万兆以太网MAC设计（2）MAC_RX模块

前言

上文我们打通了了万兆以太网物理层和数据链路层，其实就是会使用IP核了，本文将正式开始MAC层设计第一篇，接收端设计。

一、模块功能

MAC_RX模块功能如下：

• 解析接收的报文：接受报文的目的MAC、源MAC、报文类型
• 将XGMII接口输入数据转化为AXIS的数据流形式传递给上层用户

难点在于数据格式的转化，最主要的是尾端KEEP信号该如何与有效数据进行对齐。
数据恢复的过程：

1. 判断起始位SOF和起始位的位置：起始字节8‘hFB’位置存在俩种情况：第一种情况自然是在接收数据的第一个字节位置，但也存在在第五个字节位置的情况，所以需要分情况讨论。
   
2. 关键字段信息提取：根据起始位置的不同，目的MAC以及源MAC和类型信息都要分情况进行讨论。
3. 数据恢复：同理，恢复数据也需要讨论。
4. 结束位EOF以及结束位的位置判断 ：结束位有八种情况，一拍数据64bit，结束位可能存在在任何一个byte上。
5. 尾端KEPP对齐，根据起始位位置以及结束位位置，尾端KEEP信号需要讨论各种情况。
6. AXIS数据转换 ：前面相当于把KEEP和DATA信号处理好了，然后还需要产生VALID、LAST、USER信号。

二、代码

设计思路参考了FPGA奇哥系列网课

注意一下几点：

1. 老生常谈的大小端问题，进入该模块的数据全部应该是大端数据，我完全是按照大端进行处理的。
2. LAST信号和KEEP信号分类讨论条件是一样的，俩者是在数据尾端同时进行变化的，根据最后一拍有效数据字节数的多少，LAST信号会在不同的时刻拉高（在r_eof拉高或w_eof拉高时刻）。
3. USER信号是用户自定义的，我这里暂时定义为接收数据的源MAC的低16位加类型（16位）。
4. 万兆以太网控制字符定义：
   

