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//
// Copyright 2019 Ettus Research, a National Instruments Brand
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Module: axi_embed_tlast_tkeep
//
// Description:
//
// This module takes the TLAST and TKEEP values of an AXI-Stream interface
// and embeds them into the data stream. This allows a data pipe to be used
// that isn't wide enough for the TDATA, TLAST,and TKEEP to be passed through
// in parallel. Since TLAST and TKEEP are only usually needed for one word
// per packet, this also reduces the amount of memory required to store a
// packet. Note that this module only supports TKEEP at the end of a packet
// when TLAST is asserted. See also axi_extract_tlast_tkeep.
//
// This embedding is accomplished by using an escape sequence using the word
// 0xDEADBEEF as the escape code. If TLAST and TKEEP are both 0 (the usual
// case) then no escape sequence is used. Any word that has "DEADBEEF" in the
// most significant position is considered an escape word. The least
// significant bits of the escape word contain the TKEEP and TLAST bits. The
// word following the escape word is the normal data word associated with
// those TLAST and TKEEP values.
//
// Here are some examples for the case where DATA_W = 64
//
// 0x1234567887654321 with TLAST=0 and TKEEP=0 becomes
// 0x1234567887654321
//
// 0x1234567887654321 with TLAST=1 and TKEEP=0 becomes
// 0xDEADBEEF00000001 0x1234567887654321
//
// 0x1234567887654321 with TLAST=1 and TKEEP=2 becomes
// 0xDEADBEEF00000005 0x1234567887654321
//
// 0x1234567887654321 with TLAST=0 and TKEEP=1 becomes
// 0x1234567887654321 (because TKEEP is ignored when TLAST=0)
//
// 0xDEADBEEFFEEDCAFE without TLAST=0 and TKEEP=0 becomes
// 0xDEADBEEF00000000 0xDEADBEEFFEEDCAFE
//
// 0xDEADBEEFFEEDCAFE with TLAST=0 and TKEEP=1 becomes
// 0xDEADBEEF00000002 0xDEADBEEFFEEDCAFE
//
module axi_embed_tlast_tkeep #(
parameter DATA_W = 64,
parameter KEEP_W = DATA_W/8
) (
input clk,
input rst,
// Input AXI-Stream
input [DATA_W-1:0] i_tdata,
input [KEEP_W-1:0] i_tkeep,
input i_tlast,
input i_tvalid,
output i_tready,
// Output AXI-Stream
output reg [DATA_W-1:0] o_tdata,
output o_tvalid,
input o_tready
);
localparam ESC_WORD_W = 32;
localparam [ESC_WORD_W-1:0] ESC_WORD = 'hDEADBEEF;
//---------------------------------------------------------------------------
// Parameter Checking
//---------------------------------------------------------------------------
if (DATA_W < ESC_WORD_W+KEEP_W+1) begin : gen_assertion
// Cause an error if DATA_W is not large enough.
DATA_W_is_not_large_enough_to_store_escape_code_TKEEP_and_TLAST();
end
//---------------------------------------------------------------------------
// State Machine
//---------------------------------------------------------------------------
localparam PASS = 0;
localparam ESCAPE = 1;
localparam ST_IDLE = 0;
localparam ST_DATA = 1;
reg [0:0] state = ST_IDLE;
reg [0:0] next_state;
reg [0:0] select;
always @(posedge clk) begin
if (rst) begin
state <= ST_IDLE;
end else begin if (o_tready)
state <= next_state;
end
end
always @(*) begin
case(state)
ST_IDLE: begin
if (i_tlast && i_tvalid) begin
next_state = ST_DATA;
select = ESCAPE;
end else if ((i_tdata[DATA_W-1 -: ESC_WORD_W] == ESC_WORD) && i_tvalid) begin
next_state = ST_DATA;
select = ESCAPE;
end else begin
next_state = ST_IDLE;
select = PASS;
end
end
ST_DATA: begin
select = PASS;
if (i_tvalid) begin
next_state = ST_IDLE;
end else begin
next_state = ST_DATA;
end
end
endcase
end
//---------------------------------------------------------------------------
// Output Multiplexers
//---------------------------------------------------------------------------
always @(*) begin
case(select)
PASS : begin
o_tdata = i_tdata;
end
ESCAPE : begin
o_tdata = {DATA_W{1'b0}};
o_tdata[DATA_W-1 -: ESC_WORD_W] = ESC_WORD;
o_tdata[ 1 +: KEEP_W] = i_tkeep;
o_tdata[ 0 +: 1] = i_tlast;
end
endcase
end
assign o_tvalid = (select == PASS) ? i_tvalid : 1'b1;
assign i_tready = (select == PASS) ? o_tready : 1'b0;
endmodule
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