verilog hdlc实例

下面是一个简单的Verilog HDLC实例：

module hdlc_rx (
input clk,
input reset,
input rx_data,
input rx_valid,
output rx_frame_valid,
output reg [7:0] rx_frame_data
);

reg [7:0] shift_reg;
reg [7:0] crc_reg;
reg [3:0] state;

parameter IDLE = 4'd0;
parameter FLAG_FOUND = 4'd1;
parameter DATA_RECEIVED = 4'd2;
parameter CRC_CHECK = 4'd3;
parameter FRAME_COMPLETE = 4'd4;

always @(posedge clk) begin
if (reset) begin
shift_reg <= 8'b00000000;
crc_reg <= 8'b00000000;
state <= IDLE;
rx_frame_valid <= 0;
rx_frame_data <= 8'b00000000;
end else begin
case (state)
IDLE: begin
if (rx_valid && rx_data == 8'b01111110) begin
state <= FLAG_FOUND;
end
end
FLAG_FOUND: begin
if (rx_valid) begin
shift_reg <= {shift_reg[6:0], rx_data};
if (rx_data == 8'b01111110) begin
state <= FLAG_FOUND;
end else if (shift_reg == 8'b00000001) begin
state <= DATA_RECEIVED;
end else begin
state <= IDLE;
end
end
end
DATA_RECEIVED: begin
if (rx_valid) begin
shift_reg <= {shift_reg[6:0], rx_data};
crc_reg <= crc_reg ^ shift_reg;
if (rx_data == 8'b01111110) begin
state <= FLAG_FOUND;
end else if (crc_reg == 8'b00000000) begin
state <= CRC_CHECK;
end else begin
state <= IDLE;
end
end
end
CRC_CHECK: begin
if (rx_valid && rx_data == 8'b01111110) begin
rx_frame_data <= shift_reg[7:0];
rx_frame_valid <= 1;
state <= FRAME_COMPLETE;
end
end
FRAME_COMPLETE: begin
if (rx_valid && rx_data == 8'b01111110) begin
state <= FLAG_FOUND;
end
end
endcase
end
end

endmodule

这个模块实现了一个HDLC接收器，它使用一个有限状态机来接收数据帧。在接收到数据帧后，它会计算CRC并检查数据的完整性。如果数据完整，它会输出接收到的数据。