)
      IDLE: begin
        if (tx == 1'b0) begin
          tx_buffer <= FLAG_BYTE;
          tx_state <= DATA;
          tx_reg <= 1'b0;
        end
      end
      FLAG: begin
        if (tx == 1'b0) begin
          tx_buffer <= FLAG_BYTE;
          tx_state <= DATA;
        end
      end
      DATA: begin
        if (count < 8) begin
          tx_buffer <= data[count];
          count <= count + 1;
        end
        else if (count == 8) begin
          tx_buffer <= FLAG_BYTE;
          count <= 4'b0001;
          tx_state <= FLAG;
        end
      end
      default: begin
        tx_state <= IDLE;
        count <= 4'b0000;
        tx_reg <= 1'b1;
      end
    endcase
  end
end

always @(posedge clk) begin
  if (reset) begin
    data <= 8'h00;
  end
  else begin
    if (rx_reg == 1'b1) begin
      if (rx_buffer[0:7] == FLAG_BYTE) begin
        data <= 8'h00;
      end
      else begin
        for (int i = 0; i < 8; i = i + 1) begin
          if (rx_buffer[i] == 1'b0) begin
            data[i] <= rx_buffer[i];
          end
          else begin
            i = i + 1;
            data[i] <= rx_buffer[i] ^ 1'b1;
          end
        end
      end
    end
    else if (tx_reg == 1'b0) begin
      data <= tx_buffer;
    end
  end
end

endmodule

该实现采用了状态机的方式实现了 HDLC 协议的接收和发送。当接收到一个帧时，该实现将进行解码，并将结果存储在一个 8 位寄存器中。当发送一个帧时，该实现将进行编码，并将结果存储在一个 8 位寄存器中，然后将结果逐位传输。需要注意的是，该实现尚未进行完整的测试和验证，因此应该仔细检查其正确性和稳定性。