一、前言

MAC TX模块就是要将IP层传输过来的数据封装前导码、MAC地址、帧类型以及进行CRC校验，并与CRC值一块组成以太网帧。

二、模块设计

首先对输入的数据进行缓存，原因是在之后要进行封装MAC帧头，所以需要控制数据流的流动

FIFO_DATA_64X256 U_FIFO_DATA_64X256 (.clk      (i_clk              ), .srst     (i_rst              ), .din      (rs_axis_data       ), .wr_en    (rs_axis_valid      ), .rd_en    (r_fifo_data_rden   ), .dout     (w_fifo_data_out    ), .full     (w_fifo_data_full   ), .empty    (w_fifo_data_empty  )  
);FIFO_LEN_16X32 u_FIFO_LEN_16X32 (.clk      (i_clk                  ),.srst     (i_rst                  ),.din      (rs_axis_user[79:64]    ),.wr_en    (rs_axis_last           ),.rd_en    (r_fifo_len_rden        ), .dout     (w_fifo_len_out         ), .full     (w_fifo_len_full        ), .empty    (w_fifo_len_empty       )  
);FIFO_LEN_16X32 u_FIFO_TYPE_16X32 (.clk      (i_clk                  ),.srst     (i_rst                  ),.din      (rs_axis_user[15:0]     ),.wr_en    (rs_axis_last           ),.rd_en    (r_fifo_type_rden       ), .dout     (w_fifo_type_out        ), .full     (w_fifo_type_full       ), .empty    (w_fifo_type_empty      )  
);FIFO_KEEP_8X32 u_FIFO_KEEP_8X32 (.clk      (i_clk                  ), .srst     (i_rst                  ), .din      (rs_axis_keep           ), .wr_en    (rs_axis_last           ), .rd_en    (r_fifo_keep_rden       ),  .dout     (w_fifo_keep_out        ),  .full     (w_fifo_keep_full       ),  .empty    (w_fifo_keep_empty      )  
);

检测到帧长FIFO不为空之后，读取帧长、KEEP信息、TYPE信息，并根据帧长读取数据，在此过程中需要将数据转换成xgmii接口形式，并封装前导码、MAC地址、帧类型、尾部CRC。同时需要在帧起始加入起始符FB、帧结束需要加入结束符FD，在空闲时发送07.同时需要是用控制信号指示控制符。

