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//
// Copyright 2011 Ettus Research LLC
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
// Medium halfband decimator (intended to be followed by another stage)
// Implements impulse responses of the form [A 0 B 0 C 0 D 0.5 D 0 C 0 B 0 A]
//
// These taps designed by halfgen_test:
// 2 * 131072 * halfgen_test(.8/8,4,1)
// -597, 0, 4283, 0, -17516, 0, 79365, 131072, 79365, 0, -17516, 0, 4283, 0, -597
module med_hb_int
#(parameter WIDTH=18)
(input clk,
input rst,
input bypass,
input stb_in,
input [WIDTH-1:0] data_in,
input [7:0] output_rate,
input stb_out,
output reg [WIDTH-1:0] data_out);
localparam coeff_a = -597;
localparam coeff_b = 4283;
localparam coeff_c = -17516;
localparam coeff_d = 79365;
reg phase;
reg [WIDTH-1:0] d1, d2, d3, d4, d5, d6, d7, d8;
localparam MWIDTH = 36;
wire [MWIDTH-1:0] prod;
reg [6:0] stbin_d;
always @(posedge clk)
stbin_d <= {stbin_d[5:0],stb_in};
always @(posedge clk)
if(stb_in)
begin
d1 <= data_in;
d2 <= d1;
d3 <= d2;
d4 <= d3;
d5 <= d4;
d6 <= d5;
d7 <= d6;
d8 <= d7;
end
wire [WIDTH-1:0] sum_a, sum_b, sum_c, sum_d;
add2_and_round_reg #(.WIDTH(WIDTH)) add_a (.clk(clk),.in1(d1),.in2(d8),.sum(sum_a));
add2_and_round_reg #(.WIDTH(WIDTH)) add_b (.clk(clk),.in1(d2),.in2(d7),.sum(sum_b));
add2_and_round_reg #(.WIDTH(WIDTH)) add_c (.clk(clk),.in1(d3),.in2(d6),.sum(sum_c));
add2_and_round_reg #(.WIDTH(WIDTH)) add_d (.clk(clk),.in1(d4),.in2(d5),.sum(sum_d));
MULT18X18S mult1(.C(clk), .CE(1), .R(rst), .P(prod1), .A(stbin_d[1] ? coeff_a : coeff_b),
.B(stbin_d[1] ? sum_a : sum_b) );
MULT18X18S mult2(.C(clk), .CE(1), .R(rst), .P(prod2), .A(stbin_d[1] ? coeff_c : coeff_d),
.B(stbin_d[1] ? sum_c : sum_d) );
wire [MWIDTH:0] accum;
acc #(.IWIDTH(MWIDTH),.OWIDTH(MWIDTH+1))
acc (.clk(clk),.clear(stbin_d[2]),.acc(|stbin_d[3:2]),.in(prod),.out(accum));
wire [WIDTH+2:0] accum_rnd;
round_reg #(.bits_in(MWIDTH+1),.bits_out(WIDTH+3))
final_round (.clk(clk),.in(accum),.out(accum_rnd));
wire [WIDTH-1:0] clipped;
clip_reg #(.bits_in(WIDTH+3),.bits_out(WIDTH))
final_clip (.clk(clk),.in(accum_rnd),.out(clipped));
reg [WIDTH-1:0] saved, saved_d3;
always @(posedge clk)
if(stbin_d[6])
saved <= clipped;
always @(posedge clk)
if(stbin_d[3])
saved_d3 <= d3;
always @(posedge clk)
if(bypass)
data_out <= data_in;
else if(stb_in & stb_out)
case(output_rate)
1 : data_out <= d6;
2 : data_out <= d4;
3, 4, 5, 6, 7 : data_out <= d3;
default : data_out <= d2;
endcase // case(output_rate)
else if(stb_out)
data_out <= saved;
endmodule // small_hb_int
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