module TEN_GIG_MAC_RX(input           i_clk               ,input           i_rst               ,input  [63:0]   i_xgmii_rxd         ,input  [7 :0]   i_xgmii_rxc         ,output [63:0]   m_axis_rdata        ,output [31:0]   m_axis_ruser        ,//用户自定义{r_src_mac[15:0],r_type}output [7 :0]   m_axis_rkeep        ,output          m_axis_rlast        ,output          m_axis_rvalid       
);
/******************************function*****************************//******************************parameter****************************/
localparam      P_FRAME_IDLE    = 8'h07 ,P_FRAME_START   = 8'hFB ,P_FRAME_END     = 8'hFD ,P_FRAME_EEROR   = 8'hFE ;
/******************************mechine******************************//******************************reg**********************************/
reg  [63:0]     ri_xgmii_rxd        ;
reg  [63:0]     ri_xgmii_rxd_1d     ;
reg  [7 :0]     ri_xgmii_rxc        ;
reg  [7 :0]     ri_xgmii_rxc_1d     ;
reg  [63:0]     rm_axis_rdata       ;
//reg  [63:0]     rm_axis_rdata_1d    ;
reg  [31:0]     rm_axis_ruser       ;
reg  [7 :0]     rm_axis_rkeep       ;
reg             rm_axis_rlast       ;
reg             rm_axis_rvalid      ;
//解析接收数据
reg  [15:0]     r_recv_cnt          ;
reg             r_comma             ;
reg  [47:0]     r_dst_mac           ;
reg  [47:0]     r_src_mac           ;
reg  [15:0]     r_type              ;
reg             r_data_run          ;//开始产生axis输出数据
reg             r_data_run_1d       ;
reg             r_data_run_2d       ;reg             r_sof               ;
reg             r_eof               ;
reg  [2 :0]     r_sof_location      ;
reg  [2 :0]     r_eof_location      ;
/******************************wire*********************************/
wire            w_sof           ;
wire            w_eof           ;
wire [2 :0]     w_sof_location  ;
wire [2 :0]     w_eof_location  ;
/******************************component****************************//******************************assign*******************************/
assign m_axis_rdata  = rm_axis_rdata    ;
assign m_axis_ruser  = rm_axis_ruser    ;
assign m_axis_rkeep  = rm_axis_rkeep 	;
assign m_axis_rlast  = rm_axis_rlast 	;
assign m_axis_rvalid = rm_axis_rvalid   ;
//进入该模块的数据已经全部被转换为大端模式
//开始字符以及位置判断
assign w_sof =  ((ri_xgmii_rxd[63:56] == P_FRAME_START) && (ri_xgmii_rxc[7] == 1)) || ((ri_xgmii_rxd[31:24] == P_FRAME_START) && (ri_xgmii_rxc[3] == 1));
assign w_sof_location = ((ri_xgmii_rxd[63:56] == P_FRAME_START) && (ri_xgmii_rxc[7] == 1)) ? 7 : ((ri_xgmii_rxd[31:24] == P_FRAME_START) && (ri_xgmii_rxc[3] == 1)) ? 3 :0;
//结束字符以及位置判断
assign w_eof =  ((ri_xgmii_rxd[63:56] == P_FRAME_END) && (ri_xgmii_rxc[7] == 1)) || ((ri_xgmii_rxd[55:48] == P_FRAME_END) && (ri_xgmii_rxc[6] == 1)) ||((ri_xgmii_rxd[47:40] == P_FRAME_END) && (ri_xgmii_rxc[5] == 1)) ||((ri_xgmii_rxd[39:32] == P_FRAME_END) && (ri_xgmii_rxc[4] == 1)) ||((ri_xgmii_rxd[31:24] == P_FRAME_END) && (ri_xgmii_rxc[3] == 1)) ||((ri_xgmii_rxd[23:16] == P_FRAME_END) && (ri_xgmii_rxc[2] == 1)) ||((ri_xgmii_rxd[15: 8] == P_FRAME_END) && (ri_xgmii_rxc[1] == 1)) ||((ri_xgmii_rxd[7 : 0] == P_FRAME_END) && (ri_xgmii_rxc[0] == 1));assign w_eof_location = ((ri_xgmii_rxd[63:56] == P_FRAME_END) && (ri_xgmii_rxc[7] == 1)) ? 7 : ((ri_xgmii_rxd[55:48] == P_FRAME_END) && (ri_xgmii_rxc[6] == 1)) ? 6 :((ri_xgmii_rxd[47:40] == P_FRAME_END) && (ri_xgmii_rxc[5] == 1)) ? 5 :((ri_xgmii_rxd[39:32] == P_FRAME_END) && (ri_xgmii_rxc[4] == 1)) ? 4 :((ri_xgmii_rxd[31:24] == P_FRAME_END) && (ri_xgmii_rxc[3] == 1)) ? 3 :((ri_xgmii_rxd[23:16] == P_FRAME_END) && (ri_xgmii_rxc[2] == 1)) ? 2 :((ri_xgmii_rxd[15: 8] == P_FRAME_END) && (ri_xgmii_rxc[1] == 1)) ? 1 :((ri_xgmii_rxd[7 : 0] == P_FRAME_END) && (ri_xgmii_rxc[0] == 1)) ? 0 : 0;
/******************************always*******************************/
always @(posedge i_clk or posedge i_rst)beginif(i_rst)beginri_xgmii_rxd    <= 'd0;ri_xgmii_rxc    <= 'd0;ri_xgmii_rxd_1d <= 'd0;ri_xgmii_rxc_1d <= 'd0;endelse beginri_xgmii_rxd    <= i_xgmii_rxd      ;ri_xgmii_rxc    <= i_xgmii_rxc      ;ri_xgmii_rxd_1d <= ri_xgmii_rxd     ;ri_xgmii_rxc_1d <= ri_xgmii_rxc     ;end
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)beginr_sof           <= 'd0;r_sof_location  <= 'd0;endelse if(w_sof)beginr_sof           <= w_sof            ;r_sof_location  <= w_sof_location   ;endelse beginr_sof           <= 'd0            ;r_sof_location  <= r_sof_location   ;end
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)beginr_eof           <= 'd0;r_eof_location  <= 'd0;endelse if(w_eof)beginr_eof           <= w_eof            ;r_eof_location  <= w_eof_location   ;endelse beginr_eof           <= 'd0            ;r_eof_location  <= r_eof_location   ;    end