always@(posedge i_clk,posedge i_rst)beginif(i_rst)ro_xgmii_txd <= {{8{8'h07}}};elseif(r_cnt == 0|| r_cnt == 1 || r_cnt == 2)ro_xgmii_txd <= {{8{8'h07}}};else if(r_cnt == 3)ro_xgmii_txd <= 64'hFB_55_55_55_55_55_55_55;else if(r_cnt == 4)ro_xgmii_txd <= {8'hd5,ri_set_target_mac,ri_set_source_mac[47:40]};else if(r_cnt == 5)ro_xgmii_txd <= {ri_set_source_mac[39:0],w_fifo_type_out,r_fifo_data_out_ff1[63:56]};// else if(r_cnt == 2)//     ro_xgmii_txd <= {w_fifo_type_out[7:0],w_fifo_data_out[63:8]};else if(r_cnt == w_fifo_len_out + 5)case(w_fifo_keep_out)8'b1111_1111:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:0],r_crc_result[31:24]};8'b1111_1110:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:8],r_crc_result[31:16]};8'b1111_1100:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:16],r_crc_result[31:8]};8'b1111_1000:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:24],r_crc_result[31:0]};8'b1111_0000:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:32],r_crc_result[31:0],8'hFD};8'b1110_0000:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:40],r_crc_result[31:0],8'hFD,{{8'h07}}};8'b1100_0000:ro_xgmii_txd <= {r_fifo_data_out_ff4[55:48],r_crc_result[31:0],8'hFD,{2{8'h07}}};8'b1000_0000:ro_xgmii_txd <= {r_crc_result[31:0],8'hFD,{3{8'h07}}};default     :ro_xgmii_txd <= 'd0;endcaseelse if(r_cnt == w_fifo_len_out + 6)case(w_fifo_keep_out)8'b1111_1111:ro_xgmii_txd <= {r_crc_result[23:0],8'hFD,{4{8'h07}}};8'b1111_1110:ro_xgmii_txd <= {r_crc_result[15:0],8'hFD,{5{8'h07}}};8'b1111_1100:ro_xgmii_txd <= {r_crc_result[7:0],8'hFD,{6{8'h07}}};8'b1111_1000:ro_xgmii_txd <= {8'hFD,{7{8'h07}}};// 8'b1111_0000:ro_xgmii_txd <= {8'hFD,{7{8'h07}}};// 8'b1110_0000:ro_xgmii_txd <= {8'hFD,{7{8'h07}}};// 8'b1100_0000:ro_xgmii_txd <= {r_fifo_data_out_ff3[55:48],r_crc_result,8'hFD,{2{8'h07}}};// 8'b1000_0000:ro_xgmii_txd <= {r_crc_result,8'hFD,{3{8'h07}}};default     :ro_xgmii_txd <= {{8{8'h07}}};endcase// else if(r_cnt == w_fifo_len_out + 5)//     case(w_fifo_keep_out)//         8'b1111_1111:ro_xgmii_txd <= {r_crc_result[7:0],8'hFD,{6{8'h07}}};//         8'b1111_1110:ro_xgmii_txd <= {r_crc_result[15:0],8'hFD,{5{8'h07}}};//         8'b1111_1100:ro_xgmii_txd <= {r_crc_result[7:0],8'hFD,{6{8'h07}}};//         8'b1111_1000:ro_xgmii_txd <= {8'hFD,{7{8'h07}}};//         default     :ro_xgmii_txd <= {8{8'h07}};//     endcase        elsero_xgmii_txd <= {r_fifo_data_out_ff4[55:0],r_fifo_data_out_ff3[63:56]};
end
//
always@(posedge i_clk,posedge i_rst)beginif(i_rst)ro_xgmii_txc <= 8'hff;elseif( r_cnt == 0 || r_cnt == 1 || r_cnt == 2)ro_xgmii_txc <= 8'b1111_1111;else if(r_cnt == 3)ro_xgmii_txc <= 8'b1000_0000;// else if(r_cnt == 2)//     ro_xgmii_txd <= {w_fifo_type_out[7:0],w_fifo_data_out[63:8]};// else if(r_cnt == w_fifo_len_out + 2)//     case(w_fifo_keep_out)//         8'b1111_1111:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1111_1110:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1111_1100:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1111_1000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1111_0000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1110_0000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1100_0000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         8'b1000_0000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//         default     :ro_xgmii_txd <= {r_fifo_data_out_ff2[55:0],r_fifo_data_out_ff1[63:56]};//     endcaseelse if(r_cnt == w_fifo_len_out + 5)case(w_fifo_keep_out)// 8'b1111_1111:ro_xgmii_txc <= {r_fifo_data_out_ff2[55:0],r_crc_result[31:24]};// 8'b1111_1110:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:8],r_crc_result[31:16]};// 8'b1111_1100:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:16],r_crc_result[31:8]};// 8'b1111_1000:ro_xgmii_txd <= {r_fifo_data_out_ff2[55:24],r_crc_result[31:0]};8'b1111_0000:ro_xgmii_txc <= 8'b0000_0001;8'b1110_0000:ro_xgmii_txc <= 8'b0000_0011;8'b1100_0000:ro_xgmii_txc <= 8'b0000_0111;8'b1000_0000:ro_xgmii_txc <= 8'b0000_1111;default     :ro_xgmii_txc <= 'd0;endcaseelse if(r_cnt == w_fifo_len_out + 6)case(w_fifo_keep_out)8'b1111_1111:ro_xgmii_txc <= 8'b0001_1111;8'b1111_1110:ro_xgmii_txc <= 8'b0011_1111;8'b1111_1100:ro_xgmii_txc <= 8'b0111_1111;8'b1111_1000:ro_xgmii_txc <= 8'b1111_1111;default     :ro_xgmii_txc <= 8'b1111_1111;endcase        elsero_xgmii_txc <= 8'b0000_0000;
end

三、仿真图