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// The input FIFO contents should be 16 bits wide
// The first word is 1 for fast path (accelerated protocol)
// 0 for software implemented protocol
// The second word is the number of bytes in the packet,
// and must be valid even if we are in slow path mode
// Odd means the last word is half full
// Flags[1:0] is {eop, sop}
// Protocol word format is:
// 19 Last Header Line
// 18 IP Header Checksum XOR
// 17 IP Length Here
// 16 UDP Length Here
// 15:0 data word to be sent
module prot_eng_tx
#(parameter BASE=0)
(input clk, input reset, input clear,
input set_stb, input [7:0] set_addr, input [31:0] set_data,
input [18:0] datain, input src_rdy_i, output dst_rdy_o,
output [18:0] dataout, output src_rdy_o, input dst_rdy_i);
wire [2:0] flags_i = datain[18:16];
reg [15:0] dataout_int;
reg fast_path, sof_o;
wire [2:0] flags_o = {flags_i[2], flags_i[1], sof_o}; // OCC, EOF, SOF
assign dataout = {flags_o[2:0], dataout_int[15:0]};
reg [4:0] state;
wire do_payload = (state == 31);
assign dst_rdy_o = dst_rdy_i & (do_payload | (state==0) | (state==1) | (state==30));
assign src_rdy_o = src_rdy_i & ~((state==0) | (state==1) | (state==30));
localparam HDR_WIDTH = 16 + 4; // 16 bits plus flags
localparam HDR_LEN = 32; // Up to 64 bytes of protocol
// Store header values in a small dual-port (distributed) ram
reg [HDR_WIDTH-1:0] header_ram[0:HDR_LEN-1];
wire [HDR_WIDTH-1:0] header_word;
always @(posedge clk)
if(set_stb & ((set_addr & 8'hE0) == BASE))
header_ram[set_addr[4:0]] <= set_data;
assign header_word = header_ram[state];
wire last_hdr_line = header_word[19];
wire ip_chk = header_word[18];
wire ip_len = header_word[17];
wire udp_len = header_word[16];
// Protocol State Machine
reg [15:0] length;
wire [15:0] ip_length = length + 28; // IP HDR + UDP HDR
wire [15:0] udp_length = length + 8; // UDP HDR
always @(posedge clk)
if(reset)
begin
state <= 0;
fast_path <= 0;
sof_o <= 0;
end
else
if(src_rdy_i & dst_rdy_i)
case(state)
0 :
begin
fast_path <= datain[0];
state <= 1;
end
1 :
begin
length <= datain[15:0];
sof_o <= 1;
if(fast_path)
state <= 2;
else
state <= 30; // Skip 1 word for alignment
end
30 :
state <= 31;
31 :
begin
sof_o <= 0;
if(flags_i[1]) // eop
state <= 0;
end
default :
begin
sof_o <= 0;
if(~last_hdr_line)
state <= state + 1;
else
state <= 31;
end
endcase // case (state)
wire [15:0] checksum;
add_onescomp #(.WIDTH(16)) add_onescomp
(.A(header_word[15:0]),.B(ip_length),.SUM(checksum));
always @*
if(ip_chk)
//dataout_int <= header_word[15:0] ^ ip_length;
dataout_int <= 16'hFFFF ^ checksum;
else if(ip_len)
dataout_int <= ip_length;
else if(udp_len)
dataout_int <= udp_length;
else if(do_payload)
dataout_int <= datain[15:0];
else
dataout_int <= header_word[15:0];
endmodule // prot_eng_tx
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