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//
// Copyright 2018 Ettus Research, A National Instruments Company
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Module: chdr_compute_tkeep
// Description:
// This module monitors an AXI-Stream CHDR bus and uses the
// packet size field in the CHDR header to compute a tkeep
// trailer signal to indicate the the valid bytes when
// tlast is asserted.
//
// Parameters:
// - CHDR_W: Width of the CHDR bus in bits
// - ITEM_W: Width of the item bus in bits (must be a multiple of 8)
//
// Signals:
// - axis_* : AXI-Stream CHDR bus
module chdr_compute_tkeep #(
parameter CHDR_W = 256,
parameter ITEM_W = 32
)(
input wire clk,
input wire rst,
input wire [CHDR_W-1:0] axis_tdata,
input wire axis_tlast,
input wire axis_tvalid,
input wire axis_tready,
output wire [(CHDR_W/ITEM_W)-1:0] axis_tkeep
);
`include "rfnoc_chdr_utils.vh"
generate if (CHDR_W > ITEM_W) begin
localparam CHDR_W_BYTES = CHDR_W/8;
localparam ITEM_W_BYTES = ITEM_W/8;
localparam KEEP_W = CHDR_W_BYTES/ITEM_W_BYTES;
// Binary to thermometer decoder
// 2'd0 => 4'b1111 (special case)
// 2'd1 => 4'b0001
// 2'd2 => 4'b0011
// 2'd3 => 4'b0111
function [KEEP_W-1:0] bin2thermo;
input [$clog2(KEEP_W)-1:0] bin;
bin2thermo = ~((~1)<<((bin-1)%KEEP_W));
endfunction
// Read the packet length and figure out the number
// of trailing items
wire [15:0] pkt_len = chdr_get_length(axis_tdata[63:0]);
wire [KEEP_W-1:0] len_thermo = bin2thermo(pkt_len[$clog2(CHDR_W_BYTES)-1:$clog2(ITEM_W_BYTES)]);
reg [KEEP_W-1:0] reg_len_thermo = 'h0;
reg is_header = 1'b1;
always @(posedge clk) begin
if (rst) begin
is_header <= 1'b1;
end else if (axis_tvalid & axis_tready) begin
is_header <= axis_tlast;
if (is_header) begin
reg_len_thermo <= len_thermo;
end
end
end
// tkeep indicates trailing items, so for lines with tlast == 0,
// tkeep is all 1's.
assign axis_tkeep = (~axis_tlast) ? {KEEP_W{1'b1}} :
(is_header ? len_thermo : reg_len_thermo);
end else if (CHDR_W == ITEM_W) begin
// Only one item per CHDR word. So always keep it.
assign axis_tkeep = 1'b1;
end else begin
// Illegal. A item must be smaller than the CHDR_W
illegal_parameter_value item_w_cannot_be_larger_than_chdr_w();
end endgenerate
endmodule // chdr_compute_tkeep
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