end always @(posedge i_clk or posedge i_rst)beginif(i_rst)r_comma <= 'd0;else if(r_eof)r_comma <= 'd0;else if((r_sof_location == 7) && (ri_xgmii_rxd_1d[55:0] == 56'h55_5555_5555_5555) && (ri_xgmii_rxd[63:56] == 8'hd5))r_comma <= 'd1;else if((r_sof_location == 3) && (ri_xgmii_rxd_1d[23:0] == 24'h55_5555) && (ri_xgmii_rxd[63:24] == 40'h55_5555_55d5))r_comma <= 'd1;elser_comma <= r_comma;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)r_recv_cnt <= 'd0;else if(r_eof)r_recv_cnt <= 'd0;else if(r_sof | r_recv_cnt)r_recv_cnt <= r_recv_cnt + 'd1;elser_recv_cnt <= r_recv_cnt;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)r_dst_mac <= 'd0;else if(r_sof_location == 7 && r_recv_cnt == 1)r_dst_mac <= ri_xgmii_rxd_1d[55:8];else if(r_sof_location == 3 && r_recv_cnt == 1)r_dst_mac <= {ri_xgmii_rxd_1d[23:0],ri_xgmii_rxd[63:40]};elser_dst_mac <= r_dst_mac;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)r_src_mac <= 'd0;else if(r_sof_location == 7 && r_recv_cnt == 1)r_src_mac <= {ri_xgmii_rxd_1d[7:0],ri_xgmii_rxd[63:24]};else if(r_sof_location == 3 && r_recv_cnt == 2)r_src_mac <= {ri_xgmii_rxd_1d[39:0],ri_xgmii_rxd[63:56]};elser_src_mac <= r_src_mac;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)r_type <= 'd0;else if(r_sof_location == 7 && r_recv_cnt == 2)r_type <= ri_xgmii_rxd_1d[23:8];else if(r_sof_location == 3 && r_recv_cnt == 3)r_type <= ri_xgmii_rxd_1d[55:40];elser_type <= r_type;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)r_data_run <= 'd0;else if(rm_axis_rlast)r_data_run <= 'd0;else if(r_sof_location == 7 && r_recv_cnt == 1)r_data_run <= 'd1;else if(r_sof_location == 3 && r_recv_cnt == 2)r_data_run <= 'd1;elser_data_run <= r_data_run;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)beginr_data_run_1d <= 'd0;r_data_run_2d <= 'd0;endelse beginr_data_run_1d <= r_data_run;r_data_run_2d <= r_data_run_1d;end
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)rm_axis_rdata <= 'd0;else if(rm_axis_rlast)rm_axis_rdata <= 'd0;else if(r_sof_location == 7 && r_data_run)rm_axis_rdata <= {ri_xgmii_rxd_1d[7:0],ri_xgmii_rxd[63:8]};else if(r_sof_location == 3 && r_data_run)rm_axis_rdata <= {ri_xgmii_rxd_1d[39:0],ri_xgmii_rxd[63:40]};elserm_axis_rdata <= 'd0;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)rm_axis_ruser <= 'd0;else if(r_sof_location == 7 && r_recv_cnt == 2)rm_axis_ruser <= {r_src_mac,ri_xgmii_rxd_1d[23:8]};else if(r_sof_location == 3 && r_recv_cnt == 3)rm_axis_ruser <= {r_src_mac,ri_xgmii_rxd_1d[55:40]};elserm_axis_ruser <= rm_axis_ruser;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)rm_axis_rkeep <= 'd0;else if(r_sof_location == 7 && w_eof)case (w_eof_location)7       : rm_axis_rkeep <= 8'b1000_0000;6       : rm_axis_rkeep <= 8'b1100_0000;5       : rm_axis_rkeep <= 8'b1110_0000;4       : rm_axis_rkeep <= 8'b1111_0000;3       : rm_axis_rkeep <= 8'b1111_1000;2       : rm_axis_rkeep <= 8'b1111_1100;1       : rm_axis_rkeep <= 8'b1111_1110;0       : rm_axis_rkeep <= 8'b1111_1111;default : rm_axis_rkeep <= 8'b1111_1111;endcaseelse if(r_sof_location == 3 && (w_eof && w_eof_location >= 4))case (w_eof_location)7       : rm_axis_rkeep <= 8'b1111_1000;6       : rm_axis_rkeep <= 8'b1111_1100;5       : rm_axis_rkeep <= 8'b1111_1110;4       : rm_axis_rkeep <= 8'b1111_1111;3       : rm_axis_rkeep <= 8'b1000_0000;2       : rm_axis_rkeep <= 8'b1100_0000;1       : rm_axis_rkeep <= 8'b1110_0000;0       : rm_axis_rkeep <= 8'b1111_0000;default : rm_axis_rkeep <= 8'b1111_1111;endcaseelse if(r_sof_location == 3 && (r_eof && r_eof_location < 4))case (r_eof_location)7       : rm_axis_rkeep <= 8'b1111_1000;6       : rm_axis_rkeep <= 8'b1111_1100;5       : rm_axis_rkeep <= 8'b1111_1110;4       : rm_axis_rkeep <= 8'b1111_1111;3       : rm_axis_rkeep <= 8'b1000_0000;2       : rm_axis_rkeep <= 8'b1100_0000;1       : rm_axis_rkeep <= 8'b1110_0000;0       : rm_axis_rkeep <= 8'b1111_0000;default : rm_axis_rkeep <= 8'b1111_1111;endcaseelserm_axis_rkeep <= 8'b1111_1111;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)rm_axis_rlast <= 'd0;else if(r_sof_location == 7 && w_eof)rm_axis_rlast <= 'd1;else if(r_sof_location == 3 && (w_eof && w_eof_location >= 4))rm_axis_rlast <= 'd1;else if(r_sof_location == 3 && (r_eof && r_eof_location < 4))rm_axis_rlast <= 'd1;elserm_axis_rlast <= 'd0;
endalways @(posedge i_clk or posedge i_rst)beginif(i_rst)rm_axis_rvalid <= 'd0;else if(rm_axis_rlast)rm_axis_rvalid <= 'd0;else if(r_data_run && !r_data_run_1d)rm_axis_rvalid <= 'd1;elserm_axis_rvalid <= rm_axis_rvalid; 
endendmodule

三、仿真波形

仿真文件当中要遍历所有的起始位置与结束为止组合，一共16种。

以起始位在第五个byte，结束位在第一个byte为例，其波形如下，结果正确，对比其他16种情况，波形全部正确。