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//
// Copyright 2021 Ettus Research, a National Instruments Brand
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Module: rf_down_4to2
//
// Description:
//
// Implements a down-sampling filter that accepts 4 samples per cycle on the
// input and outputs 2 samples per cycle. A 2x speed clock is used to perform
// the DSP computation, so that less logic can be used to implement the
// half-band filter.
//
// Data Path : In --> Gearbox --> Filter --> Gearbox --> Out
// SPC : 4 2 1 2
// Clock Rate : 1x 2x 2x 1x
//
`default_nettype none
module rf_down_4to2 #(
parameter NUM_CHANNELS = 1
) (
input wire clk,
input wire clk_2x,
// Synchronous resets
input wire rst,
input wire rst_2x,
// Input - 4 SPC, synchronous to "clk"
input wire [NUM_CHANNELS*128-1:0] i_tdata,
input wire [NUM_CHANNELS* 1-1:0] i_tvalid,
// Output - 2 SPC, synchronous to "clk"
output wire [NUM_CHANNELS*64-1:0] o_tdata,
output wire [NUM_CHANNELS* 1-1:0] o_tvalid
);
generate
genvar ch;
for (ch = 0; ch < NUM_CHANNELS; ch = ch + 1) begin : gen_channel
//-----------------------------------------------------------------------
// Input Gearbox
//-----------------------------------------------------------------------
//
// Convert from 4 SPC on clk to 2 SPC on clk_2x.
//
//-----------------------------------------------------------------------
wire [63:0] gear_to_filt_tdata;
wire gear_to_filt_tvalid;
gearbox_2x1 #(
.WORD_W (32),
.IN_WORDS (4),
.OUT_WORDS (2),
.BIG_ENDIAN (0)
) gearbox_2x1_in (
.i_clk (clk),
.i_rst (rst),
.i_tdata (i_tdata[ch*128 +: 128]),
.i_tvalid (i_tvalid[ch]),
.o_clk (clk_2x),
.o_rst (rst_2x),
.o_tdata (gear_to_filt_tdata),
.o_tvalid (gear_to_filt_tvalid)
);
//-----------------------------------------------------------------------
// Interpolating Filter
//-----------------------------------------------------------------------
wire [47:0] filt_to_clip_tdata;
wire filt_to_clip_tvalid;
hb47_2to1 hb47_2to1_i (
.aresetn (~rst_2x),
.aclk (clk_2x),
.s_axis_data_tvalid (gear_to_filt_tvalid),
.s_axis_data_tready (),
.s_axis_data_tdata (gear_to_filt_tdata),
.m_axis_data_tvalid (filt_to_clip_tvalid),
.m_axis_data_tuser (),
.m_axis_data_tdata (filt_to_clip_tdata)
);
//-----------------------------------------------------------------------
// Saturation
//-----------------------------------------------------------------------
wire [31:0] clip_to_gear_tdata;
wire clip_to_gear_tvalid;
genvar word;
for (word = 0; word < 2; word = word+1) begin : gen_sat
axi_clip #(
.WIDTH_IN (24),
.WIDTH_OUT (16),
.FIFOSIZE (0)
) axi_clip_i (
.clk (clk_2x),
.reset (rst_2x),
.i_tdata (filt_to_clip_tdata[word*24 +: 24]),
.i_tlast (1'b0),
.i_tvalid (filt_to_clip_tvalid),
.i_tready (),
.o_tdata (clip_to_gear_tdata[word*16 +: 16]),
.o_tlast (),
.o_tvalid (clip_to_gear_tvalid),
.o_tready (1'b1)
);
end
//-----------------------------------------------------------------------
// Output Gearbox
//-----------------------------------------------------------------------
//
// Convert from 1 SPC on clk_2x to 2 SPC on clk.
//
//-----------------------------------------------------------------------
gearbox_2x1 #(
.WORD_W (32),
.IN_WORDS (1),
.OUT_WORDS (2),
.BIG_ENDIAN (0)
) gearbox_2x1_out (
.i_clk (clk_2x),
.i_rst (rst_2x),
.i_tdata (clip_to_gear_tdata),
.i_tvalid (clip_to_gear_tvalid),
.o_clk (clk),
.o_rst (rst),
.o_tdata (o_tdata[ch*64 +: 64]),
.o_tvalid (o_tvalid[ch])
);
end // for
endgenerate
endmodule
`default_nettype wire
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